UNIVERSITY Or CALIFORNIA COLLE: - ..- ; ;0" AUG 12 1974 ' IRVINE, CAUrURWIA 92664 JANUARY 1885. ,HUMAN OSTEOLOG-Y COMPRISING A DESCRIPTION OP THE BONES WITH DELINEATIONS OF THE ATTACHMENTS OF THE MUSCLES, THE GENERAL AND MICROSCOPIC STRUCTURE OF BONE AND ITS DEVELOPMENT LUTHER HOLDEN EX-PBESIDENT AND MEMBEB OF THE COURT OF EXAMINEES OF THE BOYAL COLLEGE OF SUBQEONS OF ENGLAND; CONSULTING 8UBGEON TO SAINT BABTHOL- OatEW'8 AND THE FOUNDLING HOSPITALS. ASSISTED BY JAMES SHUTER, F.R.C.S. M.A. M.B. CANTAB. ASSISTANT 8UBGEON TO THE BOTAL FBEE HOSPITAL ; LATE DEMONSTBATOB OP PHYSIOLOGY, AND ASSISTANT DEMONSTBATOB OF ANATOMY, AT SAINT BARTHOLOMEW'S HOSPITAL. WITH NUMEROUS ILLUSTRATIONS SIXTH EDITION. NEW YORK WILLIAM WOOD & COMPANY 56 & 58 LAFAYETTE PLACE 1885. THE PUBLISHERS PRINTING AND ELECTROTYPING Co., 39 AND 41 PARK PLACE, NEW YORK. PREFACE TO THE FIFTH EDITION. IN preparing the present Edition the Author has been assisted by Mr. ALBAN DOBAN, late Anatomical Assistant to the Museum of the Royal College of Surgeons of England. In revising the Attachments of Muscles, note has been taken of the highly instructive dissections, made by Mr. W. PEARSON in the work-rooms of the College, which are now in the Physiological Series of the Museum. Most of the Plates have been re-drawn. Numerous woodcuts have been added, in illustration of the Development of Bone for which, as well as for other collateral work, the author is indebted to Mr. JAMES SHUTER, Assistant Demonstrator of Anatomy at St. Bartholomew's Hospital. Grateful acknowledgments are due to Professor FLOWER, F.R.S., and to the Demonstrators of St. Bartholomew's Hospital, for valuable suggestions in special details. September 1878. PREFACE TO THE SIXTH EDITION. IN THE SIXTH EDITION a few brief Notes on Comparative Osteology have been added, with the object of facilitating the intelligent study of the human skeleton ; and these have been made practically illustrative by reference to specimens in the Museum of the Royal College of Surgeons. Several of the Plates have been re-drawn. The order in which the Bones were described in previous Editions has been slightly altered; and it is hoped that the ar- rangement in the present edition will be found more systematic and convenient. The Author has been assisted by Mr. JAMES SHUTEB, late De- monstrator of Practical Physiology, and Assistant Demonstrator of Anatomy, at St. Bartholomew's Hospital. January 1882, CONTENTS GENERAL OBSERVATIONS ON OF BONE STRUCTURE MICROSCOPIC STRUCTURE OP BONE . STRUCTURE OP CARTILAGE DEVELOPMENT OF BONE BONES OP THE SKULL Occipital Bone Parietal Bone Frontal Bone Temporal Bone Sphenoid Bone Ethmoid Bone BONES OF THE FACE Superior Maxillary Bone . Malar Bone Nasal Bone Lachrymal Bone . Palate Bone Inferior Spongy or Turbinated Bone Vomer .... Inferior Maxillary Bone . THE SKULL AS A WHOLE Sutures .... Skull-cap . Base of the Skull as seen from above Base of the Skull as seen from below I. to IV. 33 . V. 38 . VI. 41 . VII. 47 . vm.,ix. 56 . X., XI. 64 . XI. 68 68 . xn. 77 . XIII. 78 . XVI. 80 . XIII. 81 . XIII., XIV. 84 . XV. 85 . XVI. 86 . XVII. 92 92 . xvni. 94 . XVIII. 97 . XIX. 99 . XX.. XXI vili CONTENTS. PAGE Temporal, Zygomatic, Spheno-maxillary Fossae ..... 103 The Orbits . . 104 Nasal Fossae .... 107 General Observations on the Skull 109 VERTEBRAL COLUMN 116 SACRUM ..... 132 ) COCCYX , 136 \ BONES OF THE LOWER EXTREMITY . 138 Os Innominatum . 188 -I Ilium ..... 139 1 Pubes . . . . . 141 Ischium ..... 143 J Pelvis in general .... 146 Femur ..... 151 Patella 158" Tibia 159 Fibula 163 BONES OF THE FOOT .... 167 Astragalus . 168" Os Calcis or Calcaneum . 171 Scaphoid Bone .... 173 Cuboid Bone .... 174 Cuneiform Bones .... 175 Metatarsus .... 177 Phalanges ..... 180 Sesamoid Bones .... 180. OBSERVATIONS ON THE FOOT AS A WHOLE 181 INTEROSSEUS MUSCLES OF THE FOOT . 185 THE THORAX . 186 Sternum ..... 186 Ribs 189 MUSCLES OF THE BACK 198"! Muscles of the back of the Neck . 200 1 Muscles in the front of the Spine 201 J XVI., XXII. XXII. XXIII., XXIV. XXV. to XXVII. XXVIII., XXIX. XXX. to XXXII. XXXIII., XXXIV. XXXVI. to XXXVIII. XXXIX. to XLI. XLI. to XLVII. CONTENTS. IX BONES OF THE UPPER EXTREMITY Clavicle Scapula Humerus Radius Ulna BONES OF THE HAND . Carpus Metacarpus . BONES OF THE FINGERS Sesamoid Bones Interosseous Muscles GENERAL SURVEY OF THE SKELETON OsHYOIDES THE LARYNX . THE ANATOMY OF THE EAR . INDEX 202 216 219 . 224 . 224 . 235 . 235 237 XL VIII. , XLIX. LI. LIL, LIII. LIV. to LVI. . 241 . XXXVIII. , 243 LVII. . 252 . LVIII. to LXI. . 271 HUMAN OSTEOLOGY. Importance and Interest of Osteology. Whoever would become a good anatomist and a skilful surgeon must make himself master of Human Osteology. It must be, not only his first, but his principal and constant study. He cannot understand his dissections without continually referring to the skeleton. Nor can he fail to be interested from the first in the science, if in studying each bone he will compare it with the corre- sponding bone in his own body, in order that he may become familiar with what he can feel of it in the living subject. He will thus see in osteology, not death, but life. In discovering and reducing the simplest dislocation, how important it is to have a competent knowledge of the feel of the bony parts and their relations to one another! A little progress will convince him that, far from being dry, osteology is attractive, not only as conducive to professional success, but for its own sake. Under- taken in a right spirit, the study of it becomes, with many, a favorite pur- suit, and creates a natural longing to know something of the skeleton of the lower animals, that we may the better judge of the advantageous con- struction of our own; for it is only by comparison that we can judge. When the great truth unfolds itself, that our own structure appears to be but a modification of the ' one common pattern' upon which all vertebrate animals are formed, we cannot but feel with the philosophic poet, that "Tis the sublime of man, Our noontide majesty, to know ourselves Parts and proportions of a wondrous whole. COLERIDGE. Uses of the Bones. The bones form the framework which supports the soft parts of the body. All the bones, either separately or in conjunc- tion with others, form levers upon which the attached muscles act and give HUMAN OSTEOLOGY. rise to our various movements. Take a few examples. If the biceps mus- cle contracts the forearm becomes flexed; this shows that the radius is a lever (see Fig. 61). It will likewise be seen that the other bones are levers, as the lower jaw in opening and shutting the mouth; the skull as a whole in nodding the head; the vertebras in balancing and flexing the trunk; the pelvis as a whole (see Fig. 29) ; the ribs when raised and depressed in res- piration; the clavicle in shrugging or depressing the shoulders; the scapula :and the humerus in raising the arm; the ulna and the radius in flexing or extending the forearm; the carpus and metacarpus as a whole in the movements of the wrist joint; the phalanges in the actions of the fingers. In like manner the bones of the lower extremities are levers, which, when acted upon by the various muscles attached to them, give rise to locomo- tion. The bones contribute to the formation of the joints, which admit of more or less movement, depending in direction and extent upon the shape of the articular surfaces and the attachments of the muscles. Besides this, the bones of the head and trunk lodge and protect delicate organs; thus, in the skull and spinal canal we find, respectively, the brain and spinal cord; in the orbits are the eyes; in the temporal bone are the inter- nal parts of the ear; and in the bony framework of the chest are the heart and lungs, which, as well as the upper abdominal viscera, it protects. The fact that the long bones are curved in their long axes increases their elasticity, gives them some amount of spring similar to that of a bow, and helps to diminish shocks. Composition of Bone. Bone is composed of a basis of animal mat- ter impregnated with earthy salts. The analysis is easily made. If a bone be boiled in water for a few hours it loses its elasticity and its animal matter. The animal matter is found in solution in the water and is called jelly or ' gelatin/ The residual bone is white and brittle, and consists only of earthy salts. A like result may be obtained by burning or calcin- ing the bone: it first becomes black from the charring of the animal mat- ter and then white, the animal matter having been completely burnt off and nothing left but the ' earthy salts/ If, on the other hand, a bone be soaked for a few days in a solution of hydrochloric acid (about one part of the dilute acid to six of distilled water), it loses its earthy salts, becomes soft, and may be bent in any direction. Bones are used in making soup for the gelatin they yield on boiling. Notwithstanding their antiquity, fossil bones are found to contain nearly as much animal matter as recent COMPOSITION OF BONE. 3 bones. Gimbernat made soup from the gelatin of the mastodon's tooth, as Dr. Buckland afterward did from the fossil bones of the hyaena. Animal and Earthy Matter. From the above experiments bone is found to contain about one-third of animal matter, the rest being earthy salts, i.e. about 33 of animal matter and 67 of earthy salts in a hundred parts. Bones of children are softer, more elastic and less likely to be broken by slight injuries than those of the aged. This is due to the spongi- ness and great vascularity of children's bones, as well as to the fact that in them the shafts of the bones are united to the epiphyses by a layer of car- lilage. Bone when pure, i.e. when entirely divested of fat or marrow and blood-vessels, is probably a definite compound of constantly the same com- position, whether it be from a child or from an old person, but it varies in compactness and arrangement, and on these variations the differences in the strength and elasticity of bones depend. ' The following is a percentage analysis of adult human bone: 2 Animal matter 33 . 30 Tribasic phosphate of calcium . . 51 -04 Carbonate of calcium, Ca C . 11-30 Earthy salts < Fluoride of calcium, Ca F a . . .2 -00 Phosphate of magnesium . . i-jg Soda and chloride of sodium i -20 100-00 Rickety Bones. In the disease of early life called 'rickets/ in which the bones grow bent and distorted, from deficiency of earthy mat- ter, the proportions of animal and earthy matter have been found to be' Animal matter 79.75 per cent. Earthy matter 20.25 " Of all animals, the bones of birds (especially of the predaceous kind) contain the largest proportion of earthy matter. Hence their great com- pactness and white color. The bones of mammalia come next; then those of reptiles; and last of all those of fishes. As in the birds of prey, so in the carnivora, the bones have a hard and 1 Dr. Stark, 'Edin. Med. and Surg. Jour.,' April 1845; Nelaton, 'Elements de Pathologic,' vol. i. p. 636. * Berzelius's ' Analysis of Bone. ' 3 Dr. Bostock's 'Analysis of Rickety Bones.' 4 HUMAN OSTEOLOGY. compact structure. The tympanic bone of the whale is extremely hard; but the skeleton most remarkable for hardness and weight is that of the manatee, which may be seen in the Osteological Series of the Eoyal Col- lege of Surgeons of England. When the late articulator to the College was taken to task for having charged the enormous sum of 15 (instead of about 5) for articulating the manatee, he pleaded, in justification, that the bones were so hard that it had taken him unusual labor to put them together, and had spoilt many of his tools. The truth of this asser- tion is at once clear to any one who takes in his hand the weighty rib of a manatee. (See sections of ribs, No. 2,653).* Phosphate of Lime: its Importance. Of the earthy ingredients of bone the phosphate of lime holds by far the first rank; hence it is com- monly called ' bone earth/ Adult bone contains 51 per cent, of it, and about 11 per cent, of the carbonate of lime. Carbonate of lime is the principal ingredient in the hardening of shells. The phosphate of lime forms a harder compound with animal matter than the carbonate. What can be harder than the enamel of the teeth? And this consists of a very large proportion of phosphate of lime combined with animal matter. There is only 2 per cent, of animal matter in the enamel, and of the re- maining 98 parts, 88J- consist of phosphate of lime. Phosphate of lime enters not only as the principal earthy ingredient into the composition of bone, but is contained, more or less, in nearly all the tissues of the body. Of all inorganic materials it appears to be the most essential both for vegetable and animal life. Therefore it is not only a most important article of diet, but a necessary manure. ' Those parts of plants which experience has taught us to be the most nutritious, contain the largest proportion of. the phosphates such as bread-corn, peas, beans, and lentils/ * It has been ascertained by experiment, that if animals have their entire supply of phosphate of lime cut off, after some weeks of illness, they are attacked with diarrhoea, which soon kills them. Their bones are found to be very soft; and it is not unlikely that the phosphates are absorbed from their bones and supplied to other structures, such as the nerves and muscles. It is the quantity of phosphate of lime in the bones which makes them so valuable as manure. The bones are boiled to obtain the gelatin or * Throughout the work the numbers refer to specimens in the Osteological Series in the Museum of the Royal College of Surgeons of England, unless otherwise stated. 4 Liebig's 'Letters on Chemistry,' p. 522. PKOPEKTLES OF BONE. 5 glue; afterward they are crushed in a mill, and, as * bone dust/ form an extensive article of commerce. Strength of Bone. The strength of bone, contrasted with other substances, is remarkable. The following materials stand in point of strength to each other thus: Fine freestone, as 1 '0 Lead 6-5 Elm and ash 8-5 Box, yew, oak 11-0 Bone . 22-0 Hence bone is twice as strong as oak. A cubic inch of bone will support 5,000 Ibs. weight. 6 Besides this, we shall presently see that bone is so constructed that it gives great strength with but little expenditure of materials. The specific gravity of bone is from 1*87 to 1'97. Elasticity of Bone. In consequence of the animal matter they contain, bones possess a certain amount of elasticity. If a skull be thrown upon the ground, it will rebound. The degree of elasticity varies in dif- ferent bones, according to their form and texture. The clavicle, for instance, owing to its curved form, is remarkably elastic a property which enables it to break the shock of a fall upon the hand. If one end of a clavicle be placed at a right angle against a hard substance, and the other end struck smartly with a hammer, the bone will rebound to a dis- tance of nearly two feet. The ribs, too, are exceedingly elastic. The Arab children are said to make excellent bows with the ribs of camels. Perhaps the best instance of elasticity in bone is the clavicle (merry- thought) of the bird. It acts as a spring, and restores the base of the wings to their proper position after the action of the muscles of flight. All the long bones are more or less curved, which gives them the benefit of elasticity. Classification of Bones. Though the bones present every variety of form and size, yet, for convenience of description, anatomists divide them into three classes 1. The long and round; 2. The broad and flat; 3. The short and cubical, or irregular. The long and round form the great levers of the limbs, and are moved by muscles. The broad and flat are found chiefly in the skull and pelvis, and protect the viscera. The short 5 Gregory's 'Mechanics,' vol. i. c. 5. 6 HUMAN OSTEOLOGY. and irregular allow more limited motion combined with great strength, as the bones of the spine, the carpal and tarsal bones. Nomenclature. In describing the different parts of a bone, we use terms Latin, Greek, or English which denote either the form of the part, or its fancied resemblance to some natural object, or the purpose it serves. We soon become familiar with such terms as * eminences,' ' depres- sions/ ' processes/ ' tuberosities/ e spines/ c foramina/ ' notches/ ' canals/ ' sinus/ ' fossae/ ' trochanters/ ' condyles/ etc. Again, there are parts of bones named after some celebrated anatomist, who first described them: for instance, the ' aqueduct of Fallopius/ ' the antrum of Highmore/ ' the fissure of Glaser/ the ' canal of Vidius/ These memorials of anatomists, though interesting to historians, are rather encumbering to anatomical nomenclature, and are therefore very much to be deprecated. Structure of Bone : Naked Eye. Let us examine, first, the struct- ure of bone, as it can be seen with the naked eye; afterward, its minute structure with the microscope. Lastly, we will study the development and growth of bone. The best way to obtain a rough idea of the structure of bone is to make a vertical section through one of the long bones say the femur all the way down (Plate I.). We then see that the outer part, or 'wall/ of the bone is compact like ivory; the interior is hollow, forming the ' medul- lary canal/ or cavity containing the marrow. The ends, which expand to form the joints, are composed of a beautiful network of plates and tubes of bone, forming what is called ' cancellous or spongy tissue/ which in the recent state is also filled with marrow. Shaft of Bone hollow. What are the advantages of bones being hollow? The amount of material being the same, a hollow cylinder is much stronger than a solid one. It is proved'that the crushing pressures of two cylinders of equal weight and length, of which one is hollow and the other solid, are, respectively, as the diameters of their transverse sections; provided always that the diameter of the tube be within cer- tain dimensions. Thus, let a b, c d (Figs. 1 and 2) represent the sections of two cylinders; then the strength of the tube c d is to that of the solid a J as the line d c is to the line a I. ' 6 Bishop ' On Deformities', 1852, p. 14. GENERAL STRUCTURE OF BONE. 7 In some animals which seldom or never leave the water, the bones have no medullary cavities, but are completely filled by cancellous tissue. This is the case in the penguins (Nos. 1138 to 1140), the whales, and amphibia, whose solid bones appear to act as ballast. In the early part of the seventeenth century, Galileo observed in nature a variety of instances in which the strength of bodies was made very great consistently with lightness by the arrangement of their struct- ure. This most profound philosopher, when accused of atheistical opin- ions, and interrogated before the Inquisition as to his belief in a Supreme Being, picked up a straw from the floor of his prison, and replied, 'If there were nothing else in nature to teach me the existence of a Deity, even this straw would be sufficient.' Air Cells in Bone. Strength and lightness are thus combined in the economy of bones. This principle is carried to the extreme in the bones of birds, which are filled with air instead of marrow. There is a communication between the lungs and the cavities in the bones of birds (Nos. 1107-8); and the air which fills the bones being warm, renders them still lighter. The extent to which air is admitted into the bones of birds is generally in proportion to their powers of flight. The ostrich (No. 1114), which never flies, has air only in the bones of his legs. The great beak of the hornbill forms one large air cell (No. 1492); even the thin columns of the cancellous tissue in the interior are hollow and filled with air. In this bird, as well as in the toucan, every bone of the skeleton, down to the little bones of the claws, is filled with air. In the little ' apteryx* of New Zealand, which has no available wings, and in the penguin, which rarely leaves the water, no bones of the skeleton except those of the skull receive air. In the bones of the chick there are no medullary cavities; as the bird grows its bones become hollowed out, and filled with marrow, which is subsequently, in the mature bird, removed and replaced by warm air. In mammalia there are no air cells except in the bones of the head. There are large air cells (sinuses) in the frontal, sphenoid, ethmoid, palate, maxillary and mastoid bones in man. Bone divisible into Layers. Although the compact tissue of bone seems hard and solid as stone, yet it is made up of layers placed so close together, that there is no apparent interval between them. Toward the articular ends (Plate I. Fig. 3), the layers gradually separate to form the cancellous tissue, and the compact tissue becomes thinner in proportion. In bones long weather-beaten in a churchyard, these layers may be peeled 8 HUMAN OSTEOLOGY. off one after another; or if the earthy matter be removed by acid, the animal matter admits of being stripped off like so many leaves. It is essential to bear in mind this lamellar structure of bone, because it explains what is observed in cases of inflammation of bone namely, that the enlargement of the blood-vessels together with the inflammatory deposit separates the layers from each other, and thus causes the bone to expand and be perceptibly increased in diameter, as seen in the adjoining wood-cut (Fig. 3), taken from a prepara- tion in the museum of St. Bartholomew's Hospital. Cancellous Tissue: Arrangement. The cancellous tissue occu- pies the interior of bones, and chiefly the articular ends. It is formed by the separation of the component layers of the bone, and these are con- nected by cross plates and fine tubes, which form a kind of lattice-work with a most delicate and elegant arrangement. The cancellous archi- tecture of bones is arranged upon this principle: its columns always run along the lines of greatest pressure, thus combining the greatest strength and elasticity with lightness. A beautifui example of this is seen in the section of the cancellous tissue of the thigh-bone (Plate I.). At the lower part, toward the knee, the layers run vertically that is, in the direction of the axis of the shaft, this being the line of pressure when the body is erect. But in the neck of the thigh-bone the layers are arranged in de- cussating curves like Gothic arches, one within the other, and sustain with the greatest mechanical advantage the weight transmitted on to the heads of the thigh-bones. (Norm. Hum. Ost., Nos. 211 to 222). Cancellous Tissue: Properties. Though so light and spongy, the cancellous tissue is able to support a great weight without giving way. "We may form some idea of its strength from the following experiment: 7 A cubic inch of cancellous texture was taken from the lower end of the femur, and placed with its principal layers upright. Four cwt. was then placed upon it, but it did not give way in the least. Six cwt. made it sink half an inch. Yet the cubic inch of bone itself did not weigh more than 54 grains. Not only is cancellous tissue strong as well as light, but it possesses another advantage that of diminishing shocks. When a ball of ivory strikes another, as in the game of billiards, the whole force of the shock is transmitted from one to the other; but let a ball made of the 1 ' Outlines of Osteology, ' p. 368. T. Ward. GENERAL STRUCTURE OF BONE. 9 cancellous tissue be interposed, and then see how the shock will be broken. This property of diminishing shocks is of course greater when the bone is in its natural state and filled with marrow. The spaces formed by the cancellous tissue vary in size and shape, but freely communicate with each other, and with the holes on the surface of the bones. This is easily proved by boring a hole at one end of a bone, and pouring mercury into it: we shall find that the mercury will run out freely through the natural holes at the other end. * Marrow, Yellow. The interior of the shaft of a long bone is filled with yellow marrow; a substance composed almost entirely of fat (96 per cent.); that is, in bones that are healthy. Like all other fat, it is re- moved in cases of great emaciation in general dropsy, for instance; and its place is supplied by an albuminous fluid. Hence the bones of a drop- sical subject are always the least greasy, and the best adapted for skeletons. Marrow, Red. The cancellous tissue of the articular ends of long bones, and of the bodies of the vertebrae, the sternum, the ribs, and the bones of the cranium, contain another kind of marrow of a red color. This red marrow differs from the yellow, in that it contains little or no fat not more than 1 per cent. It consists of 75 per cent, of water and 25 per cent, of solid matters, chiefly albumen. It is this kind of marrow which is found in all the bones of the foetus, and in infants. Hence it is sometimes called foetal marrow. Examined with a high magnifying power, it is found to contain a number of oval, many-nucleated cells (Plate IV. Fig. 9). Cells of this form are found in most rapidly growing tumors and are called ' myeloid ' cells. They form the greater part of the so-called myeloid tumors. 8 Blood supply of Bones. At the articular ends of any long bone, or on the body of a vertebra, we observe a number of holes. Near the lower end of the thigh-bone we might soon count as many as 200 or more. What are these holes? The smaller transmit the articular arteries which nourish the vascular cancellous tissue. The larger contain veins which run by themselves. These veins of the cancellous tissue are large and nu- merous. They traverse and ramify through this tissue in various direc- tions in special canals with thin walls of bone. They are well seen in a section through the body of a vertebra (Plate XXV. Fig. 7), also in the cancellous tissue (termed ' diploe ') of the cranial bones. From a surgical point of view these ' diploic' veins are interesting, on account of their lia- 8 'Lectures 011 Surgical Pathology.' Sir J. Paget, F.R.S. 10 HUMAN OSTEOLOGY. bility to inflame after severe injuries of the head: such inflammation may lead to suppuration in the diploe, which is often fatal. The adjoining figure (4) shows the large venous canals in the ' diploe ' of the skull-cap. Again, on the outside of the shaft of a long bone there are a number of minute grooves, which run for the most part parallel to the shaft, and lodge blood-vessels. At the bottom of these grooves lie a multitude of 4. Veins in the Diploe of the Skull. still more minute holes, barely visible to the naked eye, but easily seen through a small pocket-lens. These holes transmit the blood-vessels from the ' periosteum/ or membrane covering the bone, to the compact tissue. Artery of the Marrow. The marrow in the interior of the bone is supplied with blood by the ' medullary artery/ This artery reaches the marrow through a very distinct canal (canal for the nutrient artery of the medulla), which runs obliquely through the shaft, near its middle. In a long bone like the femur there are generally two of these, situated at the back part. As soon as the artery reaches the medullary cavity, it divides into two branches, an ascending and a descending, which ramify in and supply the marrow, and finally communicate with the f articular ' arteries already described. Thus the several parts of a long bone are supplied with blood as fol- lows: The compact wall of the shaft by blood-vessels from the perios- teum; the marrow in the interior by a special medullary artery; and the cancellous tissue of the ends by the articular arteries. The blood-vessels of these several parts are not exclusive, but communicate more or less with each other when the parts of the bone have united with the shaft. Hence they readily reciprocate their morbid actions, and inflammation arising in the one part may spread to the other. Now, although these three orders GENERAL STRUCTURE OF BONE. 11 FIG. 5. Blood-Vessels of Perios- teum. of blood-vessels do communicate in the bone, yet we cannot be surprised to find that when a bone is broken below the canal for the nutrient artery of the marrow, the lower fragment, being deprived of part of its supply of blood, in some cases becomes atrophied and thinner.' Periosteum : its use. A fibrous membrane, termed the periosteum, invests the bones everywhere except at the insertion of strong tendons, and where covered with cartilage. This perios- teum consists of two layers, an external one, tough and fibrous, and an internal one (osteo- genetic), soft and cellular, in which the blood- vessels break up into minute branches before penetrating the pores on the surface of the bones. The adjoining figure shows the arrange- ment of the blood-vessels of the periosteum. The periosteum likewise provides each of the vessels entering the bone with a fibrous cover- ing. It assists in the formation of bone, and afterward in its nutrition. If, therefore, the periosteum be torn from the surface of a bone, there is a risk that a layer of the subjacent bone will lose its vitality and be cast off. Medullary Membrane. The medullary canal and the cells (marrow spaces) of the cancellous tissue are lined by an extremely delicate mem- brane, termed the ' endosteum.' It is much more delicate than the perios- teum; nevertheless, it supports the marrow, and provides a stratum for the subdivisions of the medullary artery, before they penetrate the contiguous bone. Nerves in Bone. Periosteum and bone unquestionably possess nerves. This is proved by absolute demonstration, and by disease. Nerves may be traced into some of the minute foramina on the shaft of a long bone, and into the articular ends. A nerve also enters the medullary canal with the nutrient artery of the medulla, and divides like the artery into an ascending and a descending branch. Of all the bones, the tibia presents the largest canal for the nutrient artery of the marrow; in this bone also it is easy to trace the entrance of the nerve with the artery. Though bone in health has but little feeling, when diseased it becomes highly sensitive. There is such a thing as ' neuralgia ' of bone. Every Curling, ' Medico-Chir. Trans. ' vol. xx. 12 HUMAN OSTEOLOGY. surgeon must have witnessed how sensitive are granulations from bone. Indeed, it is probable that the severe pain attendant on the ulceration of articular cartilage is occasioned by the pressure of the cartilage on the bone granulations beneath it. Lymphatics of Bone. The lymphatics of bone have been actually demonstrated by injecting the lymphatics of the body of a vertebra. 10 It has been recently proved by injections that the blood-vessels of Haversian canals are surrounded by perivascular lymphatic vessels. 11 This accounts for the fact that ivory pegs introduced into bones, for the purpose of consolidating ununited fractures, are in some instances absorbed. MICKOSCOPIC STRUCTURE OF BOKE. This is a most interesting and instructive study. It reveals to us that bones are as minutely provided with blood-vessels and nerves as the softer parts of the body. Being as fully organized as other parts, we cannot wonder that they are subject tolike diseases. We have to investigate how the bones are formed in early life, how they grow to maturity, how their health is maintained, how their injuries are repaired. Would anyone, looking at a solid bone, expect to find that even its hardest parts are tun- nelled out by a network of minute canals containing blood-vessels; and that from these canals other tubes, infinitely more minute, and connected with a series of reservoirs, radiate in all directions and convey nutritious fluids? General Idea : Haversian Canals. Let us first get a general idea of the microscopic structure of bone, and go into details afterward. If a transverse section from the shaft of a long bone be ground extremely thin, and examined with a power of about 20 diameters (Plate II. Fig. 5), we see a number of holes, with dark spots grouped around them, in a series of tolerably concentric circles. These holes are sections of the canals (termed 'Haversian') 111 which transmit blood-vessels into the sub- stance of the bone. The dark spots are minute reservoirs, called ' lacunae/ They look like solid bodies, but they are cavities and are occupied during life by soft ' bone corpuscles/ concerning which more will be said here- after. Different parts of the section show that the Haversian canals vary 10 Cruikshank, 'Anatomy of the Absorbent Vessels/ 1790, p. 198. 11 Budge, ' Archivf. Microso. Anatomic,' bd. 13. 12 Dr. Clopton Havers, an English physician of the seventeenth century, was the first to describe these canals. Bfcl. Fibre- cartilage. m m ' Hyaline cartilage. BONE. ' Longitudinal section of Haversian canals Transverse section of Hawersian ca.na.ls. f/r / f/A ^ 7 Lacunae and Car.alicali Ki^ily magnified lOOdia' : ifeB8:: ^<'' ^SK' wi^iir, Hawerstan systems. MICROSCOPIC STRUCTURE OF BONE. 13 considerably in size and shape. They are generally round or oval. Those nearest to the circumference of the bone are very small; but toward the medullary cavity they are seen to be larger, and at last open out into the cells of the cancellous texture. Haversian Lamellae. The same section examined with a higher power (Plate II. Fig. 7) shows that the Haversian canals are surrounded by a series of concentric lines, resembling the transverse section of the branch of a tree. These lines are termed the 'lamellae/ They are so many layers or rings of bone that have been developed within the Haver- sian canal. Even the smallest Haversian canal was, when originally formed, a much wider space, and circumscribed by only a single layer of bone; but in process of growth the canal becomes gradually contracted by the deposit of successive layers of bone. The dark spots, before al- luded to as the ' lacunae/ are situated between the lamellae; under a higher magnifying power (Plate II. Fig. 6), they look like insects. The central part or the lacuna, representing the body of the insect, is hollow, and the dark filaments which run out from it, representing the legs, are minute tubes termed 'canaliculi/ These are exceedingly numerous, and radiate from all parts of the * lacuna/ through the lamellae. Now, since the ca- naliculi of one circle of lacunae communicate most freely with those of the next circle, and the canaliculi nearest to the Haversian canal open directly into it, it follows that by means of this system of radiating tubes a com- plete communication is established between the Haversian canal in the centre, and the successive circles of bone which surround it. The nutri- ent material of the bone proceeds from the perivascular lymphatics in the central canal, and is transmitted through the canaliculi from one lacuna to another. Haversian System. Every Haversian canal taken in conjunction with its concentric layers of bone, lacunae, and canaliculi, is termed an ' Haversian system/ (Plate II. Fig. 7.) Almost all the compact substance of bone is made up of a multitude of these ' Haversian systems/ Each system is, to a certain extent, inde- pendent of its neighbor, since the lacunae of one system communicate very sparingly with those of another. In consequence of this isolation, we sometimes find, in favorable sections, that each system is more or less cir- cumscribed by a tolerably distinct white line, which is transparent bone with but few canaliculi. Haversian Interspaces. As the Haversian systems are for the most 14 HUMAN OSTEOLOGY. part circular, and arranged like sticks in a faggot, it is clear they cannot touch each other in all parts of their circumference; so that here and there triangular portions of bone fill up the gaps between them. Such portions are termed ' Haversian interspaces.' (Plate II. Fig. 7). These 'outly- ing ' portions of bone are also provided with lacunae and canaliculi, and they derive their nourishment from the surrounding Haversian systems, of which they are dependencies. The section we have hitherto been examining was a transverse one. "We must now make an equally thin section in the longitudinal direction of the shaft, and we then have quite a different appearance. (Plate II. Fig. 4.) We cut in the course of the Haversian canals, not across them; and we find that, as a general rule, they run parallel to the surface of the bone (no matter whether long or fiat), and that they communicate very frequently by transverse or more or less oblique canals. If the section be large enough to include the Haversian canals near the circumference, we find that many open on the outer surface and admit blood-vessels from the periosteum; others, again, open into the medullary canal, and admit blood-vessels from the interior. In this way the Haversi%n canals permeate the compact substance of the bone, and establish a free communication between the blood-vessels of the periosteum and those of the medulla. These canals may, in fact, be regarded as so many multiplications of sur- face for the ramifications of blood-vessels, whereby every part of the bone substance is brought within the range of nutrition. In this longitudinal section, the lamellae, instead of being arranged concentrically, are seen running in lines parallel with the Haversian canals to which they belong. Bone Tissue. At this stage of the investigation, a question naturally arises Where is the earthy material, the phosphate and carbonate of lime? To see this, the transverse section must be magnified about 1,200 diame- ters. (Plate II. Fig. 6.) We then discover that the earthy ingredient consists of an infinite multitude of minute osseous granules, which are deposited in a ' matrix ' or bed of animal matter. This mixture of earthy granules and animal matter is called 'bone tissue.' It occupies all the space between the lacunae and their canaliculi. If the specimen were steeped for a time in dilute hydrochloric acid, the osseous granules would be dissolved out of it, and the little pits in the matrix in which the gran- ules were imbedded would become apparent. So far we have acquired a general notion of the minute structure MICROSCOPIC STRUCTURE OF BONE. 15 of bone; that is to say, of the ' Haversian canals,' the ' lacunae/ and their ' canaliculi/ the ' lamellae/ and the ' osseous granules/ "We must now speak of these several parts a little more in detail; and first, of the Haversian canals. Haversian Canals. As said before, the Haversian canals are tun- nels in the compact substance of the bone, which contain the blood-ves- sels. Observe, they form no part of the essential structure of bone. Wher- ever bone is so thin as to be able to derive its nutrition from the vascular membrane covering its surface, we do not find Haversian canals in it, nor does it require any. For instance, the delicate plates of bone composing cancellous tissue, the paper-like bones in the interior of the nose, have no Haversian canals in them; but they have plenty of lacunae, which send out their canaliculi to open on the surface and imbibe the requisite nutri- tion. Bone so thin as to need no Haversian canals is called ' non-vascular* bone. Such bone lives upon the blood which flows through the minute vessels of its periosteum. Bone has, therefore, like all other living struct- ures, a self-formative power, and draws from the blood the materials for its own nutrition.. The Haversian canals vary in diameter from 10 1 00 to ^5- of an inch, the average being about -g-J-g-. The smallest are found near the outer sur- face, where the bone is the most compact; but they gradually become larger toward the interior, where they open out into the cancellous tissue, or into the medullary cavity. All, whatever their direction may be, are sur- rounded by concentric lamellae of bone; but the number of the lamellae varies around different canals from 5 to 15 or more; a smaller number in young bone, and a larger in old. All are lined by a very delicate mem- brane, continuous with the periosteum. The smallest canals contain only a single capillary blood-vessel; the larger contain a network of ves- sels, while the largest, which gradually merge into the cancellous tissue, contain marrow as well as blood-vessels. Here it may be as well to mention a fact concerning the minute struct- ure of bone, which should never be lost sight of. It is this: that every- where underneath the membrane in contact with the surface of bone, whether it be the periosteum covering the exterior, the prolongation of it lining the Haversian canals, or the medullary membrane (endosteum) lining the cancelli, there is a delicate layer of soft connective tissue, with a multitude of small corpuscles in it, termed ' osteoblasts.' Now, it has been ascertained that these osteoblasts, and the soft tissue in which they 16 HUMAN OSTEOLOGY. are imbedded, are mainly concerned in the formation and the growth of the bone; and that by the successive ossification of these tissues, the con- centric layers of bone are produced within the Haversian canals. Haversian Canals dilated by Inflammation. The knowledge of the free circulation of blood through the substance of bone gives us the key to some of the effects produced by inflammation in it. For example, as inflammation in soft parts is attended by dilatation of the blood-vessels, so is it in the case of bone. When bone is actu- ally inflamed, the blood-vessels in the Haversian canals become greatly enlarged, and cause the canals themselves to become larger by absorption of the bone tissue so much so as to give the bone, sometimes, a reddish color. In operations where the surgeon has to cut through inflamed bone, one may see the blood flowing from the cut surface of the bone, as it would from the soft parts. More than this, the distended blood-vessels may occasion not only a gradual enlargement of the Haver- sian canals, but their inflammatory deposit may cauje even a general swelling of the compact substance of the bone and a natural separation of its component layers, so that it becomes light and spongy, as seen in the adjoining figure. 13 Haversian Canals obliterated by Inflammation. On the other hand, in some cases, e.g. in chronic inflammation, we sometimes find that bones become harder and thicker than natural. They may become as hard as ivory, and can take a polish. Here the Haversian canals are nearly filled up by successive layers of bone. Indurated bone is therefore less vascular than healthy bone. A good example of ' eburnation ' of bone is occasionally seen as the result of chronic osteo-arthritis, where the articular ends of bone lose their cartilage and become hard and polished like ivory, owing to the blocking up of the Haversian canals by osseous tissue. Lacunae and their Contents. The 'lacunae' are the insect-like cavities which we find between the lamellae, arranged in concentric circles around the Haversian canals. They are characteristic of true bone, and distinguish it from 'calcifications', sometimes met with as products of disease. Formerly the lacunae and canaliculi, in consequence of their dark color, were considered to be solid; but later observations have proved them to be hollow spaces. Each lacuna in the living bone contains a 13 From a preparation in the museum at St. Bartholomew's Hospital. '>: 'j* - ' 830 ,~ ^ Si w; ^ ?" > .$/ ^, m - ^'?^f%'4^| Cartilage cells enWr^ed tnd V arranged m rows, separated by ._ _ 0teoblats replace fKe eartila^e eIb. Format o meduli&ry spaces. Ii oteculir rmmJn of c0f ied carb la^e ted with tfiin layer of bone. 1 The layers of boi\ thicks / as cs.kifid ma I bsorb*d. Section of ossifying cartilage at the E L actinic and Canaliculi, Bone coppuscles and their processes wludi occupyiljela.cil.Ti SB andcanaliculi of fiq.4* Section of ossifying carti1a.J>e.sWin^t:he loops cf Hooa vessels. IVabecube of bune . Bone corpuscle Osteoblas-ts depositing bone on trabeculse Interspaces filled with osteoblastic twsue- ,; : -p -,.,:* Section of a youn parietal bone . MICROSCOPIC STRUCTURE OF BONE. 17 soft nucleated substance termed a bone corpuscle, which sends its soft processes or 'outrunners' along the canaliculi. The bodies in the lacunae and canaliculi circulate nutritious matter through the bone. The lacunae and canaliculi can be filled with Canada balsam. It is curious that in the bones of Egyptian mummies these minute cavities are filled with the bituminous material. Such a bone corpuscle, with its processes highly magnified, is shown in Plate III. Fig. 5. As a rule, the lacunae are oval and flattened, so that one of their broad sides is turned toward the Haversian canal. The first ring of lacunae sends some of its canaliculi directly into the Haversian canal, while others communicate with the canaliculi of the second ring, and so on throughout the whole system. The nutrient fluid in the perivascular lymphatics in the Haversian canal enters the nearest canaliculi, and then the inhabitants of the nearest row of lacunae, and is gradually passed on to all the others in the Haversian system. One may say, then, that the inhabitants of the lacunae are parts of the machinery of the circulation and nutrition in the bone. Size and Shape. In man, the lacunae measure about ^-g- of an inch in their long diameter, and about -^^ in their short. It has been shown that they vary in size and shape in the four great classes of ani- mals, so that by means of this test it can be ascertained with certainty whether a given fragment of bone be part of a mammal, a bird, a reptile, or a fish. As this test is equally applicable in the case of fossil bones, it has an important bearing upon the study of geology. Another inter- esting fact is, that the size of the lacunae bears very little relation to the size of the animals to which they belong. They are nearly as large in the bones of the little lizard as they are in those of the enormous extinct lizard, the Iguanodon. But their size does bear an exact proportion to that of the blood corpuscles in the several classes of animals. Therefore, as am- phibia have the largest blood corpuscles, so have they the largest lacunae. 14 Canaliculi : Size and Office. Respecting the ' canaliculi ' (Plate II. Fig. 7), observe how exceedingly minute they are; that they run off from all parts of the circumference of the lacunae and communicate most freely with the canaliculi of the adjoining lacunae. Their diameters range from H&OQ of an inch to g ?i0'6 f an inch; but there are some even smaller. Soft nucleated corpuscles, ' bone corpuscles/ lie in the lacunae, and have many delicate branching processes, by means of which they in- 14 Discovered by Mr. Q.ueckett. 2 18 HUMAN OSTEOLOGY. tercommunicate and pass lymph from one to another. These branching processes lie in the canaliculi. Lamellae. The ' circumferential ' lamellae encircle the shaft of the bone (Plate II. Fig. 5), and result from the bone growing in thickness by a deposit of new layers on the old shaft by the deep layers of the peri- osteum. The ' Haversian ' lamellae are the concentric tubes of bone enclosing the Haversian vessel (Plate II. Fig. 7). These result from successive layers of bone being deposited around the Haversian vessel, the one within the other, encroaching more and more on the space in which the vessel lies. This process renders the bone more dense in structure. In transverse sections of fully formed Haversian systems there appear to be from five to fifteen concentric rings of bone varying in thickness from y^ to ^gVjj- of an inch. The ill-defined and interrupted layers apparent here and there in the spaces between Haversian systems are termed ' interstitial lamellae' (Plate II. Fig. 7). It seems doubtful how these interstitial lamellae were origi- nally formed; 16 it maybe that they are the remnants of Haversian systems that have been partially removed by absorption. Nails (Claviculi) of Gagliardi. In carefully-made preparations of decalcified bone, it may be seen that its constibuent lamellae are connected by fibres which perforate them either at a right or an oblique angle, and thus f bolt ' them together. These ' perforating fibres ' or bolts appear to answer a mechanical purpose. They are best shown by separating the lamellae. Thus you see not only some of the bolts pulled out, but also the holes through which they passed. 18 Osseous Granules. The earthy salts are deposited in the animal matrix in the form of exceedingly minute granules. The Germans call them 'bone crumbs.' We cannot see them, however, without a magnify- ing power of 1,200 diameters (Plate II. Fig. 6). They vary in size in dif- ferent specimens of bone. In man their size ranges from 6o \ 6 to 14 ^ 0o of an inch. They can be very distinctly seen in the skulls of small birds the canary, for instance and also in the skull of the bat, where they are so much larger than in the human subject. After a section of bone has been steeped for some time in dilute hydrochloric acid, these earthy par- 15 ' Philosoph. Trans,' 1853. Messrs. Tomes and De Morgan. 16 First described by Domenico Gagliardi, Professor of Medicine at Rome in the seventeenth century. Anatomie Ossium novis inventis illustrata. Romae, 1689, in 8vo. .MICROSCOPIC STRUCTURE OF BONE. 19 tides will be dissolved out of the animal matrix, and the little cavities in which they are imbedded can then be distinctly seen. Found in Pus from Dead Bone. It is an interesting and valuable practical fact, that these earthy granules are generally present in the pus which comes from dead bone. If a specimen of pus under such cir- cumstances be examined with a power of 500 diameters, a number of earth granules may be detected among the pus cells, proving that there is dead bone somewhere. l7 In pus coming from diseased bone there is as much as two and a half per cent, of phosphate of lime. 18 Articular Bone. By articular bone we understand a thin layer of bone situated immediately under articular cartilage; and since there is a peculiarity about the structure of it, we will allude to it here. If a section be made perpendicularly through the articular surface of any fresh bone with the cartilage attached, it will be ob- served (as seen in Fig. 7) that the car- tilage does not rest immediately upon the cancellous tissue of the bone, but upon a thin compact crust of bone which closes the cancelli. This crust, which we call ' articular bone,' varies in thickness, and is of a remarkably white color. But its chief peculiarity consists in this that it has no Haver- sian canals, and therefore is not vascu- FIQ. 7. Structure of Articular Bone. fetr. The blood-vessels of the cancel- lous tissue run up only as high as its under surface, and then turn back in loops. Moreover, its ' lacunae ' are three or four times larger than in ordinary bone, and are destitute of canaliculi. This layer of bone has no Ilaversian canals, is much less porous than common bone, and in conse- quence of its closer texture is all the stronger, and supports the articular cartilage on a very unyielding surface. Although articular bone and adult articular cartilage have no blood- vessels in health, yet they both become vascular in some cases of disease of the curtilage. . Blood-vessels, when well injected, may then be seen shooting up through the heretofore nonvascular layer of bone, into the cartilage on its surface. tt Upper cartilage cells. b Lower cartilage cells. O Articular bone. d Bone of the shaft. Mr. Queckett. Mr. Brausby Cooper. 20 HUMAN OSTEOLOGY. STEUCTTJEE AKD VAEIETIES OF CAETILAGE. Varieties of Cartilage. Cartilage, commonly called ' gristle/ is tough, flexible, and more or less elastic. There are several kinds of it, which have functions varying with their position and structure. It con- sists of nucleated cells embedded in a matrix or intercellular substance. Hyaline Cartilage. Where the matrix is translucent and structure- less it is called hyaline cartilage. Nearly the entire skeleton of the foetus has this structure at some time or another as well as the white cartilage covering the articular ends of bones. White Fibro-Cartilage. The intercellular substance may be white and fibrous, then it is called 'white fibro-cartilage/ This variety is but slightly elastic, and the cells are small and scattered (Plate II. Fig. 1). The intervertebral substance consists mainly of this variety as well as the interarticular fibro-cartilages. Yellow Fibro-Cartilage. The gristle of the ear, epiglottis, and the Eustachian tube is of a yellow color, is very elastic, and its intercellu- lar substance consists of long interlacing wavy fibres. It is therefore named 'yellow fibro-cartilage.' The cells in this variety are large and arranged in fusiform rows, each row containing from 4 to 6 cells. Cellular Cartilage. As early as the fourth week of fetal life, when the embryo, is but f of an inch long, the principal part of the skeleton is mapped out by the formation of firm masses of cells called ' cellular ' car- tilage. (Plate II. Fig. 3.) Cartilaginous Skeleton. A week later an intercellular substance has developed in this cellular cartilage, converting it into ' hyaline ' carti- lage, and giving it greater solidity. Thus, the whole foetal skeleton, with the exception of the skull-cap and the bones of the face, consist at one time of hyaline cartilage. At the fifth week bony substance begins to be deposited in the middle of the clavicle; at the sixth week in the lower jaw; and by the seventh week, when the foetus is abont an inch long (Norm. Hum. Ost., No.l), a small deposit of bone has made its appearance in the middle of nearly every bone in the body. The points at which the bony deposit commences in a bone are called its ' centres of ossification/ It will th'erefore be under- stood that the deposition of bone does not take place at the same time in all parts of the cartilage, but only about these 'centres of ossification.' Meaning of Centres of Ossification. Every bone has a definite OSSIFICATION. 21 number of these centres, which always appear in the same place; and from these centres the ossification extends according to a regular plan. The number of centres varies in different bones. Some bones have only a single centre; others two, three, five, seven, etc. ; and the bone called the 'sacrum' has as many as thirty-three centres from which its ossifica- tion is completed. Observe, the centres of any given bone do not all appear at once; some appear before birth, others after it, but all in regular succession, and at stated periods, according to the degree of importance of the bone, and the function which it has to perform; e.g. the lower jaw and the ribs ossify early, because suction and respiration are brought into play at birth. As a general rule, each centre appears first in the middle of the cartilage; and thence the ossification extends toward the circumference in the flat bones, and toward the extremities in the long bones. Almost all the bones, then, in infancy and childhood are made up of so many distinct bony pieces united together by cartilage; and these several pieces remain distinct until the stature of the individual is complete, after which they are all consolidated. Perichondrium. All kinds of cartilage, with the exception of that which covers the ends of the bone (articular cartilage), are invested with a white fibrous membrane, termed ' perichondrium.' This, like the peri- osteum of the bones, contains plexuses of blood-vessels ramifying all over the cartilage. Cartilage contains no blood-vessels. But when diseased, it has been proved by injection that blood-vessels do shoot into the cartilage through the layer of articular bone beneath it. 19 Ossification of Femur. As an example of what can be seen of the process of ossification with the naked eye, let us follow out that of the thigh-bone (Plate IV. Figs. 1 to 6). The future bone is at first sketched out in hyaline cartilage. About the seventh week after conception, the first centre of ossification appears in the middle of the shaft as is the case in all the long bones (Fig. 1). From this point ossification gradually extends up and down the shaft, which is all ossified before the other cen- tres appear. About the last month of foetal life, a second centre appears in the lower endj which forms the knee (Fig. 3). About the end of the first year after birth, a third centre appears at the upper end or head of 19 See ' Catalogue of Histological Series, 1 Mus. Roy. Coll. Surg., vol. i. plate viii. Fig. 11. 22 HUMAN OSTEOLOGY. the bone (Fig. 4). In the course of the fourth year, a fourth centre appears in the projection termed the * trochanter major' (Fig. 5). In the course of the fourteenth or fifteenth year a fifth and last centre appears in the 'trochanter minor' (Fig. 6). 'Diaphysis' and 'Epiphysis.' Thus, then, the thigh-bone has five centres of ossification. The shaft or body of the bone, which ossifies first, is called the f diaphysis; ' the other parts are termed ' epiphyses.' As these epiphyses, during the period of growth, are only united to the shaft by a layer of cartilage, the separation of an epiphysis by violence is not an unfrequent accident in childhood. When growth is complete, all the epiphyses are consolidated with the rest of the bone, and no cartilage remains except at the articular surfaces, where there is a thin layer of it which breaks the shocks at the joints. An ' epiphysis,' therefore, is a portion of bone growing upon another, but separated from it by cartilage. Order of Union of Epiphyses to Shaft. It is worth observing, in the long bones, that the epiphyses of that end toward which the canal for the medullary artery runs, are the last to commence to ossify. It is a curious fact, also, that the order in which the epiphyses unite to the shaft of a bone is just the reverse of that in which they begin to ossify. Thus, the epiphysis of the trochanter minor, though ossifying last, unites first. The same may be said of the trochanter major, of the head of the femur, and, lastly, of the lower end. At the age of twenty- one, or near it, they have all united to form a single bone. The fibula is the only exception to the above rules, its lower epiphysis ossifying first and uniting first to the shaft. In Sauropsida, the place of the epiphyses is taken by thick pads of cartilage, which gradually ossify from the shafts. These are, therefore, not true epiphyses. Birds, however, have a centre of ossification which appears in the upper projection of cartilage on the tibia. This may be seen in the leg of a common fowl. Advantages of several Centres. The fact that bones are developed from several ossific centres, separated by layers of cartilage, is advanta- geous to the growing animal. For example, it is necessary to have the shaft of a bone ossified to support weight, while other parts remain cartilage and diminish concussion, thus acting as buffers. ' The young lamb or foal,' to use the words of Professor Owen, ' can stand on its four legs as soon as it is born; it lifts its body well above the ground, and quickly begins to run and bound. The shock to the limbs themselves is broken and cli- Ffc.6. ft showing the iprmatioriof larietal bone of aTcebus. .Haversian canals Cells from TOE tiCl ma.rrcv/. Section OSSIFICATION. 23 minished at this tender age by the division of the supporting long bones by the interposition of the cushions of cartilage between the diaphyses and the epiphyses/ We see, moreover, a definite use in separate centres of ossification for the bones of the head, not only as facilitating growth, but also the process of birth. The bones of the skull-cap, being connected only by membrane, overlap each other a little during parturition, and thus a large head is ad- mitted through a comparatively small pelvis. Bones developed in Membrane. Most of the bones in the human body pre-exist in the shape of cartilage, and form what is called the ' car- tilaginous skeleton,' which supports the embryo. But there are some bones which do not pre-exist as cartilage, and are formed directly in mem- brane, namely, the bones of the skull-cap (the frontal bone, the parietal, the upper half of the occipital, the squamous and tympanic parts of the temporal); also, the bones of the face; and lastly, the inner plate of the pterygoid process of the sphenoid. In short, none of the bones of the skull pre-exist as cartilage, except those which form the base of the skull. The base is sketched out in cartilage at a very early period of fcetal life, and forms a support to the young brain. The cap of the skull, at the time we are speaking of, is simply membranous. Ossification in Membrane. We will examine first what can be seen of the formation of bone in membrane with the naked eye, taking the parietal bone as an example. In the early embryo (Norm. Hum. Ost., Nos. 1 to 43) the covering of the brain is composed of two closely united membranes an outer, termed the ' pericranium J ; and an inner, termed the ' dura mater ' : between these the bone is laid down. About the end of the second month after conception, a centre of ossification appears in the middle of the space which is to be occupied by the parietal bone. From this point the deposition of bone spreads in radiating fibres (Plate IV. Fig. 7). Similar centres of ossification appear simultaneously in other parts of the soft covering of the brain, and, radiating in the same man- ner, sketch out the rudiments of the several bones of the skull-cap. For some time the individual bones are connected simply by membrane; and even at birth they can overlap each other a little, and so facilitate partu- rition. Long after birth, indeed, there are parts of the skull-cap closed in by membrane only, as every one knows who has felt the head of an in- fant (Plate XVIII. Fig. 4). These unossified parts are called the ' fon- tanelles/ from the visible pulsations of the brain beneath them, like the 24 HUMAN OSTEOLOGY. welling up of a spring. As the child grows, the rays from the edges of the bones meet and dovetail so as to form what are called the * sutures ' (Plate XVIII. Fig. 2). For a long period of life the sutures may be sepa- rated; indeed, a thin film of animal matter is left unossified between the interlocking teeth of the bone, which considerably diminishes the shock to the brain from a blow on the cranium. As old age creeps on, even this film of animal matter ossifies, and the cap of the skull becomes a solid dome of bone, with all trace of the sutures lost. Microscopic Examination. Let us now study what can be learned with the microscope of the process of ossification in membrane, taking that of the parietal bone as an example. The membrane or animal basis to be ossified is composed of fibres like those of common connective tissue. The fibres interlace freely and the meshes between them are filled with blood-vessels and closely packed granular corpuscles termed ' osteoblasts.' These are all the materials re- quired for bone building. Changes in the Membrane. The centre of ossification is at the (future) parietal eminence. Just before the appearance of the bone salts, the membrane becomes thicker and more vascular. Its component fibres radiate in thicker bundles from the centre toward the circumference, sketching in advance the lines in which the bone is to be laid. Meantime the ' osteoblasts' have enormously multiplied. Osteoblasts: their Function. The ' osteoblasts ' (bone buds or germs) are granu- lar nucleated corpuscles about the size of the colorless corpuscles of the blood. They are so named because they and their descendants ap- pear to take most important parts in the actual formation of bone. It is probable that they are not all destined to a like future. But one of their chief functions appears to be to ab- stract from the blood the bone salts, to deposit them in and around the fibres of the mem- brane, and to become themselves ossified, and buried in the fabric of the bone, as the bricks of a building are in the mortar. From the centre of ossification the deposit of bone shoots out in needle-like rays (trabeculffi) toward the circumference, as shown in the FIG. 8. Diagrammatic sketch of part of an Ossifying Parietal Bone of a Four Months' "Foetus. (From a Preparation in the Museum of the R. C. of Surgeons.) OSSIFICATION. 25 annexed wood-cut (Fig. 8). Under a high power the rays of bone can be seen covered with layers of osteoblasts, which successively ossify, and thus the trabeculae grow in thickness. The best place to study the process is at the points of the rays where the membrane is more or less transpar- ent. The dark rays may be seen lying amongst the crowd of osteoblasts, and some of the osteoblasts in various stages of ossification upon the rays. We may thus infer how the bone grows in extent. To see how the bone grows in thickness, a section should be made across the rays where they are a little thicker. Such a section (Fig. 9) shows that the rays become connected by cross arches, and thus form channels in A. Periosteum. B. Trabecute of bone. Osteoblasts with blood-vessels. FIG. 9. Vertical Section through an Ossifying Parietal Bone. which the blood-vessels and bone-building materials lie. These channels are the Haversian canals. Seme of them remain as cancellous tissue; others are gradually filled by the ossification of concentric layers of os- teoblasts and become Haversian systems. (Plate IV. Fig. 8.) Bone Corpuscles : Origin. The interesting but difficult question as to the origin of the bone corpuscles and their connecting processes has been for many years under .discussion. But the now generally accepted doctrine is, that they are developed from some of the osteoblasts. It has been already observed that the osteoblasts have probably not all the same future. It is the destiny of some to become ossified. It may be the des- tiny of some to become marrow cells: while others are destined to be de- veloped into bone corpuscles, and perform their allotted functions shut up in their bony crypts (lacunae) and their connecting processes in bony tubes (canaliculi). The evidence of this development of osteoblasts into bone corpuscles is derived from the fact that some of them can be seen in the successive stages of their transformation. Ossification in Cartilage. We will now endeavor to explain that the process of ossification in cartilage, rightly understood, is essentially like ossification in membrane. In both cases the materials for bone-build- ing are similar, namely, connective tissue, blood-vessels, and the little cor- puscles termed 'osteoblasts.' The old school used to teach that the carti- 26 HUMAN OSTEOLOGY. lage was directly transformed into bone tissue. But this is not the modern doctrine. The microscope has proved that the cartilage is only a temporary structure, that, having answered a temporary purpose, it is re- moved, and that true bone tissue, of which the materials are derived from the periosteum, is substituted in its place as a new product. Previous to its removal the cartilage undergoes remarkable structural changes, which prepare the way and shape the direction in which the bone is afterward laid down. These preparatory changes are the en- largement of the cartilage cells, and the calcification of the intervening matrix. If we examine the calcified portion of the epiphysial cartilage we find there that the cells are arranged in rows which are parallel to the axis of the bone. It is this appearance which is familiarly known as ossifying cartilage (Fig. 11J). Periosteum. Cartilage cells in calcified matrix. Periosteal ingrowths invading the car- tilage cells. Fio. 10. Diagram of Periosteal Ingrowths from the First Phalanx of Great Toe of a Fretus. (Transverse Section.) As the term calcification might be taken in a wrong sense, it should be clearly understood that it is not the same thing as ossification. Cal- cification is the infiltration of an animal tissue with earthy salts, as in the case of shells, or in the cranium of cartilaginous fishes. Ossification means the formation of true bone a highly organized structure. Calci- fication, in the process before us, is the forerunner of ossification. Thus much premised, let us examine the process of ossification as ob- servable in the cartilaginous shaft and at the epiphysial ends of what is to be a long bone. Calcification of Cartilaginous Matrix. The process begins by the appearance of an opaque spot in the centre of the miniature shaft. This opacity is occasioned by the enlargement of the cartilage cells, and the calcification of the matrix. These changes spread gradually from the cen- OSSIFICATION-. 27 tre up and down the shaft, but stop short of the ends, which are continu- ally growing in advance. Ingrowths of Periosteum. At the same time and to the same ex- tent that the preceding changes are taking place in the cartilage, the deep layer of its surrounding perichondrium (future periosteum) sends off vascular shoots (periosteal ingrowths) of connective tissue charged with osteoblasts which penetrate the calcified cartilage and soon make it hol- low; the enlarged cartilage cells disappearing one after another, and their places being taken by the ' osteoblastic tissue ' from the periosteum (see Fig. 10). Crust of Bone around Shaft. Pari passu with this tunnelling of calcified cartilage by the ingrowths, the deep layer of the periosteum is Epiphysis. Rows of cartilage cells in calcified matrix. Tubular spaces filled with osteoblastic tissue. Circumferential crust of porous bone. General medullary cavity. Periosteum. (The dark spots throughout the diagram te dark spots throughout FIG. 11. Diagram of a Longitudinal Section of Foetal Long Bone. at work laying down a gradually thickening crust of true bone around the shaft (Fig. 11, d). This process is not preceded by cartilage, but is direct membranous ossification, as in the tabular bones of the skull. Summing-up. To form a a correct idea of these separate processes, the mind must grasp them as going on all together, not one after the other. Their general results may be summed up as follows (Fig. 11): 1. The cartilage at the middle is hollowed into a cavity (general medullary) and 28 HUMAN OSTEOLOGY. filled by osteoblastic or bone-building tissue and blood-vessels (e). 2. The shaft is surrounded by a circumferential crust of porous bone; the first rudiment of the true wall (d). 3. The cartilage toward the ends is tun- nelled (by periostea! ingrowths) into irregular tubular (medullary) spaces, also filled with osteoblastic tissue (c). These spaces freely communicate with the general medullary cavity, but are blocked toward the growing ends by a boundary line of cartilage (b). It is in these spaces that blood- vessels in injected preparations can be seen running up to the cartilage cells. 4. The walls of these tubular spaces are formed by the slender re- mains (trabeculse) of the calcified matrix. These slender remains serve as the foundation upon which the true bone is laid and by which its can- cellous architecture is directed. For the more minute observation of the process of ossification in carti- lage, it is best to take the ' line of ossification ' at the epiphysis of a long bone. The enlarged diagram (Fig. 12) is intended to illustrate it. Near the top of the diagram the cartilage cells are seen enlarged and arranged in rows (J). The calcified matrix, represented by dots, lies not only between the rows, but between the cells, so that it makes trans- verse as well as vertical septa between them. A little lower, we see the tubular spaces, filled with the bone-building materials, namely, osteoblas- tic tissue and blood-vessels (c and d). The blood-vessels form loops along the line of ossification, where the osteoblasts, having absorbed the transverse septa of calcified matrix, are invading the cartilage cells which disappear. "We see how the tubular spaces are formed by the vertical remains (trabe- culas) of the calcified matrix; how these spaces communicate here and there with each other where osteoblasts have absorbed their walls; how the remains (trabeculae) of the calcified matrix form a basis upon which the osteoblasts are deposited and transformed into bone (e). The ossified osteoblasts are represented dark at the bottom of the diagram. The actual appearances of the process of ossification at the epiphysis, as seen under the microscope, are represented in Plate III. Figs. 1 and 2. Experiments with Madder. That bones grow in thickness by ad- ditions to their surface, and not by interstitial deposit, is proved from the interesting experiments made with madder. It was accidentally discovered by Mr. Belchier, that madder tinges the bones red. He gives the follow- ing account of the circumstances under which the discovery was made. 20 He happened to be dining with a calico-printer on a leg of fresh pork, and 20 ' Philosoph. Trans. ' for 1736, vol. xxxix. OSSIFICATION. 29 was surprised to observe that the bones, instead of being white, as usual, were red. On making inquiry, he found that the pig had been fed on the refuse of the dyeing vats, \vhich contained a large quantity of the coloring substance of madder. This fact naturally attracted the attention of physi- ologists. The red tinge was found to be communicated much more quickly to the bones of growing animals than to those full grown. The bones of a a. Epiphysis. Hyaline cartilage. b. Rows of cartilage cells In calcified matrix, which is represented by dots. c. Tubular spaces filled with osteoblastic tissue, consisting of osteoblasts, blood-vessels, and connective tissue. d. The dark lines represent blood-vessels f running up the tubular spaces. e. The osteoblasts, transformed Into bone on 4 the trabeculae of calcified matrix, are repre- sented dark. No bone corpuscles are shown. Fio. 12. Epiphysial End of the Shaft of a Long Bone. (Enlarged from a, 6, c, Fig. 11, with the addition of the Blood- Vessels.) young pigeon were tinged a rose color in twenty-four hours. In the adult bird it took fifteen days to do it. The effect of madder upon bones depends upon this: The coloring principle of the madder (Rubia tine- tor um) has a strong affinity for phosphate of lime. It appears, however, that the vegetable dye does not combine with the phosphate of lime already formed, but only with that which is actually forming and being deposited in the bones. Therefore, since the dye tinges only the most recent de- 30 irrMAX OSTEOLOGY. posit of bone, it is possible to produce alternate rings of white and red bone, by periodically administering and withholding the madder as an article of diet. These rings will be observed not only at the circumfer- ence of the bone, but also within the Haversian systems. Growth in Length of Bones. Bones increase in length, not so much by interstitial deposit, as by addition to their ends; that is, by pro- gressive ossification of the layers of cartilage which intervene between the ends of the shaft and the epiphyses. These layers of cartilage furnish the animal basis of ossification, by constantly growing, while they ossify on their upper and lower surfaces. When the cartilage ceases to grow, ossification still goes on till the component parts of the bone are all united by bony matter; and thus the stature of the individual is determined. If from inflammation or other cause the epiphyses unite sooner than they ought to do, then one limb may be shorter than the other. That bones grow chiefly by addition to their ends was proved by Hunter. He intro- duced shots at definite distances into the shaft of a growing bone of a common fowl, and examined them a fortnight or three weeks afterward. The distance between the two shots was found only half as much increased as the distance between a given shot and the end of the bone. (Phys. Ser. Nos. 188, 189.) Value of Periosteum. Such is an outline of the structure and for- mation of bone. It is a subject interesting not only for its own sake, but because it helps us toward the explanation of what we are every day seeing of the progress of disease, and the repair of injuries in bone; and what is more, it helps us toward a rational treatment of them. To give a few examples. Look at the value of the periosteum. Suppose a portion of periosteum to be detached by injury or disease from the surface of a bone, a part of the subjacent bone will run great risk of dying. It will not necessarily die, because its blood-vessels may still be filled from within, owing to the free communication between the blood-vessels of the perios- teum and those of the marrow. In a case of compound fracture, where there are loose fragments of bone, we ought not to remove any that are still connected to their periosteum. Or, when a portion of the skull-cap sliced off by a sabre cut adheres firmly to a flap of the scalp, the flap with the bone should be re-applied, and the cure will frequently be effected without death of bone. In the Hunterian Museum are several skulls which have suffered from severe sabre cuts. The portions of bone thus sliced off were once detached, and afterward re-united a little out of their PERIOSTEOL 31 proper places, BO that the lines of original separation and subsequent union can be distinctly seen. (Path. Ser. Xos. 2892 to 2899). Again, there are cases in which, either from exposure to cold or from direct injury, acute inflammation of the periosteum of the shaft of a bone ensues, effusion of fluid takes place beneath it, and severs the connection between it and the bone. The death (necrosis) of the entire shaft may be the consequence. Then, what happens? As the inflammation subsides, the bone-secreting layer of the periosteum forms new bone around that which is dead, and by degrees encloses it in a bony case. The dead bone lies loose in this new case, having been detached from the articular ends, which do not die like the shaft, and for the reason that the epiphysial ends receive sufficient blood for their nutrition from the articular arteries, independently of what they receive from the shaft. The articular ends of the old bone become in time the articular ends of the new. Thus, the periosteum has formed a new shaft with a capacious cavity in its interior, in which the old bone is enclosed, and will remain so, and be a source of irritation for years, un- less removed by a surgical operation. Although the periosteum holds the first rank of all the structures which repair bone, still we are not to suppose that it is absolutely essential to the process. Under certain circumstances we find various other structures becoming transformed into bone. For example: In a case of compound fracture of the leg, where a portion of the entire circumference of the tibia, including its periosteum, was taken away, the vacancy in the bone was filled up by new osseous substance secreted by the surrounding soft tissues, and there was no shortening of the limb.* 1 Again, we occasionally see the intervening soft tissues forming bridges of bone, and so repairing a fracture where the broken ends themselves are widely apart. Material which Repairs Fracture. Fractures are repaired by a material similar to that out of which bone was originally formed. The animal matter which is first laid down is of a fibrous or cartilaginous nature or a mixture of both, as the case may be and then earthy salts are deposited in it. In the case of a simple fracture, where the broken ends are kept in contact and perfectly immovable by surgical appliances, the bones unite almost like an incised wound of soft parts. After all the effused blood is absorbed from between the* broken ends, a soft fibrous substance (blastema) full of osteoblasts is thrown out from the ends of the broken bone, which forms a thin layer of animal matter (intermediate 11 Stanley, ' Diseases of the Bones,' p. 108. 32 HUMAN OSTEOLOGY. callus) between them. This gradually hardens, and the bone earth is then deposited in the blastema and cells. So the ends are united. This occu- pies a period varying from four to ten weeks, according to the bone broken; e.g. the clavicle and the ribs unite more quickly than other bones, probably from their greater vascularity. The process is simply an excess of nutrition. Apparently more new bone than is necessary is formed. The excess fills up the medullary cavity, at the seat of fracture, and rounds off corners if there be any. But when the permanent uniting medium is strong, all that is seemingly superfluous is gradually absorbed, and the medullary canal is restored to its original condition, after a period varying from six to twelve months. On the other hand, if the fracture be not kept steady for instance, in the case of animals a kind of temporary splint is formed in the shape of a broad and thick ferule of cartilage, which ossifies around the ends of the broken bone, and keeps them almost im- movable, while the permanent process of repair is going on between them. This ferule, termed the provisional callus," does not disappear until the fracture has been thoroughly repaired. 22 ' Callus' is the term applied by the old surgeons to the materials by which frac- tures are repaired. Occipital .tone, ~Protu~berance eminence Tubercle for the attachment of ', """' ' *'^&% "the, Superior constrictor of Pharynx V',^% ,_ /^&**^f$4 Ant r condylo\d foramen, process Groove fur sup. ^ x .- lonqitwdl SiriUC. mi, m Occ.ipitaTsitVv * . Antrcondyloid I 1 S l.fera,,.^ >v" VZ^iP -tminentinnnorri-nata ^^ _.' _ '" . Baeilir ;;: groove. N'.'Vi r E ^ 3 roove ."for lateral sirf: Irif-'petroszil sinus. BONES OF THE SKULL. FOR convenience of description the bones of the skull are generally divided into those which form the ' cranium ' or brain case, and those which form the skeleton of the face. Each of these will first be described separately, and afterward the skull will be examined as a whole. 2 Superior Maxillary,, 2 Malar, 2 Nasal, 2 Palate, 2 Lachrymal, 2 Inferior Turbinated. Vomer, Inferior Maxillary. ( Occipital, J Frontal, 14 2 Parietal, BONES OF ;: f 2 Temporal, THE CRANIUM. 1 ., < Sphenoid, BONES OF < THE FACE. [ Ethmoid, THE OCCIPITAL BONE. (PLATE V.) Foramen Magnum : Basilar Process. The occipital bone con- tributes to form part of the base of the skull, as well as the back of the head. There is a large oval hole in it, called the ' foramen magnum/ which transmits the spinal cord and its membranes, the two vertebral arteries, and the two spinal portions of the spinal accessory nerves. The hole is very much larger than the parts which pass through it: all the intervening space is occupied by the cerebro-spinal fluid which supports and protects the cord. The narrow part of the bone, in front of the hole, projects, with a considerable inclination upward, when the bone is held in its proper position that is, with the foramen magnum horizontal; it is called the ' basilar process/ because it is wedged into the base of the skull. It is at the top of the pharynx. This relation is of practical im- 34 HUMAN OSTEOLOGY. portance. It is well to know that the basilar process is within reach of the finger when introduced deeply into the mouth, and that, conse- quently, we can explore it satisfactorily, so as to ascertain how far a poly- pus may be connected to it. The end of the basilar process is joined to the body of the sphenoid bone, in early life, by cartilage; but in the adult this cartilage becomes ossified. On its under surface (Plate V. Fig. 1) we notice a tubercle, exactly in the middle line, to which the aponeurosis of the pharynx is attached; and laterally, rough surfaces for the attach- ment of the 'rectus capitis anticus major' and 'minor.' On the upper surface (Plate V. Fig. 2) of the basilar process there is a gently sloping groove (basilar groove), which supports the ' medulla oblongata.' The medulla is not in actual contact with the bony groove; a thin layer of fluid is interposed, which, like a water-bed, protects this important part of the nervous system from concussion. On each side of this groove is another, but much smaller (petrosal) groove, which lodges the inferior petrosal sinus, by which some venous blood is returned from the brain. 43 Occipital Part. The expanded and vaulted part behind the foramen magnum contributes to form the skull-cap. On the convex or cutaneous surface, about the middle, we notice a rough prominence, called the ' oc- cipital protuberance/ plainly to be felt at the back of the head. From this we trace down to the foramen magnum what is termed the ' crest ' of the occiput, which gives attachment to the ligamentum nuchae at the back of the neck. From this middle protuberance and crest trace outward, toward the borders of the bone, two lines on either side, termed the 'superior and inferior curved lines.' These lines, as well as the rough surfaces between them, more or less evident in different instances, indicate the attachments of muscles at the back of the neck. The precise attach- ments of these muscles are mapped out on the right side of the drawing; and in examining them, understand, once and for all, that the blue outline denotes the insertion of a muscle; the red, the origin. It is right to explain that the origin of a muscle is the term applied to its most gen- erally fixed attachment; the insertion of a muscle is the attachment which is usually the more movable. However, it should be understood that a 98 The term 'sinus' is used very vaguely in anatomy. It means, generally, the hollow of anything. Thus the air-cavities in'the bones of the head are termed ' sinuses' When used in reference to the brain, a 'sinus' means a channel formed by the fibrous membrane (dura mater) of the brain, for the return of its venous blood. OCCIPITAL BONE. 35 precise rule cannot be laid down with regard to these terms as applied to muscles, since the origin or fixed attachment, and the insertion or mova- ble one, may under altered conditions be reversed. Thus, the bone near the superior curved line gives origin to the ' tra- pezius ' and ' occipito-frontalis/ and insertion to the ' sterno-cleido-mas- toideus' and ' splenius capitis.' The surface between the two lines gives insertion to the ' complexus.' Below the inferior line are the insertions of the ' rectus capitis posticus major,' the * rectus capitis posticus minor/ and the 'obliquus superior/ Condyles and Condyloid Foramina. The articular processes called the ' condyles ' are placed one on either side of the foramen magnum along its anterior half. They are kidney-shaped and convex, with their anterior ends converging. Moreover, they slant so that their inner margins are lower than their outer; and they thus fit into the ' cups ' of the ' atlas ' or first cervical vertebra. Owing to this arrangement, and the great strength of the connecting ligaments, dislocation of the head from the atlas is ex- ceedingly rare. More than this, by fitting together the two bones, you find that the condyles of the occiput are much longer than the cups which receive them; this permits the backward and forward motion of the head. On the inner side of each condyle is a rough surface or ' tubercle/ to which are attached the ' odontoid ' or ' check ligaments ' which limit the rotation of the head. Outside each condyle is the 'anterior condyloid foramen.' The direction of this foramen is outward and forward. It gives passage to the ' hypoglossal ' or ninth nerve, which, proceeding from the medulla oblongata, is distributed to the muscles of the tongue. Immediately above the ' anterior condyloid foramen/ or canal, as it should be called, there is a heaping-up of bone, which, not having received a name, may be termed the ' eminentia innominata.' It looks like a strong bony bridge over the canal, and strengthens the base of the skull like a flying arch just over the condyle. Behind each condyle is a deep depression or ' fossa/ at the bottom of which is mostly found a ' posterior condyloid foramen.' 24 The fossa, by making room for the cups of the atlas, enables us to move our heads further backward than we otherwise could have done; and the foramen at the bottom of it is the opening of a canal which runs horizontally forward into the ' groove for the lateral sinus ' 24 In some skulls there are no 'posterior condyloid foramina.' In fifty skulls which I have examined I find them more frequently present than absent. Either the right or the left foramen may be absent. 36 HITMAN OSTEOLOGY. (Plate V. Fig. 2), and transmits a vein from the lateral sinus to the ver- tebral vein outside the skull. Immediately external to the condyles, the bone forms on each side a projection, termed the 'jugular eminence/ On its under surface (Plate V. Fig. 1) there is a roughness for the insertion of the * rectus capitis lateralis/ On its upper or cerebral surface is a deep 'grobve for the lateral sinus/ one of the large venous canals which return the blood from the brain. Trace this groove forward, and observe that it turns suddenly downward, forming a kind of gulf, sometimes termed the ' jugular fossa ' which lodges the commencement of the internal jugular vein. Looking at the base of the skull (Plate XIX.) observe further, that it contributes, with the petrous part of the temporal bone, to form the ' foramen lacerum posterius/ Cerebral Surface. On the concave surface (Plate V. Fig. 2) observe two deeply grooved thick ridges of bone, crossing each other, the one vertical, the other horizontal: these grooves contain the sinuses of the brain. The groove of the vertical ridge contains the ' superior longitu- dinal sinus ' above, and the ' occipital sinus ' below the crossing. Near the foramen magnum, the groove for the occipital sinus generally subdivides into two smaller ones, which gradually lose themselves around its margin. The horizontal groove contains the great ' lateral sinus/ By referring to Plate XIX. this great groove may be traced in its winding course along the occipital bone across the posterior inferior angle of the parietal bone, the temporal, and then on to the occipital again, down as far as the ' fora- men lacerum posterius/ The grooves for the lateral sinuses are seldom of equal size on both sides of the skull. Generally, the right is larger than the left; hence the larger size of the right internal jugular vein. Besides being grooved for the sinuses, the ridges give attachment to pro- cesses of the ' dura mater/ which support the lobes of the brain. The horizontal ridge gives attachment to the ' tentorium cerebelli/ the longi- tudinal ridge to the ' f alx cerebri ' above, and the ' f alx cerebelli ' below the crossing. "Where the ridges cross each other, there is a heaping-up of bone, termed the ' internal occipital protuberance/ This is by far the strongest part of the bone, and protects the back of the cranium; besides which, at this protuberance, no fewer than six sinuses of the brain meet, viz. the superior longitudinal, the two lateral, the two occipital, and the straight. The meeting of these sinuses is termed the 'torcular Herophili/ Hero- OCCIPITAL BONE. 37 philus fancied that the blood flowing in here would be 'twisted* or Between the ridges there are four ' fossae ' which receive the lobes of the brain the two upper, the posterior lobes of the cerebrum, the two lower, the lateral lobes of the cerebellum. Hold the bone to the light, and see how thin are the walls of the fossaa for the cerebellum; this is well pro- tected by the mass of muscles at the back of the neck. Connections. The occipital bone is connected with six other bones; namely, with the two parietals by the remarkably serrated ' lambdoid ' suture, with the two temporals, with the sphenoid, and with the atlas; the latter being articulated to the condyles by movable joints. The sutures are simply named after the bones which they connect: for in- stance, we speak of the ' occipito-parietal ' suture, the ' petro-occipital,' the ' occipito-mastoid,' and the ' spheno-occipital/ All these connections are well serrated, except the ' spheno-occipital/ which is quite effaced in the adult skull, and the 'petro-occipital.' Ossification. The occipital bone is developed from four distinct centres, ^ which appear about the seventh week of foetal life one for the basilar part, one for the occipital, and one for each condyloid part (Nor. Hum. Ost. No. 35). These segments are, respectively, the 'basi-occi- pital/ the ' supra-occipital,' and the two ' ex-occipital ' foatal elements of the bone. They all meet and form the foramen magnum, and all are distinct at birth. The occipital and condyloid parts unite about the fourth year; the basilar and condyloid about the fifth. In very few skulls, there projects from the lower surface of the jugular eminence a more or less prominent tubercle, the l par-occipital process.' It is the analogue of a transverse process. It is quite a deviation from the human type, but is very constantly developed in the mammalian series. There is a good specimen of the process in the Nor. Hum. Ost. Ser. (No 747), in a skull from an aboriginal of one of the Philippine Islands. The process is even longer than the mastoid process, and pre- sents an articular surface for joining the transverse process of the atlas. There is a similar process in a skull in the museum of St. Bartholomew's Hospital. There are also two specimens of it in the Museum of Anatomy, in Kichmond Street, Dublin. Comparative Osteology. In all mammalia, as in man, there are two occipital condyles, fitting into two corresponding articular surfaces on the atlas. In birds and reptiles (Sauropsida), however, there is but 38 HUMAN OSTEOLOGY. a single occipital condyle, in front of the foramen magnum, in the middle line. This should be seen and noted, as it is one of the distinc- tive features of the above-named classes. (See separate series in the Mus. Roy. Col. Surg.) The cells which contain air and separate the inner and outer tables of the skull in the frontal bone of man extend as far back as the occipital bone in elephants. See sections of the elephant's skull (No. 2657). In quadrupeds the prominence of the crest and external occipital protuberance bears a direct relation to the development of the ligamentum nuchae which supports the head, and is usually in proportion to the weight of the head and its appendages. Compare the head of a deer, elephant, and tiger with that of a man in these particulars. In the moles the liga- mentum nuchas will be seen to be nearly all ossified. PARIETAL BONE. (PLATE VI.) This broad, roof -like bone derives its name from paries, a wall, as it forms so much of the wall of the skull-cap. It is the only bone belonging exclusively to the vault pf the cranium. With its fellow of the opposite side it makes the keystone of the arch which spaas the brain. The two pillars of the arch are the squamous portions of the temporal bones (Fig. 23, skull as a whole). It is convex on the outer surface, concave on the inner, and four-sided. Outer Surface. On the outer or convex surface (Fig. 1), notice the 'parietal eminence.' This is the spot in which the ossification of the bone began. Below the eminence is a curved line, termed the ' temporal ridge/ which gives attachment to part of the ' temporal aponeurosis.' The surface below this line forms part of the ' temporal fossa/ which gives origin to the ' temporal muscle.' The four angles of the bone are ' anterior superior/ 'anterior inferior/ ' posterior superior/ and ' posterior inferior.' Cerebral Surface. The concave cerebral surface has four kinds of marks or impressions upon it. Firstly, over the general surface there are large shallow grooves corresponding to the convolutions of the brain. Secondly, along the upper border is a half groove for the superior longi- tudinal sinus, and across the posterior inferior angle is a complete groove Parietal Foramen. ,v-- &$ ' ^al eminence PostrSup r C\. Ari^le. % L Wor-mi an loonc -''f^V^ *% Rg.i. %g . pV "*' ****^| llfLpor^l^l . ^e^P^ .S c , r iJ tnus' Parietal Bone Groove forLonbitudinal sinus An^le Groove for Lateral sir Groove for middle Menin^eal Artery PARIETAL BONE. 39 for the lateral sinus on its way from the occipital to the temporal bone. This should be borne in mind in articulating these bones with the parietal. Thirdly, running close to and parallel with the anterior border is the groove for the middle meningeal artery, from which ramify over the rest of the bone a number of smaller channels. Fourthly, near and along the upper border are seen a number of rounded depressions, which in the re- cent state contained the so-called Pacchionian bodies. Toward the back part of the upper border is mostly seen a foramen ('parietal foramen') which transmits a vein from the superior longitudinal sinus to the outside of the skull, and often an artery from the middle meningeal to the tem- poral artery. Connections. The parietal bone is connected by sutures with five bones (Plate XVIII.), as follows: With the opposite parietal bone, by the interparietal or ' sagittal ' suture; with the frontal bone, by the fronto- parietal or ' coronal ' suture; with the temporal bone, by the temporo- parietal or 'squamous' suture; with the occipital bone by the occipito- parietal or * lambdoid ' suture, and with the sphenoid bone, by the spheno- parietal suture. In all adult skulls the sagittal suture, though for the most part extremely serrated, is much less so near the parietal foramina. When obliteration of this suture takes place in age, it always begins oppo- site these holes. Do not fail to notice the beautiful arrangement of the sutures of the parietal bone: the sutural edges are bevelled on alternate sides, so that the bone cannot be driven in without previous fracture. Ossification. It is developed from one centre, which makes its appearance at the parietal eminence, about the seventh week of foetal life. Fontanelles. The term ' fontanelles ' is given to those membranous intervals in the foetal skull which are seen at the four angles of the parietal bone. These unossified parts are so called from the pulsations of the brain beneath them, perceptible in infants, like the welling up of water in a spring. They are produced in the following manner. Ossification commences in the centre of the bone, and advances toward the circumfer- ence; therefore, the most distant parts of the bone are the last to be ossi- fied. These points are the angles where the several bones eventually meet. There are in all six ' fontanelles ' (Plate XVIII. Figs. 4 and 5). Observe the shape of the anterior and posterior ' fontanelles/ and of the two lateral. The anterior, situated between the adjacent angles of the parietal bones and the ununited halves of the frontal, is lozenge-shaped, and remains open for some time after birth; indeed, it is not (as a rule) entirely oblit- 40 HUMAN OSTEOLOGY. erated till the fourth year. The posterior, situated between the parietals and the apex of the occipital bone, is triangular and nearly closed at birth. These 'fontanelles' are of especial importance to the accoucheur, as by the feel of them the finger can detect, during parturition, the position of the head of the child. The lateral ' f ontanelles ' are of less importance, and generally obliterated before birth. Right or Left? In studying osteology the student must learn to hold each bone in a similar position to the corresponding one in his own body. Now in order to do this in the case of single bones, such as the occipital or frontal, all that it is necessary to know is (1) either the top or the bot- tom, and (2) either the front or the back of the bone. But in all bones which occur in pairs (i.e. of which there is a right and left) six aspects must be considered, viz. a top and bottom,a front and back, an inner and outer side, and it becomes necessary in them to know three points instead of two, in order to place them in the required position, viz. (1) the top or the bottom; (2) the front or the back; and (3) the inner or the outer side. It is best to choose the most striking or obvious characters of a bone by which to determine these points, as being the quickest way of arriving at the conclusion. Thus, taking the parietal bone: (I) the inner side is recognized by its concave surface, which fits on to the brain, and is marked by its convolutions; (2) the bottom is known by its arched edge for articu- lation with the squamous portion of the temporal bone; (3) the front is known by the groove for the middle meningeal artery which runs up close to its edge. Bearing in mind these points, it is impossible to mis- take a right for a left; and with anything less than these three points, it is equally impossible to know one from the other. Comparative Osteology. In Carnivora the temporal muscles are so extensive that they meet in the middle line of the skull, where they are attached to a dense median crest of bone, which represents the temporal ridges coalesced. This is conspicuous in the skeleton of the tiger. It is interesting to note that the dog is not born with this median ridge; at birth the temporal muscle extends only partly up the side of the head. As the dog grows the muscle rises further up the head until it meets its fellow in the middle, and then the ridge begins to be developed. This progressive increa&3 of the muscle may be due to the habit puppies have of worrying everything they meet with, or it may be the result of an hereditary tendency. Temporal fossa \ Part of the roofoFtVieTsIose process Nasal spine frontal $inus__ Part oi- the roof O f the Nog " ^Lachrymal fossa. Flace for the -pulley. \Grooves formm^ \N(ththeEtVnnoic!l;< tVie interna.1 orbital foramina.. FRONTAL BONE. 41 In elephants and owls the inner and outer tables of the parietal bones are separated by enormous air cells. In man the two originally distinct halves of the frontal unite and form one bone. In bats the two parietals, which in us remain distinct, unite and form a single bone; this is also the case in many rodents, as the hare, but in the rabbit they remain separate. In Ruminants and Solidungula the parietals are united. FRONTAL BONE. (PLATE VII.) The situation of the frontal bone is implied by its name. As it forms not only the forehead, but the roof of the orbits, we naturally divide it into a ' frontal plate' and an ' orbital/ Frontal Plate. The anterior surface of the 'frontal plate* is smooth and convex, and gives breadth and height to the forehead. Ob- serve, first, the two 'frontal eminences,' one on each side, familiarly called the ' bumps ' of the forehead. They are the two points from which the bone was originally formed, and their greater or less prominence indi- cates to a certain extent the amount of brain behind them. Not so the two projections lower down, termed the 'superciliary ridges': these do not correspond to prominences of the brain, but are occasioned by air- cavities termed the 'frontal cells' or ' sinuses,' situated between the two ' tables ' of the skull. And here it may be well to mention, that the cap of the skull consists of two layers of compact bone, called, respectively, the outer and inner ' tables ' of the skull, and separated by an interme- diate cancellous tissue termed the ' diploe.' We shall allude to the advan- tage of this structure hereafter (skull as a whole, Fig. 20); meantime, observe that the frontal cells are formed by the separation of these tables. To see the extent of the cells, one ought to make vertical sections as shown in Plate XXIII. The Frontal Sinuses. There are some points of interest about the frontal sinuses. 1. They communicate freely with each nostril through a canal termed the ' infundibulum ' (Fig. 2); therefore it is possible for 42 HUMAN OSTEOLOGY. insects to reach them." A lady had a kind of centipede (Scolopendra electrica) for a year in one of her frontal cells. It gave her intense pain, and was expelled at last, alive, during a fit of sneezing. 28 It is by no means uncommon to find the larvae of insects in the frontal cells of ani- mals. Sir C. Bell states that a man, having slept in barns, was afflicted with pains in the forehead, ' which were relieved after he had discharged from his nose a worm belonging to that class which spoils the corn/ 2. As they are lined by a continuation of the same mucous membrane which lines all the other passages of the nose, we have a ready explanation of the aching pain in the forehead in cases of influenza, or a common head cold. 3. In cases of fracture of the base of the skull involving the walls of the cells, it is possible for fragments of the brain to escape from the nose. The author has seen a case of this kind where the patient recovered with- out any permanent ill effects except partial loss of smell. 4. If the outer wall of the cells be injured by violence or disease, the air, in sneezing or coughing, is liable to escape under the skin of the forehead; this condi- tion is called 'surgical emphysema/ 87 A boy was kicked by a horse on the forehead, so that the frontal cells were exposed. There resulted a fistulous opening, through which, when the nose was held, he could blow out a candle. 5. They not only contribute to the lightness of the skull, but increase the resonance of the voice. They are not developed until about the age of puberty, and steadily increase in size afterward. In some tribes for instance, in the native Australians they are but slightly developed; 28 and hence arises that want of resonance for which their voice is remarkable. 29 Even in Europeans their size and extent vary exceedingly. A good idea may be formed of their size in some persons, by the fact that they may lodge a musket-ball: A soldier was wounded at the battle of Talavera by a ball which struck him on the forehead and lodged in the frontal sinus. It was readily removed by enlarging the opening, and the man recovered. 30 The author has seen a case precisely similar, in a soldier who was wounded in the Crimea. The sinuses are commonly separated by a bony partition, often incomplete. 25 ' Histoire de 1'Academie des Sciences,' 1708, 1733. 26 Blumenbach. 27 Hyrtl, ' Topog. Anatomie. ' 28 Professor Owen. 29 On this subject see an excellent work by Amman, ' De Loquela, ' written in 1700. 30 Guthrie, 'Commentaries on Surgery,' 6th edition, p. 374 FRONTAL BONE. 43 The ' bumps ' are not prominent in children, because the tables of the skull do not begin to separate to any extent before puberty. From an examination of more than 100 skulls, it appears that the absence of the external prominence, even in middle age, does not necessarily imply the absence of the sinus itself, since it may be formed by a retrocession of the inner table of the skull. In old persons, as a rule, when the sinuses enlarge, it is by the inner table encroaching on the brain case. The skull wall follows the shrinking brain. The range of the sinuses may extend even more than half-way up the forehead, and backward for an inch or more along the orbital plate of the bone. Sometimes one sinus is larger than the other, and consequently the ' bump ' on one side of the forehead may naturally be more prominent than that on the other. In the Nor. Hum. Ost. Ser. (Nos. 153 to 155) in the Museum of the Eoyal College of Surgeons, there is an instructive collection of horizontal sections through the frontal bone at the level of the sinuses. In a specimen from a man set. 32, it may be observed that though the sinuses are very extensive, there is no external protuberance. In another from a man aet. 47 there are no sinuses, yet there is a great external protuberance. One obvious conclusion from all this is, that the ' bumps ' on the forehead mapped out in this situation by phrenologists, under the heads of ' Locality/ ' Form/ 'Time/ ' Size/ etc., do not necessarily coincide with any convolutions of the brain. Orbital Margin. The margin of the orbit, termed the * supra-or- bital arch/ is composed of thick and massive bone, as is, indeed, the entire circumference of the orbit. But the ' internal and external angular processes ' in other words, the piers of the arch are remarkably strong, and form buttresses for its support. Near the inner third of the arch is the ' supra-orbital foramen/ or it may be a ' notch/ for the transmission of the supra-orbital nerve and artery. It is this nerve which is affected in ' brow ague/ At the external angular process is the starting-point of the 'temporal ridge/ to which the temporal aponeurosis is attached (Plate XV. Fig. 2); and just below this is a little surface of bone which contributes to form the 'temporal fossa ' for the origin of the temporal muscle. Cerebral Surface. On its cerebral surface (Plate VII. Fig. 2), the ' frontal plate * is concave, and mapped out by the convolutions of the brain and the grooves of the anterior meningeal arteries (small vessels given off from the ethmoidal branches of the ophthalmic), and the rami- 44 HUMAN OSTEOLOGY. fications from the middle meningeal artery, on either side. In the middle line is the groove for the commencement of the superior longitudinal sinus. Trace the groove downward and observe that its margins gradu- ally approximate, and lead to a small hole, the 'foramen caecum/ The foramen caecum sometimes leads into the frontal sinus, sometimes directly into the nose; or it may open on the posterior or anterior surface of the nasal bones. It sometimes contains a small artery. Though called ' blind/ it generally transmits a small vein from the longitudinal sinus into the frontal cells; and this is one of the anatomical reasons assigned why bleeding from the nose relieves congestion of the brain, and why the old practitioners were in the habit of leeching the nose. Very often the margins of the groove for the longitudinal sinus coa- lesce, so as to form a small ridge, before they reach the foramen caecum. They give attachment to a perpendicular sheet of the dura mater (termed, from its shape, the ' falx cerebri '), which separates the hemispheres of the brain. Therefore, when we see a frontal bone with a well-marked ridge along the beginning of the longitudinal groove, it is but the ossification of part of this fibrous membrane. Pieces of bone occasionally occur in the falx cerebri, which remind us of the tentorium cerebelli in some Carniv- ora, as tigers, seals, and cats, in which the tentorium is for the most part bony instead of membranous (Nos. 4608 and 4483). Orbital Plates. The 'orbital plates' (Plate VII. Fig. 2) extend horizontally backward, and form a concave roof for the orbit, and a part of the anterior fossa of the cranium. Hold them to the light, and observe how thin they are. In extreme old age, when the diploe of the skull becomes absorbed, the orbital plates have sometimes large holes in them. At any time of life their thinness renders them liable to be perforated by sharp instruments thrust into the orbit. Wounds of the brain from such accidents are sometimes met with. Sir C. Bell speaks of a young man having been killed by the thrust of a foil which had lost its guard, and passed through the orbital plate into the brain. Their ' cerebral sur- face ' is slightly convex, and generally ridged and furrowed by the impres- sions of the brain. The orbital plates of the frontal bone are more or less arched in different skulls. Of course the more they are arched the more they encroach on the cranial space, and therefore the less room there is for the anterior lobes of the brain. Contrast the skull of a monkey with that of a man, and you will observe a marked difference. Their lower surface is concave, more especially near the external angular FRONTAL BONE. 45 process, where there is a depression (' lachrymal fossa') which lodges the lachrymal gland. Again, near the internal angular process there is a trace of a slight depression, indicating the attachment of the cartilagi- nous pulley of the ' superior oblique ' muscle of the eye. Ethmoidal Notch. The orbital plates are separated by a wide gap, called the ' ethmoidal notch/ because it receives the cribriform plate of the ethmoid bone, which here fits into the base of the skull. (Plate XIX.) On each side of the irregular margins of the notch observe the incomplete cells with thin walls. These cells correspond with, and are closed by, the ethmoidal ceUs (Plate XL Fig. 2). The largest ceU of all is in the front; and this, as seen in Plate VII. Fig. 2, leads into the frontal sinus. All of them are filled with air, and lined by mucous mem- brane continuous with that of the nose. At the front part of the notch is the ' nasal spine ' of the frontal bone. This little perpendicular pro- jection generally broken off in taking the skull to pieces supports the proper nasal bones (Plate XXIII. Fig. 1), and helps to form the septum of the nose, by uniting with the perpendicular plate of the ethmoid bone. On either side of it is a little groove which forms part of the roof of the nose (Plate VIL Fig. 1). Immediately in front of the nasal spine is the jagged surface which receives the nasal bones, and the nasal process of the superior maxillary bone (Plate XVI. Fig. 2). Lastly, on the margin of the ethmoidal notch, notice two grooves which, with the ethmoid bone, form the ' anterior and posterior ethmoidal foramina/ The anterior transmits the ' nasal ' branch of the ophthalmic division of the fifth nerve, and the anterior ethmoidal artery and vein; the posterior, the posterior ethmoidal artery and vein. Connections. The frontal is connected with twelve bones, of which two, the sphenoid and ethmoid, are single. It is united to the two parietal bones by the ' fronto-parietal ' or ' coronal suture ' (Plate XVIII. Fig. 2). Concerning this suture, see how admirably it locks the bones together, and secures the arch of the skull. The margin of the frontal bone is bevelled at the expense of its inner table above, of its outer table below; and the parietal bone is adapted accordingly. The lower half of its tem- poral margin unites with the greater wing of the sphenoid. Its external angular process is connected to the malar bone; its internal angular pro- cess, to the nasal bone and nasal process of the superior maxillary. Its orbital plate is connected to the sphenoid, ethmoid, and lachrymal bones. Look well into the orbits and see these several connections. They form 46 HUMAN OSTEOLOGY. a continuous suture from one external angular process to the other. This is called the 'transverse frontal suture.' Ossification. The frontal bone is developed from two centres, which appear one on each side, in the situation of the frontal eminence, about the seventh week of foetal life. These lateral halves meet and form a vertical suture down the middle of the forehead, termed the ' frontal ' suture; so that in children the two halves of the bone are easily separated. Generally this suture becomes obliterated during the second year; but sometimes traces of it persist, as seen in the skull, Plate XVIII. ; hence the practical rule not to mistake it for a fracture. 81 The frontal bone gives attachment to three muscles; namely, to part of the ' temporal,' part of the ' orbicularis oculi,' and the ' corru gator supercilii.' Comparative Osteology. In some animals, such as the Carnivora (see skull of tiger) the temporal muscle extends so far forward that there is no room for articulation between the malar bone and the external angu- lar process of the frontal. Thus, in these skulls the temporal fossa and the orbit are not separated by bone as in man. This character runs throughout the Carnivora, Rodentia, Edentata, and Pachydermata. In some animals the air cells are very numerous and large. Let any one who, admiring the intelligence of the elephant, imagines him to have a huge brain, put his hand into the foramen magnum of the skull which stands on the pedestal in the Mus. Eoy. Coll. Surg. and explore the cranial cavity. He will find that this forms but a small portion of the size of the head. And now looking at the sections of the skulls in the case be- hind it, he will see that the larger part of the skull is formed by cells or air spaces between the tables of the frontal, parietal, and occipital bones, which often separate the inner and outer tables of the skull to the extent of a foot. These m ke a vast increase in the size of the skull an increase of advantage, however, i.s it affords additional leverage for those muscles which are inserted into the back of the skull, and raise the massive head, including the trunk, tusks, and jaws. The place to aim at in this animal is just above the root of the trunk, where the case of the brain is not much thicker than a shilling. These sinuses are also well developed in the owl and the giraffe. In the great extinct sloths the upper, back, 31 Dr. Leach and others, who have examined the immense collection of crania in the Catacombs at Paris, have remarked that the number of adult skulls in which the frontal suture remained unobliterated was about one in eleven. PLATE VIII. IVL-astoid portion "Kastoid foramen icjuamous portion, Zygoma. . Tubercle at Di^astricus Mas tend process IpT. fJ"* Eminent^. articularis. Glenoid cavity. rlenoifl fi&gure . Vaginal process portion. J/leatus au<3litorius externus. Styloid process. Middlle Zygoma 3up^ Petrosa\ einug Mfatus auditorvus inter PU Carotid TEMPORAL BONE. 47 and side walls of the cranium were thus inflated with air; so that in these instances the brain is protected by a double skull, with air between the two. This modification not only lightened the skull, but protected the brain from the falling trees uprooted for food by these animals. The horns of animals such as oxen, sheep, and antelopes, consist of a horny sheath supported upon a long mass of bone which grows from the surface of the frontal bone. These horns last the lifetime of the animal, excepting, indeed, in the case of the prong-horned antelope at the Zoo- logical Gardens, which has twice shed its horns (No. 3713). The antlers of the deer consist entirely of bone, and grow from a projection on the frontal bone, and are shed annually; even the Wapiti deer sheds its huge antlers every year, and the extinct Irish elk formed no exception to this rule. Antlers are very vascular, and are covered by a vascular membrane, termed the ' velvet/ until the full growth, when they lose the ' velvet/ and are themselves ultimately shed. The horn of the rhinoceros is simply horny, and has no shaft of bone in its interior. TEMPOKAL BONE. (PLATE VIII.) Three Parts. This bone occupies the temples. It is a complicated bone, even on the surface; much more so in its interior, because it includes the organ of hearing. It consists of three parts, a squamous portion, situated in the temple; a mastoid, forming the little projection behind the ear; and a, petrous, which contains the organ of hearing, and projects like a wedge into the base of the skull. This division is very convenient: but the natural divisions of the bone are 1. The squamous; 2. the periotic, comprising the petrous and mastoid; and, 3, the tympanic, or small ring of bone .which surrounds the membrana tympani, and by its outward growth comes to form the external auditory passage. These parts are separate in the human foetus, and permanently so in many of the lower animals. Squamous Portion. The squamous portion, named from its scale- like appearance, forms part of the wall of the temple. It is very thin; hence the danger of a blow here. Its smooth outer surface is entirely covered by the temporal muscle, to which it gives origin. Its inner sur- 48 HUMAN OSTEOLOGY. face is marked by the convolutions of the brain, and by a narrow groove which sweeps, in a curved direction, from before backward, indicating the course of the posterior branch of the middle meningeal artery. (Plate VIII. Fig. 2.) Zygoma.. At the lowei part of the squamous portion there is an out- growth of bone, termed the ' zygoma' (^vycoj^a, a bolt or bar). It pro- jects horizontally forward, and can be easily felt on the side of the face. It is connected by a strongly serrated suture with a similar projection from the malar bone; so that the two together form an arch (' zygomatic arch') beneath which the temporal muscle plays. (Plate XV. Fig. 2.) The base of the zygoma is very broad, and appears to spring from two roo ts, an anterior and a posterior: in the space between them is the ' glenoid cavity/ which forms the socket for the lower jaw. The poste- rior root (supra-mastoid ridge) runs backward in the same line with the zygoma, and forms the upper boundary of the glenoid cavity: after that, it passes over the meatus auditorius externus, and then it gradually fades away, marking the line of separation between the squamous and the mastoid divisions of the bone. In the negro race, this supramastoid ridge is strongly marked, and is characteristic of a degraded type of skull (see two Tasmanian skulls, Nor. Hum. Ost. Nos. 1096-1097). The anterior is the main root; it is very broad and strong, runs transversely inward and forms the front boundary of the glenoid cavity. It is called the ' emi- nentia articularis.' This is crusted with cartilage in the recent state, and forms additional surf ace for the play of the lower jaw. Under ordinary circumstances, the 'condyle' of the jaw is in the glenoid cavity; but while the mouth is opening widely, the condyle can be felt sliding so far forward that the finger can be placed into the socket behind it. In fits of laughter or of yawning, the condyles may be suddenly dragged in front of the articular eminences by the muscles; and then the jaw is dislocated into the zygomatic fossa. Under such circumstances a person presents a very ridiculous appearance, since the mouth remains wide open until the dislocation is reduced. At the base of the zygoma we notice a little tubercle ('tubercle of the zygoma'), to which is attached the external lateral ligament of the lower jaw. Lastly, the upper edge of the zygo- ma gives attachment to the temporal aponeurosis; the lower edge gives origin to the masseter muscle. Glenoid Cavity. The ' glenoid cavity ' (yXijvt?, a socket), or socket for the lower jaw, is concave and oval, with the long diameter transverse, TEMPORAL BONE. 49 or nearly so. At the bottom of it notice a fissure, termed the ' fissura Glaseri/ or ' glenoid fissure/ the remains of the original separation be- tween the squamous and tympanic portions of the bone. The part in front of the fissure is the socket for the jaw: the part behind it is occu- pied by a lobe of the parotid salivary gland. Pass a bristle up the fissure, to see that it leads to the tympanum of the ear. The glenoid fissure con- tains the ' processus gracilis ' of the ' malleus/ the tympanic artery, the ' laxator tympani ' muscle, and is usually said to transmit the ' chorda tympani ' nerve; but this nerve, strictly speaking, runs through a little canal, close by the fissure termed ' Canal of Huguier/ Between the glenoid cavity and the meatus auditorius there is a slight process which affords support to the lower jaw, and guards against dislocation backward. This ' postglenoid process ' is generally well marked in African skulls, and always so in the gorilla, the animal which approaches man so nearly. Mastoid Portion. The ' mastoid portion ' forms the prominence of bone which is felt behind the ear termed the mastoid ' process ' (ftaffrds, a nipple). This process gives insertion and great leverage to some of the muscles which move the head round, viz. the ' sterno-cleido-mastoideus/ under that the ' splenius capitis/ and still deeper the ' trachelo-mastoid/ Beneath all these muscles the occipital artery runs to the back of the head, along a slight groove in the bone, internal to the digastric fossa. These muscles, as seen in Plate VIII. Fig. 1, are also inserted into the rough surface above and behind the mastoid process. If a section be made through the process, it is found to contain large and freely commu- nicating cells, termed ' mastoid/ which open into the back part of the tympanum. These cells, like the tympanum itself, contain warm air, which is admitted from the back part of the nostrils through ' the Eusta- chian tube/ They not only make the bone light, but are useful to the sense of hearing, by allowing more space for the vibration of the air. Like the frontal cells, and indeed all the air-cells in the bones of the skull, they are not developed till the approach of puberty. In cases of deaf- ness, arising from obliteration of the Eustachian tube, it was formerly the practice to make an opening into the mastoid cells, in order to admit free access of air into the tympanum. The success attending this proceed- ing induced Just Berger, physician to the King of Denmark, to have the operation done upon himself; but he died twelve days afterward from ex- tension of inflammation to the membranes of the brain; and the death of this illustrious man brought the operation into disrepute. Internal to the 50 HUMAN OSTEOLOGY. mastoid process is a deep fossa, termed the ' digastric fossa/ where the 'digastric ' muscle arises. Behind the process is a hole, called the ' mastoid foramen/ through which a vein runs from the lateral sinus to the outside of the head. This explains why leeches, applied behind the ears, relieve congestion of the brain. Lastly, on the cerebral aspect of the mastoid portion, notice the 'groove for the lateral sinus/ Petrous Portion. The ' petrous portion ' derives its name from the hardness of its constituent bone (nerpos, a rock). It projects horizontally into the base of the skull (Plate XIX.), and so carries far out of harm's way the delicate organ of hearing which it contains. Its shape is like a tri- angular pyramid with the apex inward; so that, for descriptive purposes, it may conveniently be divided into three surfaces an anterior, a posterior, and an inferior: then there is a base and an apex. Our best plan is to examine each of these parts separately, that we may be able to answer the question, what is seen on the anterior, what on the posterior surface, and so forth. Take the base first. Meatus Auditorius Externus. At the base of the petrous portion is the orifice of the passage to the ear, termed the ' meatus auditorius externus/ It is situated immediately behind the glenoid cavity, and its boundaries are chiefly formed by a curved plate of bone, called the ' pro- cessus auditorius.' Observe, first, that the edge of it is very jagged, for the attachment of the cartilage of the ear; and then look carefully down the passage to see that this curved plate of bone forms its boundary wall all round, except at the uppermost part. This inspection will probably suggest that the whole plate is something superadded to the rest of the bone, a sort of after-growth; which is precisely the case. In the foetus there is no meatus, but simply a ring of bone forming three-fourths of a circle, the deficiency being at the upper part. This ring is ossified independently about the third month, is quite distinct from the other parts, and to it is attached the membrane of the drum of the ear (membrana tympani) ; so that at this early period it might be rudely compared to a hoop with a membrane stretched across it. In many animals this remains permanently a distinct bone, under the name of the 'tympanic bone/ (Plate XVIII. Fig. 5.) In process of time, however, the hoop begins to grow out on its external side, and thus becomes a canal or meatus, which, as it grows longer, gradually coalesces with the other constituents of the bone. Respecting the shape of the passage, observe that it is oval, with the ^.-Ca-nal ftr Tensor ty mpani. .look "here Foi~ ^r i*roces?s Cochleari fbrmia ""'Eustachian tube. Gleuoison's T\erye. ...Jugular Eossa. Foramen for A.rnoV4's ner vt . Stylo -masto'id foraTnen . .... ..Groove For occipital artery. Digastric fossa*. Maatoid foramen. TEMPORAL BOME. Groove for middle >wetimgesLl artery. Depression. Fo- Gaisser wn. b&rt^V SupTPe.Vposal aiutrc TEMPORAL BONE. 51 long diameter nearly vertical; therefore all specula used for examining the ear ought to be of the like shape. The narrowest part of the passage, in the recent state, is about the middle; hence if a foreign body, such as a pea, happen to get into the ear, it is generally pushed through the nar- row part by clumsy efforts to extract it, and then the moisture of the ear causes it to swell, and makes its extraction most difficult and painful. A boy, eight years of age, had a grain of Indian corn thrust into his ear by one of his schoolfellows. The schoolmaster, in his wisdom, endeavored to remove it by attaching a piece of wax to the end of a stick, and thrust- ing it into the passage. Four days afterward, the boy was brought, with his ear in a state of acute inflammation, to the doctor, who eventually succeeded in extracting the grain by means of a ' curette,' with the point bent to a right angle. The grain of corn had increased to one-third more than its natural size." Petrous Portion: Anterior Surface. The anterior surface (Plate IX. Fig. 2) of the petrous portion forms part of the middle cerebral fossa which lodges the middle lobe of the brain, and bears more or less marks corresponding to the convolutions. About the middle of it is a little emi- nence, indicating the position of the ' superior semicircular canal ' (a part of the internal ear). More forward, is a small furrow leading to an open- ing termed the ' hiatus Fallopii/ which transmits the ' great petrosal ' nerve. Immediately to the outer side of this is a smaller furrow and opening, which gives passage to the 'lesser petrosal nerve/ Near the apex is a depression for the 'Gasserian ganglion/ External to this is the termination of the ' carotid canal/ Lastly, at the angle where the squa- mous and petrous portions meet (Plate IX. Fig. 1), you will observe two tubes running backward parallel to each other, like a double-barrelled gun (except that they lie one above the other): they both lead to the tympa- num. The upper of the two is the canal for the ' tensor tympani ' muscle; the lower, which is by far the larger, is the Eustachian tube, or passage which conducts the air from the pharynx to the tympanum. The thin partition separating the two barrels is called the 'processus cochleari- formis/ Petrous Portion: Posterior Surface. The posterior surface of the petrous portion forms part of the posterior fossa of the base of the skull. (Plate XIX.) The most prominent object upon it is the 'meatus auditorius internus' (Plate VIII. Fig. 2), a large canal which runs nearly ** ' Aural Surgery, ' p. 179. Mr. Wilde. 52 HUMAN OSTEOLOGY. horizontally outward, and transmits the ' seventh pair ' of nerves, consist- ing of the auditory nerve (portio mollis), and the motor nerve of the face (portio dura). It also transmits the auditory artery, a branch of the basilar. The meatus is much larger than the nerves which it transmits, the space between them and the bony canal being filled by a fluid (cere- bro-spinal), which surrounds and supports the brain. In fractures through the base of the skull involving the meatus, the fluid sometimes oozes out through the external ear: this, therefore, is regarded as a very grave symptom in cases of injuries to the head. A transverse section near the bottom of the meatus would show that it is divided by a small ridge of bone into two unequal parts, as seen in Fig. 13. In the upper and smaller of the two is the commencement of a special canal (aquaeductus Fallopii) for the motor nerve of the face; in the lower there are several minute apertures arranged in a spiral form (lamina cribrosa), through which the Aquseductus Fallopii. Ridge of bone. Lamina cribrosa, through which the nerves pass to tJie cochlea. Fro. 13. fibres of the auditory nerve reach the internal ear. About a quarter of an inch behind the meatus is a slit-like opening which looks backward, and is termed the ' aquwductus vestibuli.' This, though about a quarter of an inch long, soon contracts so much that it will barely admit a bristle. It leads to the vestibule of the internal ear. Immediately below the meatus there is a conical pit, which is wide at first, but gradually con- tracts to a minute canal, leading to the cochlea, termed the ' aqueeductus cochkce.' These minute ' aqueducts ' leading to the internal ear sometimes transmit small blood-vessels. Petrous Portion: Inferior Surface. The inferior surface of the petrous portion presents an irregular aspect, and has many holes in it (Plate IX. Fig. 1). Beginning near the base, notice, first, the ' styloid process/ so called from its resemblance to an ancient * style,' or pen. It is, originally, distinct from the rest of the bone, but gradually coalesces TEMPORAL BONE. 53 with it at the end of the third year. This long * process ' descends with a slight inclination forward, and gradually tapers to a sharp point. Its length varies in different skulls; generally it is about half an inch long. In old skulls it is sometimes longer: there is a skull in the Museum of St. Bartholomew's Hospital which has a styloid process three inches long. It gives origin to three muscles and two ligaments. The muscles are for the movement of the tongue and pharynx; they arise as follows: the ' stylo-pharyngeus,' from the inner side of the base; the * stylo-hyoideus/ from the middle and outer aspect; and the ' stylo-glossus/ from the front of the process (Plate VIII. Fig. 1). To the tip itself is attached the ' stylo-hyoid ligament/ which runs downward and forward to the lesser cornu of the os hyoides. The styloid process is nothing more than ossifi- cation of part of this ligament. The other ligament attached to the pro- cess is the ' stylo-maxillary/ which separates the submaxillary from the parotid gland. Lastly, the fore part of the root of the styloid process is surrounded by a kind of bony sheath, termed the ' vaginal process,' about which there is nothing to be remarked except that it is a continuation of the plate of bone which forms the hinder part of the glenoid cavity. Between the mastoid and styloid processes is a hole termed the * stylo- mastoid foramen/ (Plate IX. Fig. 1.) It gives exit to the motor nerve of the face (portio dura), which entered the bone at the meatus audi- torius internus. The stylo-mastoid artery, a branch of the posterior auri- cular, enters at this foramen, and supplies the tympanum. If you intro- duce a stiff bristle into the hole, you will probably succeed in passing it through the bony canal traversed by the nerve from its entrance to its exit. The canal is a complete tube of bone, called the 'aquaeductus Fallopii ' " after the anatomist who first described it. (Plate LIX.) The passage of this nerve through the temporal bone renders it liable to be injured in fractures of the base of the skull, or in disease of the ear; and this explains the paralysis of one side of the face which sometimes occurs under these circumstances. On the inner side of the stylo-mastoid foramen is a deep depression termed the ' jugular fossa.' This, with a corresponding part of the occi- pital bone, forms the ' foramen lacerum posterius.' (Plate XX.) Here the lateral sinus pours its blood into the commencement of the internal jugu- lar vein, which forms a great bulge and fills the fossa. Here also the eighth pair of nerves leaves the skull (through a little notch in the front 33 Fallopius was a distinguished Italian anatomist, born 1523, died 1563, 54 HUMAN OSTEOLOGY. part of the foramen lacerum) ; and here, one of the posterior meningeal arteries, a branch of the occipital, enters it. On the outer wall of the jugular fossa, near the root of the styloid process, we find the minute foramen which transmits the auricular branch of the pneumogastric nerve. In front of the jugular fossa is the large circular commencement of the canal in the petrous bone, through which the carotid artery enters the skull ('carotid canaF). The canal mounts nearly perpendicularly for a short distance, and then, turning forward and upward, emerges at the apex of the bone. On the plate of bone which separates the jugular fossa from the carotid canal, there is a minute foramen which transmits the tympanic branch of the glosso-pharyngeal nerve. S4 Near the apex is a rough surface which gives origin to the ' tensor tympani ' and ' levator palati ' muscles. The apex itself presents nothing more than the termi- nation of the carotid canal, and helps to form one of the boundaries of the jagged hole at the base of the skull, termed the ' foramen lacerum me- dium.' (Plate XX.) Along the sharp border between the anterior and posterior surfaces of the petrous portion remark the groove for the ' superior petrosal sinus/ which discharges itself into the lateral sinus. The faintly indicated groove along the fore part of the lower border of the posterior surface is for the ' inferior petrosal sinus/ The nearness of these venous chan- nels to the cavity of the tympanum explains the bleeding from the ear which sometimes occurs in fractures running through the petrous portion of the temporal bone. Connections. The temporal is connected with five bones. The squamous portion is connected to the parietal bone and the great Aving of the sphenoid bone by the ' temporo-parietal ' and ' temporo-sphenoidal ' sutures, concerning which the following mechanism must be noticed; namely, that the squamous part overlaps the parietal above, but is itself overlapped by the sphenoid below an arrangement which greatly con- tributes to the security of the arch of the skull. The mastoid part is connected, above, to the posterior inferior angle of the parietal by the ' masto-parietal ' suture, and, behind, to the occipital by the ' masto-occipitaP suture. The petrous part is wedged into the base of the skull between the sphenoid and occipital bones. (Plate XIX.) The zygomatic process is connected to the malar bone by a strong suture, the 34 Arnold's nerve is the auricular branch of the pneumogastric; Jacobson's nerve is the tympanic branch of the glosso-pharyngeal. TEMPORAL BONE. 55 * zygomatic/ which slopes downward and backward. Lastly, the glenoid cavity articulates with one of the condyles of the lower jaw. In the living subject, an inter-articular fibro-cartilage, lined above and below by synovial membrane, separates the two articular surfaces, and protects this part of the skull from the effects of a blow under the lower jaw. Ossification. The temporal bone is developed from four centres of ossification; namely, one for each of the following parts: the squamous, including the zygoma; the petrous and mastoid, or periotic bone; the tympanic or processus auditorius; and lastly, the styloid process. Some of these remain permanently distinct bones in many of the lower animals; and it is worthy of remark, that even in the human subject traces of the union of all are visible even in advanced age. The most curious develop- ment is that of the tympanic part; it is a simple ring of bone in the foetus, grooved inside for the attachment of the membrana tympani, which eventually grows out so as to form the meatus auditorius. (Nor. Hum. Ost. Nos. 34 and 43.) In the foetus, the mastoid part is very small, and gradually enlarges toward puberty by the formation of the mastoid cells. The styloid part is for a long time cartilaginous after birth, and ossifies slowly with age. The ossification of the squamous part commences about the eighth week of foetal life; of the petrous and mastoid, between the fifth and sixth months; of the tympanic ring, about the third month; of the styloid process, after puberty. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body if he hold the petrous portion (on which part of the brain lies) inward ; the zygoma (which articulates with tke malar) forward, and the glenoid cavity downward. Comparative Osteology. In white men the temporal bone very rarely articulates with the frontal, but this abnormality appears to be less rare in some colored races. In the Hum. Ost. Ser. it may be seen in four skulls of natives of New Caledonia, Nos. 1159, 1160, 1161 and 1146; in two Australian skulls, Nos. 1088, 1071, as well as in two remarkably long skulls in the General Ost. Ser. Nos. 126, 127. Some of these abnormali- ties may be explained, by referring to Plate XVIII. Fig. 5, in which it will be seen that where these bones meet, is the anterior lateral fontanelle. Here there is occasionally developed a small Wormian bone called the ' Epipteric bone/ (General Ost. Ser. No. 116.) If the epipteric bone unite to either the sphenoid or parietal, the articulation is normal, but if to the frontal or temporal, it is abnormal; in the Orang Outan the 56 HUMAN OSTEOLOGY. temporal bone articulates with the frontal normally, and this is also the case in nearly all the monkeys. It seems curious that the Howling Monkey (Mycetes laniger) has these articulations similar to those of man. Notice the immense zygomatic arch in the skeleton of the manatee. (No. 2647.) In crocodiles the tympanic cavity is completely walled in by bone; so that they hear by vibrations communicated through bony substance. In all the Mammalia, and in them alone, the lower jaw articulates directly with the temporal bone. By referring to No. 12 in the Nor. Hum. Ost. the tympanic bone and membrane in the foetus may be seen at the base of the skull. The fissura Glaseri is open widely, and the processus gracilis of the malleus lies in it. In all Mammalia the malleus remains very small and becomes cut off from the glenoid cavity by the outgrowth of the tympanic bone; but in birds (see Sep. Ser.) the malleus becomes largely developed, projects between the squamous and tympanic bones, and, under the name of ' quadrate bone/ comes to support and form the articulation for the lower jaw. SPHENOID BONE. (PLATES X., XI.) Constituent Parts. The sphenoid bone is so called because it is wedged in at the base of the skull between all the other bones of the cra- nium (0(prfv, a wedge, eidos, form). As it not only enters into the for- mation of the base of the skull, the orbits, the temples, and the nasal passages, but is connected with all the bones of the cranium, and many of those of the face, one cannot be surprised that it is a difficult bone to understand. Fortunately, it bears a remarkable resemblance to a bat with extended wings; so that we can shape our description accordingly. It presents, then 1. A body, or central part; 2. The two greater wings; 3. The two lesser wings; 4. The pterygoid processes, which make the two legs of the bat. -^ Body : four Surfaces. Commencing with the body, we must ex- amine its four surfaces a ' superior,' and ' inferior/ an ' anterior,' and a 'posterior.' "PLATE X. Sphenoid Bone fossa .Optic fora* T3tW.aa.inn5 c> mosum ii'.^S jS^ Hr )flH I Vainer F/ inous pro cess__^/ ^:: Ptery^oid proces >ular process Posterior aspect Levaor pa.lj>e"braE. Second Vieacl of Bectus extern'us. Bectus sup? Obliquus supT _ lendon common to __, ^ .. T%3. rising roxind tlie Foramen optricum . inferior to .ITotcnVor Palabebone Hamukrrircceas Anterior aspect. SPHENOID BONE. 57 The superior surface of the body (Plate X. Fig. 1) comprises what is seen of the body on the inside of the base of the skull. There is a deep depression in it, termed the 'pituitary fossa,' which lodges the ' pituitary* body." Another name given to it is the * sella turcica,' from its resem- blance to a Turkish saddle. In front of it is an eminence, termed the * olivary process,' from its olive-like shape. This process supports the com- missure of the optic nerve which makes a slight transverse groove (the ' optic groove ') upon it, leading on each side to the ' optic foramen ' through which the nerve enters the orbit. In front of the olivary process is a smooth and slightly concave surface, which supports the roots of the olfactory bulbs, and terminates in the middle line in the 'ethmoidal spine/ which articulates with the ethmoid bone. Each side of the ' body ' is more or less distinctly marked by a broad groove which winds upward in a gentle curve, and lodges the internal carotid artery as it passes through the * cavernous sinus ' after entering the skull; generally, a little tubercle, called the 'middle clinoid process,' rises from the side of the groove. In some skulls this tubercle is long enough to unite with the apex of the anterior clinoid process, so that the artery, in emerging from the groove, passes through a ring of bone. The two ' clinoid ' processes on each side give attachment to the ' tentorium cerebelli.' The pituitary fossa is bounded behind by a square plate of bone, which, as it represents the back of the saddle, is termed the ' dorsum sellae.' The corners of this plate project and form what are called the ' posterior clinoid processes,' thus named from their fancied resemblance to bed-posts. These are directly opposite to the * anterior clinoid pro- cesses,' of which we shall speak presently. The posterior surface of the plate slopes very obliquely backward, is continuous with the basilar pro- cess of the occipital bone, and forms an inclined plane which supports the ' pons Varolii. ' Lastly, in the side of the plate there is generally a notch which transmits the sixth nerve. The posterior surface of the body is connected with the basilar process of the occipital bone, in young subjects by cartilage, in adults by bone, so that after a certain age it is impossible to separate the ' basilar suture ' without the saw. The section shows well the structure of this part of the 85 This name was given to it by Galen, who thought that it secreted the ' pituita, ' or mucus, and that this passed down into the throat through the small foramina which are often found at the bottom of the fossa (' De usu partium,' lib. ix.cap. 1). Its functions are not even yet understood; it is generally classed as a ' ductless' or ' vascular gland, ' along with the spleen and thyroid body. 58 HUMAN OSTEOLOGY. base of the skull; namely, two plates of compact bone separated by about ^ of an inch of cancellous tissue or ' diploe.' Thus the bone is light and shocks transmitted to the base of the skull are broken. (Plate XI. Fig. 1.) Cornua Sphenoidalia. The anterior surface of the body (Plate X. Fig. 2) fits the posterior part of the ethmoid bone. It presents in the middle line a perpendicular plate of bone termed the 'rostrum/ This forms part of the bony septum of the nose, and is connected in front with the perpendicular plate of the ethmoid bone, and below with the vomer; as may be seen in Plate XXIII. Fig. 1. The surface of bone on each side of the rostrum is completed by two plates of bone, one on each side, termed the 'cornua sphenoidalia' or 'sphenoidal turbinated bones.' Although apparently integral parts of the sphenoid, yet these little bones are formed each from a special centre of ossification, are distinct in early FIG. 14. Cornua Sphenoi FIG. 15. life, and remain separable till adult age. The annexed drawing (Fig. 14) shows the * cornua sphenoidalia ' removed in a perfect state. The ros- trum of the sphenoid would fit into the gap between them. Each cornu is triangular with the apex downward. Each completely walls in the sphenoidal cell of its own side, except at the upper part, where there is a round opening in the base of the cornu which admits air from the upper meatus of the nose. Fig. 15 represents one of the cornua seen from the surface toward the sphenoidal cell. It shows the thin scales of bone which project into the cell and assist in lining its walls. However, it is right to state that these cornua sphenoidalia are rarely met with perfect. In consequence of their coalescence with the sphenoid, ethmoid, and palate bones, they are generally broken in the process of separation, so that there appears in most sphenoid bones a large irregular hole leading into the cell; as shown on one side of Plate X. Fig. 2. Sphenoidal Cells. Next come the 'sphenoidal cells' or sinuses. These are large air cavities in the body of the sphenoid, generally two in number, and separated by a more or less complete perpendicular parti- SPHENOID BONE. 59 tion. (Plate XXIII. Figs. 1 and 2.) Like the other air-cells in the bones of the skull, they are not developed in young subjects; but in the adult they gradually become large enough to excavate the whole body of the bone. The air is admitted freely into them from the upper meatus of the nose through an opening in the front wall of each sinus; and they are lined with a prolongation from the nasal mucous membrane. This communication of the sphenoidal cells with the nasal cavities explains how bleeding from the nose may occur as a symptom of fracture through the base of the skull, that is, through the body of the sphenoid. Lastly, the sides of the anterior surface of the body are hollowed out into two or three small air-cells, one below the other. (Plate X. Fig. 2.) Of these, the upper, one or more, are roofed in by corresponding cells of the ethmoid bone; and the lower by a corresponding cell in the orbital process of the palate bone. The inferior surface of the body (Plate XI. Fig. 1) assists in forming the roof of the nasal fossae; and the posterior part of this surface, con- tinuous with the basilar process of the occipital bone, looks toward the upper part of the throat, and may therefore be called the ' guttural ' sur- face. A portion of the vertical plate or ' rostrum ' is seen here also. Ob- serve that it is expanded a little toward its base. Now it is this lower part of the rostrum which is connected with the vomer, and the mode of connection is rather singular. The rostrum fits into a deep cleft be- tween the two plates or ' wings ' of the vomer, and thus serves as a foun- dation from which this bone passes forward and forms the septum of the nose. But the chief thing to notice on this surface is a process or scale of bone which projects horizontally inward, on each side, from the base of the internal pterygoid plate. These are termed the ' vaginal processes,' and their free edges rise just enough to allow the edges of the vomer to slide beneath them. This is another contrivance which fixes the vomer. Lastly, each of these plates is traversed by a small groove, or perhaps a complete canal, termed the ' ptery go-palatine canal,' which transmits the pterygo-palatine artery, and a posterior branch (the pharyngeal nerve) from the spheno-palatine ganglion. The artery is a branch of the inter- nal maxillary, runs from before backward, and supplies the top of the pharynx and the Eustachian tube. So much for the anterior, posterior, superior, and inferior surfaces of the body of the sphenoid. All that we have to remark concerning the sides of the body is, that they are grooved for the carotid artery, and that the 60 HUMAN OSTEOLOGY. smooth plate of the body in front of the sphenoidal fissure contributes to form a part of the inner wall of the orbit. (Plate XXII.) Lesser Wings. The lesser wings (or orbito-sphenoids) project trans- versely from the upper part of each side of the body. (Plate X. Pig. 1.) Their upper surface is smooth and flat, and supports the anterior lobes of the brain; their lower surface overhangs the sphenoidal fissure, and forms the back part of the roof of the orbit: hence they are sometimes called the ' orbital wings.' Their anterior margins are serrated and articu- late with the orbital plates of the frontal bone; their posterior margins are free, and in life fit into the great fissure (of Sylvius) between the an- terior and middle lobes of the cerebrum. Their base is traversed by the ' foramen opticum,' through which pass the optic nerve and ophthalmic artery into the orbit. This foramen should be described rather as a short canal directed outward and forward. Toward the ' sella Turcica ' each wing projects considerably in the form of a blunt angle, termed the ' ante- rior clinoid process '; and between this and the body of the sphenoid there is either a deep notch or a complete ring for the internal carotid artery. Greater Wings. The ' greater wings/ sometimes called the ' tem- poral ' (or alisphenoids), project from the lower part of each side of the body. Each wing presents three surfaces, which respectively enter into the formation of the base of the cranium, the orbit, and the temple. The 'cerebral surface' is concave, and marked by the convolutions of the middle lobe of the brain. The 'orbital surface' is a smooth quadrilateral plate which forms more than half of the outer wall of the orbit. (Plate XVI. Fig. 2.) Of the four borders of this plate, notice that the superior articulates with the frontal bone, and the anterior with the malar bone ; while the posterior enters into the formation of the ' sphenoidal fissure ' and the inferior into the ' sphenomaxillary ' fissure. The 'temporal surface ' is divided into two unequal parts by a transverse ' crest ' of bone; of these, the upper and larger one forms part of the temporal fossa, and gives origin to part of the temporal muscle: the lower one, which is more horizontal, forms part of the zygomatic fossa, and gives origin to one head of the ' pterygoideus externus.' The posterior angle of the great wing terminates in a sharp process termed the ' spinous process,' which fits into the angle between the squamous and petrous portions of the temporal bone, and gives attachment to the internal lateral ligament of the lower jaw, as well as origin to the ' laxator tympani ' muscle. Sphenoidal Fissure. The greater wings are separated from the SPHENOID BONE. 61 lesser by a broad and long fissure, termed the ' sphenoidal fissure/ which leads from the cranial cavity into the orbit, and transmits nerves to the eye and its appendages. The sphenoidal fissure gives passage to the third and fourth nerves, to the first or ophthalmic branch of the fifth, the sixth, a few filaments of the sympathetic nerve, and also to the ophthalmic vein. Immediately below the inner end of this fissure is the * foramen rotundum/ which transmits the superior maxillary division of the fifth nerve. Farther back and more external is the ' foramen ovale/ which transmits the inferior maxillary division of the fifth nerve, the lesser pe- trosal nerve, and. the small meningeal branch of the internal maxillary artery. Near the spinous process is the ' foramen spinosum/ through which the ' arteria meningea media ' enters the skull. Besides the foramina in the greater wing, there is often one (near the outer edge of the sphe- noidal fissure) which leads into the orbit, and transmits a branch of the middle meningeal artery. There is often another between the foramen spinosum and the foramen ovale, through which a small vein passes; this is termed the ' foramen Vesalii/ Pterygoid Processes. The 'pterygoid processes' descend nearly perpendicularly from the under part of the bone, one on either side, and act as buttresses which support the upper jaw bones. Each process consists of two parts termed the ' internal ' and ' external pterygoid ' plates. These are united in front, but diverge from one another behind, forming a deep interval called the ' pterygoid fossa/ At its lower part the ' ptery- goid fossa ' presents a deep notch which in the complete skull is filled up by the tuberosity of the palate bone. The external plate is broader than the internal and gives origin to the ' pterygoideus externus' and the ' pterygoideus internus ' muscles on its external and internal surfaces re- spectively. These muscles cause the grinding movement in mastication. Its outer surface also forms the floor of the zygomatic fossa. Respecting the internal pterygoid plate, observe that it forms the lateral and part of the superior boundary of the posterior opening of the nose, and that it has a crescent-shaped margin above, leaving room for the cartilage of the Eu- stachian tube. At the root of this plate is a shallow groove called the ' scaphoid fossa ' which gives origin to the ' tensor palati ' muscle, the ten- don of which plays round a notch on the ' hamular ' process at the end of the internal pterygoid plate. Behind the last molar tooth of the upper jaw we can distinctly feel this hamular process. Lastly, through the base of the internal pterygoid plate, a long canal, the ' pterygoid ' or ' Vidian/ 62 HUMAN OSTEOLOGY. runs from before backward, and transmits the ' Vidian' ' (' great petrosal ') nerve and artery. Look now at the anterior aspect of the pterygoid process, and observe a plate of bone, standing off like a side buttress which connects it with the greater wing. The plane of this plate forms a smooth surface, termed the ' spheno-maxillary,' and nearly corresponds in direction with that of the 'orbital surface' of the greater wing. (Plate X. Fig. 2.) We draw special attention to this plate, and give it the special name of spheno- maxillary surface because it constitutes the posterior wall of a deep fossa, termed the 'spheno-maxillary,' which, in the perfect skull, intervenes between the sphenoid and superior maxillary bones. Connections. The sphenoid is connected with twelve bones, includ- ing all those of the cranium and five of the face. The ' body ' is connected behind with the occipital bone by the basilar suture; in front with the ethmoid bone, the two palate bones, and the vomer. The ' lesser wing ' is connected to the orbital plate of the frontal bone: the 'greater wing' is connected to the orbital plate of the frontal by a rugged surface of con- siderable extent, to the anterior inferior angle of the parietal bone, to the squamous and petrous parts of the temporal bone; and to the malar bone. Lastly, the pterygoid processes are connected with the palate bones. 97 Ossification. In the early foatus the sphenoid bone consists of several parts. The posterior part of the body, termed by scientific anatomists, the ' basisphenoid ' or * post-sphenoid,' is ossified from two centres, placed side by side in the sella Turcica. Later on another pair of centres (one on each side of the former) appear, making in all four for the basisphenoid part. The greater wings, termed ' alisphenoids,' have each a distinct centre, from which the external pterygoid plates are also ossified. The front part of the body, termed ' presphenoid,' has two centres; its lesser wings (orbito-sphenoids) each have one ossific nucleus. Lastly, the internal pterygoid plates and the sphenoidal turbinated bones have each their separate nucleus of ossification. The bone then as a whole has fourteen centres. 36 Vidus Vidius was a professor at Paris, and physician to Fra^ois I. 37 In some skulls, in which the malar bone does not enter into the composition of the spheno-maxillary fissure, the sphenoid meets the superior maxillary bone. In such exceptional skulls the sphenoid would be connected with seven bones of the face. SPHENOID BONE. 63 As the preceding description may appear a little confusing to a be- ginner, the following plan will explain it better, and at the same time re- fresh the memory on the chief elements of the entire bone." PLAN OF THE OSSIFIC CENTRES OF THE SPHENOID BONE. CORNU SPHENOIDALE CORNU SPHENOIDALE (Sphenoidal turbinated). (Sphenoidal turbinated). LESSEE WING FRONT OF BODY LESSER WING (Orbito- sphenoid). (Presphenoid). (Orbito-sphenoid). I 11 1 BACK OF BODY. (Basisphenoid) . GREATER WING 2 2 GREATER WING (Alisphenoid) (Alisphenoid) and external pterygoid plate. and external pterygoid plate. 1 ' 1 INTERNAL PTERYGOID PLATE INTERNAL PTERYGOID PLATE (Pterygoid). (Pterygoid). 1 1 Comparative Osteology. The top of the great wing of the sphe- noid, passing up between the frontal and temporal bones, articulates with the anterior inferior angle of the parietal bone. The union of these two bones separates the temporal from the frontal. In those types of men where the forehead slopes backward, these bones approximate, and in some cases actually articulate with each other. (Nor. Hum. Ost., Nos. 1159, 1160, 1161, and 1146.) The size and strength of the external pterygoid plate bear a direct relation to the development of the pterygoid muscles which cause the grinding movements of mastication; conse- quently, it is highly developed in ruminants (see skulls of the deer and ox). In old skulls the sphenoidal cells often extend into part of the basilar process of the occipital bone. In the chimpanzee the sphenoidal cells extend far into the alisphenoid and pterygoid bones. 38 The cornua sphenoidalia begin to ossify about the time of birth, and do not unite to the body of the bone till the age of puberty. The internal pterygoid plates are developed from membrane, and begin to ossify about the fourth month. For full information on the development of the sphenoid bone, see Meckel's ' Archiv,' B. 1, and Quain's ' Anatomy,' 8th edition. 64 HUMAN OSTEOLOGY. THE ETHMOID BONE. (PLATE XI. FIGS. 2 and 8.) Constituent Parts. This remarkably light and spongy bone con- tains the organ of smell. It occupies the interval between the orbital plates of the frontal bone, and enters into the formation of the cranium, the orbit, and the nose. It appears, at first sight, complicated; but it is simple when one understands the plan of it. It consists of a horizontal plate, which forms part of the base of the skull; of a central perpendicu- lar plate which forms part of the septum of the nose; and of two ' lateral masses ' containing the air-cells. Each of these must be examined sepa- rately. Cribriform Plate. The horizontal plate fits into the ' notch ' be- tween the orbital plates of the frontal bone; and completes the anterior fossa of the base of the skull. (Plate XIX.) It is called the 'cribriform plate ' (cribrum, T^UOS-, a sieve), because it is perforated by holes for the passage of the olfactory nerves. High above it rises a crest of bone, termed, from its resemblance to a cock's comb, the ' crista galli.' This, which is a continuation of the perpendicular plate, gradually rises from behind, swells out as it proceeds, and stopping suddenly short, presents a broken edge which is connected to the frontal bone. The ' crista galli ' serves for the attachment of the ' falx cerebri.' It varies in size, and has often a slight lateral inclination. Sometimes it contains an air-cell. The cribriform plate does not come up to the level of the lateral masses, but lies at the bottom of a deep groove (' olfactory groove'), which, being divided by the crista galli in the middle, forms in the perfect skull two recesses which lodge and support the olfactory lobes of the bmin. The foramina at the bottom are arranged on each side in three somewhat irregular rows, an outer, an inner, and a middle. Pass bristles down these holes, and you will find that the inner and the outer rows lead respectively to the ' olfactory canals ' on the perpendicular plate and the upper spongy bones; while the middle holes run simply through the cribriform plate. These three rows of holes correspond to the three sets of olfactory nerves: namely, those that ramify on the sep- tum, those that ramify on the spongy bones, and those that supply the roof of the nose. (Plate XXIII. Figs. 1 and 2.) Close to the front of PLATE XI. Vidian canal. Scaphoid fossa '''* ?teryoid fossa I 1 'Vagi nal process$A Pterygo palatine canaL "Sup 1 ? constrictor cp Pharynx. Perpendicular plate.. AntTEthmoidal cells <;''' r Ethrno,dal ceV,tf-<" InfundibuYum. Crista^adli. ..Slit for theNasa] Nerve. ..Ant^ethrr.oidal foramen . CTibriForfn plate . ETHMOIDBONE Ul Middle Spongy bone. Perpendicular tal ate . THE ETHMOID BONE. 65 the ' crista galli ' is a long ' slit/ rather than a hole, which gives passage to the * nasal nerve ' (a branch of the first division of the fifth pair), which confers common sensation upon the mucous membrane as well as the skin of the nose. Perpendicular Plate. The perpendicular plate descends from the cribriform plate and assists in forming the septum of the nose. Notice the numerous grooves and canals on its surface, for the passage of the olfactory nerves. Its connections are well shown in Plate XXIII. Fig. 1. Behind, it is connected along a sloping line with the ' rostrum ' of the sphenoid and the vomer: in front, it is connected with the nasal spine of the frontal and the crest of the two nasal bones, of which it mainly supports the arch. The triangular gap in the septum in the dry skull is filled up, in the recent state, by the central cartilage of the nose. Lateral Masses. The ' lateral masses ' of the ethmoid (Fig. 16) are made up of irregular air-cells, surrounded by paper-like walls of bone, lined by mucous membrane con- tinuous with that of the nose. The cells are divided into two sets, an anterior and a posterior; and the cells of one set do not commu- nicate with those of the other. In the separated bone many of the cells are necessarily opened, be- cause their walls, in the perfect skull, are completed by the adjoin- ing bones. Thus, the front cells r Fia. 16. Transverse Section, to show the Lateral on the upper surface are roofed Air Ceils of the Ethmoid Bone, in by corresponding cells in the orbital plate of the frontal; those at the back of the bone are closed by the body of the sphenoid and the orbital process of the palate bone; those in front of the bone are walled in by the lachrymal; those below, by the superior maxillary bone. On the outer side of each lateral mass the cells are closed by a smooth and square plate of bone, termed the 'os planum/ belonging entirely to the ethmoid. This forms a large share of the inner wall of the orbit (Plate XXII.), where it is easy to learn its connections with the surrounding bones, by tracing the sutures between them. Lastly, notice the two notches on its upper border, which, with the frontal, form the ' anterior and posterior ethmoidal foramina/ The ' anterior ' transmits the nasal 5 66 HlTMAtf OSTEOLOGY. nerve and the anterior ethmoidal vessels; the ' posterior ' gives passage to the posterior ethmoidal vessels. Turbinated Bones and Meatus. On the inner aspect of the lat- eral mass we observe two thin plates of bone standing out, one below the other, and slightly curled, like a turbinated shell. These are the ' tur- biirated' or 'spongy' bones of the ethmoid (Plate XI. Fig. 3), and can be properly seen only in a divided skull. The ' superior ' is the smaller of the two, and does not reach so far forward as the other, which is called the ' middle/ because there is a third or ' inferior turbinated ' bone, still lower down in the nose; but this does not belong to the ethmoid. Now the spaces left between these turbinated bones and the lateral masses are called respectively the superior and middle ' meatus,' or passages of the nose. Each is distinct from the other, and leads to its own particular cavities, and to no other. The superior meatus, being farther back than the middle, leads into the sphenoidal cell, and into the posterior eth- moidal cells. The middle meatus leads into the anterior ethmoidal cells, and also to the frontal cells, along a funnel-shaped canal (' infundibu- lum ') which traverses the foremost of the ethmoidal. (Plate XXIII. Fig. 2.) Unciform Process. Lastly, from the anterior part of each lateral mass an irregular plate of bone descends almost perpendicularly, and terminates in a kind of hook; hence it is called the ' unciform 39 process ' (Plate XL Fig. 3). By referring to Plate XXIII. Fig. 2, it is seen that this process is connected with the inferior spongy bone, and with the thin walls of the ' antrum* of the superior maxillary bone; it chiefly assists in narrowing the orifice of this great air-cavity. Connections. The ethmoid is connected with thirteen bones, namely, behind, with the sphenoid and two palate bones; above, with the frontal; below, with the two superior maxillary; in front, with the two lachrymal bones. The perpendicular plate is connected behind with the vomer, and in front with the two nasal bones. Lastly, the unciform pro- cess on each side is connected with the inferior spongy bone and the superior maxillary. Ossification. Until the middle of foetal life the ethmoid is all carti- lage. Ossification begins about the fifth month, by a centre for each of the lateral parts, and gradually extends into the two upper turbinated 39 The ' unciform process' is almost always broken in taking the skull to pieces; but it is evident enough in a good section of the nasal cavities. THE ETHMOID BONE. 67 bones (ethmo-turbinals). Within a year after birth another centre ap- pears for the perpendicular and cribriform plates (mesethmoid). An arrest in the progressive ossification of the perpendicular plate occasions a 'pug nose/ In the foetus at birth there are no ethmoid cells; these are not formed until the fourth or fifth year. Comparative Osteology. In man the rule is that there are three turbinated bones on each side; sometimes there is a fourth, smaller than the rest, and higher up at the back part. This fourth bone is more fre- quently met with in some colored races where the sense of smell is notori- ously acute. The curled plates of the turbinated bones are covered by a very vas- cular membrane. The upper ones afford an extensive surface upon which the olfactory nerves are distributed after their passage through the cribriform plate. By the variation of the extent of surface of these bones it will be seen that the acuteness of the sense of smell and the capability of warming the air on its way through the nose to the lungs are regulated. The sense of smell is remarkably keen in the deer tribe and carnivora, and their spongy bones are developed in proportion. It is curious that they should both in a measure depend for a living upon the development of the same sense, the one to avoid its enemies, and the other to find its prey. The spongy bones on which the nerves of. smell are distributed and those which are only covered by a vascular membrane, are widely differ- entiated in their conformation in the lower animals. In the seal, for in- stance (Nos. 3934, 3935A), which inhabits the arctic regions and neces- sarily breathes intensely cold air, the inferior spongy bones subdivide into a multitude of plates and afford a vast surface on which is distrib- uted a profusion of blood-vessels which warm the air before entering the lungs. The surface of these bones has been estimated at about 120 square inches in each nostril; a longitudinal section of such a nostril has the appearance of being completely plugged by the convoluted warming plates of the lower spongy bone; while those on which the olfactory nerves are distributed have a different form and are further back and separated by a slight interval from the others. There is no ethmoid bone in serpents, but the olfactory filaments are spread out on a plicated mucous membrane. BONES OF THE FACE. THEKE are fourteen bones of the face; namely, the two superior max*. illary, the two malar, the two nasal, the two lachrymal, the two inferior spongy, the two palate, the vomer, and the inferior maxilla. SUPEEIOK MAXILLAEY BONE. (PLATE XII.) Constituent Parts. This bone gives much character to the human face, and forms the greater part of its framework. It is exceedingly irregular in shape, and, besides forming sockets for the teeth, enters into the composition of the nose, the orbit, the cheek, and the palate. For convenience of description, we divide it into a l body/ which is hollowed out into a large air-cavity, called the 'antrum/ and four outstanding ' processes'; namely, the ' alveolar/ which holds the teeth; the ' palatine/ which forms part of the hard palate; the ' nasal/ which assists in form- ing the nose; and the 'malar/ which helps to form the prominence of the cheek. Body: Walls of Antrum. Let us take the ' body ' first, and learn its various relations well, for it is a part of great surgical interest, being liable to many diseases requiring surgical operations. The first thing to observe is, that the walls which bound its cavity have four aspects: one namely, the front looks toward the cheek; another, the upper, looks toward the orbit; a third, the inner, looks toward the nose; and a fourth, behind, looks toward the zygomatic fossa. Therefore, when a morbid growth forms in the antrum, and distends it, any one or more of these walls may be protruded. They are all very thin, the orbital espe- cially; but it is worth remembering that they are thicker in the child than in the adult. Antrum: Anterior Wall. The anterior wall of the ' antrum ' is that SUPERIOR MAJCfLLARY BONE. TuToer-os-ity ,^ " r1 "~ Lachrymal groove VgflS ;\ Nasal process. iTTf'ocu-H, gA_Te Tldo ^ cwli . Fig.l. Infra-orlaita.1 foramen. i Depressor alae nsi&i. Myrtiform fosst Canine fossa.. Surfa.ce. AntCnisal spine Pa'lkte pUtc Inner Surface. SUPERIOR MAXILLARY BONE. 69 which is generally removed to take out a morbid growth from the inte- rior, and through which we tap the antrum to let out pus, or any fluid that may have accumulated there; cysts in the antrum being by no means uncommon. There is a depression in it, called the ' canine fossa,' a little outside the eminence of the canine tooth; and above this is the ' infra- orbital foramen/ or termination of the ' infra-orbital canal/ which trans- mits the ' infra-orbital ' nerve and artery. The canine fossa gives origin to the 'levator anguli orts.' Above the infra-orbital foramen arises the 'levator labii superioris,' and more internally the 'compressor naris.' Antrum: Posterior Wall. The posterior wall of the antrum is convex, and bulges into the zygomatic fossa. 40 There are several small holes in it, leading to canals ('dental canals') which transmit the pos- terior dental branches of the superior maxillary nerve, and the superior dental branches of the internal maxillary artery. Lower down it has a very rough surface, just behind the wisdom tooth, called the ' tuber- osity/ by which it is firmly connected to the palate bone; and along the inner edge of this surface (Plate XII. Fig. 2) is a groove, which, with the perpendicular plate of the palate bone, forms the ' posterior palatine canal/ for the passage of the descending palatine nerve and artery. Antrum: Superior Wall. The superior wall of the antrum slopes downward and outward, and forms the floor of the orbit. Like the other walls of the antrum, it is thin enough to be translucent. Notice here the ' infra-orbital canal/ for the passage of the superior maxillary nerve and infra-orbital artery. It commences behind as a groove, but soon becomes a canal, which terminates on the front wall of the antrum, just below the edge of the orbit. A little before its termination, the main canal gives off one or sometimes two smaller ones, not always visible, termed the ' anterior dental canals.' These run down in the very substance of the front wall of the antrum, and transmit blood-vessels and nerves to the two incisor, the canine, and the first bicuspid teeth. To see these canals it is necessary to introduce a bristle as a guide, and then to rasp away the front wall of the bone. Near the lachrymal groove may sometimes be seen a small depression, indicating the spot where the ' inferior oblique ' muscle of the eye arises. This is the only muscle of the orbit which takes origin from the front; all the others arise from the back part, around the 40 Blandin (' Anat. Topog. ' p. 44) relates a case in which a tumor, originating in the antrum, made its way into the zygomatic fossa, and caused a swelling in the {emple. 70 HUMAN OSTEOLOGY. optic foramen. In the perfect skull (Plate XVI.) observe that the upper wall or ' orbital plate ' of the antrum is connected on its inner side with the lachrymal, ethmoid, and palate bones; but that on its outer side it forms one of the margins of the ' spheno-maxillary fissure/ at the back of the orbit. Antrum: Internal Wall. On the inner or ' nasal wall ' of the an- trum, the first thing to notice is the orifice of the antrum itself. (Plate XII. Fig. 2.) In the separate bone, this orifice is very irregular, and large enough to admit the end of a finger; 41 but in the perfect skull (Plate XXII.) it is very much closed in by thin plates from the ethmoid, the palate, and the inferior spongy bones. In the recent state the orifice is generally so contracted by a fold of the mucous membrane of the nose, that it will only admit a crow-quill. The orifice is not near the bottom of the antrum, but very high up: the consequence of this is, that when fluid collects in the antrum it cannot run out until the antrum is nearly full, or until the head is inclined horizontally with the opposite cheek downward. Antrum, Cavity of. The ' maxillary sinus/ or ' antrum/ 43 is by far the largest of the air-cells in the bones of the head. It is lined by mucous 1 membrane continuous with that of the nose, and is large enough to hold a musket-ball with ease. A ball has been known to lodge in the antrum for months, and even for years, before it was removed. 43 A ball once lodged for eleven years in the antrum, and finally made its way out through the roof of the mouth. 44 However, it varies in size, and some- what in shape, in different persons; but, as a rule, it has the form of a tri- angular pyramid, with the base toward the nose, and the apex toward the malar bone. Thin plates of bone often project into the antrum, making a kind of recess or pocket here and there; 45 and the fangs of one or more of the molar teeth generally project into it, either quite bare, or covered by a thin scale of bone. Hence the practice, adopted by some surgeons, of drawing one of these teeth, say the first or second molar, to let out matter from the antrum. Again, the fangs of decayed or otherwise in- 41 Sometimes there are two openings, separated by the thin plate (unciform pro- cess) which descends from the ethmoid bone. 42 Nathaniel Highmore was an English anatomist, born 1613, died 1684, who wrote much about the diseases of the antrum. He did not discover the antrum, for it was known to Galen as the ' sinus maxillaris. ' 43 ' Commentaries,' p. 528. Guthrie. 44 ' Anatomic Chirurgicale. ' Mr. Jarjavay. 45 See a curious case by Catlin, ' Trans. Odontolog. Soc.' vol. ii. 1857. SUPERIOR MAXILLARY BONE. 71 jured molar teeth are liable to set up disease in the antrum; and this is the explanation commonly given why morbid growths arise in the antrum more frequently than in any other of the air-cavities of the nose. The following case gives a good idea of the extent of the antrum: ' A lady suffering from tooth-ache submitted to the extraction of the ca- nine tooth of the upper jaw, with which a portion of the alveolar process was removed, making an aperture in the antrum, from which a watery fluid constantly issued. The patient, desirous of ascertaining the source of the discharge, took a pen, and having stripped off the barbs from the feathered part, found that the whole of it, full six inches long, could be introduced into the cavity. At this she was greatly terrified, believing it must have gone into the brain. She consulted Highmore, who ex- plained to her that the pen had turned spirally within the sinus, and he, besides, counselled her to submit with patience to the inconvenience of the discharge from the cavity.' 4 ' Alveolar Process and Teeth. The alveolar process is a thick and strong ridge of bone, curved so as to form with that of the other side the dental arch. It consists of two plates, an outer and an inner, connected by numerous septa which form the sockets (alveoli) of the teeth. The inner plate is the stronger; therefore, in drawing a tooth, care should be taken to incline it a little outward. The outer plate is marked by emi- nences corresponding to the fangs of the teeth; the eminence of the canine tooth being especially marked. In a child, from the end of the second to the end of the sixth year, the half of each jaw contains sockets for five teeth, i.e. for two incisors, one canine, and two molars. The formula for the ' milk dentition ' is therefore The half of each jaw contains, in the adult, sockets for eight teeth; namely, two ' incisors/ one ' canine/ two ' bicuspids (or prae-molars) ' and three ' molars.' Thus the dental formula of the adult human skull is .2+2 1+1 2+2 w 3+3_ 33i n ~*'2+2' *I+T ^2+2' W '3+3~' The eruption of the second or permanent set of teeth commences about 45 Drake's ' System of Anatomy,' 8vo. 1707. 72 HUMAN OSTEOLOGY. the end of the sixth year. The first to appear is the first permanent molar, which is therefore called the six-year-old tooth, and is the oldest tooth in an adult's head. The presence of this tooth has been used as a test of age by medical inspectors in giving certificates as to the fitness of children to work in factories. 47 Generally speaking, the twenty milk teeth are cut between the 6th and 24th months, and the thirty -two permanent teeth between the 6th and 24th years. 48 Sockets of Teeth. The sockets correspond in number and size to the fangs of the teeth they receive. They vary in depth in different in- stances. The deepest of all is the socket of the canine tooth: this is often -fo of an inch in depth in the dry bone. The first two molars of the upper jaw have three fangs each, and as many sockets. Of these fangs, two are external, one internal. In the last molar, or wisdom tooth, the fangs are generally consolidated into one. Irregularities in the shape and the direction of the fangs, whether diverging too much or converging, lead to unavoidable evils when it is necessary to extract them. Either a fang breaks, or part of the alveolus must be extracted with the fang. One cannot foresee this. Hence it follows that, now and then, even the most skilful operators break teeth or extract portions of bone. At the bottom of each socket is a minute hole, through which the vessels and nerve come up and supply the pulp cavity; and there are also numerous holes in the bony partitions between the sockets, through which vessels supply the gums and the periosteum. These are the sources of the bleeding after the extraction of a tooth. The teeth are fixed, not only by the closely fitting socket, but also by the very vascular membrane, the perios- teum, which lines the socket and adheres closely to the fang. This peri- osteum not only retains the teeth in their places, but helps to maintain their vitality, and, being elastic, breaks shocks which would otherwise be communicated to the jaws. When the dental periosteum inflames, the tooth is partly lifted out of its socket, and the teeth cannot be clenched without pain. If the inflammation goes on to the formation of matter, the periosteum quits its hold of more or less of the fang, and abscess in the socket is the result. The matter then makes its way out by the side of the tooth, or through a small hole formed by ulceration in the alveolar wall; that is, a gumboil is the result. In the dry bones, most of the teeth 47 ' The Teeth a test of Age,' in a pamphlet by Edwin Saunders, 1837. 48 'Dental Anatomy,' p. 179. Tomes, 1876. SUPERIOR MAXILLARY BONE. 73 fall out, because the periosteum shrinks, and thus the sockets become too large. The alveolar process gives origin to two muscles (Plate XII. Fig. 1), namely, to the ' buccinator ' above the three molar teeth, and to the ' de- pressor alae nasi ' above the incisor teeth, where there is a little depression, termed the 'myrtiform fossa/ Nasal Process. The nasal process ascends nearly perpendicularly, in a line with the canine tooth, and abuts, by means of a very rough suture, upon the internal angular process of the frontal bone. It supports the true nasal bones, and contributes to form the inner margin of the orbit. The principal point concerning the nasal process is the deep groove which runs almost vertically behind its orbital margin. It is called the ' lachrymal groove.' In the perfect skull it is converted into a complete canal by a corresponding groove in the lachrymal bone and a small por- tion of the inferior spongy bone. The canal thus completed lodges the ' lachrymal sac ' and ' nasal duct/ which convey the tears into the inferior ' meatus ' of the nose. It is about the size of a common goose-quill. When, from inflammation or other cause such as a tumor the canal becomes obstructed, the tears necessarily flow over and run down the cheek. To obviate this, it is often requisite to slit up one of the lachry- mal canaliculi, and introduce a probe into the nasal duct. Therefore one must know well the direction of the lachrymal canal. It runs from above downward, and slightly backward. On the outer surface of the nasal process is the prominent ridge which forms the inner margin of the orbit. This gives origin to the ' tendo oculi ' or ' palpebrarum ' and the ' orbicu- laris oculi.' A little in front of this the 'levator labii superioris et alae nasi ' arises. On the inner surface are the two ridges to which the inferior and middle spongy bones are attached, and also the smooth surfaces be- tween the ridges which respectively form part of the inferior and middle ' meatus ' of the nose. Near the top the nasal process often closes in one of the anterior ethmoidal cells at the lower half. In front the nasal pro- cess presents a sharp crescent-shaped margin, which, with the similar one on the opposite bone and the nasal bones, bounds the anterior opening of the nose, and gives attachment to the lateral cartilage. Palatine Process. The palatine process extends horizontally in- ward, and forms the anterior two-thirds of the hard palate, and the floor of the nose; the posterior third being completed by the palate bone. It is slightly arched from before backward, and is thicker in front, near the 74 HUMAN OSTEOLOGY. alveolus, than behind. On the palatine surface (Plate XX.) can be seen 1, the palatine groove for the descending palatine vessels and nerve; 2, the numerous foramina which transmit vessels into the bone; and 3, the pits made by the palatine glands. The upper or nasal surface is smooth and slightly concave. By adjusting the two superior maxillary bones to- gether, you find that the palatine processes are connected in the middle line by a very rough suture (palatine suture) ; and that they rise toward the nose in a crest, which articulates with the vomer, and forms the base of the bony septum of the nose. (Plate XXIII. Fig. 1.) This crest projects in front in the shape of a sharp spine (the ' anterior nasal spine'), to which is attached the cartilaginous part of the septum. In this pala- tine suture, immediately behind the middle incisor teeth, we see the ' ante- rior palatine canal/ (Plate XX.) Toward the palate this canal has, at first sight, only one large orifice; but if we look to the bottom of it, we shall probably find four minute openings. Two of these 49 lie in the mid- dle line, one behind the other, and transmit the naso-palatine nerves; the other two much larger, are situated one on each side of the middle line; they lead into the floor of each nostril, and transmit the anterior palatine arteries. 50 Malar Process. The malar process stands off from the outer side of the antrum. It is remarkably thick and strong, and is connected, by a very rugged triangular surface, with the malar bone. The malar pro- cess is situated just over the first and second molar teeth, and is there- fore well calculated to resist pressure in mastication. When we crack a nut, we instinctively place it under these teeth. Connections. The superior maxilla is connected with nine bones, as follows: With the malar, the frontal, the nasal, the lachrymal, the vomer, the inferior spongy, the palate bone, its fellow, and lastly, the ethmoid. We mention this bone last of all, because we wish to direct attention to a fact which we have hitherto omitted to notice, that some of its cells are closed in by half cells usually seen along the orbital plate of the superior maxillary bone. (Plate XII. Fig. 2.) 49 These ' incisor' foramina are sometimes called the foramina of ' Scarpa. ' 50 These lateral foramina are sometimes called the foramina of 'Stenson.' The description in the text concerning the anterior palatine canals applies to twenty out of forty skulls examined. Their disposition, in other cases, is very apt to vary, both as to number and size. It was Scarpa ('Annot. Anatom. ' lib. ii. p. 75) who first pointed out the varieties in these canals. In many instances one of the canals is absent; or, if present, not pervious throughout. For a more complete explanation of this ques- tion, see Quain's 'Anatomy.' SUPERIOR MAXILLARY BONE. 75 Ossification. The ossification of the upper jaw begins about the seventh week of foetal life, and proceeds so quickly, that the number of its independent centres has not yet been accurately determined. It appears to have five distinct centres: one for the alveolus behind the incisors, one for the palatine process, one for the floor of the orbit and malar process, a fourth for the portion in front of the antrum with the nasal process, and lastly, a very distinct centre," which includes the sockets of the two incisor teeth. In most human skulls, if not very old, one can trace the remains of the 'pre-maxillary' suture. (Plate XX.) It runs outward from the anterior palatine canal, and then through the alveolar border of the jaw, invariably between the second incisor and the canine tooth; and here we lose all trace of it. This is interesting surgically. In cases of double hare-lip, where the fissure is not confined to the lips, the pre- max- illary bones on each side fail to unite with the rest of the upper jaw, and often project in a hideous manner through the fissure of the lip. When removed by operation, these bones are always found to contain the cap- sules of the four incisor teeth." Right or Left ? This bone will be in the same position as the cor- responding one in the student's body, if he hold the nasal process (which articulates with the frontal) upward, the opening of the antrum inward, and the incisor teeth forward. Comparative Osteology. The teeth which grow from the pre- maxillary bones are called incisors. On a close inspection of the narwhal hanging in the Mus. Roy. Coll. Surg. the sharp spiral tusk will be found to spring from the left pre-maxillary bone. It is therefore the left in- cisor tooth. The right one usually remains undeveloped; but there is a specimen in the Cambridge Museum where both are of full length. Evi- dence of the narwhal's power of offence or defence is given by the tusks having been found buried to a depth of ten or twelve inches in the tim- bers of ships. The female narwhal has no such extraordinary growth of the incisor tooth. It is interesting to notice in the skull of the ele- phant that the suture between the superior maxillary and pre-maxillary bones is visible, and that his tusks grow from the pre-maxillary bones, and are therefore also incisor teeth. The tusks of the walrus have their origin 61 This part, in man, was first pointed out by the poet Goethe. 62 For the most recent investigations concerning the 'Formation and Early Growth of the Bones of the Human Face, ' see a very interesting and elaborate paper by Mr. G. W. Callender in the 'Philosoph. Trans.' for 1869. 76 HUMAN OSTEOLOGY. externally to the pre-maxillary bone, and are therefore canine teeth, and this animal belongs to the carnivora. (No. 3864A.) Examine the bull, and it will be seen that there are no incisors in the upper jaw. This is the case in all the Kuminants, excepting the camel, which loses the central incisors early in life. In the bull, deer, and other Euminants also notice that the so-called canines in the lower jaw are in a regular series with the six incisors, and much resemble them. They seize their food between this even row of teeth and the prehensile upper lip, and then chew it with the molars. In the order Monotremata, the one member, Echidna, has no teeth, and the other, Ornithorhynchus paradoxus, has but horny plates to repre- sent them. (See Sep. Ser.) In many of the lower animals teeth are not confined to the alveolar margins of the jaw, but are found scattered about the upper part of the alimentary canal. Thus, in the Labroid fishes (No. 96), large teeth may be seen developed upon the palate. In the perch there are teeth in the pharynx. (No. 197.) In the lobster there are horny teeth in the stomach, where the food is ground. In birds the superior maxillary, with the inter-maxillary bones, are prolonged forward, and when covered with the appropriate horny material, constitute the beak; the lower jaw also projecting forms the lower half of the beak. (Nos. 1678, 1678A.) The upper jaw is movable in parrots (No. 1438), and has a broad trans- verse articulation with the frontal. It consists of the coalesced nasal, maxillary, and pre-maxillary bones. In Primates there are never more than four incisors above, and the same number below. In the Eodents the incisors continue to grow throughout life, and are long and curved. See the Canadian beaver (No. 2165). In Cetacea the pre-maxillae, which are small in proportion to the max- illae, are prolonged far in advance of the nasal aperture, as may be seen in the skeleton of the great sperm whale in the Mus. Eoy. Coll. Surg. Examine the poison fang in a serpent from New Holland (No. 650). It is situated in the upper jaw and has a bristle passed through it, show- ing that it is tubular. This tube contains the duct of the poison gland. Look at the plates of whalebone hanging from the upper jaw of the whalebone whale. It is by means of these plates that he entangles the small molluscs on which he feeds. PLATE XIII. Sphenoid sur face _^\ 'JX,-EtWioid surface. ^r.ijc-*^^' "Ridoefbi midU'.e spongy bone v INTERNAL VIEW OF PALATE BONE. Anterior or Ma.xilla.ry surface !Exbrn1 Internal orEthmoida.1 l'osterio' r or., SpTienoiol surfajce . of the orb'ta.1 process of the Palate bone. Malar canals Orbital curface . articulalcs * infenor Spongy bona.. LACHRYMAL BONE. MALAR BONE. MALAR BONE. 77 MALAK BONE. (PLATE XIII. Fig. 3.) Three Surfaces. The malar bone forms the prominence of the cheek, a part of the margin and wall of the orbit, and the greater portion of the zygomatic arch. It is remarkably thick and strong, and resists injury, to which the face, in this situation, is so exposed. We divide it into an anterior or subcutaneous surface, a superior or orbital, and a poste- rior or zygomatic. On the subcutaneous surface there is nothing to observe except the orifice of one of the ' malar canals/ and that it gives origin to the ' zygo- maticus major ' and ' minor ' muscles. The superior surface forms part of the outer wall of the orbit, a small part of its floor, and, generally speaking, the corner only of the spheno- maxillary fissure. " There are usually two ' malar canals ' to be seen on it. By introducing bristles, it will be found that one of these leads to the subcutaneous surface; the other, to the zygomatic surface. These malar canals transmit cutaneous nerves which proceed from the orbital branch of the superior maxillary nerve to the cheek, and the zygomatic fossa respectively. The posterior surface is very concave, and forms the anterior wall of the zygomatic fossa. Three Borders. The malar bone has three free borders. One forms at least a third of the margin of the orbit, and reaches as far in- ward as the infra-orbital canal, giving origin to a few fibres of the ' leva- tor labii superioris'; a second forms the upper edge of the zygomatic arch, and running upward becomes continuous with the temporal ridge at the external angular process of the frontal bone this border gives attachment to the ' temporal fascia '; a third forms the lower edge of the arch, and gives origin to the ' masseter ' muscle. (Plate XV. Fig. 2.) Connections. The malar bone is connected with four bones: namely, by a broad and very roughly serrated surface, with the superior maxillary; 53 From an examination of many skulls, I find that the malar bone is excluded from the spheno-maxillary fissure more frequently than is generally supposed. This exclusion is effected in one of two ways; either by the immediate junction of the superior maxillary and sphenoid bones, or by the interposition of a little ' Wormian' bone just at the angle of the fissure. 78 HUMAN OSTEOLOGY. "by suture, with the external angle of the frontal, the orbital plate of the sphenoid, and the zygomatic process of the temporal. These several con- nections are so strong that the bone cannot be driven inward toward the orbit, and fractures of it are very rare. Ossification. It is developed from a single centre of ossification, which appears about the seventh week of foetal life. Right or Left ? The cheek bone will be in the same position as the corresponding one in the student's body if he hold it with the subcuta- neous surface forward (and outward); the orbital surface upward; and the articulation for the zygoma backward. Comparative Osteology. The upper process of the malar bone does not articulate with the frontal in the carnivora (Nos. 4561, 4562). In the Great Kangaroo and Wombat the zygomatic process of the malar bone extends backward so far that it forms part of the glenoid cavity and articulates with the lower jaw. NASAL BONE. (PLATE XVI. Fig. 3.) The nasal bones, situated one on either side, occupy the space between the nasal processes of the superior maxillary bones, and, together, com- plete the bridge of the nose. Their length, breadth, and degree of in- clination, determine the shape of the nose. We have to examine their anterior and posterior surfaces, and their four borders. Surfaces. Their anterior surfaces are subcutaneous, convex, and present the orifices of one or more canals, which transmit blood-vessels. Their posterior surfaces are concave, form part of the roof of the nose, and each is marked by a groove for the passage of the external branch of the nasal division of the fifth nerve. Borders. Their upper borders are broad, serrated, and firmly articu- lated with the frontal bone. Their lower borders are thin and free in the dry bone, but connected in the recent subject with the lateral cartilages of the nose. Each has, generally, a little notch in it, through which the ex- ternal branch of the nasal nerve comes and supplies the skin at the tip of the nose. Their outer borders are serrated, slightly sloped, and rest NASAL BONE. 79 upon the nasal processes of the superior maxillary bones. Their inner borders articulate with each other, in the middle line, along the ' nasal suture.* From the under surface of this suture a high ' crest' of bone projects. By putting the bones together, it is seen how their crests form the beginning of the bony septum of the nose, and how they articulate with the nasal spine of the frontal bone, and the perpendicular plate of the ethmoid. (Plate XXIII. Fig. 1.) Hence, with a depressed fracture of the nasal bones, there must be a fracture of the perpendicular plate of the ethmoid. In some rare instances, the injury extends through the perpendicular plate of the ethmoid to the base of the brain. Observing the great strength of the nasal bones and the massive arch they form, how the sides of this arch are supported by the nasal processes of the su- perior maxillae, while the centre is propped up by the nasal spine of the frontal bone, and the perpendicular plate of the ethmoid (Plate XXIV. Fig. 2), one can readily understand what makes the arch so strong, and why the bones are so seldom broken. A pretty good proof is given of the strength of the arch, when one sees a mountebank support upon it, with impunity, a ladder, with the additional weight of a man upon the steps. Connections. The nasal bone articulates with four others, namely, its fellow, the superior maxillary, the frontal, and the perpendicular plate of the ethmoid. Ossification. Each nasal bone is developed from a single centre of ossification, which appears about the seventh week of foatal life. Right or Left? This bone will be in the same position as the corre- sponding one in the student's body if he hold the thick border (which articulates with the frontal bone) upward, the convex surface forward and outward, and the short side (for articulation with its fellow) inward. Comparative Osteology. The only difference between the skulls of a tiger and a lion is that in the lion the upper ends of the nasal bones and the nasal processes of the superior maxillary bones are on the same level, whereas in the tiger the nasal bones run up considerably beyond the nasal processes. 80 HUMAN OSTEOLOGY. LACHRYMAL BONE. (PLATE XIII. Fig. 4.) Surfaces. The lachrymal bones are situated, one on each side, on the inner wall of the orbit. They are exceedingly thin and delicate, and shaped somewhat like a finger-nail; hence the name 'os unguis.' In old skulls, they are often as thin as silver paper, and sometimes perforated. One surface is directed toward the orbit; the other toward the nose. One of these bones is seen in siM in Plate XVI. Fig. 2. The external or orbital surface has a vertical ridge upon it which ter- minates below in a small hook-like process or tongue, termed ' hamulus,' which fits into the angle between the inferior turbinated and the superior maxillary bones (Plate XXIII. Fig. 2). In front of this is a groove ('lachrymal groove'), which, together with the groove on the nasal pro- cess of the superior maxilla, forms the commencement of the canal for the passage of the tears from the lachrymal sac into the nose. The ridge itself gives origin to the 'tensor tarsi.' The bone behind the ridge is smooth, slightly concave, and forms part of the inner wall of the orbit. The internal or nasal surface presents a slight furrow corresponding to the external ridge. The surface in front of this forms part of the middle meatus of the nose; that behind it always covers the anterior cells of the ethmoid bone, and sometimes a small cell or two in the frontal bone. Connections. By examining the orbit (Plate XVI. Fig. 2), you ob- serve that the lachrymal bone is somewhat square, and that it articulates by suture with the frontal above, the ethmoid behind, the superior maxil- lary in front and below. But this is not all. The hook-like process (hanmlus) at the lower edge of the bone articulates with what is called the 'lachrymal process' of the inferior turbinated bone. (Plate XXIII. Fig. 2.) So, then, it articulates with four bones. Ossification. It has one centre of ossification, which appears about the eighth week of foetal life. Right or Left? This bone will be in the same .position as the corre- sponding one in the student's body, if he hold the concave orbital surface outward, the lachrymal groove forward, and the small tongue-like process (which articulates with the lachrymal process of the inferior turbinated bone) downward. PLATE XIV. Orbital surFa.ce. Zybornatic surface $-pVieno-palat'rne foramen ..SpVienoiolal surface. lit Posterior palatine canal j;| A ...."Rid^efbr inferior spongy \>one. M Tuberosiby Groove co'mpletirig ptery^oicl fbssa iior'i7.o n tal plate - Rst PALATE BONE. OnFi'ce of posterior pUti'ne canaL for T< 'Accessory palatine canals. .r surPace. EtVimoidal surface urface of oiclal process ian crest OrWiba.\ surface ll a.ry surface. ... Tuber Anterior view PALATE BONE. 81 PALATE BONE. (PLATES XIII. and XIV.) Each ' palate bone ' is wedged in between the pterygoid process of the sphenoid and the superior maxillary bone. Each forms part of the nasal fossa, of the orbit, and of the palate. As the palate bone somewhat re- sembles the letter L in shape, we can divide it, for convenience of descrip- tion, into a horizontal and a vertical plate. Horizontal Plate. The horizontal plate completes the bony palate by fitting on to the palate plate of the superior maxillary bone. Its under surface (Plate XIV. Fig. 2) presents a transverse ridge for the insertion of the aponeurosis of the ' tensor palati.' In front of this ridge and to- ward its outer end we observe the orifice, more or less complete, of the ' posterior palatine canal,' for the transmission of the descending palatine- vessels and the larger palatine nerve from the spheno-palatine ganglion, The anterior edge of this plate is serrated and cut obliquely, so as to articulate with, and be supported by, the palate plate of the superior maxilla. The posterior edge is smooth and concave, and gives attachment to the soft palate. The inner edge firmly articulates with its fellow, by means of a ' median crest ' raised up toward the nose, precisely like the corresponding parts in the superior maxillary bones (see Plate XXIII. Fig. 1): this crest supports the vomer, and forms a basis for the septum of the nose. Behind it terminates in a pointed process, termed the 'posterior nasal spine' (Plate XX.), which gives origin to the 'azygos uvulae ' muscle. The upper surface of the plate is smooth and slightly concave, thus forming part of the floor of the nose. Vertical Plate. The vertical plate of the palate bone contributes to form the outer boundary of the nasal fossa. On its inner surface (Plate XIII. Fig. 1) is a ' ridge ' to which is attached the inferior turbinated bone. The surfaces above and below this ridge, respectively, form part of the middle and inferior ' meatus ' of the nose. Still higher is a ridge for the middle turbinated bone. On its outer surface we observe a rertical groove, which either alone, or in conjunction with the superior maxilla, forms the ' posterior palatine canal/ which transmits the descending palatine vessels and the large palatine nerve. The front part of the ver- tical plate fits along the inner wall of the antrum of the superior maxilla,. and helps to close the lower and back part of the orifice of the antrum. 6 82 HUMAN OSTEOLOGY. This part, however, is very fragile, and is generally broken in separating the bones. Tuberosity. From the angle formed by the horizontal and vertical plates projects backward what is called the ' tuberosity/ This is the thickest and strongest part of the whole bone, and it fits into and fills up the ' notch ' which is seen between the pterygoid plates of the sphenoid. Notice also that its posterior aspect presents a groove which completes the pterygoid fossa, and gives origin to a part of the ' pterygoideus inter- nus/ The groove is bounded by two rough surfaces, which diverge from each other like the letter V reversed, and fit into the borders of the notch itself. (Plate X. Fig. 2.) The anterior aspect of the tuberosity presents & very rugged surface, which articulates with th3 cuberosity of the supe- rior maxillary bone. Behind this rough surface is a smooth portion con- tinuous with the plane of the external pterygoid plate; this smooth part gives origin to some of the fibres of the external pterygoid muscle. The inferior aspect has nothing remarkable on it, except the orifices of one or two canals large enough to admit a pin. They are the ' accessory palatine canals/ and transmit the external and the small palatine nerves to the soft palate. Turn now your attention to the upper part of the palate bone, and ob- serve that at the top of the vertical plate there are two processes separated by a deep notch, which forms the greater part of the ' spheno-palatine foramen/ One of these processes is called the ' orbital/ because it fills up a little corner at the back part of the orbit; the other is called the ' sphenoidal/ because it fits under the body of the sphenoid bone. Orbital Process. The ' orbital process' springs from the top of the hone by a narrow ' neck/ and is hollow, so that it forms a cell. The cell contains air, admitted through one of the posterior ethmoidal cells. This little process 1n.asjive surfaces, unequal in extent, and looking in different directions. If you hold the bone before you, precisely as it is in your own person, and remember that it is interposed between the maxillary in front and the sphenoid behind, you will have no difficulty in recognizing the direction of the surfaces to be as follows (see Plate XIII. Fig. 2) : the superior looks into the orbit and contributes to form its floor; the external looks into the spheno-maxillary fossa; the posterior is connected with the body of the sphenoid; the internal with the ethmoid; and the anterior with the superior maxillary bone. Thus, then, we have a superior or orbital surface, an external or zygomatic, a posterior or sphenoidal, an in- PALATE BONE. 83 ternal or ethmoidal, and an anterior or maxillary: of these five two only are free, namely, the orbital and the zygomatic the other three are at- tached to the respective bones with which they are contiguous. Plate XXII. shows the little corner at the inner and back part of the orbit, which is filled up by the palate bone, and also the relative positions of the bones with which the orbital process is connected. It likewise shows that the ' zygomatic surface ' forms that part of the floor of the spheno-maxillary fossa which lies above the spheno-palatine foramen. Sphenoidal Process. The 'sphenoidal process 'is a thin plate of bone, which arches inward beneath the body of the sphenoid, and forms part of the roof of the nasal fossa. As it is generally broken in the sepa- rate bone, one can see it best in the perfect skull. (Plate XX.) The arch which it forms has three surfaces, an upper or convex surface, which closes in the pterygo-palatine canal; an under or concave surface, which is seen in looking into the nasal fossa; and, lastly, an outer, which is seen in looking at the bottom of the spheno-maxillary fossa. Spheno-Palatine Foramen. Respecting the ' spheno-palatine fora- men/ we need, for the present, merely observe, that it is an opening which leads from the spheno-maxillary fossa into the cavity of the nose, and transmits the nasal or spheno-palatine branch of the internal maxil- lary artery and nasal branches of the spheno-palatine ganglion. (Plate XXII.) Connections. The palate bone articulates with six bones, namely, its fellow, the sphenoid, the ethmoid, the inferior spongy bone, the vo- mer, and the superior maxilla. Ossification. It is developed from a single centre of ossification, which appears at the angle of the horizontal and vertical portions, about the seventh week of f oetal life. Right or Left? This bone will be in the same position as the cor- responding one in the student's body if he hold the notch (which forms with the sphenoid the spheno-palatine foramen) upward, the orbital process forward, and the palatine plate inward. 84 HUMAN OSTEOLOGY. INFERIOR SPONGY OR TURBINATED BONE. (PLATE XV. Figs. 1 and 8.) In each nasal cavity there are three spongy or turbinated bones an upper, a middle, and a lower. The upper and middle form part of the ethmoid bone, and have been already described, p. 73. We have now to examine the lower one. Its Position and Use. This thin plate of bone is well called ' spongy,' from its structure, and ' turbinated/ from its curved form. By referring to Plate XXIII. Fig. 2, you see it in situ, and observe how much longer it is than either of the others. Its internal surface, forming the convex part of the roll, looks toward the septum of the nose; its external surface forms the concave part, and bounds the inferior meatus of the nose. Both surfaces are covered with little ridges and furrows, and more or less 'horizontal canals, which lodge numerous plexuses of arteries, but chiefly of veins. This quite accords with the function served by the bone, namely, of affording an additional extent of surface which warms the air on its passage to the lungs. It has nothing to do with the sense of smell. The olfactory nerves have not been traced lower than the mid- dle spongy bone. Connections. By its upper edge it is attached along the outer wall of the nose to four bones as follows Beginning from the front, we find it attached, 1, to a ridge along the nasal process of the superior maxilla; 2, by means of a little ' tongue ' (' lachrymal process ') to just such another ' tongue ' of the lachrymal; it is this part of the bone which completes the lachrymal canal; 3, to the orifice of the antrum by means of a triangular plate termed the 'maxillary process' (Plate XV. Fig. 3,) which turns down like a dog's ear, and helps to narrow the lower part of the orifice of the antrum; 4, to the unciform plate of the ethmoid by means of a little tongue, called the 'ethmoidal process' ; 5, and lastly, to a ridge along the vertical plate of the palate bone. Notwithstanding these numerous con- nections, the bone is by no means strongly fixed in its position: in the dry skull it often falls out; and in the operation of extracting a polypus from the nose, it is quite possible to pull out part of the bone or even the entire bone with the polypus. Its lower edge is free, and generally about half an inch from the floor Lachrymal process ....Ethmo\dal process. Eift.1. In Peri DP Spongy tone, inner surface. Lachrymal bono Inferior Sponhy bone, outer surface. Groove For Naso-palatine iierve VOMER Temporal ly^ornatic. fossa .j^... \ Ft & 2 ' Sphenoidal F issure / Palate "bone, '^Ethmoid boneXLachry Crest Groove for naiss3 nerv/e. MASAL BONE. Posterior view. Anterior view. THE VOMER. 85 of the nose, so that there is just room enough to introduce the tube of a stomach-pump through the nose. Ossification. The bone has one independent centre of ossification, which appears about the fifth month of total life. Right or Left ? This bone will be in the same position as the corre- sponding one in the student's body if he hold the convex surface inward toward the septum of the nose; the maxillary process hanging downward; and the large lachrymal process in front of the smaller ethmoidal process. Comparative Osteology. See the remarks at the end of 'the Ethmoid bone.' THE VOMER. (PLATE XVI. Fig. 1.) The ' vomer* is so named from its resemblance to a ploughshare. It is a thin and delicate plate, situated perpendicularly in the middle line, and, together with the perpendicular plate of the ethmoid bone, forms the bony septum of the nose. (Plate XXIII. Fig. 1.) Two Plates. Thin as it is, the vomer consists of two plates, united in the middle, but separated above, where they become stronger, diverge from each other, and form a deep fissure which receives the ' rostrum ' of the sphenoid. The diverging edges of the fissure, called the ' wings/ fit into the little furrows beneath the ' vaginal processes ' of the sphenoid. (Plate XI, Fig. 1.) Concerning the other connections of the vomer, we hav.e to observe that the two plates of which the bone is composed sepa- rate from each other at every articular edge of it; and as the vomer receives the other bones into its grooves, so it is locked in on all sides. Connections. The vomer is connected with six bones. Below, it articulates with the crest of the maxillary and palate bones; above, with the lower edge of the rostrum of the sphenoid; in front, with the perpendicular plate of the ethmoid, and the median cartilage of the nose; behind, its edge is sharp and free, and, in the perfect skull, is seen as the septum between the posterior openings of the nasal fossae. Both surfaces of the vomer are marked by grooves for blood-vessels and nerves: but the only groove deserving notice is that which descends obliquely and transmits the ' naso-palatine nerve.' 86 HUMAN OSTEOLOGY. It is necessary to know that the direction of the vomer is not, in all persons, perpendicular. In 100 skulls the vomer was found to be perpen- dicular only in 24. There are instances in which it projects into one side of the nose to such an unusual extent, that when covered by its vascu- lar and swollen mucous membrane, the projection might easily be mis- taken for a polypus. Such mistakes are alluded to in surgical works. M Ossification. The vomer is developed from one center of ossifica- tion, which appears about the seventh week of foetal life, at the upper part, and from it each lateral plate is developed. THE INFERIOR MAXILLARY BONE. (PLATE XVII.) For convenience of description we divide the lower jaw into the arched part in front, the ' body/ and the ascending part behind, the ' ramus.' At the top of each ramus are the ' condyle ' or articular surface, the ' coro- noid ' process for the insertion of the temporal muscle, and the ' sigmoid notch/ Body and Symphysis. The convex part of the body presents, ex- actly in the center, a slight ridge, the ' symphysis/ which is the strongest part of the bone, and indicates where the two halves of the bone grew together. Its direction is vertical, or even projects forward: this is one of the characteristics of man, who alone has a chin. The ' symphysis ' terminates, below, in the triangular ' mental process/ On each side of the symphysis is a slight depression, the ' mental fossa/ which gives origin to the 'levator menti/ More externally, and generally in a line with the first prae-molar tooth, is the ' mental foramen/ which transmits the ' mental branch ' of the inferior dental nerve and artery. From the lower part of the symphysis we trace the beginning of the ' external oblique line ' or ridge, which curves backward toward the root of the coronoid process. This line gives origin to the ' depressor labii in- ferioris ' and ' depressor anguli oris/ A little below both these, is the insertion of the ' platysma-myoides ' of the neck. Along the alveolar border adjacent to the three molar teeth is one origin of the ' buccinator/ Four Tubercles. On the concave surface of the body (Fig. 2), at M Jarjavay, 'Anatomie Chir.' t. ii. p. 61. PLATE XVII. B&.l. ro^oid process, sertion cf fcetDporcdis External obfiqCte line. Mylo-ViyoicJ ri "SituaHon fcr Sublin^ua] ^land Tubercle -for Qer.io-liyo-^ossus. Tubercle for Genio-V.yoitleus, THE INFERIOR MAXILLARY BONE. 87 the symphysis, are four small tubercles, i.e. two on each side, one above the other; the upper give origin to the ' genio-hyoglossi': the lower, to the ' genio-hyoidei.' These four tubercles in some instances are conflu- ent, and appear as one. Beneath these is a well-marked depression on each side, for the insertion of the ' digastricus' muscle, which opens the mouth. On this surface is an oblique line, faint near the symphysis, but more prominent as it ascends backward below the last molar tooth. It is called the ' mylo-hyoid ridge/ because it gives origin to the ' mylo- hyoideus.' Behind and a little above this ridge, near the last molar tooth, is the origin of part of the ' superior constrictor ' of the pharynx. Below the ridge is a slight depression, indicating the position of the sub- maxillary salivary gland. Above the ridge is the place for the sub-lingual gland; but this is not well marked. Oblique Lines. These oblique lines or ridges on the two surfaces of the body are something more than mere muscular impressions. They indicate the limit between the ' alveolar ' part which contains the teeth, and the lower or ' basilar ' part of the jaw. These distinctions are made because these parts come and go at different periods of life. In infancy there is only the alveolar part; toward puberty the basilar part slowly grows to perfection: in old age when the teeth fall out, aad their sockets are absorbed, the basilar part alone remains, and the chin gradually ap- proximates the nose. The absorption of the sockets (alveoli), which is natural in old persons, often occurs prematurely. It is apt to arise from long salivation, scurvy, or purpura, and is frequently hereditary. Teeth. The teeth in the lower jaw correspond in number (eight on each side) with those in the upper, but differ from them in these par- ticulars: 1. The first two lower molars have only two fangs, an anterior and posterior, while the upper molars have three. In the third molar or wisdom tooth the fangs are often consolidated into one; 2. When the mouth is closed the teeth of the lower jaw shut within those of the upper jaw which form a larger arch; 3. The external tubercles or cusps 'of the teeth of the lower jaw fit into the hollows between the external and internal cusps of the teeth of the upper jaw; by which arrangement we are enabled to use the entire surface of the opposing teeth in grinding the food. When the jaws are closed, each tooth in one jaw is opposed by two in the opposite jaw; one good result of this is, that when we lose a tooth, the corresponding tooth in the other jaw being still more or less opposed, is still of service in mastication. 88 HUMAN OSTEOLOGY. Ramus. The ramus of the jaw mounts up from the body nearly at a right angle in adult age, when the upper and lower jaws are kept well apart behind by the molar teeth. But in infancy, before the develop- ment of the molars, and in age when they are lost, the ' angle' of the jaw becomes obtuse. Excluding its outstanding processes, the ramus is nearly square. Nearly the whole of its outer surface gives insertion to the powerful ' masseter,' which closes the jaw (Fig. 1). On its inner sur- face (Fig. 2) is the ' dental foramen/ or the orifice of the canal for the transmission of the inferior dental nerve and artery. Its inner margin is raised into a short ' spine ' for the attachment of the internal lateral lig- ament of the jaw. Leading down from the orifice is the ' mylo-hyoid groove/ which contains the mylo-hyoidean vessels and nerve. Below the groove is the rough surface for the insertion of the ' pterygoideus in- ternus/ The muscles inserted on each surface of the angle of the jaw are so thick that fractures through this part of the bone sometimes es- cape detection. Condyle. The ' condyle ' projects from the upper and back part of the ramus to form the joint of the jaw, and fits into the glenoid cavity of the temporal bone. It is oblong in form, and convex both from without inward and from before backward. The long axis is directed horizontally inward and slightly backward, so that, if prolonged, the axes of the two condyles would meet near the front of the ' foramen magnum/ Just outside the condyle is a ' tubercle ' for the attachment of the ex- ternal lateral ligament. The condyle is supported on a contracted part termed the ' neck ' of the jaw. This neck is flattened in the same direc- tion as the condyle, and is slightly excavated in front for the insertion of the ' pterygoideus externus/ The oblique direction of the condyles of the jaw renders easy the rotatory movement necessary in mastication. In masticating we can readily feel that one condyle advances toward the anterior margin of its glenoi'd cavity, while the other recedes to the posterior. Coronoid Process. The ' coronoid ' process is a triangular, lofty plate of bone, which ascends beneath the zygomatic arch and increases the leverage of the temporal muscle which closes the mouth. The inser- tion of this muscle occupies the inner surface, the apex, and front border of the process down to the last molar tooth: the greater part of the outer surface is occupied by the masseter. The ' sigmoid notch ' transmits the ' masseteric ' nerve and artery. THE INFERIOR MAXILLARY BONE. 89 The walls of the lower jaw, particularly at the basilar part, are exceed- ingly compact and tough. In operations for removal of this part of the bone, it is necessary to use the saw freely, before the bone forceps can be of any service. The interior assumes the form of ' diploe/ and is tra- versed by the ' inferior dental canal/ which carries the vessels and nerves to the teeth (Nor. Hum. Ost. No. 234). This canal begins on the inner side of the ramus, curves forward, beneath the sockets of the teeth, and, toward the front, divides into two, of which one ends at the ' foramen mentale/ the other, much diminished in size, runs on through the diploe nearly to the symphysis, and conveys vessels and nerves to the canine and incisor teeth. Ossification. The lower jaw has two centres of ossification, which appear about the sixth week of foetal life, one for each lateral half. Their junction at the symphysis takes place about the close of the first year after birth. In the lower animals the symphysial suture often remains throughout life." Comparative Osteology. In the order Monotremata, observe that there is scarcely any bend or inflexion in the lower jaw (No. 1699). The jaw of the ant-eater is also straight, thus greatly resembling that of the pelican (see Sep. Ser.). In snakes (Ophidia) the two halves of the lower jaw are not united by bone, but held together by an elastic ligament, which permits the two halves of the jaw to be separated from each other sideways to a consider- able extent. This is one of the many arrangements by which the boa is enabled to swallow its prey though larger than its own body. This is shown in the specimen of the tiger-boa (No. 602). In the lower animals the two halves of the jaw generally remain sepa- rate throughout life. In all mammalia each half of the lower jaw consists of a single piece which articulates with the squamosal bone of the skull. In all below the mammals it articulates with a modified malleus called the quadrate bone. This is well seen in the skull of the ostrich and other birds in the Separate Series. [For some interesting points as to the relation between the size of the coronoid process and the temporal fossa the student should read the Com- parative Osteology paragraph at the end of the chapter on ' The Skull as a Whole.'] 65 For a lucid and elaborate account of the development of the jaws and the teeth see ' Manual of Dental Anatomy, ' by C. S. Tomes, M. A. 1876. 90 HUMAN OSTEOLOGY. It has been said that man is the only creature which has a chin. It is most distinct in the Caucasian race, becomes faintly marked in the Negro, and does not exist in the Apes. Rodentia have never more than two incisors in the lower jaw; and usually only two, but sometimes four, in the upper. When there are four incisors in the upper jaw, as in hares and rabbits, there are two small ones behind the two large ones (No. 1916). These incisors have a persist- ent pulp, and continue to grow in adult life. They have no canines. Carnivora have milk and permanent teeth, which are enamelled, and always consist of incisors, canines, and molars. In elephants the teeth consist of tusk-like incisors, growing from per- sistent pulps, and molars. Look at the lower jaw of the crocodile (No. 717 D) and see how greatly the angle projects backward. This projection is for the insertion of the digastricus, the muscle which opens the mouth, and which acts upon the jaw as a lever of the first order. In man it acts as a lever of the second order, as it is inserted near the symphysis. To appreciate the mechanism of the lower jaw, look at the form of the joint in animals. In them it varies according to the structure of their teeth and the food they eat. There are three principal types of it: the carnivorous, the ruminant, and the rodent. The carnivorous type is a imoia tone of the "Bone? a-nd.ForaTrLi.ua- on LHfcTnner wall oF the Orbit, the five ope nm^s into the 3pheno4mudlkry fossa .the AntruTv and bones cuntra-cti-ncj its orifice. THE CEBITS. 105 somewhat retracted in its socket, the margin of the orbit is more than strong enough to protect it from the effects of violence. Each orbit is pyramidal, with the apex behind. Their axes, if pro- longed, would pass through the optic foramina, and meet behind the pituitary fossa of the sphenoid. This divergence gives a greater range of vision. The anterior opening of the orbit is quadrilateral and consists of an upper, a lower, an inner and an outer margin. In the higher types of man these openings are more rounded. Upper Wall of Orbit. The upper wall of the orbit is slightly arched, and formed by the frontal bone and lesser wing of the sphenoid. On this wall are 1, the optic foramen; 2, the fossa beneath the external angular process for the lachrymal gland; 3, the little depression for the pulley of the ' superior oblique ' muscle; 4, the supra-orbital foramen or notch, situate^, at the junction of the inner with the middle third of the orbital margin. Lower Wall or Floor of Orbit. The lower wall of the orbit slopes downward and outward, and is formed by the orbital plate of the superior maxilla, by part of the malar bone, and behind by the orbital plate of the palate bone. On this wall is the groove for the infra-orbital nerve. Inner Wall of Orbit. The inner wall (Plate XXII.) is formed by the nasal process of the superior maxilla, by the lachrymal, the os planum of the ethmoid, and the side of the body of the sphenoid bone. Here we observe the groove for the nasal duct, formed conjointly by the nasal process of the superior maxilla, the lachrymal, and the inferior spongy bone. Its direction is downward, backward, and a little outward, and it leads into the inferior meatus of the nose. Besides this, there are the 1 anterior and posterior ethmoidal foramina.' Outer Wall of Orbit. The outer wall of the orbit is formed by the malar bone and the orbital plate of the great wing of the sphenoid. Here there are one or two small foramina (malar canals), which transmit small nerves from the orbit to the skin of the cheek and temple. (See p. 77.) The outer wall of the orbit recedes more than the other parts of its circumference, giving so great a range of vision externally, that by rotating the head on each side of the spine, we can see all round. Bones Composing Orbit. Look into the orbit and examine two four-sided plates, one on the inner side belonging to the ethmoid, and one on the outer belonging to the great wing of the sphenoid. The four-sided 106 HUMAN OSTEOLOGY. plate of the ethmoid articulates above with the frontal; below with the superior maxillary bone, in front with the lachrymal and behind with the sphenoid. Besides these the orbital process of the palate bone here comes up between the sphenoid and superior maxilla (articulating with both of them) and joins the posterior inferior angle of this plate. The four-sided plate of the sphenoid articulates likewise with the frontal bone above, which arches over from the top of the aforesaid plate of the eth- moid; below, its edge is separated from the superior maxillary bone by the spheno- maxillary fissure; in front, it articulates with the malar bone, and behind, its edge is separated from the rest of the sphenoid by the sphenoidal fissure. These articulations should be traced on the bones and thoroughly mastered. Thus, seven bones enter into the composition of each orbit: namely the frontal, ethmoid, and sphenoid, the superior maxilla, the malar, the lachrymal, and the palate; but there are only eleven bones in the two orbits, since the first three bones are common to both. Sphenoidal and Spheno-maxillary Fissures. At the back of the orbit are two wide fissures for the admission of blood-vessels and nerves. The upper one is the ' sphenoidal fissure/ formed between the greater and lesser wings of the sphenoid bone. It leads into the cranium, and transmits the third and fourth nerves, the ophthalmic branch of the fifth, the sixth nerve, some filaments of the sympathetic nerve, and the ophthalmic vein. The lower one, the ' spheno-maxillary fissure' leads into the zygomatic fossa. The borders of this fissure are formed internally by the superior maxillary and palate bones, externally by the sphenoid. It is completed in front by the malar. 63 Through this fissure the infra-orbital artery and the superior maxillary nerve enter the groove along the floor of the orbit. There are some points of practical interest about these two fissures. 1. In blows on the temple, blood is apt to make its way through the splieno-maxillary fissure into the orbit, and produce ecchymosis under the conjunctiva. 2. In the operation for the removal of the superior max- illary bone, we saw through the orbital wall into the fissure, so that it is requisite to know its precise position. Concerning the sphenoidal fissure, we should know that: 1. In fracture through the base of the skull, involv- ing this fissure, the effused blood may make its way into the orbit and 63 Except in cases where the sphenoid and superior maxillary come into contact, and exclude the malar. (See note, 37.) PLATE XXIII. ITasal spine of- Fronts bone CrestoF Nasal bone Perpendicular plate of Ethmoid bone Crest oE su p^Maxillary "bone {SpTneno'tcl bone Crest oF Palate tone. View of the Septum, of tVeTSIose Prdbe.passecJ from Frontal pm us into Middle meabus Middle >pon^y bone. Superior Meatus.. Superior Sf>ony bone Ptery^o palatine canal.. Spheno -palatine Foramen Msaaie-meatus Inferior meatu s..- - bone, m'bc . .Or i Flee oF Anbrum ^Sponbybone. View of the three' Meabus* oF tY\e~Noae. NASAL FOSSJE. 107 produce ecchymosis of the conjunctiva. 2. A sharp instrument might penetrate through this fissure into the brain. Surgery has such cases on record. Here is one. Henry II. of France, one of the last princes of the House of Valois, was mortally wounded by Montgomery, captain of the body guard, in a tournament held in 1559, on the occasion of the marriage of Philip II. with Elizabeth of France. A splinter from a lance entered through the sphenoidal fissure, stuck fast and could not be ex- tracted. The king died on the eleventh day. NASAL FOSSAE. (PLATE XXIII.) These cavities open widely in front, and admit the air through the nostrils, and behind into the top of the pharynx. To study them prop- erly it is indispensable to have a skull divided longitudinally on one side of the septum, so that we can examine the roof, the floor, the outer and inner surfaces of the cavities. Boundaries of Nasal Fossae. The ' roof ' of the nasal fossae is formed by the nasal bones, by the nasal spine of the frontal, the cribri- form plate of the ethmoid, and the body of the sphenoid. It does not form a horizontal plane from before backward. It is only the cribri- form plate which is horizontal; from this, the roof slopes forward toward the nose, and backward toward the pharynx: therefore the vertical depth is much greater in the middle than elsewhere. Notice the greater thin- ness of the cribriform plate, and how easily an instrument might be thrust through this part of the roof into the brain. Herodotus, 64 in his excellent description of the process of embalming the dead, as practised by the ancient Egyptians, mentions that they drew out the brain through the nostrils with an iron hook, and filled up the void by injecting drugs. In the fine series of ancient Egyptian skulls, brought from the great necropolis of Thebes by Professor Flower, and now in the Museum of the Royal College of Surgeons (Nor. Hum. Ost., Nos. 584 to 593), it may be seen that in every one of them the cribriform plate is broken away, and the bones of the nasal fossae more or less damaged; an interesting proof of the veracity of the ancient historian. 84 ' Euterpe, ' chap. 86, 87, 88. 108 HUMAN OSTEOLOGY. The ' floor ' is nearly horizontal, and is formed by the palate plates of the superior maxillary and palate bones. In the dry bones can be seen, on each side of the septum, the orifice of the ' anterior palatine canal' (p. 74). IVJeatus of the Nose. The outer wall of the nasal fossae is made irregular by the ' meatus ' or passages in the nose, and the numerous openings leading to the air-cells, in the neighboring bones. It is formed by the ethmoid (including its two turbinated bones), the nasal, the su- perior maxillary, the lachrymal, the inferior turbinated, the palate, and the internal pterygoid plate of the sphenoid. It is important to observe the position of the turbinated bones and the three * meatus ' or passages of the nose. (Plates XXIII. and XXIV.) Superior Meatus. Beneath the superior turbinated bone lies the ' superior meatus/ into which open the posterior ethmoidal cells and the sphenoidal cells. At the back part of this meatus is the spheno-pala- tine foramen, which leads into the spheno-maxillary fossa. Middle Meatus. Below the middle turbinated bone is the ' middle meatus/ Into this open 1, toward the front, the frontal sinus (or cell), along a passage termed the ' infundibulum '; 2, the anterior ethmoidal cells (distinct from, the posterior); 3, the antrum or maxillary sinus. The orifice of the antrum is large and irregular in the dry bones; but in the recent state it is so narrowed by mucous membrane that it will just admit a crow-quill. Inferior Meatus. Below the inferior turbinated bone is the 'inferior meatus/ No air-cells open into this meatus: there is only the termina- tion of the nasal duct or channel which conveys the tears into the nose: this cannot be seen without removing part of the turbinated bone. " The openings into the several ' meatus * of the nose may be thus tabu- lated: ( The sphenoidal cells. Into the SUPERIOR MEATUS . open ^ m ( The posterior ethmoidal cells. fThe anterior ethmoidal cells. Into the MIDDLE . . . open the neck haS a rid g 6 alon g its U PP 61 ' surface to which is attached a second liga- ment (superior costo-transverse); this connects it to the transverse pro- cess above it. Tubercle. External to the neck is the ' tubercle.' It has a little facet which looks downward and articulates with the transverse process supporting the rib; in front and rather above the facet is the rougher part of the tubercle which gives attachment to a third ligament connect- ing the rib to the transverse process (posterior costo-transverse). Angle. External to the tubercle, the rib makes a curve forward, forming the ' angle.' Here there is a prominent line which runs obliquely downward and forward, and indicates the attachment of muscles, which form the outer border of the ' erector spinae.' Observe that the distance between the angle and the tubercle increases as we trace the ribs down- ward, and makes room for the great muscle of the spine (erector spinae). It is near the angle that the rib breaks when the chest is compressed, for instance, in a crowd. In this kind of fracture i.e. by indirect violence the broken ends project outward, and are therefore less liable to injure the pleura. But in direct violence e.g. a kick by a horse the THE RIBS. 191 rib breaks where it is struck, the broken ends are driven inward, and consequently are more liable to injure the pleura. Shaft. The rest of the rib arching forward from the angle along the side of the chest is called the ' shaft.' It is flattened from above down- ward, like a bow. On its inner surface, near the lower border, is a deep groove for the intercostal vessels and nerve. Observe, the groove does not extend the whole length of the rib: it begins about the angle, and is gradually lost before we come to the anterior end. The vessels and nerves are safe where they lie in the groove; but between the angle of the rib and the spine, and again in front of the chest, they are liable to be injured through the intercostal spaces. In consequence of this groove, the lower edge of the rib is much thinner than the upper, which is thick and rounded. In the groove itself are the orifices of the numerous canals which transmit blood-vessels into the interior of the rib. The ribs are the most vascular bones in the body: hence the rapidity with which they unite after a fracture.. Anterior End. Respecting the anterior end, remark that it is rough, and a little excavated to receive the costal cartilage. Right or Left ? A rib will be in the same position as the corre- sponding one in the student's body if he hold the convex surface outward, the head backward, and the groove downward. In distinguishing right from left ribs it should be borne in mind that the articular facet for the transverse process looks downward in every case. Peculiarities of certain Ribs. The first, second, tenth, eleventh, and twelfth ribs have peculiarities requiring separate notice. First Rib. The plane of the first rib is nearly horizontal. It is the shortest, the most curved, the flattest and broadest of all. Its head has a single articular surface which rests on the first dorsal vertebra. It has the largest tubercle, and this is well supported by the strong transverse process of the first dorsal vertebra. There is scarcely a trace of angle. On its upper surface we may see in a well-marked bone two slight trans- verse grooves about the breadth of a finger; the subclavian artery lies in the posterior groove as it crosses the rib, the vein passes along the ante- rior. Against this surface the subclavian artery may be effectually com- pressed. The grooves are separated on the inner border of the rib by a ' tubercle' denoting the insertion of the ' scalenus anticus.' Behind this is the rough surface for the insertion of the * scalenus medius.' Lastly, there is no groove for the intercostal artery. 192 HUMAN OSTEOLOGY. It is an interesting fact, that the compact tissue forming the concave margin of the first rib is very much thicker than that on the convex side. The first rib is the strongest of all: it has to support the manubrium sterni and the clavicles, and to protect all the important parts at the base of the neck. The first rib is very rarely fractured, being so well protected by the clavicle; but when it does happen it is a most serious accident, because it is the starting point of all the other ribs in respiration, and be- cause there are so many important vessels and nerves in relation with it. Second Rib. The second rib has little or no angle, no twist on its axis, and has, near the middle of its outer surface, a rough eminence for the origin of the second and third digitations of the serratus magnus. It has a short groove for the intercostal artery. Tenth Rib. The tenth rib has a single ' facet ' on the head, for the tenth dorsal vertebra. Eleventh and Twelfth Ribs. The eleventh and twelfth ribs being shorter and less perfectly developed, are chiefly distinguished by their negative characters. Each articulates with only one vertebra, so that the head has only one facet, does not touch the transverse process, and has no tubercle. Each is tipped with cartilage. The eleventh has a trace of an angle and a groove. In the twelfth, angle and groove are imper- ceptible. Ossification. Ossification in the ribs begins about the seventh week of fcetal life. There is one ' primary * centre for the body, an epiphysis for the head, and another for the tubercle. The epiphyses appear from the fifteenth to the eighteenth year, and unite with the rest of the bone about the age of maturity. Costal Cartilages. Respecting the costal cartilages, remember that the first seven are connected with the sternum. The first cartilage is united directly with the manubrium. The others, from the second to the seventh inclusive, are articulated to the sternum with the intervention of synovial membranes which disappear in old age. The cartilages of the eighth, ninth, and tsnth ribs are gradually bevelled off, and each joins the costal cartilage immediately above it. Moreover, synovial membranes exist between these last-mentioned ribs. The last two costal cartilages do not join those above, but merely cap the eleventh and twelfth ribs. These numerous little articulations, connected with the cartilages, much facilitate the respiratory movements of the thorax. The costal cartilages increase in length from above, and allow the PLATE XLI. C 1 s . Lumbar vei-tr:bra THE RIBS. 193 requisite play of the ribs in respiration. Their great elasticity answers two purposes. 1. They act as mechanical agents of expiration by depressing the ribs after they have been raised by muscular action. 2. A blow on the sternum is distributed over fourteen elastic arches! One can under- stand, then, why the ch^st is able to bear such tremendous blows with impunity; more especially during a full inspiration. During expiration the bones are less able to resist injury, because the muscles are not acting. Notwithstanding these beautiful provisions, the sternum is sometimes broken, especially when the cartilages of the ribs are ossified. Dupuytren mentions the case of a fireman whose sternum was broken by the fall of a piece of timber. The man was carried away, supposed to be dead. Coming up accidentally, Dupuytren replaced the sternum, and the man recovered. Thorax as a Whole. In addition to what has been said of the thorax at p. 186, attention should be directed to one or two points which might otherwise be overlooked. 1. The great narrowness of the upper opening of the chest. In an adult of average size, it measures about 2 inches from before backward, and 3 inches transversely. Yet in this seemingly narrow space there is room for the trachea, the oesophagus, the great blood-vessels and nerves at the root of the neck, besides the apex of each lung, and three muscles on each side. 2. Notice how much the ribs slope in subserviency to the mechanism of respiration. Their sternal and vertebral ends are not in the same horizontal plane; for instance, the sternal end of the third rib is not oh a level with the third dorsal verte- bra, but, roughly speaking, with the sixth. 3. Notice how much addi- tional space is gained posteriorly (for the lungs) by the backward projec- tion of the ribs. 4. Notice that the lower margin of the thorax is rep- resented by a line sloping from the end of the sternum downward and backward to the last rib. 5. Notice that the intercostal spaces are widest where the ribs unite to their cartilages; and narrowest where the ribs join the spine. Mechanism of Inspiration. It is proposed to explain now how the chest is enlarged in the transverse and in the antero-posterior direc- tion by the elevation of the ribs. The spine is fixed, and serves as a fulcrum for the ribs, which are the levers. At the moment of inspiration, the ribs, which you must remember are oblique, are raised by the intercostal muscles. The centre of motion 13 194 HUMAN OSTEOLOGY. being at the spine, it is plain that the more nearly the ribs become hori- zontal, the greater will be the distance between the spine and the sternum. Thus, let the line VV, in Fig. 56, represent the spine; the line SS the sternum; a, b, c, three ribs in their oblique position; and a' } V , c', the same ribs elevated. It is obvious that by raising th$ ribs we increase at the same time the antero-posterior diameter of the chest; or, in other words, we increase the distance between the spine VV and the sternum SS. The same diagram proves that, when the ribs are raised, the intercos- FIG. 56. tal spaces are widened; that is, a perpendicular let fall between two ribs is longer when the ribs are raised than when they are depressed. Now, when the ribs rise, they describe a rotatory movement around an imaginary axis, as shown at A B, Fig. 57, which unites their vertebral and sternal ends. In consequence of this rotation on its ends, the exter- nal surface of the rib, which looks downward and outward when at rest, looks directly oiitward when raised. Thus the transverse, diameter of the chest is increased. If the ribs were all of the same length, as in Fig. 56, the projection of the sternum, caused by their elevation, would be equal all the way down. But since the lower sternal ribs are longer than the upper, it follows that the sternum is projected in inspiration more and more toward its lower end. The ribs are raised by the external intercostal muscles (which run THE RIBS. 195 obliquely downward and forward); they are depressed by the internal intercostal muscles (which run obliquely upward and forward). These facts are rendered probable (if not absolutely proved) by the following diagram: Let V V represent the spine, 1' 2' two ribs in a state of obliquity or rest, and a' a fibre of an external intercostal muscle. Now, when the fibre a' contracts, it shortens itself: but this shortening cannot take place unless the ribs are at the same time brought more into the horizontal line, as shown at 1, 2; in other words, unless they are raised; therefore the external intercostal muscles are inspiratory muscles. The same kind of demonstration proves that the internal intercostal muscles depress the ribs, and are therefore expiratory muscles. For let b be a fibre of an internal intercostal muscle extended between the ribs 3 and 4 in a state of elevation, it is easy to see that, when the fibre b con- tracts or shortens itself, it cannot do so without bringing the ribs into a more oblique position, as shown at 3' and 4'. That the fibre V must be shorter than the fibre b may be proved by a pair of compasses. Comparative Osteology. It is curious that the gorilla and chim- panzee have each 13 pairs of ribs. So that man in his descent from his pretended ancestors must have lost a rib, for he (like the man of the woods, orang outan) has only 12. In mammalia the number of ribs on each side ranges from 9 in the bottle-nosed whale (Hyperoodon, No. 2479), to 24 in the two-toed sloth 196 HUMAN OSTEOLOGY. (No. 2387 A). The horse and tapir have 18 pairs each, and the ele- phant 19. The ribs of the manatee (No. 2647 A) are extraordinarily thick, broad, and massive. In whales some of the posterior ribs are attached only to the trans- verse processes of the vertebrae. Commonly in mammalia about 6 ribs articulate with the sternum by cartilage or bone, but in whales the num- ber so attached is much smaller, in the whale-bone whale there being only one pair of true ribs. This freedom of action allows the great play of the respiratory appa- ratus in cetacea. Some animals have the costal cartilages ossified, forming sternal ribs, as in the giraffe, crocodile, ox, porpoise, and dolphin; in many there is an intermediate rib, or shaft of bone, set in between the sternal and ver- tebral ribs (see Nilotic crocodile, No. 717 D, and monotremata, No. 1698). The ribs are mostly used solely for respiration throughout the animal kingdom. In addition to this the snakes use the tips of them to walk upon, and the flying lizard (Draco volans, No. 673) has the 5 posterior ribs so recurvated and elongated as to form the bony skeleton of the membranous sail by which he supports himself in his flight from tree to tree. The middle part of the ribs in birds (see griffin vulture, No. 1674) presents a long flat process which projects backward and rests on the rib below. These are called uncinate processes. There are no processes in mammalia corresponding to the uncinate processes in birds. They are, however, seen in alligators (No. 760 A). Sharks and rays have no ribs. What appear to be ribs in the Por- beagle shark (No. 419 A) are simply the supports of the gills, as may be understood bv a reference to the skeleton of the cod-fish (No. 147 A), which has 17 pairs of ribs. The Alausa tyrannus (No. 39 A) has not only many ribs, but a good sternum. Examine the great Nilotic crocodile (No. 717 D), and you will see that an anterior and a posterior bar forming the transverse processes of the cervical vertebrae correspond to the two processes which in the dorsal vertebras support respectively the head and the tubercle of the rib. In its middle and posterior dorsal regions the end of a transverse process supports both the head and the tubercle of the rib. There will be seen also what are called intermediate ribs, i.e. a piece of bone between the THE RIBS. 197 end of the rib and the costal cartilage or sternal rib. Some of the ribs are furnished with nncinate processes as in birds; but this is better seen iu the alligator (No. 760 A). Seven pairs of false ribs are developed as superficial ossifications of the linese transversae in the abdominal wall (see also No. 711 A). The extinct flying lizards, Pterosauria (No. 119 A), had splint-like sternal, as well as abdominal, ribs. In Ophidia (No. 630) the ribs articulate only with the ends of trans- verse processes. MUSCLES OF THE BACK. (PLATES XLII. TO XL VIII.) IiT the description of the muscles of the back the more superficial muscles, connected with the arm, will be first considered. These re- moved, the great muscles of the spine, which fill up the vertebral grooves, and keep the body erect, are exposed. Lastly, there is the mass of muscles at the back of the neck attached to the occipital bone. THE SUPERFICIAL MUSCLES OF THE BACK. These are shown in Plate XLII. The most superficial is the ' tra- pezius/ a triangular muscle of which the limits are defined by the con- tinuous dark line. The other wide-spreading superficial muscle is the ' latissimus dorsi/ Under the trapezius we have the ' rhomboidei ' and the ' levator anguli scapulae ' shown in Plate XLIV. " 0. Occiput; ligamentum nuchas: spines of all the dorsal vertebrae. Trapezius . . . < T _ . I. Spine of scapula; acromion, acromial third of clavicle. 0. Crest of the ilium. Spines of all the lum- bar, and six lower dorsal vertebras, and Latissimus dorsi . . < , _. ., ,. . ,. ,. by digitations from the three lower ribs. 1. Bottom of bicipital groove of humerus. , ( 0. Spines of last cervical and five upper Ehomboideus (manor and < dorsal vertebras. I I. Posterior border of scapula. 0. Transverse processes (posterior tubercles) Levator anguli scapulas . \ of four upper cervical vertebras. 1. Upper angle of scapula. PLATE XLli:. PLATE XL1V THE SUPERFICIAL MUSCLES OF THE BACK. 199 200 HUMAN OSTEOLOGY. The * intertransversales ' pass between the transverse processes of con- tiguous vertebrae, the ' interspinales ' between the spinous processes be- ginning at the axis. Both these sets are ill developed and mostly tendi- nous in the dorsal region. The ' transverso-spinalis ' is the mass which fills up the space between the transverse and spinous process of the vertebra. It arises from transverse, and is inserted into spinous processes. Therefore its direc- tion is oblique. It is composed of several bundles. The more super- ficial pass over many vertebrae; the deeper over one or two; the deepest run from vertebra to vertebra. The ' transverso-spinalis ' comprises the ' semi-spinalis-dorsi/ ' semi-spinalis colli/ ' multifidus spinge/ and ' rota- tores spinae ' of systematic authors. The ' levatores costarum ' arise from the transverse processes, and are inserted into the ribs below them. MUSCLES OF THE BACK OF THE NECK. (PLATE XLV.) A separate group is made of these, because they specially maintain the head erect, and move the first upon the second vertebra. The ' trapezius ' being reflected, the ' splenius ' is exposed, and beneath that the ' corn- plexus/ 0. Spines of four cervical and six dorsal ver- tebrae. Splenius capitis et colli I. Mastoid process and occipital bone; trans- verse processes of four upper cervical ver- tebrae. 0. Transverse processes of six dorsal and articu- Complexus . . -^ lar processes of four cervical vertebras. 1. Occipital bone. The above muscles being reflected, we expose the muscles of the atlas and axis; namely, the 'rectus capitis posticus major' and 'minor/ 'the obliquus superior' and 'inferior/ and the 'rectus capitis lateralis/ 0. Spine of the axis. 1. Occipital bone. ~ ( 0. Spine of the atlas. Kectus capitis posticus minor . ^ T ( I. Occipital bone. ( 0. c Rectus capitis posticus manor . \ I I. Occipital bone. PLATE XLV. Occipital "bone Interspi-nales Superior articT facet ^ dorsal verteira Superior tubercle. /' (Metapophyais.) Inferior iuberole ( Anap opby s i RuclimentT i ran sv ' process. - -Metapopkysie . .. Anapophysie . Pig.2 PLATE XLVJ. PLATE XLV1I. MUSCLES IN FRONT OF THE SPINE. 201 ( 0. Transverse process of atlas. Rectus capitis lateralis . .<__.. . ( I. Jugular eminence of occipital bone. ( 0. Transverse process of atlas. Obliquus superior . . . | L Ocdpital feone ( 0. Spine of the axis. Obliquus inferior ...-<-.. , ,_ ( I. Transverse process of atlas. MUSCLES IN FKONT OF THE SPINE. (PLATES XL VI. and XL VII.) There are three pre-vertebral muscles in the cervical region; namely, the 'rectus capitis anticus major ' and ' minor/ and the 'longus colli.' In the lumbar region are the right and left crura of the ' diaphragm/ the *psoas magnus/ and occasionally a 'psoas parvus.' 0. Transverse processes of third, fourth, Eectus capitis anticus major . -j fifth, and sixth cervical vertebrae. 1. Basilar process. ( {j Eectus capitis anticus minor . < 0. Transverse process of atlas. Basilar process. The ' longus colli ' consists of a longitudinal and an oblique portion. The longitudinal part arises from the bodies of the three upper dorsal and two lower cervical vertebras, and is inserted into the bodies of the second, third, and fourth cervical vertebrae. The oblique part arises from the transverse processes of the third, fourth, and fifth cervical vertebrae, and is inserted into the tubercle of the atlas. Other oblique fibres arise from the bodies of the three upper dorsal vertebrae, and are inserted into the transverse process of the fifth cervical vertebra. 0. Eight crus from four lumbar verte- Diaphragm . . . . { brae, left from three. 1. Central tendon. 0. Bodies and transverse processes of Psoas magnus . -j all the lumbar vertebrae. 1. Trochanter minor. ( 0. Body of last dorsal vertebra. Psoas parvus . . . . < ( I. Brim of pelvis. BONES OF THE UPPER EXTREMITY. Component Bones. The bones of the upper extremity consist of the ' clavicle/ the ' scapula/ the ' humerus/ the two bones of the fore-arm, namely, the ' radius ' and the ' ulna/ the bones of the carpus, the meta- carpus, and the phalanges of the fingers. The clavicles and scapulae form the 'shoulder girdle 5 or 'pectoral arch/ The length of the arm should be in exact proportion to the height of the individual. If the arms are fully stretched in the same horizontal line, the space from the end of the middle finger of one hand to that of the other is about equal to the length of the body. THE CLAVICLE. (PLATES XL VIII., XLIX.) Position and Use. The clavicle, or collar bone, so named from its resemblance to an ancient key, extends nearly horizontally from the upper part of the sternum to the scapula. It keeps the shoulders wide apart, giving the arm a freer range of motion; affords attachment to powerful muscles; and protects the axillary vessels and nerves. By moving the shoulder, you find that the clavicle acts as a prop, the fixed end of the prop being at the sternal joint. Hence, in fractures of the clavicle, the shoulder generally falls a little forward. The patient leans his head to- ward the injured arm so as to relax the muscles, and supports the elbow in his hand. Advantage of its Curves. The shape of the clavicle is like an italic S. It has two curves, arranged so that, viewed from the front, the sternal or inner half is convex, and the acromial or outer half concave. The sternal curve is the larger of the two. The great vessels and nerves of the arm pass under it. About the junction of the two curves the bone is most frequently broken. These curves not only make the bone stronger PLATE XLV1II. Acromvsil en<3 Under surface of clavicle Sterno-Yiyoicl . .Sternal end ArticuW surface ftrclavi'cle Coraco'id process __, Nolth, Inferior a nglft. Outer surface cf Scapula. Aeromicn. Glenoid cavity "Neck, THE CLAVICLE. 203 than if it were straight, but better able to resist shocks; since, by virtue of its elasticity, the force is partially broken at each of the curves (p. 5). The strength and degree of curvature vary considerably in different bones. They are usually greater in men than in women, and most marked in those persons who do much manual labor. Shaft. The shaft of the clavicle bears the impressions of the muscles attached to it. On its upper surface, at the sternal curve, are the origins of the ' pectoralis major ' and ' sterno-cleido-mastoid/ and on the acromial curve, the origin of the 'deltoid' and the insertion of the 'trapezius/ On its under surface are 1, a longitudinal groove for the insertion of the ' subclavius '; 2, a rough surface near the sternal end for the attachment of the ' costo-clavicular ' (or rhomboid) ligament; 3, near the acromial end, a tubercle and a ridge for the attachment of the 'conoid' and ' trapezoid ' ligaments (coraco-clavicular) : the ridge is about one inch from the scapular end here fractures of the bone are likely to escape notice, in consequence of the ligaments preventing the separation of the fractured ends; 4, near the middle is a foramen for the nutrient artery of the interior. Sternal End. The sternal end of the clavicle is thick, strong and expanded. It is oblong from before backward, and articulates, through the medium of an interarticular fibro-cartilage, with the sternum. In the recent state, when crusted with cartilage, the articular surface is slightly convex from above downward, and concave from before backward; and, moreover, its circumference projects on all sides considerably beyond the articular surface of the sternum, to which it is so firmly attached by its ligaments that dislocation is very rare, notwithstanding the small size of the articular surface of the sternum. A fracture of the clavicle is ten times more common than a dislocation of its sternal end. Part of the ' sterno-hyoid ' muscle arises from this extremity of the clavicle a little internal and posterior to the rough surface for the rhomboid ligament. At the point where the clavicle comes into friction with the cartilage of the first rib, there is often a distinct impression, a sort of improvised artic- ulation blending with the articular surface for the sternum. Acromial End. The acromial end is broad and flattened, and pre- sents an oblong surface, which looks forward and slants a little inward, to articulate with the inner border of the acromion. The plane of this articulation is such that it is very difficult to keep the clavicle in its proper place after a dislocation. 204 HUMAN OSTEOLOGY. Like all the long bones, its structure is spongy at the extremities, but very compact in the middle of the shaft, where there is a small medullary cavity. The compact wall is much thicker on the concave side of each of its curves than elsewhere. Connections. The clavicle articulates with the acromion process of the scapula, and with the top of the sternum. Ossification. The clavicle begins to ossify about the sixth week of foetal life, that is, sooner than any other bone in the body. It has only one centre of ossification for the shaft. The sternal end has an epiphysis which makes its appearance from the eighteenth to the twentieth year, and subsequently coalesces with the shaft. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body if he hold the smooth surface upward; the flat acromial end outward; and the convex side of the sternal end forward. Comparative Osteology. All Primates have clavicles to which they owe the breadth of their shoulders. In the Carnivora the clavicles do not articulate with any bone, but are simply suspended in the muscles, and are always more or less rudimentary (see Felis leo, No. 4475). Bears seldom have clavicles. There is no clavicle in the elephant (No. 2654), or Hyrax capensis (No. 3115 C). The three sub-orders of Ungulata have no clavicles, i.e. Pachydermata, Kuminantia, Solidungula, as the horse and ox. The same is true of all Cetacea, Sirenia and Crocodilia. The majority of birds have clavicles the strength of which bears a direct relation to the powers of flight. They are early anchylosed together in the middle line, and form a single bone called the furculum or merry- thought. The chief action of this elastic arch of bone would appear to be to counteract the great pectoral muscles which tend to press the humeri inward during the downward stroke of the wing. The apteryx and some parrots have no clavicles. THE SCAPULA. (PLATES XL VIII., XLIX.) Position and Use. The scapula, or shoulder-blade, is placed at the back of the chest. When the arm hangs loosely by the side, the scapula ought to extend from the first rib to about the lower edge of the PLATE XLIX. Upper surface oP clavicle, AtrtmaVenci Sternal end Acrormcn .Articular surface for clavic!^ oraEo-ljrach'ialis Short hea4 op biceps. /.ttacnment bf coraco-clavicular ligaments n u.,,'.J..^ 4rj\ iV is miner t*S Pectoral Lon^ f)=3f| nF biceps. Clenoid cavily. -tncep Inner surface oP Scapula. THE SCAPULA. 205 seventh, and the lower angle should be a little further from the spine than the upper. The inferior angle of the scapula is a good guide to the seventh rib. During life this angle is held down by the upper border of the ' latissimus dorsi/ and sometimes gives origin to some of its fibres. In emaciated persons the yielding of this muscle allows the lower end of the scapula to project very perceptibly. The scapula acts as a movable fulcrum in the motions of the arm, and gives extensive attachment to the muscles which effect the movement. It is a flat triangular bone, and so thin in places as to be translucent. We have to examine its two surfaces, its three borders and angles, and its outstanding processes. Outer Surface. The ' outer surf ace ' of the scapula (' dorsum sca- pula ') is slightly convex, and divided into two unequal parts by a very prominent ridge of bone, termed the 'spine/ The part above the spine is called the supra-spinous fossa, and gives origin to the ' supra-spinatus ' muscle; that below the spine is called the infra-spinous fossa, and gives origin to the ' inf ra-spinatus.' Near the axillary border are distinct im- pressions, indicating the origins of the ' teres major * and ' minor ' muscles. It is generally marked by the impressions of the ' arteria dorsalis scapula.' Spine and Acromion. The ' spine ' of the scapula commences at the posterior border of the bone by a smooth triangular surface over which the tendon of the trapezius plays. From this the spine can be plainly felt in the living subject as it rises into a high crest, which runs toward the neck of the scapula, where it stands out from the rest of the bone, and suddenly altering its direction at a right angle, projects forward so as to form a lofty arch overhanging the * glenoid cavity.' This arch is termed the 'acromion' (anpos ch^os). It protects the shoulder joint and gives great leverage to the powerful ' deltoid ' which raises the arm. It is not only a defence, but prevents luxation upward: without this the head of the hu- merus would not remain a moment in its socket. It is this process which gives breadth to the shoulder. On the inner border of the acromion is the surface which articulates with the clavicle; this surface slants from above inward, so that the clavicle, once dislocated, is with difficulty kept in its place. The end of the acromion gives attachment to the coraco- acromial ligament, which bridges over the gap left in the bone between it and the coracoid process, and thus completes the arch for the shoulder. Through this coraco-acromial ligament we pass the point of the knife, in excising the head of the humerus, and thus reach the shoulder-joint in a. 206 HUMAN OSTEOLOGY. moment. Reverting to the spine, we observe that it has thick rough borders; above, for the insertion of the ' trapezius,' and below, for the origin of the ' deltoid.' Inner Surface. The 'inner surface' of the scapula is concave, and called the ' subscapular fossa.' It gives origin to the ' subscapularis,' and presents three or four slanting ridges for the attachment of the tendinous septa by which this muscle is intersected. The hollows between these ridges were mistaken, even by the great anatomist Vesalius, for the im- pressions of the ribs. On this surface also observe the insertion of the * serratus magnus,' chiefly into the rough surfaces on the superior and in- ferior angles, but also into a very narrow tract along the posterior border. Glenoid Cavity. The ' anterior angle ' of the scapula is the strongest part of the bone, and here is the ' glenoid cavity ' for the articulation of the head of the humerus. This cavity is very shallow, of an oval form, with the larger end downward, and the long diameter vertical; it looks directly outward and a trifle forward, giving the arm an extensive range of motion. Its margins are rather prominent and rough, for the attach- ment of a collar of fibro-cartilage, which slightly deepens the socket. From the upper part of the margin arises the 'long head of the biceps.' Just below the cavity is the origin of the ' long head of the triceps.' Im- mediately behind the cavity is a slight constriction termed the ' neck ' of the scapula. The neck is most plainly seen behind, where it forms with the spine a deep groove (great scapular groove), leading from the supra- spinous to the infra-spinous fossa. When we speak of fracture of the neck of the scapula, we mean frac- ture behind the coracoid process. This kind of fracture is very rare. It happens to old persons from falling on the shoulder. The shock is re- ceived by the head of the humerus, and is thence transmitted to the glenoid cavity. The chief symptom of such an accident is slight lengthen- ing of the arm and dropping of the shoulder. Whoever sees for the first time a fracture of the neck of the scapula will probably mistake it for a dislocation of the head of the humerus into the axilla. There is in each case the same lengthening of the arm, prominence of the acromion, and flatness of the deltoid; in each case the head of the humerus can be felt in the axilla: but there is this important distinction, that in the case of fracture, the normal appearance of the joint can be restored by simply pushing upward the arm at the elbow, by which means the head of the humerus, with the gleuoid cavity, is at once raised to its proper position. THE SCAPULA. 207 Coracoid Process. From the upper part of the neck of the scapula, just behind the upper margin of the glenoid cavity, stands off a projec- tion termed the ' coracoid process,' from its fancied resemblance to the beak of a raven (nopag). Arising from a very broad base, it takes first a direction inward, but soon curves forward toward the acromion, like a half -bent finger, and overhangs the glenoid cavity on the inner side. Its apex is about one inch and a half from the point of the acromion, and on a lower plane. It is necessary to be familiar with the direction of these points of bone, and their accurate bearing to the glenoid cavity and to each other, since they serve as landmarks in determining the nature of obscure injuries about the shoulder. Into the front part of the coracoid process is inserted the tendon of the 'pectoralis minor,' and from the ' apex ' arises the common tendon of the ' coraco-brachialis,' and the ' short head of the biceps/ At the upper part of its root is a rough surface for the attachment of the ' coraco-clavicular ' (' conoid ' and ' trapezoid ') liga- ments which bind down the clavicle; and the border next to the acromioii gives attachment to the ' coraco-acromial ligament,' which extends across the interval between these points of bone, and completes the arch for the shoulder-joint. Three Borders. The ' superior border ' of the scapula presents, near the root of the coracoid process, a small notch, which, in the recent state, is bridged over by a ligament. It gives passage to the supra-scapular nerve. Behind the notch is the origin of the ' omohyoid ' muscle. The ' posterior border ' is always the longest in man, and is therefore called the base of the scapula: in the lower animals it is generally the shortest. It gives insertion to the ' levator anguli scapulae,' the ' rhomboideus major ' and ' minor' muscles, and, as before mentioned, to the ' serratus magnus.' The ' inferior or axillary border ' is by far the thickest and strongest, and supports the glenoid cavity. The deep groove along it gives origin to some of the fibres of the ' sub-scapularis ' muscle. Connections. The scapula is connected by its acromial process to the clavicle which serves to keep well apart the shoulders. In its glenoid cavity it receives the head of the humerus. The ' blade ' moves freely on the ribs, to which it is connected by muscles only. The sliding move- ment of the scapula on the chest can be properly understood only on the living subject. It can move not only upward and downward, as in shrugging the shoulders backward and forward, as in throwing back the shoulders, or in reaching forward as in boxing but it has a rotatory 208 HUMAN OSTEOLOGY. movement round a movable centre. This rotation is seen while the arm is being raised from the horizontal to the vertical position, and is effected by the co-operation of the trapezius with the serratus magnus. The glenoid cavity is thus made to look upward; the inferior angle slides for- ward, and is well held under the latissimus dorsi. Ossification. The scapula has seven centres of ossification. The ' primary ' centre, which appears a little behind the glenoid cavity about the seventh week of foetal life, forms all parts of the bone, except the coracoid process, the acromion, the inferior angle, and the base: these are cartilaginous at birth. There are two centres of ossification for the coracoid process. The chief centre, representing the true coracoid bone, appears soon after birth, and about the fifteenth year unites to the rest of the bone. The second centre is an epiphysis for the tip. About puberty, the other secondary centres appear; namely, two for the acro- mion (one near the summit, the other near the base); one for the inferior angle; and, lastly, one for the border of the base. They all unite to the scapula about the twenty-second year." In a practical point of view it is well to remember that the acromion is not invariably united to the spine by bone. In some rare cases it remains permanently distinct, and is united to the spine only by ligament, and may be mistaken for a frac- ture. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body, if he hold the spine backward, the acromion upward, and the glenoid cavity outward, to receive the head of the humerus which is directed inward. Comparative Osteology. The scapula is present in all mammalia. In ruminants the coracoid and acromion are absent. The elephant, rhinoceros, pig, and tapir have a very large process at the lower part of the spine, to which in man is attached a portion of the trapezius. The supra-scapular notch is converted into a foramen by ossification of the ligament in the two-toed sloth (No. 2387 F). The coracoid process is a remarkable bone in birds. In them it is of great strength and solidity, and extends from the sternum to the scapula, M The nucleus at the margin of the glenoid cavity is not to be regarded as an epiphysis, but only an occasionally present scale, like those sometimes found on the coracoid and having no morphological bearing, and scarcely worthy of notice. Pro- fessor Humphry, F.R.S. Greate .lesser Btcipital groove a.a, Extensor carpi .Extensor carpi radiaUs brevier Extensor fob comrnuri Extensor di^iH minimi Extensor carpi ulnwo - External con%le Lesser Head Corcno'ii fossa. Internal- Condyle Flexor carpi radialis.. Trochlea . Hum-jn-sranterfor view. .'Flexor d'l^ilorum sutiimis -Tlexor. carpi ulnaris. THE HUMERUS. 209 where it helps to form the glenoid cavity. It forms a buttress on each side, which supports the shoulder during the downward stroke of the wing. This process never articulates with the sternum in any mammal excepting in the ornithofhynchus and the echidna. On the top of the sternum of the echidna (No. 1708) there is a T-shaped bone called the episternum. On each of its lateral branches lies a thin plate of bone, which is the clavicle in this animal. Extending forward from the glenoid cavity toward the top of the sternum is a block of bone which corresponds to our coracoid process, and on the top of this is a second piece of bone called the epicoracoid. The coracoid being, as we may say, in two pieces is not surprising, seeing that in us the cora- coid has two centres of ossification which now and then remain separate. This coracoid will be seen to enter into the formation of the glenoid cavity. THE HUMERUS. (PLATE L., LI.) The humerus is the longest and strongest of the bones of the upper extremity. It is a lever of the third order, the fulcrum being at the shoulder-joint, and the power at the insertions of the several muscles which move the bone. It articulates with the scapula above, and the ra- dius and ulna below. Like all the long bones it has a body or shaft, and articular ends. Head and Neck. At the upper end is the smooth eminence termed the ' head.' It forms about one-third of a sphere, and articulates with the glenoid cavity of the scapula. The head of the humerus is much larger than the socket in which it plays. This arrangement, together with the shallowness and direction (p. 206) of the socket, explains the great range of motion which the shoulder-joint enjoys. It is the freest of all the joints, and resembles what mechanics call a 'universal' joint: there is no part of the body which cannot be touched by one hand or the other. The head springs from the shaft by a slightly constricted base, called the ' anatomical neck,' to which the capsular ligament of the joint is attached. Although this is so short and thick as hardly to deserve the name of neck, yet it serves the important purpose of removing the head a little awav from the axis of the shaft. In consequence of this, the axis of the 14 210 HUMAN OSTEOLOGY. head and neck forms an obtuse angle with that of the shaft. When the arm hangs quietly by the side, with the thumb in front, the precise direction of the axis of the head and neck of the humerus is upward, inward, and a little backward from the shaft a* direction which facili- tates rotation inward. In the axis of the neck of the femur, where rota- tion outward is more required than rotation inward, this direction is reversed. Eaise the arm of the skeleton to a right angle, and you observe that much of the lower part of the head of the humerus is out of the socket. This is one of the reasons why the humerus is so liable to be dislocated when the arm is extended ; the head of the bone in this position being chiefly supported, below, by the fibrous capsule of the joint. Again, when the arm is raised to a right angle, there is another point worthy of notice: that the humerus alone cannot be raised higher, for the reason that the articular surface of the head of the bone does not admit of eleva- tion beyond a right angle. When we do raise the arm beyond a right angle, the additional elevation is accomplished by the movement of the scapula upon the chest, an effect chiefly due to the action of the trapezius and serratus magnus muscles. Tuberosities. At the root of the neck, or rather at the top of the shaft, are two projections, termed the ' tuberosities/ which give greater leverage to the muscles moving the bone. They are separated by a per- pendicular groove which runs about three inches down the shaft, and is called the ' bicipital groove,' because the tendon of the long head of the biceps plays in it. In the recent state this groove is bridged over, and made into a complete canal, by an aponeurosis. Of these tuberosities the 'greater* is the more external; in a thin person it can be plainly felt immediately below the acromion. It is useful to know this in determin- ing the nature of injuries about the shoulder. It has three impressions indicating the insertions of muscles, namely one above and somewhat to the front for the ' supra-spinatus,' a second immediately behind the first for the ' infra-spinatus,' and a third below the second and quite at the back of the bone for the ' teres minor.' The insertion of this last muscle extends beyond the third impression nearly half an inch down the shaft. The ' lesser tuberosity ' is the more internal, and gives insertion to the sub- scapularis. Lastly, the tuberosities are supported by broad pedicles which run down the shaft, and form, respectively, the outer and inner margins of the bicipital groove. PLATE LT. THE HOIERUS. 211 Shaft : Bicipital Groove : Surgical Neck. The first thing to be observed in the shaft is, that its lower part is twisted inward, and that it is slightly curved forward. This twist and curve make the axis of motion at the elbow such, that the fore-arm naturally bends toward the front of the body. Immediately below the tuberosities is the ' suryiml neck ' of the humerus; so called, in contradistinction to the anatomical neck already described. Fracture of the surgical neck is common; of the anatomical neck rare. On the front of the shaft is the bicipital groove, up which the long head of the biceps runs, to be attached to the top of the glenoid cavity, so that it acts like a strap and keeps down the head of the bone. Up this groove, too, a little artery (a branch of the anterior circumflex) creeps to supply the joint. Into the outer margin of the groove is inserted the tendon of the ' pectoralis major '; into the inner margin the tendon of the ' teres major '; and into the bottom of it the tendon of the ' latissimus dorsi.' These muscles play an important part in causing displacement in fracture when it occurs through the surgical neck. There is often a double displacement: i.e. the upper fragment is drawn outward by the muscles inserted into the tuberosities, and the lower fragment is drawn upward and inward by the muscles which go from the trunk to the arm. The middle of the shaft is marked by ridges and impressions denoting the attachment of the muscles. Along its anterior aspect runs a very prominent elevation (the ' anterior border ' of some anatomist), continu- ous with the external border of the bicipital groove. Deltoid Ridge. About the middle of the outer aspect there is a rough impression (deltoid ridge) for the insertion of the ' deltoid ' which raises the arm. Near this, on the inner aspect, is a smooth surface for the insertion of the ' coraco-brachialis.' Against this surface the brachial artery can be effectually compressed. The surface looks forward and inward, and as the artery runs along it, the surgeon must remember this obliquity and apply compression in the proper direction outward and backward or the artery will slip off the bone. Here also is generally situated the foramen for the nutrient artery of the marrow, which runs from above downward. Below the deltoid ridge the shaft begins to be twisted, and becomes gradually flattened and expanded for the formation of the articular end. It is generally below the insertion of the deltoid that ununited fractures of the humerus are met with, partly on account of the injury to the nutrient artery of the medulla, and partly on account 212 HUMAN OSTEOLOGY. of the action of the deltoid in causing a displacement of the upper frag- ment over the lower. Condyloid Ridges. The lower half of the shaft presents two ridges, one on each side, called respectively the ' internal ' and ' external condyloid ridges/ because they lead to the ' condyles ' or points of bone which pro- ject on each side of the elbow. The external ridge begins just behind the insertion of the deltoid, and is the more prominent of the two; its upper two-thirds gives origin to the ' supinator radii longus/ and its lower third to the ' extensor carpi radialis longior/ It is called the supinator ridge, and is generally best developed in animals which possess great power in the fore-legs and paws for fighting or burrowing. It is rather feebly marked in man, considering the mobility and strength of his fore- arm. The ' supinator longus' is not so much a supinator, as a powerful assistant to the biceps and brachialis anticus in flexing the elbow. The internal ridge serves for the attachment of the ' internal intermuscular septum.' The front surface of this part of the shaft gives origin to the ' brachialis anticus/ which begins by two little tongues, one on each side of the insertion of the deltoid. The back part of the shaft is occupied by the origins of the outer and inner ' heads of the triceps/ which are separated by a groove directed in a spiral manner downward and outward for the passage of the muscnlo- spiral nerve and superior profunda artery. The origin of the outer head is narrow, and lies external to and above the groove, extending as high as the insertion of the teres minor. The origin of the inner head is below the groove, reaching as high as the lower limit of the teres major and covering all the lower part of the shaft, even to the external condyle. Lower End. The lower end of the humerus curves slightly forward, and presents a pulley-like surface, suited to the flexion and extension, as well as the rotatory movement of the fore-arm. On the outer side, we observe the ' lesser head ' (capitellum), which corresponds with the shal- low cavity at the end of the radius. The chief point about this head is, that it projects directly forward, so that when the fore-arm is bent there is a smooth surface ready for the rotation of the radius. On the inner side is the ' trochlea ' or pulley for the ulna. This admits of flexion and extension only. The direction of this pulley is oblique; that is, it slants from behind forward, arid from without inward, so that the fore-arm, in the act of bending, comes naturally in front of the chest. Observe that the inner border of the trochlea descends much lower than the outer, THE HUMERUS. 213 thus protecting the ulna from dislocation inward. Above the trochlea there is a deep cavity in front (coronoid fossa) which receives the coronoid process of the ulna in flexion; and a similar one behind (olecranon fossa) receiving the ' olecranon/ or the point of the elbow, in extension of the fore-arm. External to the coronoid fossa, immediately above the lesser head, is a shallow depression for the head of the radius in extreme flexion. Between the ' olec- ranon and coronoid fossae' the bone is trans- lucent, as is well seen in Fig. 59, which ex- hibits a section through the joint. In con- sequence of this thinness, a transverse fracture FIG. 59. Section to show the through the hurnerus in this situation is not Trochlea rf^eHumerus. uncommon. From the displacement produced c ' Coronoid P 1 * 88 - so close to the elbow joint this accident is very liable to be mistaken for a dislocation of the radius and ulna backward. However, the bearing of the condyles with respect to the olecranon enables us in most cases to deter- mine the diagnosis. If the olecranou be higher than the condyles, there is dislocation of the elbow; if not higher, the ulna is in its proper place. Condyles. The internal condyle projects more than the external, and gives origin to the powerful pronator and flexors of the hand and fingers, namely, to the ' pronator radii teres/ ' flexor carpi radialis,' ' pal- maris longus/ 'flexor sublimis digitorum,' and 'flexor carpi ulnaris.' The internal lateral ligament of the elbow is also attached to it. The external condyle gives origin, in front, to the common tendon of the ex- tensor muscles; namely, the ' extensor carpi radialis brevior,' ' extensor digitorum communis,' ' extensor minimi digiti,' and ' extensor carpi ul- naris': behind, it gives origin to the 'anconeus.' Lastly, the external lateral ligament of the elbow is attached to it. Connections. The head of the humerus articulates with the glenoid cavity of the scapula at the shoulder. At the lower end on its outer side is a round convex surface which articulates with the cup on the top of the radius; while the trochlea is adapted to the form of the sigmoid cavity of the ulna. Ossification. The humerus has seven centres of ossification. There is one for the shaft, which appears about the seventh week of foetal life when the foetus is about an inch long. About the second year after birth the centre of the head appears; and about the third year, the centre of the tuberosities. About the end of the fifth year, the centres for the 214 HUMAN OSTEOLOGY. head and tuberosities have coalesced, and form a large epiphysis on the top of the shaft. It is necessary to remember that this epiphysis includes the tuberosities (see Fig. 60). On the inner side, the line of junction runs close to the cartilage on the head of the bone: there-- fore, in the event of separation, the shoulder- joint would cer- tainly be implicated. About the beginning of the third year, ossification of the lower end commences by a fourth centre in the lesser head. About the fifth year, a fifth centre appears in the internal condyle. About the twelfth year, a sixth centre appears in the great sweep of the trochlea; and, lastly, about the four- teenth year, the seventh centre appears in the external condyle, and uniting with the others forms a large epiphysis S l dues t K at tlie lower end of tne shaft. The lower epiphysis unites to the shaft at puberty, while the upper remains separate until maturity. Therefore there may be a separation of the upper epiphysis from the shaft by violence as late as about the twenty-first year, but of the lower end not later than about the sixteenth year. (See Nor. Hum. Ost., No. 54.) It is interesting to remark, that the epiphysis of the upper end, though the first to ossify, yet remains separate from the shaft about three or four years longer than that of the lower end. This is in accordance with the rule, that, of the epiphyses of a long bone, those toward which the nutri- ent artery of the marrow runs are always the first to unite with the shaft. Remember, that the nutrient arteries of the marrow of the bones of the upper extremity run toward the elbow. In the bones of the lower ex- tremity, they run from the knee. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body, if he hold the rounded head up- ward and turned inward toward the glenoid cavity, the bicipital groove being in front. Comparative Osteology. In man the legs are longer than the arms, and grow faster than the rest of the body after birth. In apes and monkeys the converse of this is true, and, after birth, the arms grow faster than the rest of the body. In most giants the great proportion of the height is due to the length of the lower extremity. It is curious that the right humerus of the gorilla (No. 5178) is of the same length as that of the Irish giant O'Brien (Hum. Ost. Ser., No. 223), who stood about THE HUMERUS. 215 eight feet, while the height of the gorilla is only four feet four inches. The left humerus of O'Brien is 20 mm. shorter than the right, and there exists a similar difference in the two humeri of the gorilla. It may be well to mention that the corresponding bones of opposite sides commonly differ a little in length, without giving rise to any obvious deformity. The olecranon and coronoid fossae occasionally communicate by a small hole in man. This seems to be pretty constantly the case in the Bush- man, gorilla, tapir and dogs. (See Separate Series, Mus. Roy. Coll. Surg., as well as in the articulated skeletons.) Above the inner condyle in many carnivora is a foramen (supra-con- dyloid) which transmits the median nerve and the brachial artery. (See Separate Series, Mus. Roy. Coll. Surg. : tiger, lion, and leopard. ) A trace of this foramen occurs now and then in man by the ossification of a part of the fibrous band which passes over the median nerve and from which the pronator teres arises. 93 The deltoid ridge is especially prominent in the Carnivora (see that of the seal). It is extensive in the rhinoceros, the tapir, and the horse, which have heavy limbs to raise. The tuberosities are very large in the heavy-limbed rhinoceros and the heavy-boned dugong. Notice how extensive the supinator ridge is in the aye-aye and the beaver. In moles the clavicle articulates with the humerus (No. 2400 C). There is no complete articulation between the humerus and fore-arm in Cetacea, nor between their carpus, fore-arm or digits; the upper extrem- ity forming a flipper which has free movement only at the shoulder joint. (See the Cachalot Whale.) In flying birds, notice the large foramen, at which the air enters the cavity in the bone immediately below the head, and feel the great light- ness of their bones. The humerus of the adjutant (No. 1306) is a mere shell. A bone of this bird, thirteen inches long, weighed only half an ounce, while a corresponding one seventeen inches long of an ostrich, weighed half a pound, that is, it was sixteen times as heavy. In snakes there is no trace of fore-limb, and consequently no humerus (No. 629). 93 On the supra-condyloid foramen read Hyrtl, "Topogr. Anat.' vol. ii. p. 283; also Gruber, ' Canalis supra Condyloideus bumeri,' Mem/ de 1'Acad. Imp. de St. Petersbourg, 1859, p. 57; and Professor Struthers, ' Edin. Med. Jour.' 1848. 216 HUMAN OSTEOLOGY. Near the end of the humerus of the turtle there is a line which may appear to denote an epiphysis, but it simply marks the limit to which the cartilaginous cap extended in the recent bone (see No. 1016). These animals have no epiphyses. THE EADIUS. (PLATES LIL, LIU) The radius is the external of the two bones of the fore-arm, and is so called from its resemblance to the spoke of a wheel. In learning this bone, keep in mind that both its ends rotate upon the ulna, and admit of the pronation and supination of the hand. Axis of Rotation. In a well-articulated skeleton the axis of rota- tion of the radius is represented by an imaginary line drawn from the centre of the head of the radius to the centre of the circle of which the sigmoid cavity at the lower end is a segment; in other words, to the centre of the lower end of the ulna. The lower end of the radius is much larger than the upper, and is the chief support of the hand: now since the radius receives all shocks from the hand, it is more liable to be broken than the ulna. Like the humerus, the radius and ulna are both levers of the third order, as seen in Fig. 61. The fulcrum F is at the elbow-joint the weight to be f f tto raised is the fore-arm W the power P is the insertion of the biceps. The biceps acts to the greatest advan- tage when the arm is bent to a right angle, because the power acts at a right angle to the lever. Head, Neck, and Tubercle. The upper end of the radius is called the ' head ': it has a shallow circular cup, which articulates (when the fore- arm is bent) with the lesser head of the humerus, and in the recent state is held in its place by the strong ' orbicular ' ligament which encircles it. Observe that the head has a smooth circular border, which rotates in the lesser sigmoid cavity of the ulna. This rotation of the radius can be dis- tinctly felt in one's own person below the external condyle of the humerus; a fact of great value in determining the existence of frac- ture or dislocation. Below the head, is the constricted part termed the ' neck '; and below this, is the ' tubercle ' which gives insertion to the PLATE LI I. Oler.ra.non Greater s'i|rnoidoavi-ty id cavity Coronnicl -j>n>ceaa. 2.^ origin of Flscor SMblimisdi^itoruTn. 2". a >>ea4 of Pronabor terca. Head 3tyloid process. tyloid process Radius Uln Anterior view. THE EADIU8. 217 tendon of the ' biceps.' This tubercle projects on the inner side of the bone, so that the biceps can supinate, as well as betid, the fore-arm. The posterior half of the tubercle is rough for the insertion of the tendon; the anterior half is smooth, and is the seat of a bursa which facilitates the play of the tendon. Shaft. The outer side of the shaft is thick and rounded; and from this side its front and back surfaces gradually converge to a sharp edge, which faces the ulna (see Fig. 62), and gives attachment to the interosseous membrane represented by the dotted line. The shaft is slightly arched outward, by which arrange- FIG 62 ment it increases the breadth of the forearm, and gives more power to the 'pronator teres/ 84 The bones are fur- thest apart when the hand is placed vertically with the thumb upward: hence, fractures of the fore-arm are put up with the hand vertical, that there may be less risk of the opposite bones uniting. On the front surface of the shaft there is a blunt ridge leading from the tubercle obliquely toward the outer side of the bone. It gives origin to part of the ' flexor sublimis digitorum.' Above this ridge is the insertion of the ' supinator brevis,' and below it is a slightly excavated surface for the origin of the ' flexor longus pollicis.' Below this is the insertion of the ' pronator quadratus.' On the outer and 'back part of the middle of the shaft is a rough surface for the insertion of the ' pronator teres.' This insertion being at the outer and back part of the shaft, gives the muscle greater power of pronation. In amputation of the fore-arm it is desira- ble to saw through the bones below the insertion of this muscle, that the stump may have the benefit of a pronator. The posterior surface of the shaft is marked by the origin of the ex- tensor muscles of the thumb; namely, the ' extensor ossis metacarpi pol- licis,' and the ' extensor primi internodii pollicis.' Lower End. The lower end of the radius expands into a surface slightly cupped transversely, as well as from before backward, which ar- ticulates with the ' scaphoid ' and ' semilunar ' bones of the carpus. In the recent state, if not in the dry bone, this surface is divided by a slight ridge; the part for the ' scaphoid ' is triangular, while that for the ' semilunar ' bone is square. On its inner side is the concave articular surface (' semilunar' 94 The radius of the skeleton of the gorilla in the Museum of the College of Sur- geons is extremely arched. The power of his arms is enormous. 218 HUMAN OSTEOLOGY. or ' sigmoid ' cavity), which rotates upon the lower end of the ulna. On its outer side is the conical projection, termed the ' styloid ' process, of which the apex gives attachment to the external lateral ligament of the wrist; while the base gives insertion to the tendon of the ' supinator radii lon- gus.' In front, the lower end has a rough and elevated margin for the attachment of the powerful anterior ligament of the carpus: and behind there are four grooves for the passage of the extensors of the wrist and fingers. (Plate LVI.) Beginning from the outer side, we observe: 1, a groove for the ' extensor ossis metacarpi pollicis/ and the ' extensor primi internodii pollicis '; 2, a groove for the * extensores carpi radiales, longior ' and ' brevior '; 3, a very distinct and slanting groove for the ' extensor secundi internodii pollicis '; 4, a groove for the ' extensor indicis ' and the 'extensor communis digitorum.' In the recent state these grooves are made complete canals by the ' posterior annular ligament.' The lower end of the radius is composed of cancellous tissue covered by a thin layer of compact bone, as shown in the adjoining Fig. 63. In falls, therefore, upon the palm of the hand, the lower end of this bone, which receives the full force of the .shock, is very liable to be broken transversely about half an inch or an inch above the wrist joint. This fracture of the radius is commonly called Colles's fracture, after the Irish surgeon who first accurately described it. The lower fragment, with the hand, is thrown backward so as to through the Lower make an unnatural swelling on the back of the fore-arm: end of the Radius, n^oTTteSmp^t tne u PP er fragment protrudes on the palmar aspect of the fore-arm just above the wrist. Now a fracture with such displacement is liable to be mistaken for a dislocation of the wrist. The two injuries may be distinguished as follows: If the styloid process be in the same line with the shaft of the radius, the injury is probably a dis- location of the wrist backward: if it be not in the same line, there is probably a, fracture of the lower end of the radius, which is by far the more frequent accident of the two. Connections. The radius articulates above with the humerus, and rotates in the lesser sigmoid cavity of the ulna. Below, it articulates with the scaphoid and semilunar bones of the wrist, and rotates upon the head of the ulna. Ossification. The radius has three centres of ossification: one for the shaft, and one for each end. The upper end begins to ossify at the PLATE LIU. Olecranon Subcutaneous ncl^e -from WhicK arises aponeurosis common io the Plexor carpt ulnaris, Plexor dig' r ) 1 p ro ' !un ^ ljs ' Extensor carpi ulnaris TJlna Radius "Posterior View THE ULNA. 219 fifth year, and is united at the seventeenth. The lower end begins about the second year, and is not united till the age of eighteen or twenty. (Nor. Hum. Ost., No. 54.) This is in accordance with the general law, that epiphyses unite with the shafts in the inverse order of their ossifi- cation. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body, if he hold the rounded head up- ward, the bicipital tubercle inward, and the oblique line forward. Comparative Osteology. In ruminants the ulna and radius are immovably united. The ulna is at the back of the radius, and forms a very prominent olecranon, on the top of which may be seen an epiphysis in the fore-limb of the bison. In the zebra (Solidungula) the ulna is represented by an olecranon adhering to the back of the radius, but in the elephant the ulna is very large and the radius is small. (See the Separate Series, Mus. Roy. Coll. Surg.) In bats and birds the radius is enormously long, forming the principal support of the wing in the former (No. 2616 H). THE ULNA. (PLATES LIL, LIII.) The ulna, so called because it forms the elbow (oaXevrf), is the inner of the two bones of the fore-arm. Upper End. Its upper end presents a deep semicircular cavity, with a smooth ridge at the bottom, which accurately fits on the trochlea of the humerus, and forms a perfect hinge-joint admitting of flexion and extension only. (See Fig. 64.) This is called the 'greater sig- moid' " cavity, in contradistinction to a smaller one, termed the 'lesser sigmoid,' which is placed on its outer side, and forms a socket for p^ wlse^n through the the rotation of the head of the radius. In f ront Grea ter8ig m oid cavity of the uina. of the greater sigmpid cavity is a rough projection, termed the ' coronoid process' (nopGjyjj, the top of a curve), the rough surface in front of 95 So called from its fancied resemblance to the letter Sigma, which the Greeks originally used in the form of the English C. 220 HUMAN OSTEOLOGY. which gives insertion to the ' brachialis anticus ' (a flexor of the fore- arm) and origin to the second head of the 'pronator teres/ and the second head of the 'flexor sublimis digitorum."" Besides this, it limits the flexion of the fore-arm. When the fore-arm is flexed on the arm as much as possible, the point of the process strikes against the fossa at the lower part of the humerus, and prevents further flexion. In dislocation of the ulna backward the coronoid process is very liable to be broken: this complication makes reduction more easy, but subsequent retention of the bones in their proper place more difficult. A r iolent action of the brachialis anticus may break off the coronoid process: but this is very rare. An instance of this happened to a boy about eight years old, in consequence of hanging with one hand from the top of a high wall. 97 "When it is broken, the coronoid process unites by ligament, owing to the separation of the fragments by the brachialis anticus. At the base of the coronoid process, below the insertion of the ' brachialis anticus/ is a rough tubercular elevation for the insertion of the oblique ligament, the other extremity of which is attached to the radius just below the tubercle for the biceps. Olecranon. Behind the sigmoid cavity is the 'olecranon' (coXevr;, elbow, and Jtpavov, head). This serves many purposes and plays an im- portant part in the perfection of the hinge of the elbow- joint. It gives leverage to the 'triceps/ which is inserted into it and extends the fore- arm. It forms a convenient knob of bone for the protection of the joint when we lean on the elbow, and it limits the extension of the fore-arm. The surgical interest about it is, that it is sometimes broken by a fall upon the elbow; and the fracture generally takes place just at the slight constriction or notch where the olecranon joins the shaft: so that the joint is involved in the mischief. Fractures of the olecranon, like those of the patella and coronoid process, unite, generally, by ligament, because it is so difficult to keep the fragments in apposition. But if the tendi- nous expansion from the triceps be not torn, the union may take place by bone. In almost all injuries about the elbow-joint, however swollen the parts, one can always feel the olecranon and the internal condyle of the humerus. In determining, therefore, the nature of obscure injuries about this joint, 6 y er y often the coronoid process gives origin to a second head of the flexor lon- gus pollicis. *' Mr. Liston, ' Practical Surgery.' THE ULNA. 221 it is useful to know that, when the arm is extended, the tip of the olecra- non and the internal condyle are about one inch apart and in the same transverse line. When the arm is bent to a right angle, the olecranon is an inch and a half from the condyle and below it. By this test dislo- cation of the ulna backward and fracture through the lower end of the humerus can be distinguished. Shaft. The shaft of the ulna is triangular, and tapers gradually from the upper toward the lower end, which inclines a little outward toward the radius and terminates in the little ' head' round which the radius rolls. A transverse section, seen in Fig. 65, shows the shape of the radius and ulna about the middle. We observe that their sharp edges are turned toward each other, and that to these is attached the interosseous membrane (represented by the dotted line) which connects the bones. Together, they form a shallow concavity in front and behind, wherein the muscles of the fore-arm are lodged. The greater part of the front as well as of the inner surface of the shaft is occupied by the origin of the ' flexor profundus digitorum.' On the front, too, is the canal for the nutrient artery of the medulla. It runs toward the elbow like that in the radius. Lower down is the origin of the ' pronator quadratus.' The back part of the shaft is marked by ridges and surfaces for the muscles thus: near the elbow is the trian- gular surface for the insertion of the ' anconeus '; next comes the ridge for the origin of the ' supinator radii brevis,' which also arises from the depression just below the lesser sigmoid cavity. Below the supinator brevis arise in succession parts of the ' extensor ossis metacarpi pollicis/ of the ' extensor secundi internodii pollicis/ and also the ' indicator.' "" Of the three edges of the shaft, the external gives attachment to the interosseous membrane; the anterior is covered by the origin of the ' flexor profundus digitorum'; the posterior gives attachment to a strong aponeurosis, which covers the muscles on the inner side of the fore-arm, and affords additional surface for the origin of the ' flexor carpi ulna- ris,' the 'flexor profundus digitorum,' and the ' extensor carpi ulnaris.' The posterior edge (or Bridge of the ulna, as it is generally called) de- serves the more notice, because being subcutaneous it can be traced from 98 It is not uncommon to find that some of the fibres of the ' extensor primi inter- nodii pollicis ' arise from the ulna. 222 HUMAN OSTEOLOGY. the olecranon to the styloid process, and is therefore an important guide in cases of doubtful fracture. Before reaching the elbow the ridge bifurcates, and encloses a triangular space, which is also subcutaneous: here we feel for fractures of the olecranon. Lower End. The lower end of the ulna is termed its ' head/ It can be plainly felt at the back of the wrist when the hand is pronated. It has, on one side, a convex surface, forming rather more than half a circle, round which the radius, and with it the hand, rotates to the same extent. It has also another articular surface, lined with a synovial membrane, which looks toward the wrist joint, and corresponds with the interartic- ular fibro-cartilage interposed between it and the cuneiform bone of the wrist. The ulna does not reach down quite so low as the radius; the fibre-cartilage, however, partly fills up the interval. This difference in the length of the two bones allows more extensive horizontal movement of the wrist toward the ulnar side of the fore-arm. The styloid process projects from the lower end of the lack part of the ulna, and thus does not interfere with the rotation of the radius; it gives attachment to the internal lateral ligament of the wrist. Between the process and the head there is a groove on the posterior aspect of the bone for the passage of the tendon of the ' extensor carpi ulnaris ' (Plate LVL); and inferiorly, the process is separated from the head by a depres- sion for the attachment of the triangular fibro-cartilage of the wrist. The styloid processes of the radius and ulna can be readily felt beneath the skin, and are important guides in the determination of injuries of the wrist, whether fracture of the radius or dislocation. The relative position of the styloid processes with regard to the axis of motion at the wrist will settle the question. Connections. The ulna articulates, above, with the trochlea of the humerus and with the head of the radius; below, it articulates with the sigmoid notch of the radius, but is prevented from articulating with the cuneiform bone of the wrist, by the intervention of an interarticular fibro-cartilage. Ossification. The ulna has three centres of ossification, one for the shaft and coronoid process, one for the lower end, and a third for the olecranon. The lower end begins to ossify about the fifth year, and unites to the shaft about the twentieth. The top of the olecranon remains car- tilaginous until the age of eight, about which time it begins to ossify: it coalesces with the base about puberty. (Nor. Hum. Ost., No. 54.) THE ULNA. 223 Right or Left ? The bone will be in the same position as the cor- responding one in the student's body if he hold the greater sigmoid cavity upward; the lesser sigmoid cavity, which receives the radius, outward; and the styloid process behind. Comparative Osteology. The ulna in many birds will be seen to be very long, like the radius, forming the largest part of the length of the wing, and to be dotted by a line of small tubercles along its outer surface where the wing feathers are attached. See the length of the ulna in the Frigate bird (No. 1188 A) and the prominent feather-tubercles in the Adjutant (No. 1306). Contrast the great length of the ulna and radius in the swift flying birds, as the Frigate (No. 1188 A) and Albatross (No. 1189) with the shortness of those which do not fly, as the Great Auk (No. 1118), the Ostrich (No. 1362), and the Cassowary (No. 1357 A). BONES OF THE HAND. (PLATES LIV.,LV.,LVI.) THE skeleton of the hand consists of twenty-seven bones. The first eight are the little bones of the carpus; the five succeeding bones con- stitute the metacarpus: these support the bones of the fingers. Each finger has three bones, termed, in order from the wrist, the first, second, and third or ungual phalanges. The thumb has only two phalanges. THE CARPUS. (PLATE LVI.) Number and Names. The carpus consists of eight little bones, arranged in two transverse rows of four bones each, thus forming a broad base for the support of the hand. What is the advantage of so many bones in the wrist? It confers strength and elasticity and permits some motion. The contiguous surfaces are crusted with cartilage and form synovial joints. Suppose there had been a single bone instead of the eight carpal bones, how much more liable it would have been to fracture and dislocation. As it is, dislocation of one or more bones of the carpal range is a rare occurrence; but it does happen sometimes. Sir C. Bell tells us that ' the boy that played the dragon in a pantomime at Covent Garden, fell upon his hands, owing to the breaking of the wire that sus- pended him, and he suffered dislocation of some of the carpal bones in both hands.' The bones of the carpus are named as follow, beginning from the radial side: FIRST OR PROXIMAL Row . ' SCAPHOID,' ' SEMILUNAR,' ' CUNEIFORM,' ' PISIFORM. ' SECOND OR DISTAL Row . ' TRAPEZIUM, ' ' TRAPEZOID, ' ' os MAGNUM, ' ' UNCIFORM. ' The student will obtain a better idea of the general shape and arrange- ment of these bones by examining them, at first, collectively. For this purpose it is very desirable that he should have before him an articulated hand, as well as the separate bones. PLATE LIV. Plexor carpi ulnaris Groovef>rFIxO!-tarpi rad ialis A-bduclcr pollicis t poll.cis Palmar, surface-, THE CARPUS. 225 Carpal Arch. The outline of the carpus as a whole is oblong, with the broad diameter in the transverse direction. Its bones are wedged together, and so form an arch with the concavity toward the palm, which gives passage to the flexor tendons of the fingers. Fig. 3 in Plate XXXVIII. snows that the piers of the arch are formed on one side by projections from the scaphoid and trapezium; on the other, by the pisi- form and the hook of the unciform. The arch is converted into a com- plete tunnel by the anterior annular ligament. Radio-carpal Joint. To begin with the bones of the first row. Excluding the pisiform, which is only an outstanding ' sesamoid ' bone, it will be seen that the scaphoid, semilunar and cuneiform bones form a con- vex articular surface, which, with the lower end of the bones of the fore- arm, forms the radio-carpal joint. This joint admits not only of the move- ments of flexion and extension, but also of the horizontal movements of the wrist (abduction and adduction). The upper articular surfaces of the first row of bones are prolonged further down their dorsal than their pal- mar aspect: hence the free movement of extension at the wrist. The articular surfaces of the scaphoid and semilunar bones fit into the radius; while that of the cuneiform, which is the least extensive of the three, would articulate with the ulna, but for the intervention of the triangular fibro-cartilage attached, in the recent state, to the lower end of the ulna. The bones of the first row articulate with each other by plane surfaces crusted with cartilage, but they are so firmly connected by ligaments that there is very little movement between them. Intercarpal Joint. Collectively, the lower ends of the first row form, with the bones of the second row, an important movable joint, which we call the ' intercarpal.' It is very different in form from the first joint (radio-carpal) of the wrist, since its outline is alternately convex and con- cave. By means of this second joint we get a great range of flexion and extension at the wrist. If there had been only a single joint for this amount of motion, it would have been comparatively insecure, and very liable to dislocation, whereas dislocation of the wrist happens very rarely indeed. By reference to Plate LVI. it is seen that the lower part of the scaphoid has a convex articular surface which corresponds with the tra- pezium and trapezoid, and also a concave one, which, with a concavity in the semilunar and cuneiform bones, forms a deep socket for the reception of the head of the os magnum and the unciform. Articulations of First Row. The scaphoid articulates with five 15 226 HUMAN OSTEOLOGY. bones inclusive of the radius; the semilunar with five inclusive of the radius; the cuneiform with three; and the pisiform with one, namely, the cuneiform. In consequence of the flexors and extensors of the wrist being inserted below the second row of carpal bones, they necessarily act on the ' inter- carpal joint ' as well as on the radio-carpal. Thus a greater amount of motion is provided at the wrist than it otherwise could have possessed with safety. If such free motion had been given to one joint, the angle of flexion must have been great and the ligaments looser than would have been consistent with the security of the joint. Bones of the Second Row. The trapezium and trapezoid form a shallow socket for part of the scaphoid, while the os magnum and unci- form form a convexity, which fits into the deep socket formed by the sca- phoid, semilunar, and cuneiform in the first row. Below, the second row articulates with the metacarpal bones, as follows: The trapezium with two, that of the thumb by a concavo-convex surface, and partly with that of the index finger; the trapezoid with one, that of the fore- finger; the os magnum with three, that of the middle finger, and beside this with those of the index and ring fingers; and the unciform with two, those of the ring and little fingers. Thus the trapezium supports the metacarpal bone of the thumb; the trapezoid that of the index finger; the os magnum that of the middle finger; and the cuneiform those of the ring and little fingers. The consequence is, that the metacarpal bones present different degrees of mobility, that of the thumb being the most movable, those of the fore and middle fingers the least so. Articulations of Second Row. Like the bones of the first row, those of the second articulate with each other by plane surfaces firmly connected by ligaments. The trapezium articulates with four bones; the trapezoid with four; the os magnum with seven; the unciform with five. Distinction of Individual Bones. Thus far we have examined the bones of the carpus collectively; how are we to distinguish them in- dividually? Whoever remembers what has been already said, will readily recognize the separate bones; and if the rule laid down for the parietal (page 39), which has been applied to the other bones, be also applied to these, there cannot be much difficulty in determining to which hand a given bone belongs. Scaphoid Bone. The ' scaphoid ' bone may be told by its boat- shaped socket (ffnacprf, a boat), by its long narrow groove on the dorsal as- THE CARPUS. 227 pect between its two convex surfaces, and by its ' tubercle ' for the attach- ment of the ligaments of the wrist (anterior annular and external lateral). Right or Left ? This bone will be in the same position as the corre- sponding one in the student's body if he hold the concave surface forward for articulation with the os magnum, the tubercle outward for articula- tion with the trapezium and trapezoid, and the groove toward the dorsum. Semilunar Bone. The ' semilunar ' bone may be told by its semi- lunar shape (whence the name). There is a narrow crescentic surface on its outer side for articulation with a similar surface on the scaphoid, and a broader crescentic surface on its inner side for articulation with a similar surface of the cuneiform. In the concavity of the bone there are two articular surfaces: the outer, a large one for the head of the os magnum; and the inner, a smaller one for its slight articulation with the unciform. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body if he hold the concave surface for- ward for articulation with the os magnum and unciform; the narrower crescentic surface outward for articulation with the scaphoid, and the small non-articular surface toward the dorsum. Cuneiform Bone. The ' cuneiform ' bone may be told by its little round articular surface for the pisiform bone, and its concavo-convex surface below for the unciform. Right or Left ? The bone will be in the same position as the cor- responding one in the student's body if he hold the crescentic surface outward for articulation with a similar surface of the semilunar; the con- cave surface forward for articulation with a corresponding surface on the * unciform '; and the round flat surface toward the palm for articulation with the pisiform. Pisiform Bone. The ' pisiform ' bone may be told by its pea-shape (whence its name); and by its round flat ar- ticular surface for the cuneiform. Right or Left ? This bone will be in the same posi- tion as the corresponding one in the student's body if he hold the articular surface toward the dorsum of the hand, to articulate with the cuneiform; the projection forward, and the groove toward the outer side. In this position the bone will be seen to lean outward, toward the palm, thus resembling the unciform process of the unciform bone. 228 HUMAN OSTEOLOGY. Trapezium. The ' trapezium ' (so named from its shape) may be told by its saddle-shaped articular surface for the metacarpal bone of the thumb; by the deep groove for the tendon of the ' flexor carpi radialis/ and the prominent ridge on the outer side of that groove for the attach- ment of the anterior annular ligament, and the origins of the ' opponens pollicis ' and ' abductor pollicis. Right or Left ? This bone will be in the same position as the cor- responding one in the student's body if he hold the tubercle toward the palm, the saddle-shaped surface forward to articulate with the metacarpal bone of the thumb, and the process which articulates with the base of the metacarpal bone of the index finger, inward. Trapezoid Bone. The ' trapezoid' bone (so named from its shape) may be told by its four articular surfaces and four angles. Right or Left ? This bone will be in the same position as the cor- responding one in the student's body if he hold the small non-articular surface toward the palm; the concave surface backward to articulate with the scaphoid, and the convex surface outward to articulate with the tra- pezium. Os Magnum. The ' os magnum ' is the largest and most important of all the carpal bones. It lies directly in the axis of the hand, and articulates with seven bones. Its large round ' head ' forms the ball for the socket in the scaphoid and semilunar above. Its outer border artic- ulates with the trapezoid; its inner with the unciform; its lower with the third metacarpal bone chiefly, and also with the second awd fourth. Its posterior dorsal surface is flat and roiigh; its anterior bulges a little for- ward. Right or Left ? This bone will be in the same position as the corresponding one in the student's body if he hold the convex head back- ward to articulate with the concave surfaces of the scaphoid and semilunar; the flattened articular surface inward for the unciform, and the tubercu- lated non-articular surface toward the palm. Unciform Bone. The ' unciform ' bone may be told by its remarka- ble hook -like process; whence its name. Right or Left ? This bone will be in the same position as the cor- responding one in the student's body if he hold the convex surface back- ward for articulation with the concave surface of the cuneiform; the unciform process toward the palmar aspect, and the flat surface for articu- lation with the os magnum outward. PLATE LV. Extensor carpi radi Extensor carp> ulnaris Dorsal surface THE METACARPUS. 229 Muscles attached to the Carpal Bones. No muscles are con- nected with the dorsal surface of the carpus. On the palmar aspect the pisiform gives insertion to the ' flexor carpi ulnaris/ and origin to the ' abductor minimi digiti.' The trapezium gives origin by its 'ridge 'to the ' opponens pollicis,' to parts of the ' abductor pollicis,' and outer head of the 'flexor brevis pollicis.' The trapezoid and os magnum to the ' flexor brevis pollicis.' The unciform gives origin by its ' process' to the ' flexor brevis minimi digiti,' and to the ' opponens minimi digiti.' Ossification. The carpus is entirely cartilaginous at birth. Each bone ossifies from a single nucleus. The nucleus of the os magnum ap- pears in the first year; that of the unciform in the second; that of the cunei- form in the third; those of the trapezium and semilunar in the fifth; that of the scaphoid in the eighth; that of the trapezoid in the ninth; that of the pisiform in the twelfth. This is the last bone in the body to ossify. Comparative Osteology. In many of the Carnivora, as the seal, walrus, tiger, and dog, the scaphoid and lunar are anchylosed into one mass. In the bat, the scaphoid lunar and cuneiform form only one bone. In the dugong, all the carpal bones are anchylosed into three bones, the distal row being in one piece. In birds, as in other animals, they are diminished in number accord- ing to the disappearance of the digits which each usually supports. The carpus of the orang-outan, baboon, and several other monkeys contains one more bone than that of man, which seems due to the divi- sion of the scaphoid into two parts. (See Separate Series, Mus. Roy. Coll. Surg.) THE METACARPUS. (PLATES LIV., LV.) The metacarpus consists of the five bones which support the phalanges of the thumb and fingers. They are described as the first, second, third, fourth, and fifth, counting from that of the thumb; and, regarding them as ' long bones,' which they much resemble in their general struct- ure, we speak of their shafts and their two ends; the upper end being termed the ' base,' the lower, the ' head ' of the bone. Shafts. The ' shafts ' are slightly concave towards the palm, form- ing the hollow of the hand. They are made somewhat triangular on section by the impressions of the ' interosseous ' muscles which occupy tlu- 230 HUMAN OSTEOLOGY. ' interosseous spaces/ The apex of the triangle is on the palmar surface, the base on the dorsal surface forming the support of the extensor tendons of the fingers. Bases. Their ' bases ' articulate not only with the bones of the car- pus, but, by ' lateral facets,' with each other: that of the thumb, how- ever, stands out alone, so as to oppose all the others. It is one of the great characteristics of the hand of man, that the point of the thumb can touch with perfect ease the tips of all the fingers. Heads. The lower ends or ' heads ' are rounded for articulation with the first phalanges of the fingers. The articular surfaces of the heads extend chiefly toward the palm. They allow the fingers not only to be flexed and extended, but to be moved laterally. On each side of their heads are a tubercle and a deep pit for the attachment of the thick and strong lateral ligaments. The shaft of each metacarpal bone has a canal for the nutrient artery of the medulla. In the second, third, fourth, and fifth metacarpal bones, the direction of this canal is upward; but in the metacarpal bone of the thumb its direction is downward. Metacarpal Bone of the Thumb. The metacarpal bone of the thumb is distinguished by the characteristic saddle-shaped surface at the base, which articulates with the trapezium. Besides which, its shaft is l - shorter, broader, and stronger than the others, in accord- ^Lj^Sjjflfr ance w ^h the many and powerful muscles which act upon HOT^^T **' There are no less than nine muscles to work the Bfl^y thumb. Its great mobility in all directions, so essential to the power and perfection of the human hand, depends upon this saddle-shaped joint at its base; and its power '^ of antagonizing the fingers is owing to its base being set yS^'S^utveS- off on a P lane anterior to them. But for a little buttress carpal, outer side. of k one w hi c h projects from the inner and front part of the trapezium, the thumb would fall into the same line as the fingers, and would not possess that power of opposing them which makes the human hand such a wonderful instrument." On the palmar aspect of its head, observe two smooth surfaces occasioned by the play of the outer and inner sesamoid bones which are connected with the tendons of inser- tion of the ' flexor brevis pollicis.' Right or Left ? This bone will be in the same position as the cor- 99 Mr. Lockwood, Demonstrator of Anatomy at St. Bartholomew's Hospital. TJW. Radius. Extensor inclicis Eyb r m'minrn .Ex t?" carpi ulnao-'is Supinitor radiilon^us. I Hxtrossts metacarpi pollic'is' rnnnternoclii polhws. View of the Inter-carpel Joint, THE METACARPUS. 231 responding one in the student's body if he hold thfe rounded head forward, the flattened surface toward the dorsum, and the process of bone at the base toward the inner side. Metacarpal of Fore-finger. The metacarpal bone of the fore- finger is distinguished by its deeply indented surface at the base, which is immovably wedged with three of the carpal bones; also by having a ' lateral facet ' on the inner side for the third metacarpal. (Fig. 68.) Inner side. Inner side. Outer side. FIG. 68. Base of Second Right FIGS. 69 and 70. Base of the Third Right Metacarpal. Metacarpal. Right or Left ? This bone will be in the same position as the cor- responding one in the student's body if he hold the rounded head for- ward, the flattened surface toward the dorsum, and the facet for the insertion of the extensor carpi radialis longior outward. Metacarpal of Middle Finger. The metacarpal bone of the middle finger may be known by its having a smooth square surface at the base for the os magnum, and an angular projection at the corner of it for the insertion of the ' extensor carpi radialis brevior.' It has also 'lateral facets ' on each side. Sometimes, as seen in Fig. G9, the inner facet is divided into two. Right or Left ? This bone will be in the same position as the cor- responding one in the student's body if he hold the rounded head for- ward, the flattened surface toward the dorsum, and the pointed process for the insertion of the extensor carpi radialis brevior outward. Metacarpal of Ring Finger. The meta- carpal bone of the ring finger articulates with the imciform and part of the os magnum. It may be distinguished by its smaller size: by the inner side, outer side. FIGS. 71 and 72. Base of Fourth absence of the angular projection at the base, Right Metacarpal. which is flat; and by its having two facets on the outer side and one on the inner (Figs. 71, 72). 232 HUMAN OSTEOLOGY. Right or Left ? fThe bone will be in the same position as the corre- sponding one in the student's body if he hold the head forward, the flat- tened surface toward the dorsum, and the single facet on the side of the base inward for articulation with the metacarpal bone of the little finger. Metacarpal of Little Finger. The meta- carpal bone of the little finger may be recognized by its concavo-convex surface at the base to articu- late with the uncif orm bone, and by its having only one lateral facet, namely, on the outer side (Fig. Outer side. inner side. 73). The projection on the inner side of the base FIGS. 78 and 74. Base of . ., .... Fifth Right MetacarpaL is for the ' extensor carpi ulnaris.' Right or Left ? This bone will be in the same position as the cor- responding one in the student's body if he hold the rounded head for- ward, the flattened surface toward the dorsum, and the non-articular side of the base inward. Ossification. Each metacarpal bone has a centre of ossification for the shaft and proximal end, which appears about the eighth week of foetal life. Each also has an epiphysis at its distal end, of which the nucleus appears about the fourth year. The metacarpal bone of the thumb, however, has its epiphysis at the proximal end, like the pha- langes of the fingers. All unite to the shafts about the twentieth year. 100 (Nor. Hum. Ost., No. 54.) Comparative Osteology. In all birds excepting the extinct archje- opteryx the metacarpal bones are anchylosed together. (See the Sepa- rate Series in the Mus. Roy. Coll. Surg.) Contrast the short metacarpal bones of the elephant with the enor- mously long ones of the horse or giraffe. 100 To the rule stated there are certainly exceptions. I have seen preparations clearly showing separate epiphyses at the bases of the metacarpal bones of the fore and middle fingers. I have also seen a separate epiphysis at the head of the metacarpal bone of the thumb. Whether these additional epiphyses be normal or exceptional, they always unite the first to the shaft, in accordance with the direc- tion of the artery of the marrow, which in the metacarpal of the thumb runs toward the head, in those of the fingers toward the base. THE BONES OF THE FINGERS. (PLATE LIV.) General Description. Each finger consists of three bones, succes- sively decreasing in size, and termed respectively the first, second, and last or ungual 'phalanges.' The thumb has only two phalanges. A general description will suffice for all. The structure of each phalanx is precisely like that of the great long bones, and a longitudinal section through one of them would display the great thickness of the compact wall of the shaft. Considering the phalanges as ' long ' bones, we speak of their shafts and their articular ends. The shafts are convex on the dorsal surface, and flat on the palmar; on each side of this flat surface is a ridge for the attachment of the fibrous sheath (theca), which keeps the tendons in their places. First Phalanges. The first phalanges are distinguished by their greater length, and by the shape of their metacarpal ends, which do not form strictly hinge- joints, but have concave oval surfaces, with the long diameters transverse, adapted for lateral movement as well as flexion on the heads of the metacarpal bones. In accordance with this lateral move- ment, we observe, on each side, a tubercle for the insertion of the in- terosseous muscles which produce it. Their distal ends are divided by a shallow groove into two little condyles with the lateral tubercles and de- pressions for the lateral ligaments. Second Phalanges. The second phalanges are shorter than the first, and are recognized by the shape of their proximal ends, which have two little concave surfaces, with an intervening ridge, and so form a hinge with the little condyles of the first phalanges. The first phalanges have only one articular surface at their proximal ends, and are thus distin- guished from the second. Each has also a tubercle behind, into which is inserted the extensor tendon. Third Phalanges. The last or ungual phalanges are the shortest. 234 HUMAN OSTEOLOGY. Their ends expand into a horse-shoe shape, smooth on one surface for the support of the nails, and rough on the other for the support of the pulp of the fingers. Unequal Length of Fingers. It has been asked, What are the advantages of the fingers being of unequal length? Close them upon the palm, and then see whether or not they correspond. This difference in the length of the fingers serves a thousand purposes, to which the works of human art and industry bear ample testimony. Ossification. Each phalanx has two centres of ossification: one for the shaft and distal end; the other for the proximal end, which remains an epiphysis till about the twentieth year. 101 (Nor. Hum. Ost., No. 54.) Comparative Osteology. In the separate series in the Mus. Roy. Coll. Surg. it will be seen that the elephant has five digits; the elk four, viz. the 2nd, 3rd, 4th, and 5th; the ox two, the 3rd and 4th; the rhinoceros three, the 2nd, 3rd, and 4th; the tapir four, the 2nd, 3rd, 4th, and 5th; the zebra and horse one, the 3rd. The flipper of the whale, which corresponds to the front limb, has no nails: some of the digits have more than three phalanges. (See the round- headed whale, No. 2518 B, and the lesser fin- whale.) Bats (Cheiroptera) have their four ulnar digits very much elongated, forming the framework for the wing. At least three of these digits bear no nails. The hook at the top of the bat's wing is the thumb-nail. (See Sep. Ser. Mus. Eoy. Coll. Surg., as well as No. 2416 E and 2416 G to 2416 L.) In the digitigrade Carnivora, as the tiger and cat, the sharp claws are firmly fixed into the ungual phalanges, and these are under ordinary circumstances bent backward on to the back and outer side of each cor- responding second phalanx by an elastic ligament, and are thus held out of the way as long as the flexor profundus digitorum remains at rest. When a cat pats you in play she only uses the flexor sublimis digito- rum; but when she claws you in anger she uses her flexor profundus digitorum, which flexes the ungual phalanx and brings down the claAv. That which is commonly called the knee in the horse, is really the wrist. From this joint down to the foot extends the greatly elongated third metacarpal bone. 101 The centre of ossification in the shaft of every long bone appears in its middle, excepting in the case of the ungual phalanges, which commence to ossify at their distal ends. SESAMOID BONES. 235 In birds three fingers can be traced as forming the extremity of the wing. (See Sep. Ser. Mus. Roy. Coll. Surg.) The phalanges were very numerous in the Ichthyosauria. (Pal. Ser., No. 222, Mus. Eoy. Coll. Surg.) SESAMOID BONES. (PLATE LIV.) Position and Use. These little bones are so called from their re- semblance in size and shape to the grain * sesamum.' They are met with in the substance of tendons in the neighborhood of joints the ' patella,' or 'knee-pan/ being the best example. Their use is to increase the leverage of the tendons. The thumb has two of these bones beneath its metacarpal joint, which increase the leverage of the ' flexor brevis polli- cis.' We rarely find any in the fingers. Comparative Osteology. Of all animals, the mole has the most remarkable apparatus of ' sesamoid ' bones. Its prodigiously strong dig- ging feet are provided with many of them, which increase the leverage of the brachial muscles, and enable the animal almost to swim through the earth. INTEROSSEOUS MUSCLES. Number and Arrangement. There are seven interosseous muscles FIQ. 75. Four Dorsal Interossei, Drawing from the Middle Line. FIQ. 76. Three Palmar Interossei. Drawing toward the Middle Line. in the hand: '" four on the dorsal aspect, and three on the palmar. The - If we considered the adductor pollicis as a palmar interosseous muscle, there would be four palmar and four dorsal, all supplied by the ulnar nerve. 236 HUMAN OSTEOLOGY. dorsal interossei arise by two heads from the opposed sides of the meta- carpal bones, and are inserted into the first phalanges of the fingers, so that they separate the fingers from each other; in other words, they draw the fingers from a stationary line supposed to pass down the centre of the middle finger, as represented by the dotted line in Fig. 75. The palmar interossei arise each from one metacarpal bone, and are inserted into the fingers, so that they bring them together; in fact, they draw toward the stationary line down the centre of the middle finger, as shown in Fig. 76. GENERAL SURVEY OF THE SKELETON. A GENERAL survey of the human skeleton shows how admirably it is adapted to the erect attitude. Adaptation of the Skeleton to the Erect Position. 1. When a man stands erect, an imaginary vertical plane (a b) supposed to fall through the top of the head, would pass through the occipito-atlantoid, lumbo-sacral, sacro-iliac, hip, knee, and ankle-joints; in a word, through all the joints which transmit the weight to the ground. This explains why a man can carry a weight on the top of his head easier than in any other way. Position of Foramen Magnum and Condyles. 2. The foramen magnum and the condyles of the occiput are nearly horizontal (when the head is held upright) and they are advanced almost to the middle of the base of the skull, and thus the head is nearly balanced on the cups of the atlas. The head has a slight tendency to drop forward, but this is limited by the ligamentum nuchae. Contrast the position of the condyles in the human skull with that of the orang- outan, in which the condyles are not only placed nearer to the back of the head, but obliquely, making an angle of 40 with the horizon. The lower we go in the scale, the greater is the contrast. In the horse, for instance, the plane of the condyles and foramen magnum is vertical. In this, and all other herbivorous quadrupeds, the weight of the head is sus- Flo- 77- tained by an enormously strong and elastic ligament (ligamentum michse, or pack-wax), the strength of which is in proportion to the weight of the head and its tendency to drop. It extends from the lofty spines (withers) of the anterior dorsal vertebrae to the crest of the occiput. Direction of the Face. 3. The face is placed perpendicularly under the cranium, so that the planes of the face and forehead are par- allel, and this characteristic of the human face is well adapted for the 238 HUMAN OSTEOLOGY. erect attitude. If man went 011 all fours, he would habitually see and smell nothing but the ground. As it is, the direction of the orbits is hori- zontal, and therefore gives the greatest range of vision; and the direction of the nose gives the greatest range of smell. We are reminded here of the beautiful lines ' Pronaque dum spectent animalia caetera terram, Os homini sublime dedit, ccelumque tueri Jussit, et erectos ad sidera tollere vultus. ' OVID, Metam. I. 84-86. Breadth of the Thorax. 4. The thorax is much broader in the transverse than in the antero-posterior diameter. This great breadth of the chest is peculiar to man and the highest species of ape; it throws the arms farther apart, and gives them a more extensive range; besides which, it diminishes the tendency there would otherwise be in the trunk to fall forward. Contrast this with the chest of quadrupeds, compressed later- ally and deep from sternum to spine, so that the fore legs come nearer together, and fall perpendicularly under the trunk. Curves of the Spine. 5. The vertebral column gradually increases in size toward the base. It is curved, which makes it all the stronger, and better adapted to break and diffuse shocks: and these curves, waving alternately, distribute the weight in the line of gravity. This line passes through all the curves, and falls exactly on the centre of the base. Ob- serve, moreover, the length and size of the spinous processes in the lumbar region for the origin of the ' erector-spinse.' Shape and Inclination of the Pelvis. 6. The weight of the ver- tebral column is supported on a sacrum broader in proportion than in any other animal. The iliac bones are widely expanded and concave in- ternally; they support the viscera and give powerful leverage to- the muscles which balance the trunk. The whole pelvis is remarkably broad, and thus the base of support is widened; and the plane of its arch so inclines as to transmit the weight from the sacrum (or crown of the arch) vertically on to the heads of the thigh bones: lastly, the deepest and strongest part of the socket for the thigh bone is in the line of weight: consequently, the joint is never more secure than in the erect position. With the broad and capacious pelvis of man, contrast the long and nar- row pelvis of animals, which, instead of forming an angle with the spine, is almost in the same line with it. GENERAL SURVEY OF THE SKELETON. 239 Lower Limbs. 7. In proportion to the trunk, the lower limbs of man are longer than in any other mammal, the kangaroo not excepted. Their great length prevents their being adapted for locomotion in any but the erect attitude. The femur has a long neck, set on to the shaft at a very open angle, so that the base of support is rendered still wider. The long shaft of the femur inclines inward, bringing the weight well under the pelvis, which is obviously of great advantage in progression: and when the leg is extended, the femur can be brought into the same line with the tibia; thus the weight is transmitted vertically on to the hori- zontal plane of the knee-joint, while the articular surfaces of the bones are expanded and give adequate extent of support. Contrast our long lower limbs with the short and bowed legs of the gorilla, chimpanzee, and orang-outan. Watch attentively one of these three apes (the highest of the mammalia below man) in the act of walking; you will find that he supports himself alternately on the right and left knuckles as well as on his feet. Feet. 8. The foot of man is broader, stronger, and larger in propor- tion to the size of the body than in any other animal; so that man can stand on one leg, which no other mammal can do. Its strong component bones form a double arch of exceeding elasticity, which touches the ground at both ends, and receives the superincumbent weight vertically on its c crown/ The great bulk and backward prolongation of the os calcis at right angles to the tibia support the arch behind, and form a powerful lever for the great muscles of the calf, which raise the body in progression, while the bones of the great toe are proportionately strong, and form the chief support upon which the body may be raised. Upper Limbs. 9. We see, then, that the whole fabric of the skele- ton is so adjusted as to exempt the upper limbs from taking any part in its support. These are kept wide apart by the clavicles, and their com- ponent joints admit of the freest range of motion. The twenty-seven bones at the extremity of each constitute those instruments of consummate perfection, the ' HANDS,' of which, even if a formal dissertation 103 had not been written, one might well forbear to speak, since they have such elo- quence of their own. ' Nam caeterae partes loquentem adjuvant, hae, prope est ut dicam, ipsae loquuntur: his poscimus, pollicemur, vocamus, dimittimus, minamur, supplicamus, abominamur, timemus; gaudium, 103 < The Hand, its Mechanism and Vital Endowments, as evincing Design.' Lon- don, 1834, by Sir Charles Bell, F.R.S. 240 HUMAN OSTEOLOGY. tristitiam, dubitationem, confessionem, pcenitentiam, modum, copiam, numerum, tempus, ostendimus.' 104 Comparative Osteology. Some of the vertebrata have bones which do not exist in man as such and are only represented in him by fibrous or cartilaginous tissue. Thus there is the bone of the heart, ' os cordis,' in the bullock bos taurus (No. 4), an example of the visceral system of bones or splanchno-skeleton. Another instance is the bony sclerotic of many fishes and some birds. This is well seen in a specimen from the sun-fish (No. 5). There was a ring of bone in the sclerotic of the extinct flying lizards (Pterosauria), as well as in that of the Ichthy- osauria, the life-size models of which animals are seen at the Crystal Palace. In the Phocida?, Trichechus, the walras, and in many dogs, is found the ' os penis' (Nos. 3906, 3907, 3908, 3909, and 3910, the last showing a fracture which has been repaired). Another is the ' intercla- vicula' found in Reptilia. It is often, too, present in birds, though it is in them confluent with the clavicles. In many of the Lacertilia a par- tially ossified, or cartilaginous rod runs up from the symphysis of the ischia, and supports the front wall of the cloaca, and is called the ' os cloacae.' In all pouched animals (Marsupialia), as in the kangaroo (Ma- cropus major, Ost. Ser. Coll. Surg. Mus. 1724), and in the Monotremata (that is, in Echidna and Ornithorhynchus, Ost. Ser. Coll. Surg. Mus. 1698, 1699), are found the marsupial bones: ossifications, or often only chondrifications, of the internal pillars of the external abdominal rings. 1W Quintilian. PLATE XXXVIII. Qs-TiycMcles, .(rreafcer corn* Lesser cor nu. Body .Mylofyoiaeus Attachtnentof ThyroV^ 1 '^ ition for Thyroid carVda^e. Yer-tical section of oe-'hyoi AreK of tlie Carpus. CaTc'aneo-scapKo'id ligamenfc OS HYOIDES. (PLATE xxxvm.) Position and Use. The os hyoides, so called from its likeness to the Greek letter Upsilon, is situated between the larynx and the root of the tongue. It is suspended from the styloid processes of the tempo- ral bones by the stylo-hyoid ligaments, often partly ossified in man, and, generally, distinct bones in animals. When the neck is in its natural position, it can be plainly felt on a level with the lower jaw, and about one inch and a half behind it. It serves to keep open the top of the larynx, and affords attachment to the muscles which move the tongue. It is divided, for the sake of description, into a ' body ' or front part, and a ' greater ' and a ' lesser cornu ' on each side. Body. The 'body' (basi-hyal part) is the thickest and strongest part. Its upper surface is marked by the impressions of the muscles at- tached to it. There are, generally, a transverse and a perpendicular ridge: the latter is in the median line. Often there is a little projection from the middle, which is interesting as a rudiment of the process to which is attached the lingual bone of animals which runs into the sub- stance of the tongue. Its under surface is slightly excavated (as seen in Plate XXXVIII. Fig. 2), which shows a transverse section through the centre of the body. Into this hollow the thyroid cartilage rises behind the os hyoides in deglutition. The plane of the body is nearly horizontal; the anterior thyro-hyoid ligament is attached to its posterior border. Cornua. The greater cornu (' thyro-hyal ' part) projects backward about one inch and a half, not quite horizontally, but with a slight incli- nation upward, and terminates in a blunt end, tipped with cartilage. Until the middle period of life, the great cornu is united to the body by cartilage; but^this ossifies in the progress of age. The lesser cornu (' cerato-hyal ' part) is not much larger than a barley- 16 242 HUMAN OSTEOLOGY. corn, and projects backward at an acute angle from the junction of the body and the greater cornu. It articulates with the body by a little joint, and is freely movable: the stylo-hyoid ligament is attached to the end of it. The many muscles attached to the hyoid bone are shown in the plate. The os hyoides is connected to the thyroid cartilage by three liga- ments, which contain a large quantity of elastic tissue. These ligaments are: 1. The anterior tliyro-hyoid (Plate LVII. Fig. 1), which extends from the ' pomum Adami ' to the upper and back part of the body of the os hyoides. 2. The two posterior thyro-Jiyoid, which extend, one on each side, from the end of the great cornu of the os hyoides to the supe- rior cornu of the thyroid cartilage. The vacant space left in the dried preparation between the hyoid bone and the thyroid cartilage is closed in the recent state by the thyro-hyoid membrane. Ossification. The bone is ossified from five centres one for the body, and one for each of its four cornua. The body and greater cornua begin to ossify in the last month of foetal life. The lesser cornua begin to ossify in the first year, and generally in middle age unite to the rest of the bone. Comparative Osteology. The posterior surface of the hyoid bone is concave from side to side and from above downward. This concavity is characteristic of the higher mammalia. In the gorilla it will lodge the tip of the finger, while in the howling monkey, Mycetes laniger, it develops into a sac large enough to hold a pigeon's egg. Notice a remarkable anterior projection from the front of the body of the hyoid bone of the horse, seen also more or less in many other ani- mals and especially in birds. (Sep. Ser. Mus. Koy. Coll. Surg.) PLATE LVI1. THE LARYNX. (PLATE LVII.) Situation and Use. The larynx is situated at the top of the trachea or windpipe. It answers a double purpose. It guards the opening through which the air passes into the lungs: it is the organ of the voice and of song. Its framework consists of a number of cartilages connected by joints and elastic ligaments in such a way that they can be moved upon each other by appropriate muscles; the result of this motion being to act upon two elastic ligaments termed the ' vocal cords/ upon which the voice essentially depends. Thyroid Cartilage. The thyroid cartilage (Ovpeos; a shield) is so named because it shields the delicate apparatus behind it. It consists of two lateral symmetrical plates (alas), united in front at an angle which forms the prominence termed ' pomum Adami.' This prominence, which is greater in the male than in the female, has a ' notch ' at the upper part, as if a portion of the angle had been sliced off to permit the carti- lage to rise with greater facility behind the os hyoides in deglutition. More than this, there is a bursa of considerable size which diminishes friction between the surfaces. The bursa is practically interesting, be- cause it may enlarge and form a cyst in front of the neck, sometimes as large as a pigeon's egg. Outer Surface and Ridge. Look at the outer surface of the ala of the thyroid cartilage (Fig. 1). It has an oblique ridge, running down- ward and forward, with tubercles at each end, indicative of the attach- ments of muscles. The ridge gives origin to the ' thyro-hyoid ' and inser- tion to the ' sterno-thyroid ' muscles. Behind the ridge is the origin of the inferior constrictor of the pharynx, extending down to the side of the cricoid cartilage. The posterior border of the ala is nearly vertical, and gives insertion to the stylo-pharyngeus. The inferior border of the ala has generally two curves, and gives insertion to the ' crico-thyroid ' muscle. This muscle arises from the side of the cricoid cartilage; conse- quently, when it acts, it draws the two cartilages together. 244 HUMAN OSTEOLOGY. Cornua. The posterior part of each ala has two projections, termed its ' cornua ' superior and inferior. The superior cornu gives attachment to the posterior thyro-hyoid ligament. The inferior cornu articulates with the cricoid cartilage. This is a perfect joint, provided with a syno- vial membrane and ligaments. It is important to remember that the form of the joint admits of only vertical movement of the thyroid carti- lage, the axis of motion being a transverse line drawn through both joints. Upon this movement depends the tuning of the vocal cords. Angle. So much for the outside of the thyroid cartilage. Now for the parts attached within the angle. To see them properly, one of the ala3 should be removed, as in Fig. 2. You then observe that the follow- ing objects are attached to the angle, beginning at the top: 1, the anterior thyro-hyoid ligament; 2, below this, the apex of the epiglottis; 3, lower down, the false vocal cords; 4, still lower, the true vocal cords; 5, below these, the origin of the ' thyro-arytenoideus '; lastly, at the lower border of the angle, is the attachment of the ' crico-thyroid ' ligament. Cricoid Cartilage. The cricoid cartilage (Plate LVII.) forms a complete ring (whence its name), a little broader in the antero-posterior diameter than in the transverse. It is situated at the top of the trachea, immediately below the thyroid cartilage. The ring is not of the same depth all round. It is narrow in front, and from this part the upper border of the ring gradually rises, so that, behind, the ring is a full inch in vertical depth, and occupies part of the interval between the alas of the thyroid. This slope of the cricoid toward the front permits the ver- tical play of the thyroid. It cannot be too strongly impressed upon a student that he should make his finger familiar, in his own neck, with the projections of the thyroid and the cricoid cartilages, and the slight depression between them, indicating the site of the crico-thyroid mem- brane. These parts lie, one below the other, in the middle line of the neck, and are the guides in the operation of laryngotomy and trache- otomy. The operation of laryngotomy consists in dividing the crico-thy- roid ligament transversely close to the cricoid cartilage, that the incision may be as distant as possible from the vocal cords. Passing from the front toward the side of the cricoid cartilage, notice the origin of three muscles, namely the ' crico-arytenoideus lateralis ' along the upper edge (Fig. 2); the ' crico-thyroid ' in the middle (Fig. 1); and, lower down, a portion of the ' inferior constrictor of the pharynx/ At the back part of the cricoid cartilage (Fig. 3) there is on either THE LARYNX. 245 side a broad excavation for the origin of the t crico-arytenoideus posticus. ' Generally these muscles are separated by a slight vertical crest which gives attachment to some of the longitudinal fibres of the oesophagus. At the top of the cricoid are the two small oval articular surfaces, one on each side, for the arytenoid cartilages, to be examined presently. The side of the cricoid articulates with the inferior cornu of the thyroid cartilage by means of a perfect joint, provided with a synovial membrane and ligaments. The structure of this joint permits the two cartilages so to move upon each other that their opposite borders can be approximated Tsy the ' crico-thyroid ' muscle. It deserves especial attention, because the degree of this approximation regulates the tension of the vocal cords. Lastly, the lower border of the cricoid is horizontal, and connected to the first ring of the trachea by an elastic membrane. Arytenoid Cartilages and Cornicula Laryngis. The arytenoid cartilages, so named from their resemblance to an ancient ewer(apvTcn va), are situated, one on each side, at the upper part of the cricoid (Fig. 3). Each is somewhat pyramidal in form, with the apex above, looking to- ward its fellow, and slightly curved backward. The apex of each is sur- mounted by a nodule of cartilage, termed the ' cartilage of Santorini ' {'corniculum laryngis'). The base presents an oval concave surface, which forms a perfect joint, with a corresponding convex surface, on the cricoid cartilage. This joint has a loose synovial membrane and liga- ments, so that the arytenoid cartilages admit of being approximated or separated, a freedom of motion which is essential to the dilatation and contraction of the glottis or chink between the true vocal cords through which the air enters the trachea. Tubercles of the Arytenoid. At the base of each arytenoid car- tilage (Plate LVIL Fig. 2) observe the anterior tubercle to which the true vocal cord is attached, and the posterior tubercle, which gives inser- tion to two muscles namely, the ' crico-arytenoideus lateralis ' and the * crico-arytenoideus posticus ': these muscles are inserted, not into the same side, but into opposite sides of the tubercle : the effect of which is that they antagonize each other. Each arytenoid cartilage has three surfaces a posterior, an anterior or external, and an internal. The posterior surface is excavated and has attached to it the * arytenoideus ' muscle (Fig. 3), which crosses from one curtilage to the other, and fills up the gap between them. The anterior surface is also excavated, and occupied by the insertions of the ' crico- 246 HUMAN OSTEOLOGY. arytenoideus lateralis ' and the ' thyro-arytenoideus.' The internal sur- face is flat, looks toward its fellow of the opposite side, and contributes to form part of the margin of the glottis. Epiglottis. The epiglottis is a structure composed of yellow elastic cartilage situated at the base of the tongue, and projecting over the upper part of the larynx like the flap of a valve. In shape it somewhat resem- bles the leaf of an artichoke. Its apex is attached to the angle of the thyroid cartilage. Its ordinary position is perpendicular, or nearly so, leaving the glottis free for respiration; but during deglutition the larynx is raised, and the tongue is depressed, so that the epiglottis becomes more horizontal, drops like a valve over the top of the larynx, and tends to prevent the entrance of food into it. This falling of the epiglottis is not produced by any special muscle; it is simply mechanical. Cuneiform Cartilages. These cartilages are the smallest and least essential of the whole group. They are found in the ' aryteno-epiglot- tidean fold/ a prominent line of mucous membrane running on each side from the edge of the epiglottis to the apex of the arytenoid cartilage. They are thin and narrow, not much larger than pins' heads and not constant. Thus there are nine cartilages in all, of which four namely, the thy- roid, cricoid and two arytenoid are composed of hyaline cartilage and are prone to ossify in old age. The remaining five are of yellow elastic fibre-cartilage, and have but little tendency to ossify. Vocal Cords, True and False. The vocal cords are four elastic ligaments, two on each side, extending horizontally backward from the angle of the thyroid cartilage to the anterior part of the arytenoid. The two lower, and the most important, are termed the ' true ' vocal cords, be- cause, by their vibration, they produce the voice : the two upper cords are called 'false/ because they have little or nothing to do with the voice. The rapidity and accuracy with which the true vocal cords can change their tension, their form, and the width of the slit between them, render the voice the most perfect of musical instruments. Attachments of Vocal Cords. The precise attachments of these cords are best seen in the dried larynx, in which all the surrounding soft parts have been removed, as shown in Plate LVII. Fig. 2. The true vocal cords are attached in front close together to the angle of the thyroid cartilage, about a quarter of an inch from its lower edge, and they diverge as they pass backward to be attached to the anterior tubercle of the base THE LARYNX. 247 of the arytenoid. The false cords also proceed from the angle of the thyroid a little higher than the true, to about the middle of the front part of the arytenoid. In the recent larynx these cords are not free all round, like the strings of a violin; they are Only free along the sides which face each other; everywhere else the true cords are in contact with muscle, and the false with fat and areolar tissue. Length of Vocal Cords. What is the length of the true vocal cords? During life, their length is continually varying, to a slight degree, with the pitch of the voice; but, in the dead subject, they are about five-eighths of an inch in the adult male. From an examination of several male larynges, the cords are found to differ more or less in length in different individuals, though not more than one-twelfth of an inch. These individual differences in the length of the cords make cor- responding variations in the natural tone of the voice: e.g. tenor, bary- tone, or base. A deep voice coincides with the longer cords; a shrill voice with the shorter. In the female the cords are about one-fourth shorter than in the male. In boys, too, they are much shorter than in the adult; hence the peculiar voice of boys. At puberty the cords lengthen with the development of the larynx, and the voice is said to break. Epiglottis Thyroid cartilage False vocal cord Ventricle True vocal cord Rima glottidis. Thyro-arytenoideus muscle Cricoid cartilage Trachea FIG. 78. Perpendicular Section, showing the Ventricles of the Larynx. Ventricles of the Larynx. In the perfect larynx is a little recess on each side between the true and the false vocal cords, like a little side pocket. These recesses are called 'the ventricles' of the larynx, and 248 HUMAN OSTEOLOGY. are best examined by cutting open the larynx. Their shape, depth and situation are represented in the outline of the subjoined Fig. 78, taken from a transverse perpendicular section of the larynx. They appear to allow free space for the vibration of the vocal cords and probably strengthen the voice. They are lined by the mucous membrane of the larynx, and the bottom of each is supported by the ' thyro-arytenoideus ' muscle. The length of the ventricles from before backward corresponds with the length of the vocal cords. Their greatest vertical depth is toward the front, which is the part represented in the section. Size of the Ventricles. The ventricles of the larynx are large enough to lodge a foreign body, such as a pea. A pill forced down a child's throat against its will has been known to catch in one of the ventri- cles, and occasion death, after a few struggles, from spasm of the glottis. Rima Glottidis. The term ' rima glottidis ' or ' glottis ' is applied to the interval between the true vocal cords through which the air passes into and out of the trachea. It is about one inch in length. Its boun- Thyroid cartilage. darleS ( Fi S' 79 ) ar6 f 1TOed ^ the VOCal TTU v i cord cords and by the arytenoid cartilages. The vocal cords form about the anterior two-thirds, the cartilages about the posterior third of the opening. The Arytenoid cartilage. r glottis admits of being made wider, or Elastic ligament. narrower, or may even be completely FIG. 79.-shape of the Glottis when at rest. c i ose a, by the action of muscles which we shall examine presently. In a state of rest it is triangular; the apex being in front at the thyroid cartilage, and the base between the aryte- noid, as shown in Fig. 79, where the arytenoid are cut through on a level with the vocal cords. When the glottis is dilated in inspiration by the * crico-arytenoidei postici,' it becomes spear-shaped, as seen in Fig. 81. During expiration the glottis gradually resumes its triangular shape or state of rest; and this return to a state of repose is effected, not by muscle, but by an elastic ligament shown in Fig. 81, which draws the arytenoid cartilages toward the mesial line. The glottis, like the chest, is dilated during inspiration by muscular tissue; like the chest, also, it is contracted during expiration by elastic tissue. Muscles of the Larynx. There are nine muscles which act spe- cially upon the rima glottidis four on each side, and one in the middle. The four on each side are the ' crico-thyroidei,' the ' crico-arytenoidei THE LARYNX. 249 postici,' the 'crico arytenoidei laterales,' and the ' thyro-arytenoidei.' The single one in the middle is the ' arytenoideus. ' Crico-thyroid Muscles. The ' crico-thyroid ' is a short and strong muscle. It arises from the side of the cricoid cartilage, and is inserted into the lower border of the thyroid, including the lesser cornu. Its ac- tion is to stretch the vocal cords. It does this by depressing the thyroid Arytenoid cartilage. Crieo-aiytenoid joint. <5- Crico-thyroid joint . . Thyroid cartilage. Thyroid cartilage depressed. True vocal cord. True vocal cord stretched. Crico-thyroid muscle. Cricoid cartilage. FIG. 80. Diagram showing the Action of the Crico-thyroid Muscle. cartilage, the arytenoid cartilage remaining fixed. Under this condition the thyroid cannot be depressed without increasing the distance between the attachments of the vocal cords, as shown by the dotted line in Fig. 80. Consequently the ' crico-thyroid,' when in action, must elongate the vocal cords. Crico-arytenoidei Postici. Each ' crico-arytenoideus posticus' arises from the posterior part of the cricoid cartilage, and is inserted into Vocal cord Thyroid cartilage . Cricoid cartilage . . Arytenoid cartilage Elastic ligament . , (.crico-arytenoid) Crico-arytenoideus Mentis. Ideal pivot. Crico-arytenoideus posticus. FIG. 81. Glottis Dilated. Muscles dilating it represented wavy. the posterior tubercle of the arytenoid. The muscle is seen in action liy wavy lines) in Fig. 81. Its action is to dilate the glottis. It 250 HUMAN OSTEOLOGY. does this by drawing the posterior tubercle of the arytenoid toward the mesial line, and therefore the anterior tubercle from the mesial line. In this movement the arytenoid cartilage rotates upon the cricoid as upon a pivot. Moreover, the arytenoid cartilage is a lever of the first order; the fulcrum or ideal pivot being intermediate between the power at the posterior tubercle and the weight or resistance at the anterior. The muscle in question is a most important one. It is a muscle of inspira- tion. It dilates the glottis every time we inspire. During expiration, when the glottis is restored to its state of rest, not by muscular action, but by an elastic ligament, the ' crico-arytenoid,' marked in Fig. 81, the muscle relaxes, and has time to rest. This alternate contraction and relaxation of the ' crico-arytenoidei postici ' is perpetually going on, from the first moment of life till the last. Crico-arytenoideus Lateralis. Each ' crico-arytenoideus lateralis ' arises from the upper border of the cricoid cartilage, and is inserted into Vocal cord iWm ^JIlBL^^. Thyrc-arytenoideus. Arytenoid in 111 " Elastic ligament . . . Crico-arytenoideus posticus. FIG. 82. Glottis Closed. Muscles closing it represented wavy. the posterior tubercle of the arytenoid. Its action is to assist in closing the glottis, as seen in Fig. 82. It does this by rotating the arytenoid cartilage in a way directly the reverse of the muscle last examined. Arytenoideus. The 'arytenoideus' muscle arises from the back of one arytenoid cartilage, and is inserted into the back of the other. (Plate LVII. Fig. 3.) It clasps the two cartilages together, and therefore as- sists very materially in closing the glottis. 106 105 Certain muscular fibres in the aryteno-epiglottidean folds of mucous membrane assist the ' arytenoideus ' and the ' crico-arytenoidei laterales ' in closing the glottis. All these little muscles together form, as Henle has shown, a ' sphincter' of the glot- tis, a highly developed and complicated homologue of the single and simple sphincter muscle which embraces the entrance of the larynx in reptiles. THE LARYNX. 251 Thyro-arytenoidei. Each of these muscles arises from the angle of the thyroid, and is inserted into the front surface of the base of the arytenoid. They relax the vocal cords, since they tend to draw together the cartilages to which they are attached. More than this, they assist in narrowing the glottis. But their special action appears to be that of bringing the lips of the glottis parallel to each other; that of placing them, in fact, in the ' vocalizing ' position. The glottis must be made not only a very narrow chink, but its lips must be brought parallel to each other, before they can be made to vibrate by the stream of the air, in such a manner as to produce voice or song. The motions of the glottis in singing, speaking, breathing, and coughing can be distinctly seen in the laryngoscope. The following is a tabular arrangement of the action of the muscles of the larynx: ( Crico-thyroidei stretch the vocal cords ) govern the pitch of ANTAGONISTS { } ( Thyro-arytenoidei relax the vocal cords ) the notes. Crico-arytenoidei postici open the glottis ) / govern the opening ANTAGONISTS { Crico-arytenoidei laterales l doM ^ glQtti8 V rf ^ Arytenoideus , J ; THE ANATOMY OF THE EAR IN describing the anatomy of this intricate and delicate organ, a general outline of its structure will first be given, and afterward the details of its several parts. General Idea of the Subject. To obtain a general idea of the organ of hearing, look at the diagram, Fig. 1, Plate LVIII. In this is seen the elastic fibro-cartilage termed the ' pinna' of the ear, which col- lects the sonorous undulations of the air, and transmits them down the passage called the ' meatus auditorius externus.' This passage, about an inch and a quarter in length, is a little contracted in the middle, where its floor is a little raised. It is closed at the bottom by a fibrous membrane (membrana tympani) which is fixed in a groove in the bone, is placed obliquely, and stretched in all respects like the parchment of a drum, except that its outer surface is a little concave. Tympanum. On the inner side of the membrana tympani is a small chamber in the substance of the temporal bone, termed the ' tym- panum ' or middle ear. This chamber is filled with air, which is admitted through a tube (Eustachian tube) about an inch and a half long, leading from the back part of the nostrils into the front part of the tympanum. Thus there is an equilibrium of air on both sides of the membrana tym- pani. In fact, the Eustachian tube performs the same office for the ear as the hole which is made in the side of a drum for the necessary purpose of opening a communication with the external air. Opposite to the Eustachian tube, that is, at the back part of the tympanum, are the irregu- lar openings of the mastoid cells, which also contain air. All these air cavi- ties are lined by a continuation of the mucous membrane which lines the passages of the nose. This explains the degree of deafness which is often produced by a common cold, or other disease of the throat: the Eusta- chian tube being temporarily obstructed by the swelling of its lining membrane. Ossicula Auditus. Malleus, Incus, and Stapes. In the tym- panum itself we find three little bones (ossicula auditus) known separately THE ANATOMY OF THE EAR. 253 by names more descriptive of their shape than their office ' malleus/ ' incus/ and ' stapes/ These bones are connected by perfect joints, so as to form a continuous chain, surrounded by atmospheric air,, across the cav- ity of the tympanum; and the mucous membrane is reflected over them. The handle (manubrium) of the malleus at one end of the chain is at- tached to the ' membrana tympani/ and the foot-plate of the stapes at the other end closes the ' fenestra ovalis/ an opening on the inner wall of the tympanum leading to the ' vestibule ' of the internal ear. Both ends of the bony chain are attached to membrane, since the foot-plate of the stapes does not exactly fit into the fenestra ovalis; membrane intervening between their edges. Moreover, certain little muscles are attached to the bones, and slacken or tighten the membranes. Besides the fenestra ovalis, there is another opening in the inner wall of the tympanum, called the ' fenestra rotunda/ It leads into the cochlea and is closed by membrane. Internal Ear. The internal ear, often called, on account of its in- tricacy, the ' labyrinth/ consists of a little chamber termed the ' vesti- bule/ the three ' semicircular canals/ and the ' cochlea.' All these parts are embedded in the petrous portion of the temporal bone like passages cut out of a solid rock. Hence the great difficulty of exploring them. Bear in mind their relative position. The ' vestibule ' is in the middle, the canals are behind, and the cochlea is in front. Vestibule. The vestibule communicates, behind, with the five open- ings of the semicircular canals; in front, with the cochlea; on the outer side with the tympanum through the fenestra ovalis (occupied by the stapes); and on the inner side by minute apertures with the meatus audi- torius internus, through which the auditory nerve enters the ear. These apertures transmit those branches of the auditory nerve which supply the membranous contents of the vestibule and the semicircular canals. Cochlea. The cochlea, so named from its resemblance to a snail's shell, is an exceedingly curious structure. It is placed so that the base of the shell corresponds to the bottom of the meatus auditorius internus, while the apex points forward and outward toward the Eustachian tube. It is formed by the spiral convolutions of two gradually tapering tubes, or rather by one tube separated into two compartments by a longitudinal septum (lamina spiralis), composed partly of thin bone, but chiefly of membrane. In the diagram the course of the septum is indicated by a dotted outline. This septum is the most important part of the cochlea, because the auditory nerve expands upon it. It runs all through the 254 HUMAN OSTEOLOGY. tube, except at the apex, where it suddenly terminates in a curved hook, and leaves an aperture (helicotrema), so that the two portions of the tube communicate. One portion of the tube (scala vestibuli) opens into the vestibule; the other portion (scala tympani) leads into the tympanum through the 'fenestra rotunda/ This last foramen is open only in the dry bone; in the recent state the fenestra rotunda is closed by the ' mem- brana tympani secundaria/ which therefore has the air of the tympanum on the one side and the fluid in the cochlea on the other. The central pillar of the cochlea round which the tube makes two and a half turns is called the 'modiolus' or 'axis.' Semicircular Canals. The semicircular canals are three in num- ber, and are called, from their position, ' superior/ ' posterior/ and ' ex- ternal.' They are placed in planes at right angles to each other like the faces of a cube. Each canal forms the greater part of a circle, and opens at each end into the vestibule. There are only five openings, since two of the canals have an opening in common. Each canal has a dilatation at one end termed the 'ampulla'; this makes room for a corresponding dilatation of the membranous canal within it, upon which the auditory nerve expands. The ' ampulla/ therefore, is the most important part of each canal. Uses of these Excavations. These curious and elaborate excava- tions in the petrous bone form receptacles for a fluid in which floats the delicate membrane destined to receive the terminal filaments of the audi- tory nerve. This membrane is the very essence of the organ of hearing. It is to the ear what the retina is to the eye. In the vestibule and semi- circular canals it forms a continuous, but closed sac, which copies pretty accurately the shape of these cavities, without being in contact with their bony walls. It is bathed within and without by a thin albuminous fluid. That part of the fluid within the membrane is called the 'endolymph'; that without, the 'perilymph/ or 'liquor Cotunuii.' Within the cochlea the membrane is arranged in a different manner. It forms here the greater part of the ' lamina spiralis/ and encloses a third scale or spiral passage, the ' canalis membranacea/ or ' canalis cochleae/ absent in the macerated labyrinth. Inside this membranous canal is a series of cellular bodies arranged in a very complicated manner, and known as the ' organ of Corti.' The membranous canal is filled with endolymph; the cavities of the scala vestibuli and scala tympani are occupied by perilymph. The auditory nerve enters the ear through the meatus auditorius in- THE ANATOMY OF THE EAR. 255 ternus. At the bottom of this passage are a multitude of small foramina, which transmit the minute subdivisions of the nerve to their respective destinations. Some are distributed upon the sac in the vestibule; some upon the dilatations (ampullae) of the membranous semicircular canals; others run down the axis of the cochlea, and are distributed to the struct- ures within the canalis membranacea. Probable Function of these several Parts. Now for the ex- planation, usually received, of the function of these several parts. The waves of sound, collected by the cartilage of the ear, pass down the ex- ternal auditory passage, strike upon the membrana tympani, and cause it to vibrate. These vibrations are carried by the little bones across the tympanum to the membrane, which closes the ' fenestra ovalis,' or open- ing into the vestibule. This membrane, thus thrown into vibration, communicates motion to the fluid in the labyrinth; the filaments of the auditory nerve receive the impression and transmit the sensation of sound to the brain. The vibrations of the membrana tympani excite corespond- ing vibrations in the air within the cavity of the tympanum, which again communicates them to the membrane closing the fenestra rotunda, and through this they reach the cochlea. Here we have a ready explanation of the use of the fenestra rotunda and the membrane closing it: that is, we have, interposed between air and a fluid, a tense membrane, which is the very best medium for transmitting, with increased intensity, vibra- tions from one to the other. After the preceding sketch of the anatomy of the ear, proceed now to a more minute examination of its component parts. It is taken for granted that the learner is already familiar with the anatomy of the tem- poral bone described at page 47. Meatus Auditorius Externus. This passage leads to the mem- brana tympani. Its outer third is formed by a tubular continuation of the cartilage of the ear; its inner two-thirds by the osseous canal in the temporal bone. The cartilaginous part is united by fibrous membrane to the rough margin of the processus auditorius. The cartilage, however, does not itself form a complete tube; there is a slight deficiency at the upper part, completed by fibrous membrane. There are also one or two vertical fissures in the cartilage. These breaks in the cartilage give 256 HUMAN OSTEOLOGY. greater freedom of motion; they are interesting practically, as explaining; how collections of matter in the parotid gland sometimes make their way into the meatus auditorius. Length. The length of the meatus, measured from the middle of its external orifice to the middle of the membrana tympani, is about one inch and two or three lines. The anterior wall is about one-fourth of an inch longer than the posterior, in consequence of the oblique direction of the membrana tympani. Direction. The direction of the meatus is inward and forward. It describes a slight curve with the concavity downward. Besides this gen- eral curve, the cartilaginous part is slightly curved with the concavity forward, and the osseous part with the concavity backward. Altogether, the meatus has such a curious shape that it cannot be well understood without looking at a cast of it. Every surgeon knows how difficult it is. to see the whole of the membrane of the tympanum at one view: one can seldom see more than a part of it, however much the ear be dilated and pulled so as to straighten the outer curve. The narrowest part of the meatus is about the middle. Beyond this point we ought not to intro- duce the speculum. Meatus in the Infant. The preceding description of the external auditory meatus refers to its condition in the adult. In infancy, the meatus is extremely short on account of the non-development of the bony portion, which at this period is a mere ring (see ' Temporal Bone'). The membrana tympani, too, is almost on the plane of the base of the skull, this is a conspicuous feature in the cranium of a new-born child, where the membrane absolutely lies on the floor of the meatus. It is most im- portant that a surgeon should bear these facts in mind when examining the ears of very young children. Insects sometimes find their way down the meatus and cause intense pain. An instance is related by Wilde 108 which is worth giving, if only to show how to dislodge them: ' I remember being out shooting with a friend, who, suddenly exclaiming, " Oh, an earwig!" and throwing aside his gun, fell on the ground, making the most piteous groans, and rolling about in agony. Suspecting that some insect had got into his ear, I pro- cured some water from a ditch, and poured it into the meatus. While watching the result, a little animal, well known among anglers as the hawthorn fly, crept out, and my friend was instantly relieved.' 106 Wilde, 'Aural Surgery, ' p. 178. PLATE LVIII. Kittens, Merabrano_iy rn^ani, . .Tymoajium* EustacKitn tube* D ia^ram. o fKe Ear* [Opening into Masloid cells, Jerestra rctunSsu nestra ova-lisi Canal forHensor.tympam UiustacHiecn tube , Groove ixr5"MJem"bran a lym pan i \\ foramen cViorclas...-*' : JPyrarnltl -'' for Stapeiiius;, Prepara,tion to shew inner* -wall of tympaTTunn. THE ANATOMY OF THE EAR. 257 Membrana Tympani. The membrana tympani is a thin, semi- transparent, fibrous membrane, of a greyish color, placed very obliquely at the bottom of the meatus auditorius externus. Its direction is down- ward, forward, and inward. This obliquity increases the extent of sur- face; so that every wave of sound, reflected down the meatus, must fall upon it. Its circumference, which is nearly circular, is fixed into a groove in the bone, so fine that it might have been traced with the point of a needle. (Plate LVIII. Fig. 2.) This groove, however, does not form a complete circle: it is deficient at the upper part, where the membrana tympani is, more obviously than elsewhere, continuous with the skin lin- ing the meatus. The membrana tympani is not flat, like the parchment of a drum, but slightly conical, with the apex toward the tympanum. This shape seems given to it by the handle of the malleus, which draws the membrane a little inward. The handle of the bone can be seen in the living subject, like a thin white streak, which is not quite vertical, but inclines slightly backward. Many times a hole exists in the upper part of the membrane, even in cases where there is no obvious defect of hearing during life. This suffi- ciently explains why some persons who are not deaf can blow the smoke of tobacco through the ear as well as through the nose. Structure of the Membrana Tympani. Thin as it is, the mem- brana tympani is very strong. It has three strata: an outer stratum of cuticle; a middle, fibrous, on which its strength chiefly depends; and an internal, mucous. (Plate LX. Fig. 3.) The middle stratum is composed of fibres radiating and circular, but no longer considered muscular. It is this coat which is fixed into the bony groove, and contains in its very substance the handle of the malleus. The dermal stratum is composed of an extremely thin layer of the true skin, continuous with that lining the meatus auditorius externus. The mucous lining is continuous with the lining of the tympanum. The membrane is well supplied with blood by arteries derived from the stylo-mastoid and the tympanic branch of the internal maxillary. Tympanum, or Middle Ear. We need not repeat what has been said already about the tympanum, but pass on to examine what is to be seen on its several aspects, namely: its external aspect, its internal, its anterior and posterior, its superior and its inferior. External Aspect. On the outer aspect of the tympanum there 17 258 HUMAN OSTEOLOGY. is the bottom of the meatus auditorius, closed by the membrana tympani. Internal Aspect. On the inner aspect of the tympanum (Plate 'LVIII. Fig. 2) are seen 1. The fenestra ovalis leading to the vestibule: this is open in the dry bone, but closed in the recent state by the base of the stapes which is held to the margins of the fenestra by ligamentous fibres. The fenestra ovalis looks outward toward the membrana tympani. 2. The fenestra rotunda: this, in the recent state, is also closed by mem- brane (membrana tympani secundaria); in the dry bone it leads to the tympanic scale of the cochlea, and also into the vestibule; but the fenes- tra does not communicate with the vestibule in the perfect state. The fenestra rotunda looks almost directly backward. 3. The promontory: this is formed by the bulging of the first turn of the cochlea; its surface is marked by grooves for the ramifications of Jacobson's nerve. Anterior Aspect. On the anterior aspect of the tympanum, we have 1. The bony canal for the ' tensor tympani ' (in the drawing, this canal is cut open). Just before its termination in front of the fenestra ovalis, the canal makes a sudden curve outward, in order to form a little pulley for the tendon of the muscle within. In most bones this part of the canal is broken, and has the appearance of a little spoon; for this reason, it is called the 'processuscochleariformis.' 2. The Eustachian tube. 3. The orifice of the Glaserian fissure which transmits the ' laxator tympani ' and the chorda tympani nerve. In about five specimens out of six, the chorda tympani runs through a little canal, close to, and a little above the Glaserian fissure; but this ' canal of Huguier,' as it has been termed, is of no practical moment, and hardly deserves a new name. Posterior Aspect. On the posterior aspect of the tympanum, are 1. The opening into the mastoid cells. 2. The pyramid a small pro- jection containing a canal, about the size of a bristle, which lodges the ' stapedius muscle/ At the base of the pyramid (but within it) are two minute canals which transmit, the one an artery, the other a nerve, to the stapedius. The pyramid is always supported by a minute bony column, which extends like a flying buttress from its apex to the promon- tory. 3. The foramen chordae, 'iter chordae postering.' This minute foramen is a little below the level of the pyramid, and close to the groove for the attachment of the membrana tympani. Introduce a bristle into it, and you find that it leads into the ' aqueductus Fallopii.' It transmits the chorda tympani nerve. This nerve is a branch of the facial (which, THE ANATOMY OF THE EAR. 259 remember, is contained in the ' aqueductus Fallopii ' : see Plate LX. Fig. 4). It comes up through the foramen chordae, runs, not across the tym- panum, but across the membrana tympani, outside the mucous membrane, between the handle of the malleus and the long process of the incus; it leaves the membrane through the Glaseriun fissure (or through a distinct canal) and, joining the gustatory, eventually goes to the submaxillary ganglion. Superior Aspect. On the superior aspect of the tympanum is a thin plate of bone which separates the cavity of the tympanum from that of the cranium. This is an important relation. For it shows how readily inflammation might spread from the tympanum to the base of the brain. Inferior Aspect. The inferior aspect, or floor of the tympanum, is formed by the jugular fossa, which lodges the jugular vein. A little in front of this fossa is the canal for the carotid artery, which is sepa- rated from the tympanum only by a thin scale of bone. The vicinity of these great vessels explains the sudden and profuse haemorrhage which sometimes, though rarely, occurs from the ear when diseased. Professor Porter speaks of blood gushing from the ear with a rapidity such as he never witnessed in a surgical operation. 10T Ulceration had extended into the carotid artery. In another case of sudden and profuse bleeding from the ear, Mr. Syme tied the carotid artery. 108 The patient died. He however tied the carotid in another similar case in which the patient recovered. Dissec- tion discovered that the blood came from the lateral sinus, near the jugu- lar fossa, the thin bony septum between that fossa and the tympanum having been destroyed by ulceration. Looking at the proximity of these large vessels, there is|^o wonder that bleeding from the ear, after injury to the head, makes one suspect the existence of a fracture through the tympanum. In the floor of the tympanum there are a number of minute holes, among which especially note one, the upper opening of the canal for Jacobson's nerve. The lower opening of the canal is at the base of the skull, on the little crest of bone which separates the jugular fossa from the carotid canal. The nerve in question is a branch of the glosso-pharyngeal. It enters the tympanum, and ramifies upon the promontory, forming '<" Graves's ' Clinical Medicine.' vol. i. 108 'Edinburgh Monthly Journal, ' No. III.; ' Edinb. Med. and Surg. Journal,' No. CXV. p. 319. 260 HUMAN OSTEOLOGY. what is called the ' tympanic plexus.' It supplies the mucous membrane of the tympanum. Its principal branches are generally indicated by grooves made for their passage on the promontory. In a preparation where there appeared to be neither groove nor nerve, the nerve was subsequently found lodged in a complete bony canal within the pro- montory. Aqueductus Fallopii. The ' aqueductus Fallopii/ or canal for the facial nerve, which supplies all the muscles of expression of the face (Plate LIX. Fig. 1.), commences at the bottom of the meatus auditorius internus; it runs for a short distance outward, then turns horizontally back- ward along the inner wall of the tympanum, just above the fenestra ovalis, and, lastly, descending behind the tympanum, emerges at the stylo-mas- toid foramen. Its course suggests how liable the nerve is to be injured in fracture through the temporal bone, or in disease of the ear. While in this canal the nerve sends off three important branches, all to ganglia. These are shown in Plate LX. Fig. 4. The first branch, the greater petrosal, or Vidian, runs down the hiatus Fallopii to the spheno-palatine ganglion; the second, or lesser petrosal, goes to the otic ganglion; the third, or chorda tympani, runs with the gustatory nerve to the submaxil- lary ganglion. Two less important nerves are also given off from the facial in the aqueductus Fallopii, namely, the external petrosal which communicates with the sympathetic on the middle meningeal artery, and the nerve to the stapedius muscle. The objects seen on the inner wall of the tympanum may be better understood in the following tabular form: - 21 Mastoid cells. / r^T^Pyi C anal for tens r tympani. \ , Pyramid for stapedius. / v^v-n } Eustachian tube. Foramen chord^T / ; ^^Jft^-.-J Glaserian fissure. Little Bones in the Tympanum. The three little bones in the tympanum are drawn larger than natural, but in their proper relative position, Plate LIX. Figs. 2, 3, 4, and 5. In Fig. 3, you are supposed to be looking at them from the meatus auditorius; in Fig. 2, from the PLATE LIX. s 1? all op ii Hiafcns'Fallopn Groove for JseobsonsUerve, Carotid canal. Incus, TfoiHeu?. 3"hort process. ../.Stapes. $tapes ' Outline of V'-. ./ "Handle. Inner view, Mem:tympani.J *. '' Base THE ANATOMY OF THE EAR. 261 inside of the tympanum. The dotted line in each figure is intended to represent the outline of the membrana tympani. Malleus. The malleus or hammer presents a head, a neck, and a handle (manubrium). The ' head ' is the large round part above the mem- brana tympani. It articulates posteriorly with the incus by means of a concavo-convex joint, crusted with cartilage and provided with a synovial membrane. The ' neck ' is the narrow portion between the head and the handle. From the front of the neck springs the ' long process ' or ' pro- cessus gracilis ' which runs down the Glaserian fissure and gives insertion to the ' laxator tympani/ In infants this ' processus gracilis' may be re- moved whole, together with the rest of the malleus; but, in the adult, it is adherent to the temporal bone and cannot be extracted entire. The handle or ' manubrium ' descends nearly perpendicularly from the neck. Near the root of the handle is a little projection called the ' short process,' which presses against the upper part of the membrana tympani. The handle itself terminates in a slightly flattened, outwardly curved extremity, a little below the centre of the membrane. On the inner side of ihe handle and below the processus gracilis, is inserted the ' tensor tympani.' Right or Left ? This bone will be in the same position as the cor- responding one in the student's body, if he hold the articular surface backward, the handle downward, and the processus brevis outward. Incus. The incus, or anvil, lies behind the malleus. It has a body, a short, and a long process. The body is convex, placed above and behind the membrana tympani, and has a concavo-convex surface which articulates with the head of the malleus. The ' short process ' extends horizontally backward into the mastoid cells, and is fixed there by a liga- ment. The 'long process' descends nearly vertically, parallel to the handle of the malleus, and, like it, is a little convex outwardly. Toward the extremity it suddenly turns up and supports, on a narrow pedicle, the orbicular process formerly termed ' os orbiculare ' (Fig. 5). Right or Left ? This bone will be in the same position as the cor- responding one in the student's body, if he hold the short process back- ward, the long process downward and inward. Os Orbiculare. The little ' os orbiculare,' considered by some as a separate bone, is always anchylosed in the adult to the long process of the incus; but it is connected with the stapes by a very distinct joint. The Stapes. The stapes, or stirrup, is placed horizontally, with the base in the fenestra ovalis. It has a head, a neck, two ' crura ' or 262 HUMAN OSTEOLOGY. branches, and a base or foot-plate. The head articulates by a concave surface with the orbicular process of the incus. The neck gives attach- ment behind to the 'stapedius.' (Plate LX. Fig. 2.) The anterior branch of the stirrup is shorter and less curved than the posterior; both are grooved on their concave sides, and the interval is closed by a mem- brane. It has been stated that the groove in the cms forms half an Haver- sian canal, lodging a small vessel. 10 ' The ' base ' is similar in form to the fenestra ovalis, which it nearly fills, and their margins are united by an annular ligament. The lower border of the base is straighter than the upper, and its anterior extremity is the sharpest. Right or Left ? This bone will be in the same position as the corresponding one in the student's tympanum, if he hold the base inward, its straighter side downward, and the shorter limb forward. Ossification. All the bones in the tympanum are ossified and well developed at birth. The ear-bones of a new-born infant and those of the giant O'Brien, seven feet seven inches high, are very nearly the same size. Of the four bones, the stapes is the most essential to hearing. Disease may destroy the others, and still the patient may hear: but when the stapes falls out, the fluid in the vestibule escapes, and inevitable deafness results. Little Muscles moving the Bones in the Tympanum. There are two well-marked muscles with distinct tendons attached to the bones in the tympanum, namely, the tensor tympani and the stapedius. (Plate LX. Figs. 1, 2.) The ' laxator tympani ' is still described as a muscle by some anatomists, though its muscular structure is doubted by many. Tensor Tympani. The ' tensor tympani ' is a well-marked muscle. It arises from the apex of the petrous bone, and from the cartilage of the Eustachian tube, and is inserted into the handle of the malleus, just be- low the processus gracilis. The muscle is lodged in the bony canal running above and parallel with the Eustachian tube; and when its tendon reaches the end of the canal, which forms an elbow, it is reflected at a right angle to reach its insertion. From origin to insertion the muscle is enclosed in a strong fibrous sheath. The tendon slides within the sheath, and has asynovial membrane. Laxator Tympani. The ' laxator tympani ' arises from the spine of the sphenoid bone, runs up the Glaserian fissure, and is inserted into the processus gracilis of the malleus. Like the last muscle, it is sur- 109 ' Beitrage zur Anatomic des Steigbilgels, ' Archiv ftir Ohrenheilkunde, vol. v. Eysell. Laxator t\ ..Semicircular canals . .Malleus icus ..Cochlea.. ;?lfc^r t v mp an^^-^taaKkn tube. .Kalleus. .Te nsor tytnpaovi Cut'icularlav? LaxaboriympaTii .Greater petrosal orVidian nerve, ' .Lesser petrosal nerve J [ nerve. L.5pheno -palatine oan^lion- THE ANATOMY OF THE EAR. 263 rounded by a sheath. Whilst there is no doubt whatever about the mus- cularity of the ' tensor tympani/ many modern anatomists believe the ' laxator tympani ' to be a ligament. Stapedius. The ' stapedius ' arises in the canal of the pyramid. Its little tendon, coming oat of the canal at the apex, is reflected outward, and inserted into the posterior part of the neck of the stapes. Anato- mists are not agreed about the precise use of the stapedius. One of its actions would appear to be to tilt the steps backward, and thus diminish the pressure upon the fluid in the vestibule. The internal ear or labyrinth, comprising the vestibule, semicircular canals, and cochlea, should now be examined. And first of the vestibule, entered through the 'fenestra ovalis.' Vestibule. The vestibule is of an ovoid form, measuring about ^th of an inch in its long diameter, and rather less in its short. Posteriorly it receives the five openings of the semicircular canals and the opening of the ' aqueductus vestibuli '; anteriorly, and at its lower part, is the open- On the inner j Fovea hemispherica for saccule wall. I Fovea hemielliptica for utricle Superior semicircular canal External semicircular canal Aqueductus vestibuli. Posterior semicircular canal ( Fenestra ovalis Outer wall.-( Opening of vestibular scale of cochlea ( Opening of tympanic scale of cochlea FIG. 84. Diagram of the Right Vestibule, and the Openings into it. ing into the vestibular scale of the cochlea; on its external wall is the ' fenestra ovalis.' In all, then, there are eight openings into the vestibule. The internal wall of the vestibule corresponds with a part of the bottom of the ' meatus auditorius internus.' On this inner wall, as shown in Plate LXI. Fig. 3, are two slight depressions separated by a bony ridge. The upper is called the ' fovea hemielliptica/ and lodges the utricle; the lower, or 'fovea hemispherica/ lodges the saccule. The ridge dividing these 'foveae' is known as the 'crista vestibuli.' The utricle and the saccule, as will be seen, are distinct parts of the membranous labyrinth. The fovese, as well as the crista vestibuli, are riddled with minute fo- ramina, only visible with a lens, through which the filaments of the audi- tory nerve enter the vestibule. The vestibule and its eight openings are represented in the annexed diagram, Fig. 84. 264 HUMAN OSTEOLOGY. Semicircular Canals. The three semicircular canals are called, according to their position, the ' superior/ the * posterior ' (both vertical) and the 'external' (horizontal). The superior canal crosses the petrous bone at right angles, and stands out in relief on its anterior surface. Its ' ampulla ' is at the outer orifice. The posterior canal is the longest of the three. It runs parallel with the posterior surface of the petrous bone, and makes a little relief just above the aqueductus vestibuli. Its ' am- pulla' is at the lower orifice; its upper orifice joins the narrow end of the superior canal. The external canal is the smallest of the three; it lies horizontally in the petrous bone behind the superior and external to the posterior canal; its convexity is directed backward. Its ampulla is at its outer orifice. Cochlea. The cochlea is so placed that its base is at the bottom of the meatus auditorius internus, where it receives filaments from the audi- tory nerve. Its apex is directed forward and outward close to the canal for the tensor tympani. It makes two turns and a half, which run from left to right in the right ear, and from right to left in the left, round the central axis termed the ' modiolus.' Its first turn, bulging into the tym- panum, makes the 'promontory.' The outer wall of the coil is composed of a lamella of very hard bone, like the semicircular canals: the inner wall is also formed of compact bone, but the interior of the ' modiolus ' is spongy. The last half-turn presents peculiarities, and the best way to examine them is to remove the ' cupola ' or rounded apex of the cochlea, as seen in Plate LXI. Fig. 4. The last turn forms a kind of half -funnel (infundib- ulum). Into the apex of this funnel, which is continuous with the modi- olus, there opens a canal which runs through the centre of the modiolus. Round the free border of the half-funnel projects the hook-like termi- nation (hamulus) of the lamina spiralis. All this is seen only in the dry bone. In the recent state there would be simply the aperture of com- munication (helicotrema), between the two scales of the cochlea. The tympanic scale runs on that side of the lamina spiralis which looks toward the base of the cochlea. Near the beginning of that scale is the minute termination of the aqueductus cochleae. (Plate LXI. Fig. 3.) Bony Lamina Spiralis. The bony lamina spiralis, the only por- tion of the most essential part of the cochlea which can be seen in the dry bone, is shown in Fig. 85. It commences at the lower part of the vestibule immediately above the fenestra rotunda. (Plate LXI. Fig. 3.) From this, which is its broadest part, it gradually diminishes in breadth Postf Semicircular canals ' r r ' ,. ; ! .Aqueductus "Fallopii .CocHlea. 'Canal for Carotid artery. 'Tenestra. ovalis. Fenestrst rotunda. FoVealiemiellipticaL., "Fov e a. "K eyy> Vsioh erica. '-' ' Fenest-a rotunda ^^SSS^^P" ''vAqueoluctus vesfciliuli LamiTiaj ,5ernicircu1ar canals and CocMea cut open. Vestibule opened te s>iew its inner wall . ntre of modiol^s.i^ijj HaTnuiug of Lamina sp.ir&Ti9. Apex of Cochlea, THE ANATOMY OF THE EAR. 265 as it winds round the axis into the apex of the cochlea, never reaching more than half across the tube, and it finally terminates as a little hook (hamulus) in the funnel of the last coil. On the concave side of this hook is situated (in the recent state) the helicotrema or aperture of com- munication between the two scales. Examined with a lens, both surfaces of the lamina spiralis will be seen to be furrowed by canals which give passage to the nerves before they reach the membranous part of the sep- tum. It is composed of two very delicate and brittle plates which sepa- rate from each other at the axis. In the tympanic scale are seen the ori- fices of the canals just alluded to; they are separated by little columns of Cupola - Hook of lamina spiralis Inf undibulum Lamina spiralis Vestibular scale Lamina spiralis Tympanic scale Meatus auditorius interims FIG. 85. bone which give rise to a fluted appearance, as shown in Fig. 85. These columns themselves are made up of bundles of little tubes, enclosing the filaments of the auditory nerve. Modiolus. The axis (modiolus) of the cochlea is conical. The base is at the bottom of the mcatus internus; the apex does not extend beyond the second turn of the cochlea, and joins the funnel formed by the last coil. The axis is composed of brittle and porous bone, and its interior is traversed by numerous canals which transmit the cochlear nerves to the lamina spiralis, Fig. 86. One canal (canalis centralis modioli), larger than the rest, runs through the centre of the axis, and opens on its sum- mit that is, at the apex of the funnel. It transmits a nerve to the last half turn of the lamina spiralis. The Meatus Internus. The meatus auditorius internus is situated on the posterior surface of the petrous bone. Its direction is nearly hori- zontally outward; its length, about three-eighths of an inch. Its diameter varies a little in different bones, but is always larger than that of the nerves which it transmits. The interval between the nerves and their bony canal is occupied by 266 HUMAN OSTEOLOGY. the cerebro-spinal fluid. In fractures through the base of the skull, in- volving the meatus, this fluid sometimes oozes out through the external ear. Whenever you observe this after an injury to the head, the case must be regarded as very grave. In thirteen cases of injury to the head admitted into St. Bartholomew's Hospital, blood or watery fluid flowed from the ear. Of these thirteen, six died, and in all six the corresponding Vestibular scale ? . . . Lamina spiralis .... Tympanic scale .... Cochlear nerve petrous bone was found fractured. In the seven cases that recovered, five had bleeding from the ear, and two only had a discharge of fluid. So that, although a watery discharge be a very unfavorable symptom, it is not necessarily a fatal one. By cutting away the greater part of the meatus, as in Fig. 87, the bot- tom of it is found to be divided by a crest of bone into two compartments tus Fallopii. ^ for the nerves to the utricle, the superior and external semicir- r canals. Crest of bone. Openings for the nerve to the saccule. ^Opening of a canal which transmits the nerve of the posterior semicir- cular canal. cribrosa, through which the nerves pass to the cochlea. / X Fio. 87. Foramina at the Bottom of the Right Meatus Auditorius Internus. of unequal size, an upper and a lower. In the upper and smaller one, there are two openings, of which the anterior is the aqueductus Fallopii (transmitting the facial nerve); the posterior, when examined with a lens, presents a number of minute foramina which transmit the divisions of the vestibular nerves which supply the utricle, the superior and the ex- ternal semicircular canals. THE ANATOMY OF THE EAR. 2G7 In the lower and larger depression, we observe the base of the axis of the cochlea, termed ' lamina cribrosa/ because it has a double row of fo- ramina arranged spirally, as shown in the figure. Now take any one of these foramina, which appear scarcely larger than the point of a pin, magnify it with a lens, and you find that it becomes a fossa pierced by holes varying in number from three to seven. So fine are the canals which transmit the filaments of the cochlear nerve! In the centre of the lamina is the orifice of the central canal of the axis, which is the largest of all. Behind the lamina are two (sometimes three) openings leading to minute perforations which transmit the nerve to the 'saccule/ Lastly, on the posterior wall of the meatus is the orifice of a very constant canal (represented by the dotted outline) which gives passage to the ves- tibular nerve of the posterior semicircular canal. Ampulla of superior semicircular canal. Ampulla of external semicircular canal Utricle . Saccule. Ampulla of posterior semicircular canal FIG. 88. Membranous Labyrinth and Nerves of the Left Ear. Membranous Labyrinth. The membranous labyrinth comprises the two little bladders, termed the * utricle ' and the * saccule/ in the ves- tibule, and the membranous semicircular canals together with part of the cochlea. It floats in the perilymph, and contains the endolymph. It is partly represented in Fig. 88. Utricle. The utricle occupies the upper half of the vestibule. It is very difficult to make a good display of it. The best way to examine it, is to remove very carefully the roof of the vestibule and that of the supe- rior semicircular canal, and then to put the preparation into water. All the membranous semicircular canals open into it. It floats free in the perilymph except at its fossa, the ' fovea hemielliptica/ where it is retained against the sieve-like plate of bone through which the utricular nerves enter. The utricle sends a slender canal down the aqueductus vestibuli, which ends in a blind extremity outside that aqueduct at the back of the petrous part of the temporal bone. This canal is joined, close to its 268 HUMAN" OSTEOLOGY. origin, by another from the saccule. Thus the utricle and saccule do communicate, though indirectly. Saccule. The saccule is smaller than the utricle and situated below it, close to its appropriate fossa, the ' fovea hemispherical It is attached to this fossa by the saccular nerve in the same way as the utricle is attached by nerve filaments to the fovea hemielliptica. The saccule is connected with the membranous canal of the cochlea by a small duct, the ' canalis uniens/ The utricle communicates with the saccule in the indirect manner just described. Hence the different parts of the membranous labyrinth communicate throughout, like the same parts in the bony labyrinth. Otoliths. On the inner wall of the utricle and saccule, at the spot where the nerves spread out upon them, is a small mass of crystals of carbonate of lime. The two masses are the 'otoconia' or 'otoliths/ and are homologues of the large white ' ear-stones ' seen in the cod and whit- ing, and found in most of the osseous fishes. 110 Membranous Semicircular Canals. The membranous semicir- cular canals, except at their ampullae, fill only about one-third the space of the bony canals; the remainder is occupied by the perilymph. The nerve destined to each membranous ampulla spreads out only on that surface of the ampulla which is toward the convexity of the rest of the canal. The nerve does not advance beyond the ampulla, but ramifies on a crescent-shaped septum (septum transversum) which projects into the interior. Membranous Cochlea. The membranous cochlea forms a third scale, the ' scala media ' or ' canalis ' or ' ductus cochlearis ' (Fig. 89), separating the scala vestibuli from the scala tympani. Its floor is at- tached to the margin of the bony lamina spiralis (L. Sp. 0. V., L. Sp. O. T.) and reaches across to the outer wall of the cochlea, to which it is attached by a process of periosteum, the 'ligamentum spirale' (L. Sp.). This floor is named ' membrana basilaris/ or ' membranous lamina spiralis.' The roof is a very delicate membranous lamina, the ' membrane of Reissner'; it is turned toward the vestibular scale. Hence the 'scala 110 For details concerning the minute structure of the vestibule and the connec- tion of the otoliths with certain hair-like bodies belonging to the nerve-filaments, see Dr. Urban Pritchard's paper on ' The Termination of the Nerves in the Vestibule and Semicircular Canals of Mammals. ' ' Quarterly Journal of Microscopic Science, ' October 1876. THE ANATOMY OF THE EAR. 269 media ' is bounded by the ' membrana basilaris/ ' the membrane of Riess- ner ' ; and the segment of the outer wall of the cochlea included between the outer attachments of these two membranes. This ' canalis cochlearis ' communicates at one end with the saccule by the ' canalis uniens,' so that the endolymph is continuous in both those cavities; at the other end, toward the apex of the cochlea, it terminates in a blind extremity fixed to the wall of the cupola, partly bounding the helicotrema* FIG. 89. Vertical Section of the First Turn of the Cochlea, showing the Membranous Cochlea and the Position of the Organ of Corti. After Waldeyer and Quain. Organ of Corti. In this ' canalis cochlearis/ resting on the ' mem- brana basilaris/ are two rows of cells (Fig. 89 O.C.), an outer and an inner, leaning toward each other, so that there is a tunnel (T.C.) formed between them. They are covered, but only partially, by a membrane (membrana tectoria) attached to the edge of the bony lamina spiralis. Their singular characters and very complicated appendages are subjects too minute to be described here. 111 111 Corti's ori