THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA PRESENTED BY PROF. CHARLES A. KOFOID AND MRS. PRUDENCE W. KOFOID ANATOMICAL MEMOIES OF THE LATE JOHN GOODSIR THE ANATOMICAL MEMOIES OF JOHN GOODSIE F.K.S. LATE PROFESSOR OF ANATOMY IN THE UNIVERSITY OF EDINBURGH EDITED BY WILLIAM TUENEE, M.B. PROFESSOR OF ANATOMY IN THE UNIVERSITY OF EDINBURGH WITH A BIOGRAPHICAL MEMOIR BY HENEY LONSDALE, M.D. FORMERLY LECTURER ON ANATOMY VOL. II. EDINBURGH ADAM AND CHARLES BLACK 1868 Printed by R. CLARK, Edinburgh. l\ \J( I CONTENTS OF VOL. II. DIVISION I. PAGE I. ON THE ORIGIN AND DEVELOPMENT OF THE PULPS AND SACS OF THE HUMAN TEETH . . 1 (Edinburgh Medical and Surgical Journal, Jan. 1839.) II. ON THE FOLLICULAR STAGE OF DENTITION IN THE RUMINANTS, WITH SOME EEMARKS ON THAT PRO- CESS IN THE OTHER ORDERS OF MAMMALIA . 53 (Transactions of British Association for Advancement of Science, August 1839.) III. ON THE MODE IN WHICH MUSKET - BULLETS AND OTHER FOREIGN BODIES BECOME INCLOSED IN THE IVORY OF THE TUSKS OF THE ELEPHANT . 56 (Transactions of Royal Society of Edinburgh, January 18, 1841.) IV. ON THE SUPRA -RENAL, THYMUS, AND THYROID BODIES ...... 66 (Philosophical Transactions, January 22, 1846.) V. ON THE MORPHOLOGICAL RELATIONS OF THE NER- VOUS SYSTEM IN THE ANNULOSE AND VERTEBRATE TYPES OF ORGANISATION . . . .78 (Edinburgh Philosophical Journal, January 1857.) VI. ON THE MORPHOLOGICAL CONSTITUTION OF THE SKELETON OF THE VERTEBRATE HEAD . . 88 (Edinburgh Philosophical Journal, January 1857.) VII. ON THE MORPHOLOGICAL CONSTITUTION OF LIMBS . 198 (Edinburgh Philosophical Journal, January 1857.) M370133 VI CONTENTS. DIVISION II. PAGE VIII. ON THE EMPLOYMENT OP MATHEMATICAL MODES OP INVESTIGATION IN THE DETERMINATION OF ORGANIC FORMS ..... 205 (Daily Mail, July and August 1849.) IX. ON THE HORIZONTAL CURVATURE OF THE INTERNAL FEMORAL CONDYLE; ON THE MOVEMENTS AND RELATIONS OF THE PATELLA, SEMILUNAR CARTI- LAGES, AND SYNOVIAL PADS OF THE HUMAN KNEE-JOINT . . . . . 220 (Edinburgh Medical Journal, July 1855.) X. ON THE MECHANISM OP THE KNEE-JOINT . . 231 (Abstract in Proceedings of Royal Society, Edinburgh, January 18, 1858.) XI. ON THE CURVATURES AND MOVEMENTS OF THE ACTING FACETS OP ARTICULAR SURFACES . 246 XII. LECTURE ON THE RETINA . . . .265 (Edinburgh Medical Journal, October 1855.) XIII. ON THE MODE IN WHICH LIGHT ACTS ON THE ULTI- MATE NERVOUS STRUCTURES OF THE EYE, AND ON THE RELATIONS BETWEEN SIMPLE AND COM- POUND EYES ..... 273 (Proceedings of Royal Society, Edinburgh, April 6, 1857.) XIV. LECTURE ON THE LAMINA SPIRALIS OF THE COCHLEA 282 (Edinburgh Medical Journal, December 1855,) XV. ON THE ELECTRICAL APPARATUS IN TORPEDO, GYM- NOTUS, MALAPTERURUS, AND RAIA . . 289 (Edinburgh Medical Journal, August and September 1855.) XVI. A BRIEF REVIEW OF THE PRESENT STATE OF OR- GANIC ELECTRICITY ..... 306 (Edinburgh Philosophical Journal, October 1855.) CONTENTS. VU PAGE XVII. ON THE CONFERVA WHICH VEGETATES ON THE SKIN OP THE GOLD-FlSH ..... 345 (Annals and Magazine of Natural History, IX., 1842.) XVIII. HISTORY OF A CASE IN WHICH A FLUID PERIODI- CALLY EJECTED FROM THE STOMACH CONTAINED VEGETABLE ORGANISMS OF AN UNDESCRIBED FORM (SARCINA VENTRICULI) . ' . . . 351 (Edinburgh Medical and Surgical Journal, LVIL, 1842.) XIX. ON A DISEASED CONDITION OF THE INTESTINAL GLANDS ...... 372 (Edinburgh Monthly Journal of Medical Science, April 1842.) XX. STRUCTURE AND PATHOLOGY OF KIDNEY AND LIVER 379 (London and Edinburgh Monthly Medical Journal, May 1842.) Anatomical and Pathological Observations. Edin. 1845. XXI. CENTRES OF NUTRITION .... 389 XXII. THE STRUCTURE AND FUNCTIONS OF THE INTES- TINAL VILLI ..... 393 XXIII. ABSORPTION, ULCERATION, AND THE STRUCTURES ENGAGED IN THESE PROCESSES . . . 403 XXIV. THE PROCESS OF ULCERATION IN ARTICULAR CAR- TILAGES ...... 408 XXV. SECRETING STRUCTURES . . . .412 XXVI. THE TESTIS AND ITS SECRETION IN THE DECAPO- DOUS CRUSTACEANS . . . .429 XXVII. THE STRUCTURE OF THE SEROUS MEMBRANES 430 Vlil CONTENTS. PAGE XXVIII. STRUCTURE OF THE LYMPHATIC GLANDS . . 439 XXIX. THE STRUCTURE OF THE HUMAN PLACENTA . 445 XXX. THE STRUCTURE AND ECONOMY OF BONE . 461 XXXI. THE MODE OF REPRODUCTION AFTER DEATH OF THE SHAFT OF A LONG BONE . . . . 465 XXXII. THE MODE OF REPRODUCTION OF LOST PARTS IN THE CRUSTACEA . . . . .471 XXXIII. OF THE ANATOMY AND DEVELOPMENT OF THE CYSTIC ENTOZOA . ... 476 XXXIV. DESCRIPTION OF AN ERECTILE TUMOUR . 504 (Monthly Medical Journal, 1845.) XXXV. DESCRIPTION OF A CONGENITAL TUMOUR OF THE TESTIS ...... 506 (Northern Journal -of Medicine, 1845.) XXXVI. THE CURVATURES OF THE ARTICULAR SURFACES AND THE GENERAL MECHANISM OF THE HIP- JOINT 508 EXPLANATION OF THE PLATES. DEVELOPMENT OF THE TEETH. PLATE I. page 1. a. Fig. 1. A tooth-germ a bulging on a mucous membrane. b. Diagrams illustrating the three stages of dentition. Fig. 1. Follicular. 2. Saccular. 3. Eruptive stage. c. Diagrams illustrative of the formation of a temporary and its corresponding permanent tooth from a mucous membrane. Fig. 1. Mucous membrane. Fig. 2. Mucous membrane, with a gra- nular mass deposited in it. Fig. 3. A furrow or groove on the granular mass. (Primitive dental groove.) Fig. 4. A papilla (a tooth germ) on the floor of the groove. Fig. 5. The papilla enclosed in a follicle in the bottom of the groove (the latter in the condition of a secondary dental groove). Fig. 6. The papilla acquiring the configuration of a pulp, and its sac acquiring opercula. The depression for the cavity of re- serve behind the inner operculum. Fig. 7. The papilla become a pulp, and the follicle a sac, in conse- quence of the adhesion of the opercular lips. The second- ary dental groove in the act of closing. Fig. 8. The secondary groove adherent, except behind the inner operculum, where it has left a shut cavity of reserve for the formation of the pulp and sac of the permanent tooth. Fig. 9. The last change rendered more complete by the deposition of the granular body (the enamel organ of Hunter, Purkinje, and Raschkow). Deposition of tooth substance commencing. Fig. 10. The cavity of reserve receding from the surface of the gum, and dilating it at its distal extremity, in which a pulp is forming. Kudimentary opercula developing near its proximal extremity and dividing it into a follicular and an extra-folli- cular compartment. Temporary tooth pulp nearly covered with tooth substance, and granular body almost absorbed. Fig. 11. The cavity of reserve become a sac with a pulp, and further removed from the surface of the gum. Temporary tooth pulp covered with tooth substance, and granular body absorbed. (See Hunter, Nat. Hist, of Human Teeth, p. 95.) Fig. 12. The temporary tooth acquiring its fang by the triple b X EXPLANATION OF THE PLATES. action described in the paper, and its sac approaching the surface of the gum. Fig. 1 3. The fang of the temporary tooth longer, and its sac touching the mucous membrane of the mouth. Fig. 14. The temporary tooth sac again a follicle ; free portion of the latter becoming shorter, and fang of the tooth receding from the bottom of its socket. Permanent tooth sac re- moving further from the surface of the gum. Fig. 15. The temporary tooth completed. Free portion of the sac be- come the vascular border of the gum ; adherent portion become what is commonly denominated the periosteum of the fang, but which in fact is a triplex membrane viz. mucous membrane, submucous tissue, and periosteum of al- veolus or jaw bone. The permanent tooth sac much re- moved from the gum, but connected with it by accord which passes through the foramen behind the temporary alveolus. Fig. 16. The fang of the permanent tooth lengthening, and the crown approaching the gum Fang of temporary tooth undergoing absorption. Fig. 17. The same change more advanced. Fig. 18. The permanent tooth appearing through the gum. Shedding of the temporary tooth. Fig. 19. The perfected permanent tooth. Fig. 20. The shed temporary tooth. d. Diagrams illustrative of the formation of the thrae molar teeth from the non-adherent portion of the primitive dental groove. Fig. 1 . The non-adherent portion of the primitive dental groove. Fig. 2. The papilla and follicle of the first molar on the floor of the non-adherent portion, which is now a portion of the secondary groove. Fig. 3. The papilla and follicle of the first molar become a pulp and sac. The lips of the secondary grove adhering, so that the latter has become the posterior or great cavity of reserve. Fig. 4. The sac of the first molar increased in size, and advanced along a curved path into the substance of the coronoid process or maxillary tuberosity. The cavity of reserve lengthened out or advanced along with it. Fig. 5. The sac of the first molar returned by the same path to its former position. The cavity of reserve again shortened. Fig. 6. The cavity of reserve sending backwards the sac of the second molar. Fig. 7. The sac of the second molar advanced along a curved path into the coronoid process or maxillary tuberosity. The cavity of reserve lengthened for the second time. Fig. 8. The sac of the second molar returned to the level of the dental range. The cavity of reserve shortened for the second time. EXPLANATION OF THE PLATES. XI Fig. 9. The cavity of reserve sending off the pulp and sac of the wisdom tooth. Fig. 10. The sac of the wisdom tooth advanced along a curved line into the maxillary tuberosity or coronoid process. Fig. 11. The sac of the wisdom tooth returned to the extremity of the dental range. MUSKET-BULLETS IN TUSKS OF ELEPHANTS. PLATE II. page 56. Fig. 1. A portion of a section of a wounded tusk ; a cement ; 5 regular ivory deposited previous to the wound ; c irregular ivory deposited after the wound. Fig. 2. A diagram illustrative of the mode of connection between the Retzian tubes of the primary and secondary regular ivory, and the cells and Retzian tubes of the different inosculating systems of the irregular ivory, after inclosure of a ball ; a cement with its osseous corpuscles ; b primary regular ivory with its Retzian tubes ; c the ball ; d the irregular ivory with its systems of tubes and cells ; e secondary regular ivory Fig. 3. A copper ball inclosed in a sphere of irregular ivory, on the surface of which are the orifices of Haversian canals. Some of the orifices have closed, and present the appearance of irregular projections. The mass has begun to be attached to the regular ivory of the tusk,, and would in time have been inclosed in it. The ball must either have passed across from the opposite side of the tusk, or must have sunk below the level of the hole by which it entered. Fig. 4. Section of a tusk across the cavity of which a ball has passed, and become inclosed in the ivory of the wall opposite the hole by which it entered. The hole is filled with irregular ivory, coated externally with cement. The cement over the ball has been disarranged by the shock. This section proves that the track of a ball across the pulp is not necessarily ossified. Fig. 5. Section of a tusk across the base of which a spear-head has penetrated and remained in the wound. The weapon has therefore been separated from the pulp by deposition of irregular ivory in the form of a tube ; a cement ; b b ir- regular ivory deposited previous to the wound ; c c regular ivory deposited after the woimd ; d irregular ivory inclosing a vacant space e, the seat of an abscess or sinus, and con- tinuous with the cavity of /, a mass of irregular ivory (coated with regular ivory) in the form of a tube surrounding the foreign body. As irregular ivory always contracts in drying, more than any other kind of dental substance, that portion of the section marked g g has been bent outwards. Fig. 6. The same section viewed in profile ; a the broken shaft of the xii EXPLANATION OF THE PLATES. spear ; 6 an irregular mass of cement formed round the orifice of the wound by the membrane of the tusk follicle, and which would have closed the wound had the weapon been removed. The wound inflicted has in this instance, as in many others, stunted the growth of the tusk at c c, so as to render the part formed after the injury narrower and weaker. Fig. 7. A longitudinal section of a tusk in which a gun-shot wound had terminated in abscess of the pulp ; a a cement ; 6 6 regular ivory deposited before the injury ; c c regular ivory deposited after the injury ; d d irregular ivory bound- ing the abscess ; e e masses of cement and irregular ivory at the margin of the shot-hole. Fig. 8. The external aspect of a portion of a tusk, which had been transversely fractured ; a a the line of fracture united exter- nally by irregular masses of cement. Fig. 9. The internal aspect of the same portion of tusk ; a a the line of fracture united by irregular ivory, a portion of which is arranged in a reticular form. This reticular ivory is interest- ing, as affording a natural analysis of the peculiar arrange- ment of parts in the irregular ivory described in the paper. Each bar of the reticular ivory is traversed longitudinally by a medullary canal, from which radiate secondary canals and Retzian tubes, the whole being coated with regular ivory. This reticular ivory differs from the ordinary form of ossified pulp, only in the greater distance between the Haversian or medullary canals, so that portions of the pulp have remained unossified between them. DEVELOPMENT OF THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. PLATE III. page 66. Fig. 1. A portion of an early embryo of the sheep. a. Heart. I. Lungs still in front of the intestinal tube. c. Wolffian body. d. Lateral mass of blastema, out of which is formed the supra- renal capsule, thymus, and thyroid. e. Cardinal vein. /. Jugular vein. g. Ductus Cuvieri. Fig. 2. A portion of the early embryo of the sheep, a. Intestinal tube and ductus vitelli. 6. Liver. c. Omphalo-mesenteric vein. d. Omphalo-mesenteric artery. c, f. Mass of blastema on the inner side of the Wolffian body, and EXPLANATION OF THE PLATES. xiii around the trunks of the omphalo-mesenteric vessels ; this is the posterior part of the lateral mass of blastema marked d in Fig. 1, and becomes in the course of development the supra-renal capsule. Fig. 3. An early embryo of the sheep. a. Head, branchial arches, and rudiment of the eye. 6. Heart. c. Ductus Cuvieri entering the auricle, and receiving d. The jugular, and e. The cardinal vein. / The lateral blastema. g. Wolffian body. h. Umbilical cord, to which is passing i. The allantois. j. The omphalo-mesenteric artery, and k. Omphalo-mesenteric vein ; traces of the umbilical vessels are also seen in the parietes of the abdomen. I. The liver and intestinal tube. m. Lungs. Fig. 4. Jugular veins and lateral masses of blastema in the sheep, soon after the latter have joined across the middle line. a. The triangular absorption of the cervical portion, which is the first indication of the separation of the thyroid. Fig. 5. The next stage, in which the thyroid is more distinct. Fig. 6. The thyroid is now quite distinct, and differs from the thymus in being opaque ; the latter exhibits opaque spots in a semi- transparent matrix. Fig. 7. The thyroid and thymus have assumed their perfect form. Fig. 8. A portion of the supra-renal capsule of the adult green monkey, slightly compressed. It exhibits the minute nucleated par- ticles of which it consists. Among these, at pretty regular distances, are seen the germinal spots. Fig. 9. A portion of the thymus of the brown bear, slightly compressed. It exhibits the nucleated particles of which it consists. These are grouped in spherical masses around centres from which they appear to have derived their origin. Fig. 10. A portion of the thymus from a human foatus. It has been taken from the surface of the gland, so as to exhibit the areolar fibres which form its delicate capsule. The pressure of the glass plates has almost obliterated the spherical grouping in the cells. Fig. 11. A portion of the membrane which covered the contiguous sur- faces of the lobes of the thymus of a human foetus (the membrane lining the reservoirs of Sir A. Cooper). It has the same structure as in Fig. 10. It exhibits no germinal membrane, but consists of an areolar or fibrous texture inter- mixed with the cells of the organ, the fibres being more XIV EXPLANATION OF THE PLATES. fasciculated, and running a straighter course than in the substance of the organ. Fig. 1 2. A portion of the thyroid from a human foetus, slightly corn- pressed. It exhibits the same structure as the thyinus, but its fibrous texture is more developed. Fig. 13. A portion of the same thyroid to show its vascular network, in the meshes of which, as in Fig. 12, the cells are seen arranged in groups. CENTRES OF NUTRITION. PLATE IV. page 389. Fig. 1. A portion of the middle and internal membranes of a large encysted tumour situated under the tongue, and removed by Professor Syme. a. The middle or second membrane, which is a germinal membrane, consisting of flattened cells, the lines of junction of which are faintly visible, the nuclei remaining as the germinal spots of the membrane. b. The internal membrane, a layer of small cells, somewhat spherical, with slightly granular contents. The external membrane of the cyst, consisting of areolar and elastic fibres, contained the blood-vessels of the morbid growth. The cyst contained a soft mass resembling thick honey in consistence. The outer layer of this mass was white, and consisted of large, flat, transparent cells or scales, with few or no traces of nuclei. The larger internal part of the mass was reddish-grey, and consisted of ovoidal cells, resembling those of the external layer, except that they were turgid with a transparent oily-like fluid, and contained nuclei in various stages of development. Fig. 2, a. Fig. 3, a. Cells of the meliceritous mass those without nuclei being those of the white external layer, the others belonging to the reddish-grey part of the mass, presenting nuclei in various stages of development. b b. Some of the latter cells, in which the nuclei have become so much developed as to distend their cells beyond the average size. In these enlarged cells, it will be remarked that the nuclei, instead of remaining as single germinal spots for each cell, have broken up into numerous spots or centres of nutrition. In a tumour of this kind, the cyst and its contents are two distinct parts, and perform two distinct actions. The cyst is the active agent in withdrawing materials of nutrition for itself and its contents from the vessels which ramify in its outer tunic. The organs which accomplish this are the germinal spots in its middle tunic, which, in virtue of forces EXPLANATION OF THE PLATES. XV of attraction in each, select and remove from the capillary vessels the matter necessary for the formation of the cells of the internal layer. These after solution pass in succession into the cavity of the cyst, to serve as nutriment for the contained cellular mass. This mass is evidently the principal element of the morbid growth. The cyst is a subsidiary or accessory part, arranged for the protection and due supply of nourishment for its principal. The cells of which this mass consists have each its own nucleus or germinal centre. These cells would appear to be of two classes those whose nuclei produce young cells in their interior for their own nutrition, but not for the reproduction of new mother-cells, and those which act as reproductive individuals for the whole morbid growth. These latter cells are marked 6 6 in Figs. 2 and 3, and con- tain numerous nutritive centres or germinal spots in their interior. The flat cells of the white external layer appear to be those individuals of the first class, which are about to close their existence, their nuclei having disappeared ; their food, therefore, no longer supplied to them, and their position in the mass removed to the exterior by the eccentric development of the younger and more active neighbouring cells. In a morbid mass of this kind, as in the textures and organs of an animal generally, certain parts are set aside as reproducers, the remaining parts performing the functions of the whole mass, texture, or organ ; just as in certain com- munities of animals certain individuals are set aside to re- produce the swarm, the others are devoted to the duties of the hive. Fig. 4. Two portions of the primary or germinal membrane from the tubes of the tubular portion of the human kidney. The germinal spots of the gland are seen imbedded in the sub- stance of the membrane. The external layer of this mem" brane, which may occasionally be seen with the nuclei detached from it, is the basement or homogeneous membrane of Mr. Bowman. In other instances, as when the epithelia are but slightly developed, it becomes difficult to decide whether we have merely the germinal membrane, or both the membrane and its epithelia before us. INTESTINAL VILLL PLATE IV. page 389. Fig. 5. Extremity of a villus immediately before absorption of chyle has commenced. It has cast off its protective epithelium, and displays, when compressed, a network of peripheral lacteals. The granular germs of the absorbing vesicles, as yet undeveloped, are seen under its primary membrane. XVI EXPLANATION OF THE PLATES. Fig. 6. Extremity of a villus, with its absorbent vesicles distended with chyle, and the trunks of its lacteals seen through its coats. Fig. 7. Protective epithelium-cells from a villus in the dog.* Fig. 8. Protective epithelium-cells cast off preparatory to absorption of chyle ; instead of nuclei, they present, in their interior, groups of globules. Fig. 9. A group of the same cells adhering by their distal extremities. Fig. 10. Secreting cells thrown out of the follicles of Lieberkiilin during digestion. Fig. 11. Diagram of mucous membrane of jejunum when absorption is not going on. a. Protective epithelium of a villus. &. Secreting epithelium of a follicle, c c c. Primary membrane, with its germinal spots or nuclei, d d. e. Germs of absorbent vesicles, f. Vessels and lacteals of villus. Fig. 12. Diagram of mucous membrane during digestion and absorption of chyle, a. A villus, turgid, erect ; its protective epithelia cast off from its free extremity ;t its absorbent vesicles, its lacteals and blood-vessels turgid. 5. A follicle discharging its secreting epithelia. PROCESS OF ULCERATION IN ARTICULAR CARTILAGE. PLATE IV. page 389. Fig. 13. a. A section of articular cartilage and absorbent membrane. In the lower part of the section the cartilage - corpuscles retain their natural size and appearance ; as they approach the rugged ulcerated edge, they increase in size, and contain numerous young cells, apparently the progeny of their nuclei ; beyond this edge, rounded masses of cells, originally con- tained within the cartilage-corpuscles, are seen embedded in the cellular absorbent mass. I. Absorbent cells of the false membrane, with two globular masses derived from the cartilage-corpuscles. SECRETING STRUCTURES. PLATES IV. V. PLATE IV. page 389. Fig. 14. Four secreting cells from the ink-bag of Loligo sagittata. Fig. 1 5. Five cells from the liver of Patella vulgata. In this instance the bile is contained in the cavities of the secondary cells, which constitute the nucleus of the primary cell. * It may be noted that both in figures. 7 and 9 the clear space at the broad free ends of the columnar intestinal epithelial cells, to which several German anatomists have recently directed attention, is figured by the author. EDS. t The author subsequently abandoned the idea that the epithelial cells were cast off during absorption. EDS. EXPLANATION OF THE PLATES. XV 11 Fig. 16. Three cells from the kidney of Helix aspersa. The contained secretion is dead white, and presents a chalky appearance. Fig. 1 7. Two cells from the vesicles of the testicle of Squalus cornubicus. The contained bundles of spermatozoa are developed from the nucleus each spermatozoon being a spiral cell. PLATE V. page 412. Fig. 1. Five cells from the mamma of the bitch. In addition to their nuclei, these cells contain milk-globules. Fig. 2. A portion of duct from the testicle of Squalus cornubicus. A few nucleated cells, the primary or germinal cells of the future acini, are attached to its walls. Fig. 3. The primary cell of an acinus in a more advanced stage. The nucleus has produced a mass of young cells. The pedicle appears to have been formed by the germinal cell carrying forward the wall of the duct. A diaphragm accordingly presents itself across the neck of the pedicle. Fig. 4. A primary cell in a more advanced stage. Fig. 5. A primary cell still more advanced. Fig. 6. Some of the secondary cells, products of the nucleus of the primary cell, are cylindrical, and are arranged in a spiral. Fig. 7. The change into cylinders, and the spiral arrangement com- pleted. Fig. 8. a. One of the secondary cells ; its nucleus a mass of young cells. 6. A secondary cell elongated into a cylinder, each cell of its composite nucleus elongated into a spiral, c. The spiral cells or spermatozoa, free. Fig. 9. A bunch of acini, in various states of development, maturity, and atrophy. The four following figures are diagrams, arranged so as to illus- trate the intimate nature of the changes which occur in vesi- cular glands when in a state of functional activity. Fig. 10. A portion of gland-duct with two acini. One of the acini is a simple primary cell ; the other is in a state of develop- ment, its nucleus producing young cells. Fig. 11. Both acini are advancing; the second has almost reached maturity. Fig. 12 The second acinus is ready to pour out its contents, the first to take its place. , Fig. 1 3. The second acinus is in a state of atrophy, the first is ripe. Fig. 14. Two follicles from the liver of Carcinus mcenas. The colour- less germinal spot is at the blind extremity of the follicle. The secreting cells become distended with bile and oil as they recede from the germinal spot. XV111 EXPLANATION OF THE PLATES. THE STRUCTURE OF THE LYMPHATIC GLANDS. PLATE V. page 412. Fig. 15. A portion of the germinal membrane of tlie human, intra- glandular lymphatics, with its germinal spots or nutritive centres diffused over it. Fig. 16. A portion of the same membrane, in which the component flattened cells, with the centres, have been rendered trans- parent, and are beginning to separate, by the action of acetic acid. Five of the glandular epithelia adhere to the mem- brane. Fig. 1 7. A diagram of a lymphatic gland, showing the intra-glandular network, and the transition from the scale-like epithelia of the extra-glandular to the nucleated cells of the intra- glandular lymphatics. Fig. 18. A portion of an intra-glandular lymphatic, showing along one edge the thickness of the germinal membrane, and upon it the- thick layer of glandular epithelia. THE STRUCTURE OF THE PLACENTA. PLATES V. VI. PLATE V. page 412. Fig. 19. The extremity of a placental villus. a. The external membrane of the villus, the lining membrane of the vascular system of the mother. 6. The external cells of the villus, cells of the central portion of the placental decidua. c c. Germinal centres of the external cells. d. The space between the maternal and foetal portions of the villus. e. The internal membrane of the villus, the external membrane of the chorion. /. The internal cells of the villus, the cells of the chorion. g. The loop of umbilical vessels. Fig. 20. This drawing illustrates the same structures as the last, and has beenlntroduced to show the large space which occasionally intervenes between the internal membrane and the external cells. It would appear that into this space the matter separated from the maternal blood by the external cells of the villus, is cast before being absorbed through the internal membrane, by the internal cellfi. This space, therefore, is the cavity of a secreting follicle, the external cells being the secreting epithelia, and the maternal blood-vessel system the capillaries of supply. This maternal portion of the villus, and its cavity, correspond to the glandular cotyledons of the ruminants, and the matter thrown into the cavity to the milky secretion of these organs. EXPLANATION OF THE PLATES. xix Fig. 21. A portion of ike external membrane, with external cells of the villus. a. Cells seen through the membrane. 6. Cells seen from within the villus. c. Cells seen in profile along the edge of the villus. Fig. 22. The extremity of a villus treated with acetic acid. All the parts are distinctly visible, and the germinal centres of the internal cells are seen surrounding the umbilical vessel. Fig. 23. A villus with a terminal decidual bar, along the cavity of which the external cells are seen to be continued, so as to pass forwards in the direction of the parietal decidua. PLATE VI. page 445. Fig. 1. A portion of the external membrane of a villus, with a lateral decidual bar. This portion of membrane is seen from its foetal aspect, and in this three or four germinal centres of the external cells are perceptible. Fig. 2. A drawing of the extremity of a villus treated with acetic acid. In this villus all the parts described are distinctly seen, and indicated by the same letters as in Fig. 19, Plate Y. Fig. 3. The extremity of a villus, with a terminal decidual bar, treated with acetic acid, to show the nuclei of the decidual cells in the cavity of the bar, and on the external membrane of the villus. Fig. 4. Two tufts connected by a terminal decidual bar. Fig. 5. A tuft with a lateral bar passing off from its stem. Fig. 6. A diagram illustrating the arrangement of the placental decidua. a. Parietal decidua. b. A venous sinus passing obliquely through it by a valvular opening. c. A curling artery passing in the same direction. d. The lining membrane of the maternal vascular system, passing in from the artery and vein lining the bag 'of the placenta, and covering e e the foetal tufts, passing on to the latter by two routes, first by their stems from the foetal side of the cavity, and secondly by the terminal decidual bars f f from the uterine side, and from one tuft to the other by the lateral bar g. Throughout its whole course this membrane is in contact with decidual cells, except along the stems of the tufts, and the foetal side of the placenta, where the decidual cells have degenerated into fibrous or areolar fibres. All that portion of the decidua which is in connection with the bars, villi, and tufts, is the central or functional portion pf the decidua, and along with the lining membrane of the maternal vascular system, or external membrane of the tufts, constitutes the true maternal portion of the placenta. XX EXPLANATION OF THE PLATES. h. Two diagrams illustrating the foctaJ cellular elements of tlie placenta! tufts. These are the internal membrane, and the in- ternal cells of the tufts, and along with the loops of umbilical blood-vessels constitute the true foetal portion of the placenta. THE TESTIS AND ITS SECRETION IN THE DECAPODOUS CRUSTACEANS. PLATES VII. VIII. PLATE VII. page 429. Fig. 1. Figures of Entozoa from the tubuli seminiferi of Orchestia littoralis, probably allied to filaria, and supposed by M. Kolliker to be the spermatozoa. This opinion, however, is incorrect, as may be seen in the accompanying draw- ings, where figures are given representing all the details of the development of the true* spermatozoa. These are all produced from cells, whereas the entozoa under considera- tion are never seen within cells, but are in all cases generally seen floating free in the seminal vessels. These filaria have only been seen, so far as I am aware, in Amphipoda and Isopoda. If they are spermatozoa, they must be produced from cells ; and from what has been stated in the text, it will be seen that in all the Crustacea, these cells, before pro- ducing the spermatozoa, undergo several metamorphoses ; and that the final changes take place in the spermatheca of the female, where the seminal animalcules are produced. In Amphipoda and Isopoda, where these supposed filaria exist, we always find them high up in the testicle, and not occa- sionally, but in great numbers. In the tertiary seminal cells also, which are floating about among them, not the slightest vestige of the worm can be observed. I am inclined to sup- pose, therefore, that these thread-like worms, supposed by Kolliker to be spermatozoa, are only parasites. Fig. 2. Representation of a primary germinal cell projecting from the wall of the seminal tube. It has just burst, and the young secondary cells are escaping and descending the tube ; during the descent they increase in size, from their nucleus throwing off nucleoli, the latter forming the tertiary generation. In this figure it will be observed that the cell-walls of the parent are quite smooth and unbroken, so that in ail proba- bility the young arise from that portion of the cell attached to the seminal tube. Fig. 3 Is a small quantity of the fluid from the spermatheca of the female crab, showing the tertiary or spermatozoal cells after they have burst from the secondary. As described in the text, the spermatheca appears to be the organ in which the seminal fluid undergoes the final and essential change which fits it for impregnation. EXPLANATION OF THE PLATES. xxi Fig. 4. This figure shows the adult seminal secondary cells from the dilated parts of the seminal tube. They are full of tertiary cells. The fluid amongst which they are floating is thick and albuminous, much more so than it is higher up or lower down the tube, and the large, clear, transparent-looking masses, are the pabulum for the nourishment of the cells It is much more abundant in this part of the organ than any- where else, and accordingly great numbers of the secondary cells, in all stages of development, are constantly found here. If a small quantity of the seminal fluid from that portion of the testicle immediately preceding the dilated part be placed under the microscope, it will be seen that the nuclei of the se- condary cells are just throwing off small nucleoli, and that the parent cell is not very much larger than when it burst from the primary. In the same part also, little or no pabulum is ob- served. As we proceed downwards, however, we find them increasing rapidly in size ; and, at the same time, an immense quantity of pabulum floating about in large masses. The lower part of the tube and the vas deferens are almost desti- tute of pabulum, the cells being satiated. Fig. 5. The secondary cells of Hyas araneus from the vas deferens. The walls of the parent cells are remarkably thin. The parent secondary cells are of enormous size in this species. Fig. 6 Represents the testicles of Carcinus mcenas, of the natural size, and shortly before they have reached the maximum state of development. The portion included between a a is the tubular or hepatic, that between 6 b is the dilated or gastric. The vasa deferentia are not seen in this species so well as in Hyas araneus, Fig. 8, c c. It is in the gastric division that the pabulum lies in such quantities. Fig. 7 Is the internal or sheathed portion of the external organs of Cancer pagurus ; proximal extremity. Fig. 8. Testes of Hyas araneus. a a. Tubular portion. 6 &. Follicular portion, c c. Vasa deferentia. Fig. 9. External organs of Cancer Pacjurus. a. Is the internal or sheathed portion in situ. b. Is the sheath or external portion. Fig. 10. External organs of Hyas araneus. A. Sheath. B. Sheathed portion. PLATE VIII. page 431. Fig. 1. First stage of development of secondary seminal cell of Gala- thea strigosa. Figs. 2, 3, 4. Second, third, and fourth stages of development of the secondary cell. Figs. 5, 6, 7, 8, 9, 10, 11, 12, 13. Various stages of development of the secondary cell of lobster. Figs. 14, 15, 16, 17. The same treated with acetic acid. XX11 EXPLANATION OF THE PLATES. Fig. 18. Tertiary or spermatozoal cells. Fig. 1 9. Secondary cell of lobster seen from armed extremity, to show the three setae. Fig. 20. Primary cell, or caecum of testicle of Pagurus bernhardus full of secondary cells, c. Attachment, b. Free extremity, a. Nucleus. Fig. 21. Primary seminal cell of Pagurus bernhardus filling with se- condary cells. As already described, these cells grow in pairs from discs on the walls of the seminal tubes, and hang free in the cavity of. the tube. It has also been described how the secondary cells are produced from the parent nucleus, namely, by means of successive growths, each of which carries off a fold of nucleus before it. a. Disc from which the primary seminal cells grow. b b. The discs on each side of it. c c. The origins of the primary seminal cells. d. One of the primary cells cut off. e. Nucleus of the primary cell in a state of activity ; it has just thrown off a series of young, marked /. In the diagram. g. Are several old walls of former growths. h. Full extremity of primary cell. Fig. 22. A small portion of the testicle of Pagurus bernhardus magni- fied, showing the manner in which the caeca hang from the walls of the seminal tube. Fig. 23. Small drop of seminal fluid of lobster, showing the secondary cells before the armature had expanded. Fig. 24. Small drop of seminal fluid of lobster from vas deferens. That part of the figure above a a, as seen under the micro- scope, presents one dense mass of secondary cells floating down towards &, where a few are seen separate. Fig. 25. A caecum from the testicle of Carcinus mcenas, showing a ger- minal spot at its apex just being filled, with secondary cells. Fig. 26. The germinal spot enlarged. REPRODUCTION OF LOST PARTS IN THE CRUSTACEA. PLATES IX. XII. PLATE IX. page 471. Fig. 1 Represents the raw surface of the proximal or adherent portion of the leg of Cancer pagurus, after the animal has thrown off the distal portion. The figure represents the parts of the natural size, and only a few hours after the separation had taken place. Fig. 2 Is a representation of the same part, after the young leg had grown to some size. It will be observed that the cicatrix, which was formed upon the raw surface a few hours after EXPLANATION OF THE PLATES. xxill separation, has now "become very strong, covers the young germ, thus acting as a means of defence from external injury. Figs. 3, 4, 5, Are the same parts in progressive states of development. Fig. 5 presents a bifurcated character ; probably from some accidental cause it thus appears smaller than it is in the normal state. Fig. 6 Eepresents the raw surface of the leg, already alluded to in Carcinus mcenas, some time after separation. A nucleated cell is seen in the centre. This drawing was made from a very small specimen, and was only procured in the stage re- presented after great difficulty. Fig. 7 Represents a longitudinal section of a very young germ, for the purpose of showing its mode of development. The fibrous- looking band which surrounds it externally, is a circular canal which belongs to a system of vessels described in the text. The four striated bodies which lie next to this canal are the rudiments of the four joints of the future limb. The striated appearance arises from the muscles already so far developed, and the albuminous matter within, and which they enclose, appears to be pabulum for their farther nourishment. The more defined globules, which may be observed floating amongst the albumen, are oil-globules. In the development of this leg, it will be observed that the external segments, or those which are analogous to the thigh and first tibial joints, are largest and most fully formed, a fact we would be led to expect, from the circumstance of their formative cells being the first thrown off from the original parent nucleus, and consequently the first that would take on a central or more independent action. From a similar mode of development, we see that the second tibial and tarsal joints are the smallest, as they are the last formed of the centres. The last or distal phalanx is the smallest of the internal segments ; those nearest the circular vessel are the largest, as was to be ex- pected from the centres which formed them, being the oldest and the first formed from the earlier generations of cells ; and those again within them are smaller, being formed from the later generations thrown off by the original parent. Fig. 8. Cells from the external series represented by c in Fig. 9. Fig. 9. Transverse section of raw surface of proximal or attached ex- tremity of the reproductive organ in leg of Cancer pagurus. This is the surface and appearance which is seen immediately upon the leg falling off ; if it is seen half-an-hour, or a little more, after the separation, it is covered with a thickish film, which shortly becomes a strong opaque cicatrix hiding every- thing beneath it. The vessels seen in Fig. 15 are also omitted, for the purpose of showing the structure of the re- productive body more clearly. EXPLANATION OF THE PLATES. a. Is the circular vessel, of the system of vessels mentioned in the text, and it surrounds 6. A fluid or semi-fluid mass, containing small nucleated cells, from which the germ is probably derived. c. Is a large mass of very large cells surrounding the circular vessel, which appear to act as a magazine of nutritive matter for the young germ during its growth. d. Is the shell membrane, which is surrounded externally by the shell. Fig. 10. A young limb of Carcinm mcenas still enclosed within its original cyst, which is formed probably from the cicatrix mentioned above. Magnified two diameters. Fig. 11 Is a very young leg of the common lobster. The reproduced leg of this species is not enclosed in a cyst, and it is not folded upon itself, but projects straight forward. Nat. size. Fig. 12 Is a figure of the natural size of one of the large claws of Pagurus bernhardus, shortly after it has burst from its con- taining cyst. Fig. 13. Enlarged view of Fig. 11. Fig. 1 4. One of the large claws of Carcinus mcenas still enclosed within the cyst. From observations made, it appears that these young legs remain within the cyst until their own covering or shell is of sufficient strength to act as a means of defence. They do not obtain a true shell for some time after the cyst has burst. Fig. 15. Raw surface of proximal extremity of leg in Cancer pagurus, shortly after the animal has thrown off the distal portion. This figure is made for the purpose of showing the distri- bution of the peculiar vessels, and their mode of running from the circumference towards the circular vessel in the centre. Fig. 1 6. Longitudinal section of young leg still within the cyst. a. Part of old leg containing the reproductive organ. " b. External cells. c. Smaller nucleated cells. d d. Cyst of young leg. e. Femur of young leg. /. First tibial joint of young leg. g. Second tibial joint. h. Tarsal joint. Fig. 17. Natural size of young leg. Fig. 18. Portion of blind extremity of one of the peculiar vessels which are attached to the blood-vessel running to the leg, Plate XII. Fig. 14. The contents are oil-globules, but in the figure have somewhat the appearance of nucleated cells. Fig. 19. An enlarged view, for the purpose of showing the connection of these vessels. EXPLANATION OF THE PLATES. XXV Fig. 20. Two of the blind extremities from raw surface of leg, where they present a clavate appearance. Fig. 21. View of the extremity, showing the dark spot supposed to be a germinal spot. PLATE XII. Fig. 9. Small longitudinal portion of shell from the large claw of Cancer pagurus, showing the thickness of the annulus or ring in it at the point of separation. Fig. 1 2. Longitudinal section of one of the legs of Cancer pagurus, showing the natural position and relations of the reproductive organ. a a. Femur. 6 6. Reproductive organ. c. Natural appearance of line of separation d. Coxa. Fig. 1 3. Enlarged foramen as it is seen on raw surface after the separa- tion. This has been hardened in boiling water, which gives it a much more defined appearance, and also enlarges it more than it naturally should be. Fig. 14 Is a small portion of the femoral artery, about half-an-inch in extent beyond the line of separation, which is covered as re- presented by the peculiar vessels. a. Distal extremity of blood-vessel. ON THE ANATOMY AND DEVELOPMENT OF THE CYSTIC ENTOZOA. PLATES VI. X. XL XII. PLATE X. page 476. Fig. 1. Magnified view of one of the young of Acephalocystis armatus still attached to the germinal membrane of a secondary parent. It is taken from the group shown in Fig. 2, and is still in an early stage of development, the circlet of teeth still being minute and not fully developed. The absorbing series of cells may be seen internally. Fig. 2. Small portion of the germinal membrane of a secondary parent of Acephalocystis armatus highly magnified. Fig. 3. Small portion of germinal membrane of Acephalocystis armatus in a state of degeneration ; nothing is seen in the membrane, which is quite homogeneous, except the small cells figured a. 6. Is the commencement of one of the cretaceous fatty masses described in the text. Fig. 4. Several of the stages of development of Cysticercus. a. First stage represents spines ; hardly if at all seen. b. Their first decided appearance. c. Third stage. XXVI EXPLANATION OF THE PLATES. d. Fourth stage. Fig. 5. Small portion of the germinal membrane of Acephalocystis armatus. Fig. 6. Small portion, highly magnified, of the granular matter from the cyst of Cysticercus. Fig. 7. Small portion of the inner surface of the external membrane of Acephalocystis armatus while in a state of degeneration. Fig. 8. Ovum from the pedicle of Cysticercus. Fig. 9. Small portion of the germinal membrane of Acephalocystis monroii, highly magnified. a. Fibrous basis. 6. Germinal vesicles. c. Secondary acephalocysts within the germinal vesicles ; this portion was taken from the large parent cyst, which is the primary animal, buried in the liver ; and each of the smaller vesicles marked c belong therefore to the secondary genera- tion, their progeny again being the tertiary generation. Fig. 10 Is a specimen of Cysticercus neglectus ruptured at the fundus of the sac, apparently for the escape of the young germs into the cavity of the cyst, where they become attached. Fig. II. Small portion of the cyst of Cysticercus neglectus magnified, showing its vascularity, and the mode of attachment of the young Cysticerci to its internal surface. Fig. 12. View from above the pedicle of Cysticercus, showing the dis- position of the teeth. In all works hitherto published on Helminth ology, there has been a great want of proper figures or descriptions of the true generic and specific characters of these animals, a point of the utmost importance for obtaining a proper knowledge of them : with this view the author has paid scrupulous attention to the leading characters, and these he has placed in the form of a synopsis at the end of the chapter. All the drawings have been made with the view of illustrating these characters more fully. The disposition of the teeth, and their forms, are perhaps the most certain ex- ternal characters. PLATE XI. page 482. Fig. 4. Magnified view of a small portion of the external or tubular membrane of Diskostoma acephalocystis. a. Larger disc. b. Smaller one on its surface. c. Tubuli. d. Extremities of tubes. e e. Gemmules, which at this stage of development may act as absorbents. Fig. 5. Natural size of Diskostoma acephalocystis. Fig. 6. Diskostoma acephalocystis in various stages of development. EXPLANATION OF THE PLATES. a a a. Small cells arising from the attached surface of the tubular membrane. This is the manner in which the original group increases in size. b. More advanced. c. First stage of second mode of development, or that for the extending of the parasite to as yet uninfested parts of the body, for the purpose of forming new groups. d. Second stage. e. Third stage. /. Root where the original germ became fixed. g. External or tubular membrane. Fig. 10. Section of Astoma acephalocystis, showing its internal structure PLATE XII. page 487. Fig. 1. Portion of sac of Cysticercus, much magnified. a. Absorbing cells of absorbing membrane. 6 6. Separate ova, after their escape from the pedicle. Fig. 2. Cysticercus neglectus very much magnified. Fig. 3. Small portion of omentum containing Cysticercus neglectus, showing the bodies considered to be young Cysticerci attached ; the omentum has been folded over, and the young (a) are seen attached to the fold. Fig. 4. The natural size of the animal supposed to be a new Csenurus Ccenurus hepaticus. Fig. 5. Magnified view of the head of Acephalocystis armatus in a more advanced stage than the former figure. Fig. 6. The germinal membrane from which it was taken. Fig. 7. The absorbing membrane of cyst of Cysticercus rattus highly magnified. Fig. 8. Teeth of Cysticercus rattus highly magnified. Fig. 10. Ovum of Cysticercus rattus highly magnified. Fig. 11. Ova from pedicle of Cysticercus rattus highly magnified. PLATE VI. page 445. Fig. 8. Gymnorhynchus horridus within its cyst. Fig. 9. exposed. Fig. 10. First stage of Ccenurus cerelralis. Figs. 11, 12, 13, 14. Second, third, fourth, and fifth stages of the dis- coidal period of development of Ccenurus cerebralis. Fig. 1 5. One of the first stages in the vertical period of development. Fig. 16. Sphairidion acephalocystis highly magnified. Fig. 7. Neuronaia monroii. (J. Goodsir.) a. Suctorial mouth. 6. Acetabulum. c. Orifice of organs, supposed to be reproductive. d. Posterior orifice, by which the sigmoidal "cistern a chyli" e. Opens, and apparently also, EXPLANATION OF THE PLATES. /. The thick-walled peculiar sac. g. Pyriform sac, a receptacle for the ova. i. Male organs. The figure also presents the arrangement of the dermal spines, and the general form of the animal. PLATE XL page 482. Fig. 2. The anterior extremity and suctorial mouth of Neuronaia monroii more highly magnified. Fig. 7. The cyst of Neuronaia monroii in a bundle of nervous fila- ments. The fissured appearance of the cyst, with its epithelia, is represented in this drawing. I am inclined to believe that the function of the cyst in this and the other Cystic Entozoa is to supply nourishment to the enclosed animal, drawing it from the surrounding parts, and throwing it into the cavity, the structure and action being identical with that in the encysted tumours as already described. The bulbous extremities of the cysts of Trichina spiralis contain masses of germinating cells, to which I am inclined to attribute the same function. Figs. 8, 9, 11. The clavate extremities of the cysts of Trichina spiralis, with their germinating absorbent cells. The epithelium and absorbent cells of the cysts of the entozoa may be considered as permanent yelk-cells in the economy of these persistent embryos. Figs. 1 and 3. Magnified drawingsj of Sarcina ventriculi described, but badly figured by me in the Edinburgh Medical and Surgical Journal, No. 151. I am still of opinion, notwithstanding the arguments of Mr. Busk, in the Microscopical Journal, that this body is a vegetable parasite, its sudden occurrence and sudden disappearance being not more extraordinary than the rapid development of many cellular structures ; the glandular epithelium, for instance, during secretion. That it is a Gonium, as has been suspected by Professor Link, appears to me improbable, as would be admitted, I believe, by that great botanist, if he had had an opportunity of observing its peculiar vegetable aspect, so different from that of an in- fusorial animal. DIVISION I, DEVELOPMENT AND MOKPHOLOGY. VoUL Plate L DIVISION I. I. ON THE OEIGIN AND DEVELOPMENT OF THE PULPS AND SACS OF THE HUMAN TEETH. PLATE I. "II est peu de sujets en medecine sur lesquels on ait tant ecrit que sur les dents ; deux cent volumes contiendraient a peine tout ce qu'on en a imprime ! Mais est-ce a dire que tout soit connu d cet egard ? Est-ce a dire que la matiere ait ete epuisee et qu'il ne reste plus rien a faire? Nullement. L'Anatomie n'a pas encore le dernier mot de la nature sur cet interessant sujet et il reste encore, quoiqu'on en dise, quelques doutes a eclaircir et plus d'une difficulte a resoudre." BLANDIN, Anat. du Systeme Dentaire, 1836. SECTION I. EXAMINATIONS OF THE DENTAL ARCHES AT DIFFERENT AGES. 1. An embryo (Fig. 1), which measured 7J lines from the vertex to the point of the coccyx, weighed 15 grains, and appeared to be about the sixth week,* was selected and prepared for the purpose of examining the state * It is difficult to determine the exact age of an embryo. The ages given in the text, therefore, must be considered as approxi- mations, being probably rather under-rated. I have given a full-sized sketch of the youngest subject in which I have observed any of the phenomena of dentition, with the weight and measurements of a few of the others. In researches of this kind, the sequences of phenomena are of more importance than their periods of appearance. Velpeau, Embryologie ou Ovologie Humaine ; Breschet, Etudes Anatomi- ques, etc., de I'oeuf dans Vcspece Humaine: Scemmering, Icones Embryonum Humanorum. B 2 ON THE ORIGIN AND DEVELOPMENT OF THE of the palate and dental arches. The cheeks were divided transversely from the commissures of the lips with fine scis- sors ; the jaws were separated, removed, and fixed to the bottom of a small capsule full of water. The point of the tongue was removed. The configuration of the mouth was then determined by means of a half-inch lens and two needles, bent at the points, and fixed in slender handles. Upper Jaw. The roof of the mouth was bounded an- teriorly and laterally by the free edge of the lip (a, Fig. 2), which is at this age thin and of great transverse extent. Within the lip (a\ but separated from it by a groove (6), to be more particularly described afterwards, there was observed a lobe of a horse-shoe shape (c), narrow anteriorly at the median line, broader, flatter, and of a rounded form on each side posteriorly. Coming out from above the internal posterior edges of this lobe (c), and firmly adhering to it, two other lobes (d d) were seen ; flat, rounded, and curving backwards and in- wards posteriorly, gradually dis- appearing by pointed extremities anteriorly. From the posterior extremities of each of the lobes now described (d d), and of the horse-shoe lobe (c), a thin semitransparent membranous fold (e e) passed back- ward on each side, attached externally to the sides of the capacious bucco-pharyngeal cavity, bounded internally by a free edge opposed to its fellow of the opposite side, and terminating posteriorly on the lateral walls of the pharynx. Adhering to the inferior surface of each of these folds was seen a smaller lobe (//) somewhat similar to the two last, and situated a little behind them. The needle placed under the folds showed that they were free and floating, except at their exterior or adherent edges, and that they constituted a partial division of the large common nasal, buccal, and pharyn- PULPS AND SACS OF THE HUMAN TEETH. 3 geal cavity into a superior and an inferior compartment. The upper wall of this common cavity was smooth and flat pos- teriorly (g) ; but anteriorly it was contracted and terminated in a longitudinal bar (Ji), which ran forwards to be attached to the superior surface of the horse-shoe lobe at the median line, and to the other parts in that neighbourhood. Under the bar Qi) a deep cavity (i i) was seen, which communicated with the exterior of the face by two small foramina, which constituted at this period the whole external nasal organ. As before-mentioned, a groove (&) was observed between the lip (a) and the external edge of the horse-shoe lobe (c). This groove (b) was deep, and its walls and lips were in close apposition. It terminated posteriorly on each side (k Jc) by becoming more shallow, and curving backwards and inwards on the inferior surface of the membranous folds (e e). There was a median frenum between the lip and the horse-shoe lobe. Lower Jaw. The under lip (a, Fig. 3), resembled the upper, and was separated along its whole extent by a groove () similar to the one above, from a semicir- cular lobe (c). Anteriorly this lobe (e) was divided into two median large (d d), and two la- teral smaller lobules (e e), the whole being firmly adherent to the floor of the mouth in front of the tongue and its frenum, which were both well developed. The lateral parts of the lobe (c) were rather indistinct, but at the point where the free edge of the lip terminated, it extended transversely and posteriorly, became thick and bulbous (//), and exhibited on its surface a narrow shallow groove of a sigmoidal form (g g), which was continuous with the groove behind the lip. There was a median labial frenum. On the external sides of the membranous folds in the 4 ON THE ORIGIN AND DEVELOPMENT OF THE upper, and of the posterior parts of the lobe in the lower jaw, the cut surfaces of the cheeks made by the scissors were seen (I l t 1 1). The mucous membrane over its whole extent was thin, and of a greyish-yellow colour, the lobes granular, very friable, and of a dead white. The breadth of the upper alveolar arch was 14 line, and the length of the same was 1 line. 2. The jaws of an embryo which measured 1 inch, weighed 20 grains, and appeared to be about the seventh week, were prepared and examined as in the former case. Upper Jaw. The free edge of the lip (a, Fig. 4) was not so extended as at the sixth week. The horse-shoe lobe (c) had become broader and more developed pos- teriorly, and anteriorly exhibited three lobules, one median (m), and two lateral. and anterior (n n). The two lobes observed on each side of the palate in the former embryo (d d, f /, Fig. 2), had disappeared, hav- ing apparently coalesced ; the posterior one (/) being curved forwards to join the anterior (d), in the point (s t Fig. 4), while the combined mass had contracted itself towards the front of the mouth within the limits of the horse-shoe lobe (c). The cleft had slightly diminished, but was still of sufficient width to display the whole of the undivided nasal cavity. The lip (a) was so lax as to admit of being moved by the middle. The horse-shoe lobe (c) could also be pressed by the same means inwards and backwards. When these two parts were separated, the mucous membrane was seen to form a duplicature (&), between the lips and a ridge (0), which ex- tended from the posterior part of the dental arch to the outer extremity of the lateral lobule (n). PULPS AND SACS OF THE HUMAN TEETH. 5 The median portion of the dental arch was formed by the two lateral lobules (n n) 9 which separated the lips from the median lobule (m), and extended also a little on each side of it. The lateral portions of the arch presented externally the ridge (o), formerly mentioned, smooth and convex on its exter- nal surface, internally moulded into three curves, the anterior long and shallow, the second deeper, the third or posterior almost semicircular. Behind the last curve, the internal edge of the ridge formed a deep notch, which swept outward and forward, so as to mould the former into an almost isolated lobule ( ^ dental arch, there existed a groove (h, Fig - 5 - Fig. 5), very distinct posteriorly, but having no outer lip an- teriorly. The inner lip (m), presented posteriorly a large lobe ON THE ORIGIN AND DEVELOPMENT OF THE (n), under which the needle was easily inserted for a short distance. In the middle, this lip (m) was thin, elevated, and curved over the groove (h). Anteriorly it became broader, and curved still more over the groove, and was divided into two median larger lobules (d) y and two lateral smaller (e). Between the two median (d) there was a notch at the attach- ment of the lingual frenum. The outer lip (/) was defi- cient anteriorly, so that the groove was bounded in that situation by the under lip (a), which was loose, free, and turned outwards. Posteriorly the outer lip (/) was well de- veloped, and came out from under the posterior lobe (n) of the inner lip, so as to render the grove (h) pointed, and curved backwards and inwards. This lip (/) extended only about half-way towards the median line, and appeared flat, or in the same continuous plane with the floor of the groove. It was also curved outwards, so as to overhang the labial mucous membrane. The groove presented an elevation (o) of its floor near its posterior extremity. There was a labial frenum. The mucous membrane possessed the same physical properties as at the sixth week. The lobes were not so granular, but tougher and more consistent. Breadth of superior arch 1 J line, length 1. 3. The jaws of an embryo at the second month, having /% been prepared in the usual man- ner, presented the following ap- pearances : Upper Jaw. The lip (a, Fig. 6) was more movable, and its free edge less extended. The cleft in the palate had diminished, exist- ing only as a small angular defi- ciency (x) in the pendulous por- tion. The horse-shoe lobe was still perceptible under the PULPS AND SACS OF THE HUMAN TEETH. 7 form of a bulging (c), represented as turned aside to ex- hibit the objects under it. The lobule (r) had increased in size, so as to extend further backwards, and to appear on the posterior lateral parts of the palate. The median lobule (m) had become triangular, the anterior edge being formed by the curve of the palate somewhat pointed in front, the lateral edges being straight and meeting in an angle behind, from which the median line of suture or raphe of the palate proceeded. The median lobule (m) had increased re- latively, the lateral lobules (n ri) only absolutely. The posterior portion of the dental groove (&) was longer, wider, and not so much curved. The bulging or papilla (1) was more distinctly isolated ; and at the anterior extremity of the second curve in the ridge (0), another papilla (2) had appeared as a production from the latter. This papilla (2) was bounded externally by a lamina (p\ which was also a production from the edge of the ridge (o\ and was notched at its inner margin, where it was applied to the side of the papilla. The dental groove then terminated in a point, at the outer extremity of the lateral lobule (ri). There was a labial frenum. Lower Jaw. The posterior portion of the dental groove had undergone no material change, but had become deeper, and con- tained in the situation of the ele- vation marked (o, Fig. 5), a distinct ' ~~~ rounded papilla (1, Fig. 7). Fur- ther on, another papilla (2) bounded externally by a notched lamina (a) had appeared. This combined papilla and lamina was exactly similar in its configuration and relations to that marked (2, Fig. 6). The anterior part of the groove had become more distinct, not because it had acquired an outer lip, but because its floor had risen above the level 8 ON THE ORIGIN AND DEVELOPMENT OF THE of the labial mucous membrane. There was a labial frenum. The breadth of the superior arch was If line ; length li. 4. The jaws of an embryo nine weeks old were examined under water. Upper Jaw. No material change had taken place in the configuration of the palate, except that the median lobule (ra, Fig. 8), had di- minished relatively, and in the trans- verse direction, while the lateral lobules (n) had increased relatively, and also in the transverse direction. A longitudinal lobule (y), had also appeared on the surface of the median lobule (m). The cleft (x) in the soft palate was smaller. The posterior part of the dental groove was wider. The papilla (1), had become more prominent, and the lips of the groove had almost met before and behind it. The papilla (2) is larger. A little further on, corresponding with the lateral lobule (n\ on each side, two papillae (3 and 4), with notched laminse in front of them, had appeared. The centrals (3), or those on each side of the median line, were the most distinct. Lower Jaw. The lips of the dental groove had approached so as to require separation by the needle to exhibit its contents dis- tinctly. The papilla (1 or 2, Fig. 9) had undergone little change, but two very indistinct bulgings (3 and 4) had appeared on each side of the labial frenum, the centrals (3) being the Fig. 9. largest. The breadth of the superior arch was If line ; the length 1-J line. PULPS AND SACS OF THE HUMAN TEETH. 9 Fig. 10. 5. In an embryo of the tenth week the following ap- pearances presented themselves : Upper Jaw. Very little change had taken place in the lateral lobules (n, Fig. 10), or the median (m) and its additional lobule (y). They had all increased absolutely, and if any relative change had taken place, it was in the trans- . verse diminution of the median (m) and the movement forward of its additional lobule (y). The palate had advanced anteriorly, so as not only to have encroached in some de- gree upon the median and lateral lobule, but also to have thrown itself into folds immediately behind them. The outline of the horse-shoe lobe (which is represented in the sketch as turned aside to exhibit the dental groove), was still observed. There was an indistinct uvula. The papillae (1 and 2) had sunk completely into follicles, and could only be seen by looking into the open mouths of the latter. The mouth of (1) was bordered by four laminae or lids, that of (2), by three, as represented in the sketch. The papillae (3 and 4) had not increased much, but their notched laminae had become more distinct. At the posterior extremity of the floor of the dental groove, on the inner side of the lobule (q, Figs. 4, 6, 8, 10), a slight bulging (5, Fig. 10) was seen. The upper lip had receded in the neigh- bourhood of the median line, so as to have U disappeared almost entirely at that spot, the centre of the upper dental arch being Fig. n. exposed. Lotver Jaw. The bulgings on each side of the median line (3, 4, Fig. 11), which were so indistinct in the last subject, 10 ON THE ORIGIN AND DEVELOPMENT OF THE had become well developed and inclosed in follicles, through the mouths of which they were seen. A similar change was observed in reference to the papilla (2). The follicles had been produced by the stretching across of productions from the outer lip (which was very indistinct) towards similar but much smaller productions from the inner lip (which was still very prominent). The lines of junction of the septa were visible, and the mouths of the follicles pre- sented an unfinished appearance. The papilla (1) had become surrounded by an incomplete follicle, in consequence of the production of a notched lamina from the outer lip of the groove, which lamina was almost met by a smaller slip of membrane from the inner lip. The breadth of the superior arch was 2 lines, length II line. 6. IWi or 12^ week. Upper Jaw. The median lobule (m, Fig. 12) had diminished so much transversely, as to have become an- tero-posterior ; while its supplement- ary lobule had become attached to the frenum of the lip. The lateral lobules (n) had increased much transversely, and appeared each to be divided into an anterior and a posterior portion. They were compressed by the true palate, which was folded at this part, as at the tenth week, into wrinkles, the longest and anterior of which stretched across the median line from the right to the left side. The papillas (3 and 4), with their fol- licles, were fully developed. The other two papillae (1 and 2, Fig. 10) had not undergone much change, but the small bulging (5, Fig. 10) had now become a distinct papilla, and its follicle had begun to show itself. The uvula was well marked. Lower Jaw. The lines of junction of the interfollicular PULPS AND SACS OF THE HUMAN TEETH. 11 septa had almost disappeared, and the mouths of the follicles had become more distinct. The mouths of the three anterior follicles had an an- terior lip, the free edge of which was directed somewhat inwards. It was ne- cessary to lift up this lip with the needle to obtain a view of the contained papilla. At the posterior part of the dental groove, another papilla with a notched lamina, both productions from the external lip, had appeared (5, Fig. 13). Breadth of superior arch 12i lines ; length, 2. 7. I3th week. Upper Jaw. There was little change in the configuration of the palate since the former week. The lobe running across the median line was still visible. The frenum of the upper lip had become closely attached to, and continuous with, the median lobule. The outlines of the horse-shoe lobe were still perceptible, and on its external side the lobule, all along marked (r), was visible. The outer lip of the dental groove, or the external alveolar process, was equally developed all around. The upper lip was still much retracted. There were ten papillae inclosed in open-mouthed follicles, and ranged at nearly equal distances all around the dental groove.* The four anterior papillse were flattened from before back- wards with a straight edge, and were somewhat similar to the future incisive teeth. The next one on each side was a simple cone. The two posterior on each side were also conical, but flattened transversely, so as considerably to resemble carnivorous molars. Each of these papillae ad- hered by its base to the fundus, while its apex, as during the eleventh and twelfth weeks, presented itself at, or, as in the present instance, protruded from, the mouth of its * Arnold, Salzburg Med.-CMrurg. Zeitung, 1831, Erster Band, p. 236. Valentin, Handbuch der EntivicJcelungs-geschichtc des Mcnschen, p. 482. 12 ON THE ORIGIN AND DEVELOPMENT OF THE follicle. The point of the needle could be introduced through the mouth, so as to move the papilla about in the interior of the follicle. By removing the outer lip of the dental groove, and the outer wall of all the follicles by the scissors, a good view was obtained of the configuration of these parts (Fig. 14). The follicles were " Y V V observed to be mere duplications of the membrane of the groove, and consequently of the general gastro-intestinal mucous membrane. The inner surface of the follicles was of a greyish-yellow colour. The papillae had increased relatively so as to protrude from the mouths of their follicles. They were granular, friable, and of a dead- white colour. Lower Jaw. No remarkable change had taken place in the lower jaw, except in the relative enlargement of the papillae, and in the distinct development of the follicle of the posterior papilla (5, Fig. 13). The outer lip of the dental groove was not very distinctly marked, but the inner was well developed. The breadth of the superior arch was 3 lines, and the length was also 3 lines. 8. 14th week Upper Jaw. The median lobule had undergone little change, the lateral lobules had become broader from before backwards, apparently in consequence, of the retraction of the palate, which, instead of exhibiting on its anterior part the confused transverse wrinkles formerly mentioned, presented on its lateral divisions (corresponding to the horse-shoe lobe) four or five parallel rugae, which were apparently remains of the wrinkles. The upper lip had again become full, so that its free edge was on a level with the surface of the palate. The soft outer edges of the palate and the anterior edges of the lateral lobules were now closely applied to the outer lip of the dental groove, so as to close the PULPS AND SACS OF THE HUMAN TEETH. 13 latter in a valvular manner. When these edges viz. the continuous semicircular outline of the whole palate were raised by the needle, the dental groove and its contents viz. ten papillae in their follicles were seen. It was observed that the follicles had increased relatively, the papilla only absolutely, in consequence of which the latter, instead of pro- jecting from, had receded within, the mouths of the former. The mouths of the follicles had apparently become smaller. This had arisen in consequence of the greater development of the laminae which were seen in the earlier 3 stages. There were two, an anterior and a posterior, for the four anterior follicles ; three, an internal and two external for the third on each side ; and four for the two posterior on each side (Fig. 15). Close upon the inner / side of the mouth of each of the follicles fl there was observed a little depression in the w/ form of a crescent, its concave edge being to- wards the former. These depressions were most distinctly marked at the four or six anterior follicles, where they were situated immediately behind their inner lips (a a a a a). Lower Jaw. The papilla had receded. The laminae of the follicles were more developed (Fig. 16). Little depressions or lunulae had appeared similar to those in the upper jaw. When the membrane of the dental groove with its adherent follicles and their pulps, was stripped off, the dental nerves and vessels were found running along under the follicles, and distributing vascular branches and a nervous twig to each of them (Fig. 14). Each of the individual follicles, with its papilla, vascular branches, and nervous twig, exactly resembled a large hair- bulb with its nerve and vessels exposed after the hair has 14 ON THE ORIGIN AND DEVELOPMENT OF THE been extracted. Breadth of the superior arch, 3i lines ; length, 3 lines. 9. 15th week Upper Jaw. The outer edges of the palate, which in the last embryo lay unattached on the outer lip of the dental groove, in the present subject adhered firmly to it, except along a small portion posteriorly (a, Fig. 17). This adhesion was firm anteriorly on both sides of the median line, then became weaker, and posteriorly at the non-adherent portion (a\ be- tween the lobules (r and t\ the lips of the groove retained their original smooth edges. When the lips of this non-adherent portion were separated by the needles, its floor and walls exhibited nothing but the greyish-yellow mucous membrane of the original groove. The outer lip of the dental groove was visible all around the ex- ternal margin of the palate, and was divided on both sides into three parts, an anterior (u\ a lateral (o), and a posterior (). On the inner side of the latter was seen the longitudinal lobule, which has hitherto been marked (r). The median lobule (m) was rounded anteriorly, and had a process (?/, Figs. 8 and 10), which stretched forwards between the lobules (u u). This was the additional lobule formerly mentioned. The sides of the median lobule were straight and converged to its pos- terior extremity, which was circular, and was received into a curve in the middle of a transverse band, constituting the anterior boundary of the palate, which appeared to have re- ceded still more than in the last subject, and to have exposed still more completely the lateral lobules (n n). The four rugse seen in the last subject had become ridges beautifully crenated, and converging, as represented in the sketch, towards a curve, reversed and opposite to the one formerly mentioned in the PULPS AND SACS OF THE HUMAN TEETH. 15 middle of the transverse band of the palate. This last curve was the result of the anterior junction of the lobes (d d } Fig. 2), and was traced through all its phases to its present state. The median suture of the palate proceeded from it posteriorly. The dental groove being torn open by means of the needles, its lips were found to have adhered pretty firmly, as before mentioned, but a feeble adhesion only had taken place between its walls so as to allow its contents to be restored to their original condition by means of a blunt instrument. This was carefully done under water, and the mouths of all the follicles with their laminse were displayed. The latter were more developed than in the last subject, and completely concealed the papilla. The former required to be lifted up in order to display the latter. Careful observation during the separation of the contents of the groove disclosed the important fact that the general adhesion had not obliterated the little crescent- shaped depressions behind the mouths of the follicles. These retained the smooth greyish-yellow colour of the walls of the original groove, and from this circumstance could be distin- guished from the general flocculent appearance of the other parts. Lower Jaw. The outer lip of the dental groove had in- creased in size, and was as prominent as the inner, except posteriorly, where the latter still retained its posterior lobe ; but the most remarkable change which had taken place since last week was the complete adhesion of both lips, as in the upper jaw, with the exception of a small portion posteriorly, which still retained the peculiar appearance of the dental groove, and in which nothing could be seen but the smooth mucous membrane ( , Fig. 18 ). When the dental groove was torn open, as was done in the upper jaw, the laminse (which were highly developed) of the 16 ON THE ORIGIN AND DEVELOPMENT OF THE follicles, and the walls of the groove, were found to be rough and flocculent from adhesions, with the exception of the little depressions formerly mentioned, which still retained their ori- ginal appearance. Breadth of the superior arch, 5 lines ; length, 4 lines. 10. Wth week. Upper Jaw. The palate retained the appearance it had in the last subject, with the exception of the median lobule, which had become narrow in front, and broad posteriorly. The raphe of the dental groove had become firmer, so as to give a much more defined and permanent ap- pearance to the non-adherent portion posteriorly, which was now seen to great advantage, its fine greyish mucous mem- brane gradually running at its edges into the white tough substance of the palate and gums. Having separated the lips of the non-adherent portion (a, Fig. 19), a papilla, sunk in an open fol- licle, with three or four laminae, was visible (6). The membrane of the palate and max- illary arch being stripped from the bone, and its surface of adhesion examined, lines cor- responding with the .sutures of the bones were observed ; one the median, another the intermaxillary, and a third with the palato-maxillary. Five tooth-sacs were also observed on both sides of the maxillary arch. These were divided into three groups, two in the first or anterior, one in the second, and two in the third or posterior. These groups were covered with a flocculent spongy membrane, which was easily stripped off by the forceps, and when this was carefully done, it became evident that the sacs which were formerly grouped together by this membrane were individually isolated, and formed of a thin grey diaphanous membrane, similar to the one formerly men- tioned as covering the bottom of the dental groove, and con- stituting the membrane of the follicles. The careful detach- PULPS AND SACS OF THE HUMAN TEETH. 17 ment of the external spongy membrane from the posterior group showed, what was not at first observed, that there was at the posterior part of the posterior sac another very small one, which by careful examination was seen to be the fundus of the open follicle in the non-adherent portion of the dental groove. The adhesion of the lip and walls of the groove had now become so strong, that it was impossible to separate them. The only way, therefore, in which its contents could be examined was by transverse sections. When these sections were made between the different sacs, they displayed scarcely any traces of the dental groove ; but when they passed through any place perpendicular to the surface of the gum, and near to the middle of any of the sacs, they exhibited the appearances represented in the marginal sketch (Fig. 20). The deciduous tooth pulp (a), which was lately a free pa- pilla ; (6), the section of its sac, which was a follicle when the pulp was a papilla ; (d), the line of adhesion of part of the walls of the dental groove leading from the shut sac to (c), the raphe of the groove ; (e), the section of the non-adherent portion of the groove in the situation of the lunula, which existed behind (/), the inner laminae of the sac (&), in its former follicular condition. From the consideration of this section (Fig. 20), the mode in which the original follicle, the non-adherent depression behind the inner laminae, and the walls of the dental groove, were connected after full adhesion of all the neighbouring parts, will be easily understood. The little cavity (e) adhered by its anterior and inferior extremity to the line of adhesion (d) t so that it and the sac of the milk-tooth were both con- nected to the raphe of the edges of the dental grooves by lines of attachment, which resembled two petioles proceeding from a common footstalk. These lines of attachment were not 18 ON THE ORIGIN AND DEVELOPMENT OF THE tubular, but resisted all efforts to push a fine probe or bristle through them ; they were merely opaque remains of the sur- faces of junction contrasting with the semitransparent substance of the gums. Parallel sections through all the sacs exhibited similar appearances. When the contents of the sacs were examined, the pulps were found to have acquired the configuration of the bodies of the future teeth. The bases by which the molar pulps formerly adhered to the bottoms of their sacs, and which may be denominated their primary bases, had become almost divided into three secondary bases, which corresponded with the internal and two external fangs of the future teeth. This division was so far accomplished by the advancement of the internal grey membrane of the sac, under the form of small compressed canals between the base of the pulp and the external spongy membrane. These canals, which were three in number, one external and two internal, did not meet in the middle under the pulp. Deposition of tooth-sub- stance (Zahn-substanz) had commenced on the edges and tubercles. The sacs were twice as large as their contained pulps, and in the space (g, Fig. 20), which existed between them, there was observed a very soft flocculent gelatinous substance, which had no attachment to the pulp, and did not appear to adhere to any part of the sacs, except the laminae and the parts ad- joining them. Lower Jaw. The adhesion of the dental groove was not so strong as in the upper jaw. The open portion (a, Fig. 18), was fully defined, and exhibited on its floor the orifice of a follicle, containing a papilla. In other respects the lower was similar to the upper jaw. Breadth of superior arch 7 lines ; length 5 lines. 11. 5th month. Foetus minutely injected with size and vermilion. PULPS AND SACS OF THE HUMAN TEETH. 19 Upper Jaw. The lobes (t, o, u, Fig. 21) had become highly developed. The anterior one (u) was convex anteriorly, with a sharp edge directed backwards, and corresponded with the incisive teeth. The central lobe (o) had become shorter, but more prominent, like a canine tooth. The posterior (t) had united firmly with the longitudinal lobe all along marked (r), so as to close the open portion of the groove (a, Fig. 17), which was described in the two last subjects. The raphe of the groove between these two lobes w T as serrated, and a vessel was seen traversing each denticulation. The raphe then ran close along the inner edges of the bases of the lobes (o and u). The median lobule was triangular, the base posterior ; the apex in front continuous with the labial frenum, and situated between the anterior pointed extremities of the lobules, (u, u). The lateral lobules were very distinct. The other less im- portant changes which had taken place in the palate may be understood by comparing Figs. 21 and 17. The membrane of the palate, with the sacs of the teeth, was removed from the bone. The fundus of the follicle (6, Fig. 19), had now assumed the appearance of a sac, and the other ten, instead of being grouped, had become isolated. The branch of the dental artery, which supplied each of the sacs and their pulps, was seen, when it reached the fundus of the former, to give off a number of twigs, which, radiating from their common centre, proceeded perpendicularly towards the gum, near which they inosculated with others proceeding from it. The combined vessels then formed a pretty minute network in the spongy membrane formerly described. Transverse sections were now made by the scissors through all the sacs. The general appearance of. these sections was 20 ON THE OHIGIN AND DEVELOPMENT OF THE similar to that of those at the fourth month ; but the gelatinous granular substance between the pulp and the sac was of the consistence of very firm jelly, closely and intimately adherent to the whole interior of the sac, with the exception of a narrow strip all round the base of the pulp, along which strip the grey membrane of the sac retained its original appearance, and through which the radiating saccular twigs were visible, being strongly and beautifully contrasted with the cream- coloured surface of the granular substance. The mass of the granular substance had a peciiliar greyish-white colour ; its surface was cream-coloured, and had a dry chalky appearance. It had a tendency to tear in a direction perpendicular to the internal surface of the sac. Although closely applied, it did not adhere to the pulp, but, as stated above, surrounded it on all sides till within a short distance of its base " whatever eminences or cavities the one had, the other had the same, but reversed, so that they were moulded exactly to each other." In the incisives its principal mass lay " against the hollowed inside of the tooth, and in the molars it was placed directly against their base like a tooth of the opposite jaw." In the pulps of the molars, which had three canals which now passed completely across their bases, the granular substance sent a process into each of them. These processes did not meet in the centre, but disappeared near to it, and left, as in the case of the general mass, a minute portion of the grey membrane of the sac between themselves and the secondary bases of the pulp.* In the case of the molars also the dental arterial * The only authors, as far as I know, who have observed and described this gelatinous body, are Mr. Hunter in his Natural History of the Teeth, p. 94, and Purkinje and Kaschkow, in the work of the latter, entitled, Meletemata circa Mammalium dentium evolutionem. Not having been able, hitherto, to procure Raschkow's work, I can only state from Burdach (Physiologic, French ed. torn. iii. p. 498), that Purkinje's opinion appears to coincide with Mr. Hunter's as to its being the organ which secretes that enamel. Mr. Hunter has not described the processes which this body sends under the pulp, or the PULPS AND SACS OF THE HUMAN TEETH. 21 branch divided into three twigs, one for each secondary base of the pulp, and from all of these, radiating perpendicular ramuscules proceeded, as in the case of a pulp with a pri- mary base. The arterial network, which was formed in the external spongy membrane by the inosculation of these vessels with those proceeding from the gums, transmitted small branches, which ramified with such minuteness in the substance and on the surface of that portion of the grey membrane to which the granular matter adhered, that, when the latter was re- moved, the former appeared to the naked eye a mass of vermilion, but under a one-fourth of an inch lens exhibited a network of the most minute injection. No injected vessel could be seen in the granular substance.* The main dental twig, after giving off all these branches, arrived at the base or secondary bases of the pulp, and immediately divided into many branches, which ramified in a contorted flattened position, between the base or bases of the pulp and the mem- brane of the sac. From these, smaller ramifications were transmitted into the substance of the pulp, which ramified in considerable numbers in the centre of its mass, but scarcely at all near its surface or on its membrane, except in the neigh- bourhood of, and at the point where, deposition of tooth- space left between it and the base of the latter ; but his description is in other respects so correct and characteristic, that it is difficult to account for the manner in which the first part of his chapter on the formation of the enamel has been so much misunderstood. Dr. Blake (p. 34) (although he described the granular body as the inner membrane of the tooth-sacs, and as possessing " no vessels capable of conveying red blood ") supposed that Mr. Hunter meant by "another pulpy substance," the sacs of the permanent teeth. Mr. Bell also in a note, vol. ii. Palmer's ed. Hunter's Works, p. 43, states that after most accurate observations, he had come to the conclusion that the " pulpy substance" mentioned by Hunter is nothing more than the inner membrane of the sac turgid with blood and earthy matter preparatory to the secretion of the enamel. * Blake, Essay on the Structure and Fon/uUioti of the Teeth, p. 4. 22 ON THE ORIGIN AND DEVELOPMENT OF THE substance had commenced, immediately beneath which the vascularity was intense, both in the substance under, and on the surface a little beyond, the edge of the scale.* This surrounding vascularity had the appearance of a zone, and was situated in the substance and on the surface of an ele- vated portion of the pulp, which surrounded the scale of tooth- substance. The granular substance in contact with the tooth-substance and its border had begun to be absorbed, and had consequently become thinner in that situation than elsewhere, allowing the subjacent vascularity to appear through it. No vessel could be detected in the granular substance to account for the absorption of its inner surface. The ten little cavities had undergone no change, except that the two or four anterior had become rather longer, and were situated further from the surface of the groove, so as to be placed rather behind than below the sacs. The anterior cavity, in particular, although its walls were still in contact, and required to be separated by the needles under water to see its interior, had become pear-shaped. The fundus or portion furthest from the gum exhibited on its floor a fold, which lay in the direction of the edge of the future permanent tooth, and near its apex there were two other minute folds, one on the anterior wall, the other on the posterior. Beyond this the cavity terminated in an opaque IMPERVIOUS line, which soon disappeared. The substance of the gums had become infiltrated with a quantity of gelatinous matter very similar to the granular substance of the sacs. In consequence of this infiltration the line of junction of the walls of the dental groove had become obliterated, the substances of the gums had become thicker, and the sacs more removed from the surface. The open portion of the groove (a, Fig. 19) had disappeared, * Sevres, Easai sur I 'Anatomic d la Physiologic dcs Dents, p. 20. PULPS AND SACS OF THE HUMAN TEETH. 23 Fig. 22. but a longitudinal section showed that the lips only had adhered, the walls had not. The follicle (6, Fig. 22) had become a sac, in conse- quence of which a cavity (&) remained be- tween it and the surface of the gum. Gela- tinous substance had been deposited in the sac (6), and in the neighbourhood of the cavity below it (b), as in the other sacs. The lower jaw exhibited changes analogous to those in the upper. 12. Child at Birth. A longitudinal section was made through the posterior part of the under jaw, when the sacs and pulps of the posterior milk-molar, and of the first permanent molar, and the arrangements represented in Fig. 23, were observed. (5) The sac and Fig. 23. pulp of the posterior milk-molar ; (6) the sac and pulp of the first permanent molar ; (&) the cavity marked (b, Fig. 22). The sac of the permanent tooth (6) was now almost wholly imbedded in the base of the coronoid process of the jaw. The cavity (b) which was attached to the upper part of the sac of the permanent tooth by its posterior extremity, adhered by its anterior extremity to that point of the gum which was attached to the anterior edge of the base of the coronoid process, so as to drag its surface at that point into a dimple. The cavity (b) was consequently longer than it was at its first formation. The granular substance had wholly disappeared. The interior of the sacs had a villous highly-vascular appearance, like a portion of injected intestinal mucous membrane. The original opening of the sac (6) into the cavity (6) was indicated on its inner surface by an indistinct circular lip. The sacs 24 ON THE ORIGIN AND DEVELOPMENT OF THE) of one of the central incisives of the same fcetus exhibited externally nothing peculiar. After a transverse section, it was found to be composed of two, the temporary and permanent combined. The walls of the temporaiy sac (b, Fig. 23) were composed of an external membrane, which was rather thick and con- densed ; the inner could be separated from it, and had the appearance, as in the molar sacs, of an injected villous membrane. The little permanent sac was situated in the substance of the outer membrane of the temporary sac, as if the latter had been split to receive it. It was lined by a membrane similar to that of the temporary, and exhibited near the lower end of its posterior wall the incipient pulp, which was evidently a development of the fold observed in that situation at the fifth month. It terminated towards the gum by an indistinct pointed extremity, from which a short opaque impervious line proceeded, near to which the anterior and posterior folds, observed at the fifth month, were seen. 13. The lower jaw of an infant about eight or nine months old, in which the central incisives had cut the gum, was pre- pared by removing a section from its external posterior lateral aspect, so as to expose the sacs of the posterior milk-molar, and of the anterior permanent molar (x, Fig. 24). The latter (6), instead of being buried in the base of the coronoid process, was situated further forward, and the cavity (ft) having been displayed by a longi- tudinal section of the former, was found, comparatively speaking, to have recovered its original small extent, being attached in- feriorly to the top of the sac (6), and superiorly to the an- terior edge of the base of the coronoid process. PULPS AND SACS OF THE HUMAN TEETH. 25 Upon examining the two incisive teeth which had cut the gum, it was found that a bristle could be inserted between their surfaces and the gum for one-third of an inch. Through the soft parts a transverse section was made, which was after- wards continued through the jaw and one of the teeth by means of a very fine saw. It was now observed that the tooth (#, Fig. 24, y) had acquired nearly two-thirds of its fang, and that the sac had again become an open follicle (&). This follicle was shorter than the whole length of the tooth by the length of the pro- truding portion of the latter. At the mouth of the follicle, its lining membrane was continuous with the surface of the gums, and continued free till it arrived at the termination of the enamel, where it united to the surface of the fang of the tooth, but could be separated from it as a continuous membrane, and at the lower end of the root it became continuous with the surface of the pulp, whose base was yet considerable. Upon removing the bone in front of the neighbouring lateral tooth, which had not yet passed through the gum, it was observed that the extremity of its fang, or rather the fundus of its sac, was deeper in the jaw than that of the central by a length equal to the protruding portion of the latter. This change of level had not, however, taken place in the case of the alveoli, that of the central being rather deeper than the lateral. The space intervening between the bottom of the alveolus of the central tooth and the fundus of its sac was occupied by a spongy filamentous tissue, through which the dental vessels and nerves proceeded. 14. The lower jaw of an infant, which had cut all its milk-teeth, and which was probably between four and five years old, was prepared in the same manner as the last. The sac of the anterior permanent molar (6, Fig. 25) was situated under the gum in front of the coronoid process, and a 26 ON THE ORIGIN AND DEVELOPMENT OF THE new sac and pulp of a smaller size (7) had appeared buried in the base of that process. The cavity (b) was again lengthened out, being attached anteriorly, at the anterior edge of the base of the process, to the gum, and posteriorly to the top of the new sac (7). That portion of the cavity formerly attached to the sac (6) was now almost obliterated. 15. The posterior part of the .lower jaw of a child about six years old was prepared by removing a section from its internal posterior aspect, and making at the same time a longitudinal section of the gum. The sac (7, Fig. 26) had ad- vanced from under the coronoid process ; and another very small sac and pulp had appeared en- closed in a bony crypt under the process, and communicat- ing through the upper part of the bony cell of the sac (7) with the gum, where it terminated in an opaque line or tail, the last remains of the surface of adhesion of the dental groove. SECTION II. A DESCRIPTION OF THE PULPS AND SACS FROM THEIR FIRST APPEARANCE IN THE EMBRYO TILL THE ERUPTION OF THE WISDOM-TEETH. When we examine the upper jaw of a human embryo at the sixth week, there is perceived between the lip and a semi- circular lobe of a horse-shoe form (which is the primitive condition of the palate) a deep narrow groove which ter- minates on each side, behind the former, by curving inwards on the soft mucous membrane. As this groove becomes PULPS AND SACS OF THE HUMAN TEETH. 27 gradually wider, and the lip more lax in a direction from behind forwards, there appears on its floor posteriorly, and proceeding in the same direction, a ridge (the external alveolar process) which speedily divides the original groove into two others ; the outer one forming the duplicature of mucous membrane from the inside of the lip to the outside of the alveolar process, the inner one constituting what may be very properly denominated the primitive dental groove, as the germs of the teeth appear in it. The inner side of the ridge already mentioned, after being cut into three grooves whose concavities look inwards, and of which the posterior is the deepest, terminates in a rounded lobule, which is continuous with it anteriorly, while externally, internally, and posteriorly, it is bounded by that portion of the original groove which was situated behind the semicircular lobe. The curves of the ridge are occupied by bulgings of the semicircular lobe, so that the ridge and lobe, with their curves and bulgings, are exactly similar to the arrangement of the mucous membrane of the second compartment of the stomach of the porpoise. At some period between the sixth and seventh week a longitudinal portion is cut off from the internal posterior edge of the semicircular lobe, extending as far forwards as the middle bulging, and about the same time the posterior bulging becomes isolated and defined, under the appearance of an ovoidal papilla, the long diameter of which is antero-posterior. This papilla is the germ of the anterior superior milk-molar tooth, the first tooth-germ which appears in the development of the human body. It is at this period a simple free granular papilla, like many others on the surface of the mucous membrane and skin. About the eighth week or second month a second papilla appears at the point of projection of the ridge, between the middle and anterior curve. This papilla, which is the germ of 28 ON THE ORIGIN AND DEVELOPMENT OF THE the superior milk canine tooth, is rounded and granular, and is bounded externally by a triangular lamina, which spreads out into, and is continuous with, the inner edge of the ridge, having its apex notched so as to fit the external aspect of the papilla. During the ninth week the ridge advances in an indistinct manner to the median line, and there appears on each side of that line an oblong papilla with a notched lamina in front of it, and immediately afterwards another smaller papilla and lamina external to the former. These last papillae are the germs of the incisive teeth, and are placed in connection with the lateral elements of the intermaxillary system. The primitive dental groove, which before the appearance of the incisive germs terminated anteriorly at the outer ex- tremity of the lateral intermaxillary lobules, now extends forwards to the median line. The longitudinal lobule, and the lobule opposite to it also, have lengthened out posteriorly, and the intervening portion of the primitive groove has become wider and not so curved. The sides of the groove before and behind the anterior molar papilla have been gradually approaching one another. During the tenth week the incisive papillae make very little advance, their anterior laminae only increasing some- what in size. Processes from the sides of the primitive dental groove, particularly the external one, approach and finally meet before and behind the papilla of the anterior molar, so as to inclose it in a follicle, through the mouth of which it may be seen. A similar follicle is gradually formed round the canine by the advancement inwards of its external notched lamina, which at first appeared as a production of the ridge or external lip of the groove. The germ of the posterior milk- molar also appears as a small papilla towards the end of this week behind the anterior molar, at the side and apparently as a production from the rounded lobule, which terminates pos- teriorly the outer ridge. PULPS AND SACS OF THE HUMAN TEETH. 29 During the eleventh and twelfth week the incisives ad- vance steadily. Septa pass between them from the outer to the inner side of the groove, so that their papillae become completely sunk in well-developed follicles. No material change takes place in the anterior molar or canine ; but the posterior molar papilla enlarges, and the terminal lobule of the outer ridge folds gradually round it, so as to constitute its follicle, behind which there still remains a portion of the primitive groove. The changes which ensue during the thirteenth week con- sist in the completion of the follicle of the posterior molar, and in the gradual change which takes place in the shape of the different papillae. Instead of remaining, as hitherto, simple, rounded, blunt masses of granular matter, each of them assumes a particular shape. The incisives acquire in some degree the appearance of the future teeth ; the canines become simple cones ; and the molars become cones flattened transversely, somewhat similar to carnivorous molars. During this period, too, the papillse grow faster than the follicles, so that the for- mer protrude from the mouth of the latter, while the depth of the latter varies directly as the length of the fangs of their future corresponding teeth, the canine follicle being deepest, etc. etc. While the papillse are changing their shape, the mouths of the follicles are undergoing a change which con- sists in the development of their edges, so as to form operciila, which correspond in some measure with the shape of the crowns of the future teeth. There are two of these opercula in the incisive follicles, one larger, anterior, and rather ex- ternal, the second smaller, posterior, and internal. There are three for the canines, an external and two internal, and four or five for the molars, each corresponding with a tubercle ; while their edges correspond with the grooves on the grinding surfaces of these teeth.* * It would be interesting to ascertain whether the opercula of the human 30 ON THE ORIGIN AND DEVELOPMENT OF THE The inner lip of the dental groove (or the outer edge ol the palate), which has been increasing for some time past, is now, at the fourteenth week, so large as to meet and to apply itself in a valvular manner to the outer lip or ridge, which has also been increasing. The follicles at this time grow faster than the papillae, so that the latter recede into the former. The molar papillae gradually acquire two or three additional small compressed tubercles on their sides, and their apices become less conical, so that they still more resemble the molar teeth of the carnivorous mammals.* The opercula of the follicles continue to increase, so as almost to hide their contained papillae. The primitive dental groove, which at this period contains ten papillae in as many follicles, and is situated on a higher level than at first, may be now more properly denominated the secondary dental groove. It is when in its secondary condition that the groove affords a provision for the production of all the permanent teeth, with the exception of the first or anterior tooth-follicles may not be rudimentary organs, which are to attain their utmost development in the sacs of the elephantoid, ruminant, and other compound teeth, under the form of depending folds for the secretion of the intersecting enamel and cement plates. One may easily conceive the mode of formation of a composite tooth-sac, by supposing the opercula, after their edges have met, to dip down back to back between the divisions of the pulp, till they almost meet the common body of the latter. * This is another instance of the law of progressive development, by virtue of which an organ, in the course of its formation, passes through phases which correspond to permanent conditions of the same organ in other animals. A human molar tooth-pulp is at first rounded, as in certain fishes ; then conical, as in other fishes and reptiles ; then conical, but flattened transversely, gradu- ally acquiring two or more additional conical tubercles, as in the carnivorous mammals ; and finally, by the equalisation of the primary and secondary tubercles, assuming the shape of the molars in the quadrumanous animals and man. In the elephantoid, ruminant, and rodent animals, it probably under- goes a further and ultimate change in the deepening of the rudimentary grooves on the grinding surface. PULPS AND SACS OF THE HUMAN TEETH. 31 molars. It is about the fourteenth or fifteenth week that we begin to observe preparations made for this provision, -by the gradual appearance of a little depression in the form of a crescent, immediately behind the inner operculum of each of the milk-tooth follicles. The concave edges of these depressions are in contact with the attached margins of these opercula. Those of the centre incisives appear first, then the laterals, canines, anterior bicuspids, posterior bicuspids. About this time the opercula close the mouths of the follicles, but with- out adhering, the anterior closing first, then the laterals, and so on in succession. The lips and walls of the secondary groove now begin to cohere in a direction from behind for- wards, the opercula and every part of the groove, with the exception of the ten depressions for the permanent teeth, be* coining rough, flocculent, and adherent. The follicles have now become the sacs ; the papillae the pulps of the milk-teeth ; and the crescent-formed depressions vacant cavities of reserve, to furnish delicate mucous membrane for the future forma- tion of the pulps and sacs of the ten anterior permanent teeth. The general adhesion does not invade that portion of the primitive dental groove which is situated behind the posterior milk-molar follicle. This small portion retains its original appearance, greyish-yellow colour, and smooth edges, for a fortnight or three weeks longer, and affords a nidus for the development of the papilla and follicle of the anterior per- manent molar-tooth, the fundus of its follicle being situated immediately behind the sac of the posterior milk-molar. The cavities of reserve for the ten anterior permanent teeth are at this period minute compressed sacs, with their sides in contact, and situated between the surface of the gum and the milk-sacs. The papillae of the milk-teeth, from the time that their follicles close,* become gradually moulded into their peculiarly * Herissant in the Mem. de I'Acadcmie Royale, 1754, p. 664, described two grnns the " gencive permanent, " and the " gencive passagere. " His ideas 32 ON THE ORIGIN AND DEVELOPMENT OF THE human shape. The molar pulps begin to be perforated also by three canals, which, proceeding from the surface to their centres, gradually divide their primary base into three second- ary bases, which become developed into the fangs of the future teeth. While this is going on, the sacs grow more rapidly than the pulps, so that there speedily exists an intervening space in which is deposited a gelatinous granular substance, at first in small quantity, and adherent only to the proximal surfaces of the sacs ; but ultimately, about the fifth month, closely and intimately attached to the whole interior of these organs, except for a small space of equal breadth, all round the base of the pulp, which space retains the original grey colour of the inner membrane of the follicle ; and as the primary base of the pulp becomes perforated by the canals formerly men- tioned, the granular matter sends processes into them, which, adhering to the sac, reserve the narrow space described above between themselves and the secondary bases. These processes of granular matter do not meet across the canals, but dis- appear near their point of junction. The granular matter is closely applied, but does not adhere to the surface of the pulp. " Whatever eminences or cavities the one has, the other has the same, but reversed, so that they are moulded exactly to each other." Each branch of the dental artery, as it arrives at the fundus of its destined sac, sends off a number of radiating twigs, which run in the substance of the cellular submucous tissue (which constitutes the outer membrane of the sac) towards the gum, from which others proceed to inosculate with them. The on the subject appear to have been derived from the examination of jaws in which the lips and walls of the secondary dental groove "gencive passagere," had not become completely adherent or obliterated. In this way the indistinct mouths of the milk-tooth sacs on the floor of the groove "gencive permanent," did not escape the notice of this most accurate observer. The cartilages of the gum described by Serres (Essai, p. 10) are to be considered as the walls of the groove in the semicartilaginous condition which they assume after closure. PULPS AND SACS OF THE HUMAN TEETH. 33 combined twigs then ramify minutely in the true membrane of the sac without sending the smallest twig into the granular substance.* The dental branch, after giving off these saccular twigs, divides into a number of contorted ramifications between the base of the pulp and the sac, which from smaller ramusculi are transmitted into the pulp itself. In the case of the molars, the main branches divide into three secondary branches, one for each of the secondary bases. From these, three sets of saccular twigs, and three packets of contorted pulp-vessels, take their origin. While these changes have been taking place in the sacs of the milk-teeth, the follicle of the first permanent molar closes, and granular matter is deposited in its sac. The walls of that portion of the secondary groove below it do not adhere ; the edges alone do so. There is, therefore, a cavity of considerable size below the sac of this tooth, or between it and the surface * Mr. Fox (Natural History of the Human Teeth, p. 20) and Mr. Bell (Anatomy of the Teeth, p. 54, and in a note, p. 39, vol. ii. Palmer's edition of Hunter's Works) have both misunderstood the statements of Mr. Hunter and Dr. Blake on the relative vascularity of the membranes of the tooth-sacs. (Hunter's Natural History, p. 84, and Blake, p. 4.) What Blake denominates the internal lamella is the enamel pulp of Hunter, Purkinje, and Easchkow, the gelatinous granular substance described in the text. He, with great accuracy states that it is "more tender and delicate, and seems to contain no vessels capable of conveying red blood." Under the denomination "external lamella " he includes the proper vascular mucous membrane of the sac, and the external spongy submucous tissue. In his search after the germs of the per- manent teeth, Blake's attention appears to have been directed to the tooth-sacs when in the condition he describes. Mr. Hunter, again, who had a most correct conception of the constitution of the sacs, has, with his usual sagacity, not confounded the granular body, or, as he denominates it, "another pulpy substance," with the proper membranes of the sacs. Accordingly, in his account of the relative vascularity of the membranes of the sacs, he, when describing the manner in which a tooth is formed, has taken no notice of the pulpy substance. Dr. Blake describes the membranes of the sacs at an early period ; Mr. Hunter, again, in a child at birth, at which time the external membrane is not very vascular, and has assumed somewhat of the appearance of a fibro-cartilage. D 34 ON THE ORIGIN AND DEVELOPMENT OF THE of the gum. This cavity is a reserve of delicate mucous mem- brane to afford materials for the formation of the second per- manent molar, and of the third permanent molar or wisdom- tooth. A little before this period tooth-substance begins to be de- posited on the tubercles and apices of the pulps, which have acquired round the point of deposition a raised border and a zone-like vascularity ; and, synchronous with this deposition, absorption takes place on the inner surface of the granular matter immediately in contact with it. No vessel can be de- tected running to the point of absorption, but ultimately the granular matter becomes so thin as to allow the subjacent vascularity to appear. The absorption goes on increasing as the tooth-substance is deposited, and when the latter reaches the base of the pulp the former disappears, and the interior of the dental sac assumes the villous vascular appearance of a mucous membrane. This change is nearly completed about the seventh or eighth month. Up to this period little change has taken place in the ten anterior, or in the two posterior or great cavities of reserve. The ten anterior have been gradually receding from the sur- face of the gum, so as to be posterior, instead of inferior, to the milk-sacs. The two or four anterior began about the fifth month to dilate at their distal extremities, across which a fold appears (which is the germ of the future pulp) lying in the direction of the cutting edge of the future tooth ; and at the proximal or acute extremities of the cavities two other folds, an anterior and a posterior, appear.* These round off the un- * These two folds are strictly analogous to the opercula of the milk-tooth sacs. They never attain, however, the same high development as those of the latter, remaining in a rudimentary state, apparently in consequence of the almost saccular condition of the cavities of reserve. The existence of these laminae in a rudimentary state proves that in the formation of the permanent teeth there is a strict adherence to the law of follicular development even when, in man at least, there is no apparent necessity for it. * PULPS AND SACS OF THE HUMAN TEETH. 35 defined apices of the cavities, and are strictly analogous to the opercula of the milk-follicles. The distal fold gradually acquires the appearance of a tooth-pulp, while the proximal disappear by the obliteration of the little undefined space beyond them. The cavities of reserve have now become tooth-sacs, and under this form they continue to recede from the surface of the gum, imbedding themselves in the submucous cellular tissue, which has all along constituted the external layer of the milk-sacs, and in which the larger saccular vessels ramify before arriving at the true mucous membranes of the sacs. This implantation of the permanent in the walls of the temporary tooth-sacs gives the former the appearance of being produced by a GEMMIPAROUS process from the latter.* The dental groove was originally imbedded in an alveolar groove. As the dental interfollicular septa are developed in the former, osseous septa also begin to be formed in the latter. These osseous septa are at first in the form of bridges, but ultimately, at the sixth month, become complete partitions. * It was this imbedding of the permanent in the walls of the temporary tooth-sacs which deceived Dr. Blake, and led him to suppose that the former derived their origin from the latter. Mr. Fox supported the same view of the subject ; and Mr. Bell, in his own work (Anatomy, etc. etc. of the Teeth, p. 61), and more lately in his notes in Palmer's edition of Mr. Hunter's Works, vol. ii. p. 37, has strongly urged the same doctrine. Mr. Bell has stated that Mr. Hunter's "account of the manner in which the permanent teeth are formed is exceedingly imperfect," but it is evident that if the account of the origin of these teeth given in the text be correct, Mr. Hunter was not in error when he supposed both sets to be of independent origin. Mr. Hunter was so correct a thinker, that he did not account the circumstance of contiguity to be a proof of dependence. He was apparently ignorant of the origin of both sets, and in his usual cautious manner, when describing structure makes no observation on the subject. The author of the Edinburgh Dissector holds the same opinion as Mr. Hunter on this subject ; and in his excellent chapter on the teeth, although he does not disprove the opinions of Dr. Blake and others, cautions the student against supposing Mr. Hunter to be incorrect on this subject. 36 ON THE ORIGIN AND DEVELOPMENT OF THE As the sacs increase in size, the alveoli increase also, and when the permanent form slight projections behind the temporary tooth-sacs, niches '''' are formed for them in the posterior walls of the alveoli. Whilst this increase in the bulk of the sacs and alveoli is going on, there is no proportionate increase in the length of the jaw, in consequence of which, the sac of the anterior permanent molar has been insinuating itself into, and at the eighth month, or the full time, is almost wholly im- bedded in, the maxillary tuberosity,t and has become situated on a higher level than the milk-sacs, during which it has not only drawn the surface of the gum upwards and backwards, but has also lengthened out the great or posterior cavity of reserve. About this time the fangs of the milk-incisives begin to be formed, in the accomplishment of which three contempora- neous actions are employed viz. the lengthening of the pulp, the deposition of tooth-substance upon it, and the adhesion to the latter of that portion of the inner surface of the sac which is opposite to it. While the*fangs of the rnilk-teeth, particularly those in the front of the jaw, are lengthening in the manner now described, the pulps and sacs of the permanent teeth continue to increase, and the bony crypts which contain them to enlarge in pro- portion, the lower edges of the latter insinuating themselves between the two former. As this process continues, the jaw lengthens more rapidly, and when the infant is eight or nine months old, there is so much room in the alveolar arch, that the anterior permanent molar tooth begins to resume its former position in the posterior part of the dental arch, and the great cavity of reserve again to return to its original size and situation. About this time the central incisives begin to pass through * Bell, Anatomy, etc. of the Teeth, p. 62. f Hunter, Nat. Hist. Human Teeth, pp. 101, 102, 103. PULPS AND SACS OF THE HUMAN TEETH. 37 the gum a process which is accomplished in the following manner : The body of the tooth having been fully formed, and coated with enamel, has also been acquiring a portion of its fang by the triplex action formerly described ; in con- sequence of which, a reaction takes place between the bottom of the socket and the unfinished extremity of the fang. This reaction causes the body of the tooth and the non- adherent portion of the sac gradually to approach, and the former finally to pass through the surface of the gum. Till the time that the edge of the tooth passes through the gum, the fundus of the sac, and consequently the base of the pulp with the extremity of the fang, never change their common relative position in the jaw. At the moment, however, that the tooth passes through the gum (when the non-adherent portion of the sac resumes its primitive follicular condition, its inner membrane becoming continuous with the mucous membrane of the mouth) the non-adherent portion of the sac shortens more rapidly than the fang lengthens, in consequence of which the adherent portion with the fang itself separates from the fundus of the alveolus and the body of the tooth advances through the gum.* A space is thus left between the top of the alveolus and the fundus of the sac, occupied by cellular tissue, and traversed by the vessels and nerves. The alveolar cavity at the same time rapidly adapts itself to the new condition of its contents, advancing its edges so as to clasp the root, which has during these rapid changes been steadily lengthening a process which now goes on with greater rapidity, as it is conducted in a comparatively empty * The movement of the unfinished extremity of an incisive tooth from the fundus of its alveolus will explain what I have commonly remarked, and what must have been observed by medical practitioners, that from the time that the edge of the tooth appears through the gum, it advances more rapidly than can well be accounted for by the usual rate of lengthening of its fang. This ad- vance is not invariably rapid, but may be observed in all the incisive teeth, if careful daily examination be made during a normal dentition. ON THE ORIGIN AND DEVELOPMENT OF THE space. The pulp continues to lengthen till its base is no larger than the fasciculus of vessels and nerve which enters it. The orifice of the cavity of the tooth also diminishes to the same size, and through it the surface of the pulp becomes continuous with the adherent portion of the sac and con- sequently with the mucous membrane of the mouth. The adherent portion of the sac has now attained its maximum, and the free or open portion its minimum size, having been reduced to that narrow portion of the gum which forms a vascular border and groove round the neck of the perfected tooth* During the period that the milk-teeth have been advanc- ing along with their sockets to their perfect state and ultimate position in the jaw, the permanent sacs have been receding in an opposite direction, and have, as well as their bony crypts, been enlarging, the edges of the latter, insinuating themselves so far between the former and the milk-sacs, that at last they are only connected by their proximal extremities, and ulti- mately, when the lower edges of the crypts sink so far as to have become the posterior lips of the alveoli of the milk-teeth, the notches of communication between the latter and the permanent alveoli are forced, under the form of foramina, into a position on the anterior surface of the palate, one behind each milk-alveolus. The sacs of the bicuspids having assumed a position directly above the milk-molars, the hole * This vascular "border may be seen in healthy gums which have not been disturbed by the deposition of tartar, and is beautifully displayed in two wet injected preparations in the Bell collection, Museum of the Royal College of Surgeons, Edinburgh (Bell, C. iii. Nos. 25 and 56). It is interesting to observe that one of the first physiological effects of mer- cury viz. excitation of the gastro -intestinal compound glands and simple mucous follicles is also displayed in a similar manner in the borders which surround the necks of the teeth, which are the remains of the free portions of the tooth-sacs, while it at the same time acts upon the adherent portions and their submucous tissue, raising the teeth from their sockets, and affecting the jaw from contiguity. PULPS AND SA.CS OF THE HUMAN TEETH. 39 of communication is never removed from the sockets of the latter. The cords of communication which pass through these foramina are not tubular, although in some instances a portion of the unobliterated extrafollicular compartment of the ori- ginal little cavity of reserve may be detected in them. They are merely those portions of the gum which originally contained the lines of adhesion of the depressions for the permanent teeth in the secondary dental groove, and which have been subsequently lengthened out, in consequence of the necessarily retired position in which the permanent teeth have been developed during the active service of the temporary set. The cords and foramina are not obliterated in the child, either because the former are to become useful as " guber- nacula," and the latter as " itinera dentium," or much more probably, in virtue of a law, which appears to be a general one in the development of animal bodies viz. that parts or organs which have once acted an important part, however atrophied they may afterwards "become, yet never altogether disappear so long as they do not interfere with other parts or functions. t The sacs of the permanent teeth derive their first vessels from the gums ; ultimately they receive their proper dental vessels from the milk-sacs, and as they separate from the latter into their own cells, the newly-acquired vessels con- joining into common trunks, retire also into permanent dental canals. It was stated above that, in the child at the seventh or eighth month, when the central incisives were passing through the gums, the jaw had lengthened so much as to allow the first permanent molar to retire from the maxillary tuberosity, and to resume in some measure its position downwards and forwards in the same line with the other teeth, and also to reduce the great cavity of reserve to its primitive size. This 40 ON THE ORIGIN AND DEVELOPMENT OF THE cavity of reserve now begins to lengthen, to bulge out, and to curve backwards and upwards at its posterior extremity, under the form of a sac, into the mass of the maxillary tuberosity ; a papilla or pulp appears in its fundus, and a process of con- traction separates it from the remainder of the cavity of reserve, which still adheres to its proximal wall by one extremity, while by the other it is continued into the substance of the gum under the anterior molar. This new sac, which is that of the second permanent molar, now occupies the position in the maxillary tuberosity which the first permanent did before it. It afterwards leaves this retired position, in consequence of the lengthening of the jaw allowing it to fall downwards and forwards into the line, and on a level with the other teeth.* Before it leaves the tuberosity altogether, the posterior extremity of the remainder of the cavity of reserve sends backwards and upwards its last offset the sac and pulp of the wisdom- tooth, which speedily occupies the tuberosity after the second molar has left it, and ultimately, when the jaw again lengthens for the last time, at the age of nineteen or twenty, takes its place at the posterior extremity of the range of the adult teeth. The wisdom-teeth are the second products of the posterior * The curved lines which the posterior cavities of reserve, and the sacs of the molar teeth, describe in their progress to and from the maxillary tuber- osity, and the coronoid process, and the peculiar position in which the pulps are consequently developed, explain satisfactorily certain normal and abnormal conditions of these teeth : 1. The curves which the combined grinding sur- faces of the molar teeth present, convex downwards and backwards in the upper jaw, concave upwards and forwards in the lower. 2. The peculiar manner in which the fangs of the molars, particularly the inferior, are bent backwards. 3. The occasional horizontal position of the wisdom-teeth, the crowns of the inferior being directed forwards, those of the superior backwards. This abnormal position is the cause of much annoyance and danger to the patient, and of difficulty to the surgeon. PULPS AND SACS OF THE HUMAN TEETH. 41 or great cavities of reserve, and the final effects of develop- ment in the secondary dental groove.* In the lower jaw, as in the upper, dentition commences in a deep narrow groove, situated between the lip and a semi- circular lobe. This groove, instead of terminating in a simple curve posteriorly, as in the upper jaw, becomes shallow, and assumes a sigmoidal form upon the surface of the posterior bulbous ovoidal portion of the lobe. About the seventh week the lip becomes very loose, and separates widely from the lobe, between which and the former a ridge appears, growing from behind forwards, and dividing the original groove into two, an outer one the labial dupli- cature of mucous membrane, and an inner the primitive dental groove. This ridge, which, as in the upper, does not yet extend to the incisive portion of the jaw, is flat, or in the same continuous plane with the bottom of the dental groove, and its lip is turned out, or overhangs the labial mucous membrane. The inner lip of the groove is formed by the semicircular lobe, which has become thin, and arched over the groove, particularly anteriorly, where it is cut into four festoons, two on each side of the median line ; and posteriorly, where it still retains the appearance of an oval lobe, from under which the outer lip or ridge appears to proceed. The groove curves inwards between the two lips posteriorly, under a form which is evidently a development of the original sigmoidal groove. Near the posterior extremity of the groove there is an elevation of a small portion of its floor, which speedily becomes the germ or papilla of the inferior anterior milk- molar tooth the second tooth which appears in the primitive * It is probable that the successive dentitions of the elephant are conducted in a cavity of reserve, which must consequently exist even in the adult animal, till a late period of its life. If such be the case, the molar dentition of the ele- phant, and the formation of the human adult molars, are analogous processes. 42 ON THE ORIGIN AND DEVELOPMENT OF THE development of the human body. During the eighth week the elevation already mentioned becomes a papilla, length- ened from behind forwards, and flattened transversely. About the same time another papilla, bounded by a notched lamina, similar to those on the upper jaw, makes its appearance further forward in the groove. This papilla is the germ of the inferior milk-canine. The dental groove is about the same time continued forward to the median line, not by the advancement of its outer ridge, but by the elevation of its floor. Its posterior portion also has become wider and not so curved. During the succeeding week the incisives make their appearance, the centrals first. From this time all the eight papillae continue to increase. The notched laminae shoot inwards to the inner lip of the groove, near which they meet and join slight projections from it. About the eleventh or twelfth week the germ of the posterior milk-molar appears in the curved portion of the groove, and is developed in the usual manner. Crescent-like depressions appear in the secondary groove, on the inner side of the mouths of the milk-follicles, as in the upper jaw. The secondary groove adheres, leaving a posterior open portion, in which are developed the papilla and follicle of the first permanent molar. This follicle closes, as well as the lips of the portion of groove above it. There are now in the jaw ten milk-tooth sacs, two permanent-tooth sacs, ten anterior cavities of reserve, and two great or posterior cavities of reserve ;* the ten anterior for the development of the incisives, * The mucous membrane constituting the cavities of reserve exists in a condition which has hitherto been considered by anatomists as peculiar to the serous membranes. A dental cavity of reserve is a shut sac, lined by a true mucous membrane, which is isolated from the general mucous system, and per- forms no special function, till it is called upon to supply what it alone can afford, materials for the development of a tooth. PULPS AND SACS OF THE HUMAN TEETH. 43 canines, and bicuspids ; the two posterior for that of the second and third molar,* the coronoid process acting the part which the maxillary tuberosity did in the upper jaw. SECTION III. 1. On the Division of Dentition into Stages. As dentition is a process, not only very complicated in its details, but of very lengthened duration, extending over nearly eight months of intra-uterine, and above twenty years of extra-uterine existence, the understanding and further investigation of it may be facilitated by dividing it into stages. The most natural division, one which is not artificial, but clearly indi- cated by the phenomena themselves, is into three stages, according to the position of the pulp in relation to its con- taining cavity 1st, follicular stage ; 2d, saccular ; 3d, eruptive. We ought probably to consider, as anterior to the follicular, the papillary stage t during which the follicle or sac does not exist, and the future pulp is a simple papilla on the free surface of the gastro-intestinal mucous membrane. As this stage, * The cavities of reserve are occasionally somewhat undefined, two or three being conjoined, particularly posteriorly. Sooner or later, however, they become distinct. The great cavity frequently stretches forwards over the sacs of the milk-molars. f Most anatomists have supposed the germs of the teeth to appear as shut sacs, full of a fluid, the pulps being formed by inspissation of the latter, or by development from the walls of the former. Neither Mr. Hunter nor Mr. Bell has stated anything very definite on this subject. The pulp must be con- sidered as the principal part of the organ, and as the element which appears first. The sac is a mere subsidiary part, supplied for purposes of development and nourishment. Handbuch der Anatomic des Menschen, von. H. Hilde- brandt, besorgt. von E. H. Weber, Erster Band, p. 212 ; Handbuch der Entwickelungs-geschichte des Menschen, von Yalentin, p. 482 ; Arnold, Salz- burg Medicinisch-Chirurgisch Zeitung, 1831, Erster Band, p. 236 ; Cruveilhier, Anatomie Descriptive, vol. i. p. 518 ; Serres, Essai sur V Anatomie, etc., des Dents, p. 59; Ph. Fr. Blandin, Anatomie du Systeme Dentaire, etc., p. 87; Blake, Essay on the Human Teeth, p. 2. 44 ON THE ORIGIN AND DEVELOPMENT OF THE however, is short in its duration, and simple in its details, it may be included in the first stage. The first or follicular stage comprehends all the phenomena which present themselves from the first appearance of the dental groove and papillas till the latter become completely hid by the closure of the mouths of their follicles, and of the groove itself. It is upon this hitherto unknown stage of dentition that I have insisted so much in the former sections of this paper. The second or saccular stage is the one with which ana- tomists have been so long familiar, during which the papillae are pulps, and the open follicles which contain them are shut sacs, when the tooth-substance and the enamel, constituting the teeth themselves, are deposited. It is during this stage, also, that some of the most interesting phenomena in the formation of the alveolar processes present themselves. The third or eruptive stage includes the completion of the teeth, the eruption and shedding of the temporary set, the eruption of the permanent, and the necessary changes in the alveolar processes. When viewed in reference to an individual tooth, these three stages are distinct ; but when viewed in reference to both sets, and to the whole process of dentition, they become somewhat intermingled. When considered in the latter point of view, we may state that the follicular stage commences at the sixth or seventh week, and terminates at the fourth or fifth month of intra- uterine existence ; that the saccular commences at the ter- mination of the first, and lasts for certain of the teeth till the sixth or eighth month, and for others till the twentieth or twenty-fifth year of extra-uterine existence; and that the third or eruptive commences at the sixth or eighth month, and lasts till the twentieth or twenty-fifth year. PULPS AND SACS OF THE HUMAN TEETH. 45 On the Anterior Permanent Molar Teeth. The anterior permanent molar is the most remarkable tooth in man, as it forms a transition between the milk and permanent set. If considered anatomically, it is decidedly a milk-tooth ; if physiologically, a permanent one. In a former part of this paper, it was stated that the papilla and follicle of this tooth were developed in a small portion of the primitive dental groove, which remained open for that purpose till the fourth or fifth month, while all the other permanent teeth were pro- ductions, not from the primitive groove, but from small non-adherent portions of the secondary groove, which lay in a level superior to the shut orifices of the sacs of all the milk- teeth, and of the tooth in question the first permanent molar. In reference to its function, however, as the most efficient grinder in the adult mouth, we must consider it as a permanent tooth. It is a curious circumstance, and one which will readily suggest itself to the surgeon, that, laying out of view the wisdom-teeth, which sometimes decay at an early period from other causes,* the anterior molars are the permanent teeth, which most frequently give way first, and in the most sym- metrical manner, and at the same time, and frequently before the milk set. On the Tardy Development of the Superior Incisive Teeth. A reference to the first section of this paper will show that at the ninth week, when the {mpillse of the superior incisives are quite distinct, those of the inferior are with difficulty recog- nised. This is a fact which may be included under a law which will be more fully referred to afterwards viz. that the dentition of the upper precedes, and is always in advance of, the same process in the lower 'jaw. A week or two later, however, when the papilla? of the inferior incisives are imbedded and hid in deep follicles, those of the superior are * Bell, Anat. etc. of the Teeth, p. 133. 46 ON THE ORIGIN AND DEVELOPMENT OF THE nearly in their original condition. Although the latter recover in some degree their lost ground, yet, as every one knows, the inferior central incisive almost always cuts the gum before the superior, and the lateral sometimes does so also. In order to explain this apparent exception to the law above mentioned, it will be necessary to go a little into the history of the inter- maxillary bones, in doing which reference must necessarily be made to some of the other bones of the face and head. When the superior portion of the large common nasal buccal and pharyngeal cavity is exposed in an embryo of the sixth or seventh week, by removing the lower jaw, we observe the boundary of the future palate to be defined by what has been denominated in a former section the horse-shoe lobe (c, Fig. 2). Attached to the posterior inner edges of this lobe two other lobes are seen. These grow from behind forwards, and from without inwards, and complete the palate by joining in the median line, being assisted in doing so posteriorly by two other smaller lobes behind the posterior extremities of the horse-shoe lobe. In the two first lobes become developed the palatine plates of the superior maxillary bones, and in the two smaller posterior the palatine plates of the palate bones. The bar (h, Tigs. 2 and 4), which ultimately coalesces below with the median line of suture of the four last men- tioned lobes, is proved by development to contain the nucleus of the vomer. The median lobule (m) and its' two lateral and anterior appendages (n ri) form the anterior division of the embryonal palate. Of these three, the two lateral are observed in the course of development to contain the nuclei of what are usually denominated the intermaxillary bones. With regard to the median it may be stated that, as all the other lobules which appear in the soft pulpy texture of the foetal palate are proved by development to contain the nuclei of all the well-known bones of this region, I am inclined to consider it PULPS AND SACS OF THE HUMAN TEETH. 47 as indicative of the existence of the rudiment of a bone also, especially when the interesting antagonism, which I will show exists between it and the lateral lobules, is taken into con- sideration.* As the object of this part of my paper, however, is not to discuss the osteogenesis of the human head, but to explain why the inferior incisive teeth, although later in their appear- ance, are yet more rapid in their progress than the superior, I shall now recall some circumstances formerly detailed re- garding the development of the three intermaxillary lobules, immediately before and for some time after the appearance of the incisive papillae. During the seventh week the three lobules are equal, and there is no appearance of either the upper or lower incisive teeth. During the eighth week the median lobule has increased relatively, and the laterals only absolutely ; while as yet there is no appearance of either the upper or lower incisives. During the ninth week the median has diminished re- latively, and in the transverse direction ; the laterals again have increased relatively and also in the transverse direction. This relative transverse increase of the lateral lobules is syn- chronous with the first appearance of the upper incisives. The inferior incisives are so indistinct at this time, as to be recog- nised with difficulty as slight bulgings on the floor of the dental groove. During the next fortnight the relative size of the median * A small cartilaginous body exists in the median intermaxillary lobule of the child at birth. It is situated in front of the inferior orifice of the naso- palatine canal, and between the mucous membrane and periosteum. The median intermaxillary lobule exists in the adult palate, and may be felt behind and between the central incisives. Median intermaxillary bones and cartilages exist in certain of the lower vertebrata. The bar-like vomer of the human embryo at the sixth and seventh week reminds the anatomist of the adult vomer of the lower vertebrata. 48 ON THE ORIGIN AND DEVELOPMENT OF THE and lateral lobules remains the same, and there is no further development of the superior incisives. During the same period the inferior incisives have been rapidly increasing. Afterwards the median undergoes much relative trans- verse diminution, while at the same time the laterals acquire a remarkable relative increase, which is accompanied by a corresponding development of the superior incisives ; but the inferiors have now got so much in advance as to retain their advantage ever after. On the Laws which regulate the development of the Pulps and Sacs, and the period of appearance of each of the Tooth- Germs. In the description which has been given of the earlier phenomena of dentition, it will be perceived that many of them range themselves under the laws recognised by MM. G. St. Hilaire, and Serres viz. the law of symmetry (loi de sym- metric), the law of conjunction (loi de conjugaison), the law of balancing or antagonism (le balancement des organes), and the law of eccentric development (loi du developpement excentrique). The primitive and secondary dental grooves, the follicles, the cavities of reserve, the osseous alveoli of the milk-teeth and their septa, are all formed originally of two halves, which ultimately join according to the laws of symmetry and con- junction. The pulps of the milk-teeth* with their notched laminae are productions from the external lip or ridge of the groove. The interfollicular septa, and the osseous alveolar septa, are also developed from without inward (loi du developpement excentrique). I have already pointed out the beautiful example of * It is a curious fact, that the first tooth-germs which appear viz. those of the superior anterior and inferior anterior milk-molars are not productions from the external lip of the dental groove, but bulgings on its floor. PULPS AND SACS OF THE HUMAN TEETH. 49 antagonism which exists between the median and lateral elements of the intermaxillary system ; and I may now point out, from among the facts formerly detailed, a few instances of the same kind, which must be referred to the same general expression (loi de balancement). 1. Before the tenth week the upper lip is full and pro- minent, but at that time it begins to recede and gradually to disappear anteriorly, so as to expose the follicles and papillae of the incisive teeth. It afterwards begins to regain its former position and size, and at the fourteenth or fifteenth week it is as large as the inferior, which from the first has not changed its appearance. At the tenth week, when the lip begins to recede, the maxillary palate advances its anterior extremity, so as to con- ceal in some degree the intermaxillary palate (median and lateral lobules). When the middle of the lip has disappeared, the maxillary has not only encroached upon the intermaxil- lary, but has also thrown itself into a bundle of irregular folds at its anterior part. As the maxillary palate retires, and the folds become regular crenated rugse, the anterior part of the lip again appears, and at the fifteenth or sixteenth week, it is full and prominent, when the maxillary palate has retired to its proper position. 2. When the outer lip of the primitive dental groove sends off the laminge, which constitute the greater part of each of the interfollicular septa, and the floor of the secondary groove, the lip itself almost disappears. The inner lip, again, which contributes a very small share towards the accomplishment of this process, becomes so much enlarged as to cover the whole groove. 3. The external and internal lips of the primitive dental groove are, originally, equally prominent. The former, when it sends off the interfollicular septa, diminishes, while the latter increases. When all the follicles of the primitive groove have E 50 ON THE ORIGIN AND DEVELOPMENT OF THE been completed, the external lip begins to increase, and the internal to diminish. This increase of the external lip goes on after the closure of the secondary groove, until, at the fifth month, it becomes very prominent, and is divided into an in- cisive, a canine, and molar portion, each of which has a general similarity in shape to the acting portions of the correspond- ing divisions of the future tooth-ranges. As long as it remains in this condition it is employed by the infant as a masti- cating organ. During this period the internal lip has alto- gether disappeared, except a small portion posteriorly ; but a short time before the milk-teeth appear, it again increases, and the raphe of the dental groove, instead of being hid behind the base of the external lip, is situated on the ridge of the dental arch, which now, as at first, is composed of two equally-deve- loped portions. The raphe forms a little border in the situation just mentioned, and is familiar to the eye of the surgeon, who, by its disappearance at any particular point, can satisfy himself of the proximity of the milk-tooth under it. Careful observation of the whole process of Dentition in man leads to the following conclusions: Milk Teeth. 1. The milk-teeth are formed on both sides of either jaw, in three divisions, a molar, a canine, and an incisive, in each of which dentition proceeds in an independent manner. 2. The dentition of the whole arch proceeds from behind forwards the molar division commencing before the canine, and the latter before the incisive. 3. The dentition of each of the divisions proceeds in a contrary direction, the anterior molar appearing before the posterior, the central incisive before the lateral. 4. Two of the subordinate phenomena of dentition also obey this inverse law, the follicles closing by commencing at the median line, and proceeding backwards, and the dental groove disappearing in the same direction. PULPS AND SACS OF THE HUMAN TEETH. 51 5. Dentition commences in the upper jaw, and continues in advance during the most important period of its progress. The first tooth-germ which appears is that of the superior anterior molar, which precedes that of the inferior anterior molar. The apparent exception to this law in the case of the in- ferior incisive has already been explained. Permanent Teeth. 6. The germs of the permanent teeth, with the exception of that of the anterior molar, appear in a direction from the median line backwards. 7. The milk-teeth originate, or are developed, from the mucous membrane. 8. The permanent teeth, also originating from mucous membrane, are of independent origin, and have no connection with the milk-teeth. 9. A tooth-pulp and its sac must be referred to the same class of organs as the combined papilla and follicle from which a hair or feather is developed viz. bulbs.* * An abstract of this paper was read at the last meeting of the British Association for the Advancement of Science. Dr. Allen Thomson stated to me at that time, that he had no doubt that the fact of the milk-tooth sacs being at one period open follicles had been ob- served, but that, then, he could not inform me where I could find it mentioned. I saw Dr. Thomson in Edinburgh a few weeks afterwards, when, on looking into Valentin's work on Development (ffandbuch der EntwicJcelungs-ge- schichte des Menschen), he pointed out to me the fact that Arnold had observed that the milk-tooth sacs were formed by a duplicature of the mucous mem- brane of the mouth, and had inserted a notice of the discovery in the Salzburg Med. Chir. Zeitung, 1831, p. 236. In order that Professor Arnold's discovery (which appears to have been altogether overlooked both in this country and in France) may be more generally known, I will give all his facts as he has re- corded them. His notice occupies less than a page, and I am not aware that he has extended it elsewhere. At p. 236, loc. cit. he has observed, "In an embryo at the ninth week, we may perceive in both jaws, on the projecting edges of the gums, a proportionally pretty deep furrow, with ten depressions in it ; a little later we may see a flat surface, on which there are many open- 52 PULPS AND SACS OF THE HUMAN TEETH. ings, communicating with small sacs, into which fine bristles may be passed. At the third month the sacs of the second molars may be seen communicating with the cavity of the mouth by small holes. The openings of the remaining sacs are soon closed by the mucous membrane of the mouth. "The sacs of the permanent teeth are also formed immediately from the mucous membrane of the mouth, partly at the fourth month of foetal exist- ence, partly towards the end of that period, partly at birth. Once only, in a new-born child, I observed behind the most prominent edge of the gums several openings which led to the sacs of the incisives and canines, and which are usually already obliterated before birth." These are all the facts Arnold has recorded, and from them it appears that he was acquainted at that time with the secondary dental groove, the ten milk- follicles, and the ultimate closure of the latter. So far as we can judge from his brief notice, he appears to have been unacquainted with the mode of for- mation of the permanent follicles, supposing them to be formed immediately (unmittelbar) from the mucous membrane of the mouth, an opinion which is very prevalent among the continental anatomists. I can only account for the openings he mentions in the new-born child by arrest of development, or by supposing that he had observed a few of the Tartar glands of Serres (Glandes dentaires, Essai, etc., p. 28), which are best seen at the period to which he alludes. Having now mentioned all the facts which Professor Arnold has published, I may be allowed to state that I had made out all the facts detailed in this paper before I was aware that any of them had been on record ; that I had given an account of them at the last meeting of the British Association, before I knew of Professor Arnold's notice ; and that this paper was in the hands of the Editor of the Edinburgh Med. and Surg. Journal before I had an oppor- tunity of seeing the Salzburg periodical. I had also demonstrated the principal facts in the follicular stage of denti- tion, in 1835, to Mr. Nasmyth, to whom I am deeply indebted for the infor- mation he has given me respecting the anatomy and surgery of these organs, and in whose cabinet I at that time deposited preparations illustrative of the facts. FOLLICULAR STAGE OF DENTITION IN THE RUMINANTS. 53 II. ON THE FOLLICULAE STAGE OF DENTITION IN THE EUMINANTS, WITH SOME EEMAKKS ON THAT PEOCESS IN THE OTHEE OEDEES OF MAMMALIA. SINCE the meeting of the British Association in 1838, at which the paper on the development of the human teeth was read, I have detected the follicular stage of dentition in the pig, rabbit, cow, and sheep, but have not had an opportunity of examining it in those animals in which observations would have been most valuable. I have been able to verify, what was at that time stated as probable viz. that all the permanent teeth, with the exception of the first molar, which does not succeed a milk-tooth, are developed from the internal surface of cavities of reserve, and that the depending folds of the sacs of composite teeth are formed by the lips of the follicles advancing inwards after closure of the latter. In tracing the progress of development of the pulps and sacs of the teeth in the cow and sheep, from their first appear- ance, as minute as possible, on the full surface of the membrane of the mouth, or on the internal surface of the cavities of reserve, till they have acquired their ultimate configuration, I have to announce the fact, that at an early period of the embryonic life of these animals they possess the germs of canine and superior incisive teeth ; the former existing as developed organs in two or three genera only of ruminants, the latter being found in the aberrant family of camels. These germs present them- selves under the form of slight dimples in the primitive groove, and after the closure of the latter, they remain 54 ON THE FOLLICULAK STAGE OF for a short time as opaque nodules imbedded in the gum, in the course of the line of adhesion. The existence of germs of canines and superior incisors in the cow and sheep is highly interesting, as it shows how general the law of unity of type is within certain limits. Geoffrey St. Hilaire was the first to announce the existence of tooth-germs in the foetus of the Balcena mysticetus, a fact which has been verified by Dr. and Mr. Frederic Knox, in whose museum there is a prepara- tion exhibiting the germs under the form of sacs and pulps. Although the germs never arrive at this stage of perfection in the cow and sheep, they are yet distinct enough to indicate their existence ; and I have no doubt that when embryos of other partially or wholly edentulous mammals have been exa- mined, similar results will be obtained. The peculiar manner in which the sac of a ruminant molar, and probably of every other composite tooth, is formed, may be best seen in longi- tudinal or transverse sections of the sac and pulp of the fourth permanent molar of the sheep or cow. The internal surface of the cavity of reserve is seen to end in a fold or folds ; when these meet, they begin to curve towards the papilla, and to enter parallel to one another the cavity or notch which is simultaneously forming in the latter. As soon as the edges of the folds meet, the granular matter denominated enamel-pulp by Hunter (the formation of which was de- scribed in the human embryo, at the last meeting of the Association) begins to be deposited, cementing together the opposing folds, sealing up the new sac, separating it from the rest of the cavity of reserve, filling up the space existing between the pulp and sac, and ultimately assisting in the formation of the depending folds of the latter. A distinction must be drawn between those permanent teeth which are developed from the primitive, and those which are developed from the secondary groove. I have been in the habit of dividing the teeth of these animals, the denti- DENTITION IN THE RUMINANTS. 55 tion of which I have examined, into three classes viz. ~Lst. Milk or primitive teeth, developed in a primitive groove, and deciduous. 2d. Transition teeth, developed in a primi- tive groove, but permanent. 3d. Secondary teeth, developed in a secondary groove, and permanent. I hope that other anatomists may verify and extend this line of research, as the results appear to me not only confirmatory of certain great general laws of organisation, but as leading, by the only legitimate path, to the determination of the organic system to which the teeth belong (a subject exciting great interest at present), and as it may enable us in investigating the relations of dental tissue to true bone, to avoid the error of confounding, what there appears to be a tendency to do, analogy with affinity. In recapitulation of the principal facts it may be said : 1. In all the mammalia examined the follicular stage of dentition was observed. 2. The pulps and sacs of all the permanent teeth of the cow and sheep, with the exception of the fourth molar, are formed from the minor surfaces of cavities of reserve. 3. The depend- ing folds of the sacs of composite teeth are formed by the folding in of the edges of the follicle towards the base of the contained pulp, the granular body assisting in the for- mation of these folds. 4 The cow and sheep (and probably all the other ruminants) possess the germs of canines and superior incisives at an early period of their embryonic existence. 56 ON THE MODE IN WHICH MUSKET-BULLETS BECOME III. ON THE MODE IN WHICH MUSKET-BULLETS AND OTHEE FOKEIGN BODIES BECOME IN- CLOSED IN THE IVOKY OF THE TUSKS OF THE ELEPHANT. PLATE II. MUSKET-BULLETS are occasionally found inclosed in ivory, and every anatomical museum contains specimens of this kind. Why bullets should be so frequently met with in this situation it is not easy to say : the head of the elephant appears to be generally aimed at, and foreign bodies, when they enter the tusks, instead of being removed in the usual manner are retained by the process, an investigation of which is to form the subject of the present paper. My attention was directed to this subject by Mr. Syme, who submitted to me for examination some highly interesting specimens of bullets in ivory, presented to the Anatomical Museum of the Uni- versity by Sir John Eobison. Sir John has also kindly afforded me an opportunity of examining some remarkable examples of wounded ivory, and Sir George Ballingall has directed my attention to preparations in his possession, which have satisfied me of the truth of those opinions on the sub- ject which I shall now have the honour of submitting to the Royal Society. One circumstance was at once detected in all these speci- mens, and its importance was evident, as affording a clue to the explanation of the mode of inclosure. The circumstance to which I allude is, that in none of the specimens are the bullets or foreign bodies surrounded by regular ivory. They are in every instance inclosed in masses, more or less bulky, VoLM Plate, II ENCLOSED IN THE TUSKS OF THE ELEPHANT. 57 of a substance which, although abnormal in the tusk of the elephant, is nevertheless well known to the comparative ana- tomist as occupying the interior of the teeth of some of the other mammals, and usually considered to be ossified pulp. It was evident that the pulp had ossified round the bullet, as the first step towards the separation of the latter from it. In one specimen the bullet has become enveloped in a hollow sphere of this substance, on the surface of which the orifices of medullary canals are situated. In other specimens the irregular ivory, which surrounds the balls, had become smooth on its surface, the medullary canals had disappeared, and the regular ivory had been formed in a continuous layer over the surface of the mass. In one tusk a cicatrix was seen occupy- ing the hole through which the ball had passed, a circum- stance which, when seen in similar specimens, has greatly perplexed anatomists. It was observed, however, that in this instance the shot had passed through that part of the tusk which had been within the socket ; and bearing in mind that the tusk is an organ of double growth, it appeared pro- bable that the shot had been plugged up from within by the ossified pulp, and from without by the continued growth of cement, without any regeneration of the displaced ivory a hypothesis which was afterwards verified by examination. Before proceeding to give a more detailed account of this interesting process, I shall state very briefly the opinions of those authors who have written on the subject, so as to ascer- tain how near they had approached to the truth, and to point out the fallacies which had led them astray. Klockner mentions a ball of gold which was found by a turner of Amsterdam in the substance of an elephant's tusk. The longitudinal fibres of the tusk surrounded the metal in an irregular manner, and were separated from the sound ivory by a concentric chink situated at some distance from the ball. 58 ON THE MODE IN WHICH MUSKET-BULLETS BECOME Camper, in the Description Anatomique d'un Elephant Male, remarks that it is not unusual to see foreign bodies in- closed, or as it were soldered, into the substance of the ivory. The same anatomist also figures and describes a bullet which was inclosed in a very irregular mass of ivory, covered with long appendages, which were directed parallel to the axis of the tusk. The metallic bodies in question, he remarks, must have penetrated across the alveolus into the hollow of the tusk, and must have remained for a long time in the substance of the pulpy flesh which fills that cavity, because the ivory enveloped them on all sides, and would at length have carried them beyond the alveolus by the increase of the tooth. He supposes that the nodules which are formed around the balls and the very incomplete union of their, fibres with the sound ivory, add weight to this conjecture. Euysch, in his X. The- saurus, Plate II., figures brass and iron bullets inclosed in isolated nodules of irregular ivory. Blumenbach considers the tusks of the elephant to differ from other teeth, more particularly in the remarkable patho- logical phenomenon of bullets, with which the animal has been shot, being found, on sawing through the tusk, imbedded in its substance in a peculiar manner. He looks upon this fact as important in reference to the doctrine of a " nutritio ultra vasa." He mentions a tusk, equal in size to a man's thigh, in which an unflattened leaden bullet lay close to the cavity of the tooth, surrounded by a peculiar covering, and the entrance from without closed as it were by a cicatrix. From these facts Blumenbach concludes that the elephant's tusk, when fractured or perforated, can pour out an ossific juice to repair the injury. Mr. Lawrence, in his notes to Blumenbach's Comparative Anatomy, overlooking these cases (one of which is given in the text of his author) in which cicatrices have been seen filling up the orifices produced by balls, explains satisfactorily ENCLOSED IN THE TUSKS OF THE ELEPHANT. 59 enough those instances in which no such cicatrices exist, and concludes by denying the power of the ivory to throw out ossific matter, as asserted by Blumenbach. The author of the Ossemens Fossiles, in his chapter on the Structure, Development, and Diseases of the Tusks of the Elephant, after stating that grooves and notches on the sur- faces of the tusks never fill up, and only disappear from the effects of friction, allows that musket-balls are found in ivory without any apparent hole by which they could have entered. He does not believe that the holes are filled up with ossific deposition, as Haller and Blumenbach supposed ; but main- tains that they are never obliterated. He states that the ivory on the outside of the ball is natural, and that it is only the bone surrounding it which is irregular. The phenomena are to be explained, he says, by supposing the balls to penetrate the very thin bases of tusks in young elephants, so as to enter the pulps when still in a growing state. There appear, then, to be two circumstances, regarding which great doubts still exist first, whether a shot-hole is ever closed up ; and, secondly, how this is accomplished in a non-vascular substance like ivory. In proceeding to consider this subject, two facts must be borne in mind in reference to a tusk. The first is, that the two substances of which it is composed, ivory and cement, undergo no change of form or arrangement from vital action, after they are once deposited ; the second, that it is an organ of double growth it is endogenous as well as exogenous, the ivory being formed from without inwards, the cement from within outwards. As there are certain processes which invariably commence when a foreign body passes through or lodges in the pulp, it will facilitate the conception of the mode in which a bullet is inclosed if these be described first. Kecent researches have proved that the regular ivory of teeth is formed by the cells 60 ON THE MODE IN WHICH MUSKET-BULLETS BECOME on the surface of the pulp becoming solid from the deposition of earthy salts in their walls and cavities. It is evident from this that when a portion of the surface of the tusk-pulp is destroyed by the passage of a ball, the formation of ivory at that spot must cease. But we know that the formation of irregular ivory commences, which indicates the existence of a healing process in the pulp. The mode in which the wounded pulp heals cannot be ascertained ; but it is accomplished pro- bably by effusion and subsequent absorption of blood, depo- sition of lymph, and regeneration of the peculiar tissue of the pulp. So far this process is conjectural, but the irregular ivory, formed by the regenerated pulp, is the subject of ob- servation. When the ball passes quite across the pulp, the track heals, but does not necessarily ossify, except in the im- mediate neighbourhood of the ivory. There are two exceptions, however, to the non-ossification of the track of the ball namely, the ossification which takes place round the bullet, and that which occurs round the whole or any portion of the track, which may suppurate and form a sinus or abscess. In both these cases deposition of irregular ivory takes place, assuming the same characters as the irregular masses which appear at the two extremities of the track of the ball through the pulp. The ossification round the ball generally assumes the form of a hollow sphere. Its surface exhibits a number of holes (which are the orifices of medullary canals), and these are occasionally prolonged through stalactitic-looking processes, which lie in the direction of the axis of the tooth. The ossi- fication surrounding an abscess or sinus assumes the appear- ance of a shell of variable thickness, and directed towards one or both of the shot-holes. When thin sections of this irregular ivory are examined under the microscope, it is seen to consist of a transparent matrix, in which exist numerous medullary canals, showing ENCLOSED IN THE TUSKS OF THE ELEPHANT. 61 traces of dried pulp in their interior. From these canals, which correspond to the Haversian canals of true bone, se- condary medullary canals, similar to those in the teeth of certain fishes, radiate. The sides and extremities of these secondary medullary canals send off numerous minute tubes, which are true Eetzian tubes, and similar to those in the re- gular ivory, but not so closely set. These Eetzian tubes have a general radiating direction, and proceed in irregular wavy bundles, which sweep past one another without mingling, but branching particularly at their extremities. The great central medullary canals are very numerous, and each of them has its own system of secondary canals and Eetzian tubes. These individual systems, when seen in a mass of irregular ivory, appear globular or spindle-shaped; when viewed in section, they resemble circular or oval opaque spots with a hole in the centre. These individual systems, however, are not isolated ; for they communicate, first, by means of the central canals, which constitute an inosculating system ; and secondly, by the ramifying extremities of the Eetzian tubes, which communicate through the medium of cells more or less minute, and which are more numerous in some places than in others. The formation of the irregular ivory does not go on inde- finitely ; a limit is set to its increase, and the changes which ensue at this stage of the process are highly interesting. I have already mentioned the existence of the orifices of Haver- sian or medullary canals on the surface of the mass of irregular ivory. When the further formation of this is to terminate, these orifices are gradually closed, and appear like imperf orated projections on the surface. It is evident, therefore, that the enclosed vascular contents of the canals that is to say, the ramified processes of the tusk-pulp in the irregular ivory are cut off from the system. They dry up, and the formation of 62 ON THE MODE IN WHICH MUSKET-BULLETS BECOME ivory in the interior ceases. The peripheral surface of the irregular ivory is now, in reference to the general pulp, in the same relation as the whole internal surface of the irregular ivory of the tusk. The pulp, therefore, becomes converted into ivory, not only on the whole internal surface of the tusk, but also on the surface of the newly-formed mass. The cause of the formation of the irregular ivory to a limited extent only, when it exists as an abnormal structure, I have not been able to ascertain ; but its mode of development and limitation is highly interesting, and forms a leading distinction between a tooth and a true bone under similar circumstances. From this description it is evident that the abnormal ivory in the elephant's tusk strongly resembles, if it be not identical with, the peculiar substance which fills the pulp-cavities of the tusks of the walrus and the teeth of the cetacea, first an- nounced as a distinct species of dental tissue in a paper read before this society five years ago by Dr. Knox, and since minutely described by Ketzius, Owen, and Alexander Nasmyth. * This identity of a diseased structure in one animal with a normal structure in another is remarkable, and must be looked * Cuvier described this species of dental tissue in the tusk of the walrus, and compared it to pudding-stone. Dr. Kiiox, in the paper to which I have referred in the text, affirmed that, in addition to the cement, enamel, and ivory, a fourth substance namely, the substance described by Cuvier entered into the formation of many teeth. He stated that, in the teeth of certain fishes, this substance, or a tissue closely allied to it, constituted the greater part of their mass ; the other three elements having disappeared or become greatly diminished in bulk or importance. Ketzius has accurately described the microscopic structure of this class of dental substances as existing in dif- ferent animals. Mr. Owen has extended and confirmed the observations of Eetzius. Lastly, to Mr. A. Nasmyth belongs the merit of having pointed out the resemblance which this kind of substance (which he denominates ossified pulp) bears to diseased ivory in the tusks of the elephant, and still more closely to the substance which fills the pulp-cavity of the aged human tooth. In ignorance of Dr. Knox's previous observations, he announced this kind of ivory as a fourth dental substance. ENCLOSED IN THE TUSKS OF THE ELEPHANT. 63 upon as another instance indicating the existence of a system of laws regulating the relations between healthy and morbid tissues laws which have been speculated upon, but have never been sufficiently investigated by anatomists. Having now given the anatomical characters of the ab- normal ivory which invariably surrounds musket-bullets and other foreign bodies which lodge in the pulps of the tusks of the elephant, I shall proceed to state the various conditions under which these enter the organ, and the changes which ensue. Foreign bodies enter the tusk in three ways first, through the free portion of the tusk ; secondly, through that part of the organ which is contained in the socket ; and thirdly, from above through the base of the pulp. First. When the ball hits the free portion of the tusk, if it only penetrates to a certain depth of the ivory, no change whatsoever can take place. Neither the cement nor the ivory can be reproduced. In course of time the hole may be obli- terated, the ball may be got rid of by wearing down of the ivory, and the ivory under the hole may be strengthened by the formation of new substance. When the ball is detained by the ivory, but penetrates so far as to wound the pulp, the latter ossifies around it, and the ossified portion sooner or later becomes enveloped in new ivory. If the ball penetrates the pulp, the latter ossifies round it, and becomes attached to the hole in the ivory. If the tusk is growing rapidly, and the nucleus of pulp-bone does not speedily adhere to it, the ball will ultimately be situated above the hole. The ball may also pass across the pulp, and become at last en- veloped, along with its bony envelope, in the ivory of the opposite wall. Second. In the second class of wounds, in which the ball enters the pulp-cavity through the socket and side of the tusk, the consequent changes seem to be the following : First, 64 ON THE MODE IN WHICH MUSKET-BALLS BECOME ossification of the pulp surrounding the ball, and the ultimate application of the mass to the hole in the ivory, and, as the latter is necessarily at this part of its extent very thin, the hole is closed ; second, the application to the hole in the ivory and to the surface of the ossified pulp in it, of cement formed by the internal surface of the tusk-follicle. For although the ball may have removed, or at least torn, the follicle opposite the hole in the ivory, yet, as the tooth advances in the socket, the ball will in time arrive at a sound portion of the latter. One of the specimens exhibited to the Society proves that the wounded portion of the follicle may perform this duty sufficiently well. In it the external surface of the cement exhibits a longitudinal fissure, with smooth rounded edges, resulting from the defective formation of cement in the situation of a longitudinal rent or wound in the membrane of the follicle, through which the ball had entered the ivory. The hole in the ivory then being plugged up ex- ternally by cement, and internally by ossified pulp, the case proceeds as in the last class of wounds the ossified portion of the pulp surrounding the ball becoming enclosed in true ivory. Third. When the foreign body enters from above, without wounding the tusk, the pulp ossifies round it, and true ivory envelopes the mass in the usual manner. I have not seen any morbid ivory which could be referred to wounds of the class now under consideration ; but a very interesting account is given by Mr. Comb in the Philosophical Transactions, 1801, of a tusk in which a spear-head was found, and which could only have entered the cavity from the base of the pulp. Mr. Comb describes and figures the ossified portion of the pulp, and the manner in which it had attached itself to the ivory, and become covered by it, so as to obliterate partially and to alter the relative width of the pulp-cavity. The description I have now given of the changes which ENCLOSED IN THE TUSKS OF THE ELEPHANT. 65 ensue on wounds of the tusks of the elephant explains many curious appearances in ivory, and the difficulties anatomists and physiologists have had in understanding them. It explains the drawings and descriptions of Klockner, Ruysch, and Camper ; does away with the necessity of suppos- ing, with Blumenbach, that true ivory is regenerated, or that it can throw out ossific juice to produce cicatrices ; and leads us to believe that Cuvier, in denying the possibility of the obli- teration of a shot-hole, had allowed himself to be deceived. All difficulties are got over and contradictions reconciled by bearing in mind the different circumstances insisted upon in this paper, namely 1. That a tusk is an endogenous as well as an exogenous organ. 2. That the pulp forms irregular ivory round foreign bodies, and at wounds on its surface. 3. That the membrane of the follicle is an important agent in closing up the holes produced by foreign bodies which pene- trate a tusk through the socket. 66 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. IV. ON THE SUPEA-EENAL, THYMUS, AND THYEOID BODIES. PLATE III WHILE engaged, two years ago, in observing the structure of the lymphatic glands, my attention was directed to the thymus, thyroid, and snpra-renal bodies ; and I was led to frame a hypothesis, which, although afterwards requiring some modification, has, I conceive, nevertheless enabled me to detect, if not the real physiological, at least the morphological signification of these apparently anomalous organs. My hypothesis was, that the thyroid, thymus, and supra- renal bodies are the remains of the blastoderma ; the thyroid being a portion of the original cellular substance of the ger- minal membrane grouped around the two principal branches of the omphalo-mesenteric vein ; the supra-renal capsules, constituting other portions grouped around the omphalo- mesenteric arteries ; and the thymus, the intermediate portion of the same membrane arranged along the sides of the em- bryonic visceral cavity. Subsequent observations have satisfied me that this hypo- thesis is essentially correct, with the exception of that part of it relating to the thyroid, which body I have now ascertained to be a portion of the membrana intermedia of Eeichert, which remains in connection with anastomosing vessels between the first and second aortic arches, or carotid and sub- clavian arteries. In the embryo of the sheep, while the branchial clefts are still open, and for some time afterwards, there is a quantity of Vol. II Plate IK ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 67 blastema arranged in minute lobular masses around the ante- rior parts of the cardinal veins of Kathke, surrounding the jugular veins and ductus Cuvieri for a short distance behind the forepart of the Wolffian bodies. Immediately in front of the Wolffian bodies these lateral masses of blastema are narrow, being scarcely perceptible on the coats of the cardinal veins ; but around the ductus Cuvieri they are larger, and differ from the general texture of the embryo, in having a darker colour, in containing no fibres, in separating readily from the sur- rounding parts, and in their lobulated appearance. They extend forwards nearly to the base of the cranium, and are not connected across the median plain. They are broadest at the sides of the heart, and when the pericardium is opened, are seen through its posterior wall occupying the future situations of the lungs, which at the period stated exist as two small lobulated white bodies, projecting from the intestinal tube, behind and below the heart. These two lateral masses are the only remaining portions of the membrana intermedia : the posterior portion on each side, on the inner aspect of the anterior extremity of the Wolffian body, becomes the supra-renal capsule ; the enlarged middle portion and the outer part of the cervical portion become the thymus ; w r hile the internal anterior part resolves itself into the thyroid body. These three organs are therefore at this period continuous with one another on each side of the middle line, no isthmus having yet been formed. They are also continuous with the Wolffian bodies ; these bodies, the supra-renal capsule, the thymus, and the thyroid, forming a continuous mass, situated in the elongated angular channel, which stretches from the cranium to the coccyx on the outside of the intestinal or mesenteric laminae, and between them and the visceral laminae. The Wolffian bodies are the last organs formed out of the membrana intermedia, which assume a special structure. The 68 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. supra-renal capsules, the thymus, and thyroid, retain through- out their existence the original texture of the blastoderma. Proceeding therefore in the order of formation as well as of position from the Wolffian body, I shall state very briefly what I have observed concerning the mode of development of the supra-renal capsules, thymus, and thyroid. In the embryo- of the sheep, in which the branchial clefts are still quite open, the omphalo-mesenteric vessels well developed, the liver consisting of an equal-sized lobe on each side of the intestinal tube, the Wolffian bodies well formed, the allantois beginning to protrude from the abdomen, and the umbilical vessels already apparent, there may be seen between the internal anterior part of the Wolffian bodies and the aorta at the origin of the omphalo-mesenteric arteries, and also around the omphalo-mesenteric vein, where that vessel is passing forward into the liver, a mass of blastema spread over the internal surface of the fore-part of the Wolffian body, and arranged in one or more masses between that gland and the aorta. In embryos rather more advanced, these masses of blastema become less distinct, apparently from their increased bulk causing them to be applied more uniformly over the anterior extremities of the Wolffian bodies. They may always be detected by their whiter appearance, and by being destitute of the cross-markings produced by the ducts of the Wolffian glands. It is not till the testes, ovaries, and kidneys have appeared, that the supra-renal capsules are recognised as distinct organs ; and their progress after this period need not be considered further at present. The cardinal veins of Eathke pass forward along the pos- terior and lateral part of the Wolffian bodies ; after passing beyond the blunt anterior extremities of these bodies, each vein carries with it, or is covered by a thin layer of the bias- ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 69 tema already alluded to as forming at its posterior part the supra-renal capsule. This portion of the blastema becomes much larger at the side of the heart, round the ductus Cuvieri, behind the lateral parts of the pericardium, and in the future situation of the lungs, which have not yet left their median position. Each lateral portion of the blastema stretches from the heart forwards along the internal side of the jugular vein, par vagum, and carotid arteries. These two anterior portions of the lateral blastema, from the narrow portion forwards to the skull, are the lateral portions of the thymus and thyroid, which have not yet joined across the middle line. In embryos a little further advanced, the two portions of blastema join across the trachea in a line extending from the base of the heart to the lower end of the larynx, which has now appeared as an oblong oval swelling behind the tongue. Previous to, and also contemporaneous with, this cross junc- tion, a change has occurred in the position of the lungs and of the ductus Cuvieri. As the lungs proceed in development, they pass in a direction from behind forwards and from within outwards, moving from their original median position to a lateral one : they at the same time increase both absolutely and relatively. At the same time, a somewhat similar change takes place in the two ductus Cuvieri. They pass forward so as to appear to enter the anterior instead of the posterior extremity of the auricle, becoming in this way the anterior vense cavse, this change of position being produced apparently by a semi- revolution of the whole heart, coinciding with its elongation and the altered arrangement of the bulbous aortse. Coincident with this change in the ductus Cuvieri is a corresponding change in the position of the lateral masses of the blastema. These pass forward, become grouped around the auricles and anterior venae cavse, and join across the middle line as already stated ; but a narrow portion, particu- 70 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. larly along the left side, still passes downwards and back- wards along the cardinal veins, which have now become the azygos veins. While these changes in the veins and blastema have taken place, the lungs have increased in size, and their roots have taken up their proper position. In consequence of this change in the position of the pulmonary roots and of the ductus Cuvieri, the cardinal veins arch over the root of the lungs in the same manner as the azygos vein of the adult does. At the same time the blastema of opposite sides unites, as has been stated, across and in front of the base of the heart and root of the neck. Shortly after this period, the posterior part of the blas- tema, which has now advanced, as already stated, from the sides of the chest to the front of the heart, becomes separated by a narrow neck from the cervical portion. The posterior part has now become the thoracic portion of the thymus, and in the embryo of the sheep is largest on the left side, corres- ponding in this respect to the large size of the left vena azygos and left vena cava at this period. The cervical portion of the blastema now begins to exhibit a separation into the thyroid and cervical portion of the thymus. This is effected by the absorption of a portion of the blastema, of a triangular form, a little behind the larynx, the apex looking backwards, the concave base forwards, so that the future thyroid presents a crescentic form, its sides being as yet united to the anterior horns of the thymus, which pass along the jugular veins. The thyroid now separates more completely from the thymus, by the prolongation forwards of the absorption pre- viously mentioned from the anterior angles of the triangular portion, so as to separate the thyroid from the anterior horns of the thymus ; at the same time the posterior angle of the ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 71 absorbed portion passing back so as almost again to separate the cervical portion of the thymus into two lateral portions. As development advances the thyroid becomes more com- pletely separated from the thymus, and the lateral portions of the cervical part of the latter are united only by the narrow portion which connects them with the thoracic lobe of the organ. At this stage a distinction may be observed, with low magnifying power, in the texture of the two organs. The thyroid is more opaque and homogeneous, the thymus consists of minute granular masses imbedded in a semitransparent matrix. The component elements of the textures of the two organs is however identical namely, simple nucleated cells grouped around dark points, which I am inclined to regard as centres of nutrition. In the thyroid, these groups are sepa- rated and connected by a more or less dense highly vascular areolar texture. In the thymus this texture is weak or deficient. After this period no great change occurs in the thyroid and thymus of the sheep ; the anterior extremities of the horns of the thymus on each side presenting two bulbous enlargements near the base of the skull, close to the ganglions of the vagus. Four minute white cords may now be seen passing into the superior, and two into the inferior border of the thyroid. These are the inferior and superior thyroid arteries, branches respectively from the first and second branchial arteries. From these observations it would appear that the supra- renal capsules, the thymus, and thyroid, are persistent portions of the membrana intermedia of the germinal area of the ovum, retaining throughout their existence the original simple cellular constitution of that portion of the germinal mem- brane. I shall now endeavour to explain in how far the observa- 72 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. tions just detailed appear to me to enable us to trace the functional import and anatomical peculiarities of these organs. During the first stage of the development of the animal ovum, digestion and respiration the absorption and prepara- tion of nutriment are carried on by the blastoderma, a struc- ture consisting of nucleated cells and of vessels. The cells, of which the blastoderma consists, are the pro- geny of that previously occupying the germinal spot of the ovum, and are continually reproduced and increased in num- bers by the production of others from the nutritive centres, or secondary germinal spots distributed over it. Materials for the nutrition of the blastoderma are derived from the subjacent yelk. The matter resulting from the solu- tion of a certain number of the secondary blastodermal cells that is, of the progeny of the primary blastodermal cells, or nutritive centres is employed by the nutrient matter of the remaining secondary or proper blastodermal cells. In this way " pabulum" is afforded for two purposes the growth of the blastoderma, and the growth of the embryo itself. During the early period of the existence of the blasto- derma, before the circulation has been established, the product of solution of the elder is at once absorbed by the younger cells. During the later periods, the product of solution drops into the incipient loops of the blood-vessels, and so circulates for purposes of nutrition. This is an instance of primary lymphatic absorption, and differs in no essential particular from the same process in the animal further advanced. We may consider the blastoderma in fact, during the first period of its circulation, as containing very numerous lymphatic ducts, instead of a few, as in the more perfect animal. In the blastoderma, the process by which nutrient matter passes into the circulation, or the act of absorption, as it is usually called, is reduced to its most simple form, being con- temporaneous and also identical with the formation of the ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 73 imperfect capillary network. In the more advanced animal, when the capillary network is consolidated, the product of solution of the textures passes or drops into the intercellular or textural lacunae, which appear to be the radicles of the lymphatic system ; a system which in the adult communicates with the blood-vessels only at a few places in the neighbour- hood of the trunks of the original blastodermal veins. The blastoderma may be considered therefore not only as the first form which the being assumes after the commence- ment of development, and as a basis out of and in which its higher structures are to be raised, but also, as has been already stated, the organ of primary digestion that is, of the appro- priation arid elaboration by the individual of nutritive matter already prepared, to a certain extent, by another individual or organ. All the principal organs and parts of the future being are formed in, and out of, portions of the blastoderma. The laminae dorsales, the cerebro-spinal axis, the visceral laminae, the intestinal tube, heart, and liver, derive their origin from this source. Their original relation to this part is soon lost sight of from changes in their positions, but principally from the increased development of their original blastema, and its change into the various textures, and from the various arrange- ment of these textures in the organs. There are three organs, however, which still retain their primitive structure after all the other parts of the animal have undergone their complete development, so as finally to exhibit no trace of their original simple texture and arrangement. These organs are the supra-renal capsules, the thymus, and thyroid. The structure of each of these three organs is essentially the same : they consist of masses of nucleated cells. These cells are grouped around numerous germinal spots arranged throughout the mass, and which may be supposed to act as 74 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. centres of origin and of nutrition, each for its own group. The mass of the organ is supplied with blood-vessels to convey the blood to and from the part, and with lymphatics which receive the product of solution of the cells, and convey it back again into the general circulation, whence it was origin- ally derived. The account of the structure of the thymus given by Sir Astley Cooper is so far incorrect, as this organ contains no reservoirs or cavities in its substance. The cavities exhibited by Sir Astley Cooper in his drawings and preparations are the results of modes of preparing. They are artificial cavities formed by distension, between the somewhat smooth, highly vascular, and slightly adhering outer surfaces of contiguous lobules ; the whole organ being at the same time bound together by a stronger external areolar texture. No milky fluid is found naturally in these interlobular spaces. Indeed, Sir Astley Cooper says, that " the best mode of obtaining it is by cutting the gland into very small pieces and placing them upon gauze, which being squeezed, the solid is separated from the fluid part, and the latter escapes through the gauze." The thymus, from the time it assumes its most perfect structure till it begins to degenerate into fatty substance, con- sists of lobes connected by areolar fibres, without cavities or ducts, formed of nucleated cells grouped around germinal spots, deriving matter for the formation of their cells from arteries passing into it, and being relieved of its venous blood by returning veins, being plentifully supplied with lymphatics, which do not communicate with the supposed reservoirs, as has been suggested, but appear to take their origin, as in other parts, by intercellular lacunae, in which the walls seem gradu- ally to lose themselves, as the ducts of the liver are lost among the secreting cells of that organ. The thyroid body possesses a structure which is essentially the same as that of the thymus. It differs from the thymus ON THE SUPRA-RENAL, THYMTJS, AND THYROID BODIES. 75 in not being divided into lobules, in having the groups of cells of which it consists separated from one another by moderately strong capsular membranes, and in being more vascular, the anterior and venous trunks being much larger. The supra-renal capsules also consist of nucleated cells grouped round germinal spots, and arranged, not in lobules, but in columns passing towards the surface of the organs ; an arrangement corresponding to the radiating direction of the veins, and the converging arteries of these parts. The supra- renal and thyroid bodies are more vascular than the thymus from being developed around large arteries, while the thymus is in connection with smaller trunks, the former being de- veloped in connection with the first and second aortic arches and the omphalo-mesenteric vessels ; the latter in connection with the internal mammary arteries and other small thoracic and cervical branches. The greater density of the areolar capsule of the thyroid may probably be explained by this in- creased vascular supply. That portion of the membrana intermedia which is sepa- rated from the rest of the membrane, and included in the body of the embryo by the umbilical constriction, and which has not already been devoted to the formation of the heart, liver, pancreas, and external portion of the intestinal canal, is found massed along the trunks of the primitive venous system, the sides of the arches of the aorta, the terminal portion of that vessel, and the origins of the omphalo-mesenteric arteries. The portions of the membrana intermedia which are last of being converted into special organs, the Wolffian bodies, are the parts which project one on each side of the aorta, along the posterior part of the cardinal veins of Eathke, between the intestinal plates and visceral laminae. The portions of the membrana intermedia which remain between the upper extremities of the Wolffian bodies and the heart and liver, and which surround the origins of the om- 76 ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. phalo-mesenteric arteries, do not become converted into organs of special structure, but retain during life the original consti- tution of the membrana intermedia of the blastoderma, and increase rapidly in the embryo, constituting the supra-renal capsules. Whatever doubt may be entertained as to the exact functional import of these bodies, the identity of their ana- tomical constitution with that of the blastoderma is sufficiently evident, and their morphological signification appears to be equally so. That portion of the membrana intermedia which is situated between those two aortic arches, the extremities of which become the carotid and subclavian arteries, remains during life as the thyroid body. It receives its blood from the first and second aortic arches by two large trunks on each side, the superior and inferior thyroid arteries. That portion of the membrane which passes in two parts from near the base of the cranium back as far as the ductus Cuvieri and anterior portions of the veins of Eathke, and which are united and concentrated in front of the heart by passing from behind forwards, in harmony with corresponding motions of the neighbouring part, becomes the thymus. The structure of these three organs is identical with that of the blastoderma. Their probable function namely, to prepare by the action of their nucleated cells, and to throw into the vascular system, a matter necessary for the nutrition of the animal during the period of its active growth a func- tion which the observations and opinions of the majority of physiologists have assigned to them is also essentially the same with that of the blastoderma. The question as to the exact or intimate nature of the function of these organs can only be answered by further in- quiries in chemical physiology. It appears to me to be suffi- cient at present to insist that their function, as deduced from their structure and anatomical relations, is similar to ON THE SUPRA-RENAL, THYMUS, AND THYROID BODIES. 77 that performed by the blastoderma, whatever the exact nature of that function may be. I have therefore been led to consider the supra-renal capsules, the thymus, and thyroid, as organs essentially similar in structure ; as developments of the remains of the blasto- derma, being formed of a continuous portion of that part situated along each side of the spine, from the Wolffian bodies to the base of the cranium, the supra-renal capsules being de- veloped in connection with the omphalo-mesenteric vessels, the thymus to the jugular and cardinal veins, and ductus Cuvieri ; and the thyroid to the anastomosing branches of the first and second aortic arches, as organs performing functions, whatever these may be, analogous to those of the blastoderma, differing from them only in this, that the blastoderma not only elaborates nourishment for the embryo, but absorbs it also from without that is, from the yelk ; whereas the three organs in question only elaborate the matter which has already been absorbed by the other parts, and is now circulating in the vessels of the more perfect individual. 78 ON THE MORPHOLOGICAL RELATIONS V. ON THE MORPHOLOGICAL EELATIONS OF THE NEEVOUS SYSTEM IN THE ANNULOSE AND VEETEBEATE TYPES OF OEGANISATION.* THE term annulose is employed provisionally, and in a morphological sense, as including all animals possessing a ganglionic nervous collar and axis, and presenting, at the same time, more or less distinct indications of a segmented structure of body. Physiologists appear generally inclined to consider the central portions of the annulose and vertebrate nervous sys- tems as modified forms of the same arrangement. These forms are held to possess a general similarity of structure, and correspondence in function ; and the ganglionic collar and axis of the annulose are assumed to be homologous either with the cerebro-spinal axis, or with the series of ganglions on the posterior roots of the spinal nerves, or with the system of sympathetic ganglions of the vertebrate animal. In my own examination of this subject I have been strongly impressed with the necessity of determining the morphological character of the cesophageal collar, and the op- posite positions of the so-called brain and abdominal gan- glionic cord, before any satisfactory advance could be made in ascertaining the relations of the two forms of nervous system. The apparent morphological difference between * This and the two following papers were read to Section D at the Chel- tenham Meeting of the British Association, Aug. 5-12, 1856, and were pub- lished in abstract in the Edinburgh Philosophical Journal, Jan. 1857. EDS. OF THE NERVOUS SYSTEM. 79 them does not appear, in the estimation of physiologists generally, to present that obstacle to a satisfactory com- parison which its essentially fundamental character would lead us to expect. The difficulty has, however, been clearly stated by Professor Owen, who, in discussing the relations of the endo- and exo-skeletons in his Lectures on Fishes, page 21, ed. 1846, says " Geoffroy St. Hilaire thought it needed but to reverse the position of the crustacean to turn what had been wrongly deemed the belly upwards in order to demonstrate the unity of organisation between the articulate and ver- tebrate animal. But the position of the brain is thereby reversed, and the alimentary canal still intervenes in the invertebrate between the aortic trunk and the neural canal." I must here premise, that while I hold the general mor- phological relations of the annulose and vertebrate ner- vous systems to be identical, I do not consider these two types of organisation to be mutually reducible. On the con- trary, they are fundamentally distinct, presenting differences which demand careful consideration. It is, nevertheless, incumbent on the morphologist to ascertain in what re- spects they correspond, so as to determine their distinctive limits. My earlier conception of the morphology of the annulose nervous system was based on that of Carus. I conceived that each segment of the annulose animal contains potentially an annular nervous arrangement, set in a plane at right angles to the axis of the segment, or longitudinal axis of the animal ; that the only complete nervous ring is that one through which the oesophagus passes ; that the ganglions on this ring are arranged in the various forms of superior, lateral, and in- ferior oesophageal masses ; that the nervous rings in the post- cephalic segments are all incomplete above, and have their ganglions united into a single or double mass below ; and 80 ON THE MORPHOLOGICAL RELATIONS that all the rings are united by a series of longitudinal abdo- minal commissures. According to this view, the cesophageal collar, with its superior, lateral, and inferior ganglions, is homologous with each pair of segmental nerves, and the cor- responding abdominal ganglionic centre; the cesophageal collar being in a plane parallel to those in which the post- cephalic ganglions and their pairs of nerves are situated, but at right 'angles to the line of the series of abdominal gan- glions. I first recognised what I believe to be the real morpho- logical relations of the annulose nervous system during the delivery of a course of lectures on Invertebrate Anatomy in 1849 ; but more fully and completely during courses on the Anatomy of the Mollusca in 1850, and on the Anatomy of the Crustacea in 1851. I now perceived that the fundamental difference between the morphological relations of the annulose and vertebrate nervous systems, consists in the position of the mouth. I saw that the entire axis or central portion of the nervous system extends along the neural aspect of the body in both types of organisation ; but that while, as is well known although its morphological importance does not appear to have been perceived the vertebrate mouth opens into the haemal, the annulose mouth passes through the neural aspect of the body. In the annulose animal, therefore, the buccal entrance interferes with the nervous axis passing up between the two lateral halves of one of its longitudinal commissural or inter- ganglionic cords, so as morphologically to divide the con- tinuous axis into a pre-stomal and a post-stomal portion. These relations are most satisfactorily seen in the crus- tacea, in which the so-called brain, or supra-cesophageal gan- glion or nervous mass, is actually in front of the mouth, and not above it. OF THE NERVOUS SYSTEM. 81 In insects, annelids, and mollusca, the bulk of the buccal mass, and other necessary modifications of the oral apparatus, elevate the so-called brain, curving upwards the morpho- logical axis of the body of the animal. By comparing the indications of segments in front of the mouth, and their corresponding diverging appendages, with the arrangement and distribution of the nerves given off from the so-called brain, it appears very evident that this brain is the aggregate of the segmental nervous centres in front of the mouth. In like manner indications afforded by the segments, and their appendages immediately behind the mouth, enable us to determine whether the so-called sub-cesophageal ganglionic mass is a single segmental ganglion, or an aggregate of antero- posteriorly united segmental ganglions. In this way I was enabled to perceive that the axis of the nervous system of the annulose animal does not consist of a supra-oesophageal mass, of an cesophageal collar, of a sub- oesophageal mass, and a continuous sub-intestinal ganglionic chain ; but of a continuous line of connected and serially homologous ganglions situated in the mesial line of the neural aspect of the body. The annulose, like the vertebrate animal, is developed with its nervous axis turned away from, and its haemal axis applied against, the vitellary mass.* * From the passage in his lectures already quoted, Professor Owen would appear to consider the dorsal heart, with its anterior and posterior arterial trunks in the decapod crustacean, and consequently the dorsal vessel in the insect, arachnidan, and annelid, as corresponding to the thoracic, abdominal, and caudal aortic trunk of the vertebrate animal. On this supposition only can we understand his assertion, that when the so-called belly of the crus- tacean is turned upwards, its alimentary canal is still interposed between the aortic trunk and the neural canal. Embryology, comparative anatomy, and physiology, appear to me, however, to afford ample proof that the cardiac - arterial dorsal trunk of the annelid, crustacean, insect, or arachnidan, is ho- mologous, not with the sub-spinal aorta of the vertebrate, but with the pri- G 82 ON THE MORPHOLOGICAL RELATIONS But, in the course of development, the mouth of the ver- tebrate opens through the surface applied against the vitellary mass, whilst that of the annulose animal passes through the aspect turned away from it. The vertebrate mouth is haemal, the annulose mouth neural. Rathke formerly described the pituitary body as origi- nating in a diverticulum passing up from the pharyngeal mucous membrane through the basis of the embryo skull. I at one time conceived it to be probable that the pituitary body, and the mucous tube, in which, according to Eathke, it originates, might be indications in the vertebrate of a structure which, in the annulose animal, is converted into the mouth. This presumed neural alimentary passage may be conceived as passing up between the bodies of the anterior and posterior sphenoid bones into the Sella Turcica, along the course of the infundibulum to the third ventricle of the brain, and through the cavity of that organ to its upper surface behind the cerebellum, thus leaving the origins of the nerves of smell and vision in the pre-stomal portion of the organ, while the origin of the nerve of hearing would remain in the medulla oblongata or post-stomal portion of the cephalic nervous mass. The arterial circle of Willis, and other pecu- liar arrangements at the base of the skull and brain, appeared to support the view taken. I shall not, however, pursue this hypothesis further, because, from the observations of Eeichert, we know that the base of the cranium is not perforated in the embryo, and that the supposed canal or diverticulum was an incorrect interpretation of the peculiar appearances pro- mordial cardiac-arterial tube in all the forms of the embryo vertebrate, and, consequently, with the heart and trunk of the branchial artery of the fish. If this, then, is the real homology of the " aortic trunk " of the crustacean, and if its "brain" is in fact only a pre-stomal portion of its nervous axis, the French anatomist was quite correct in his general morphological statement, although he was not legitimately entitled at the time to employ the illus- tration. OF THE NERVOUS SYSTEM. 83 duced by the curvature downwards of the early Mammalian head.* If I have determined aright the morphological relations of these two forms of nervous system, we shall have advanced a step in our conceptions of the anatomico-physiological re- lations of the annulose and vertebrate animals, and this without losing sight of the fundamental differences, develop- mental and structural, between them. The researches of Milne-Edwards, and of Newport and others, on the annulose nervous axis may thus be physiologically associated with those of Wagner, Schroeder Van der Kolk, Owsjannikow, Jacobowitsch, and Kupffer, on the cerebro-spinal axis ; and we may now legitimately employ the annulose animal in the morphological investigation of the vertebrate skeleton. Omitting, for the present, the consideration of the mode in which the nervous systems in the Tunicata, Eotifera, and Entozoa, are reducible to the typical annulose form, I pro- ceed to make some general morphological statements, based to a certain extent on the principle indicated in this, and introductory to the two following communications : 1. The morphology of any one organic system in the annulose or vertebrate animal, cannot be safely or satis- factorily investigated, without constant reference to the others. That it must be so is evident from the fact, that all the organic systems are dependent on one another, in the constitution of the organism. 2. All sound morphological inquiry demands constant reference to the series of embryo, as well as of adult forms. 3. As morphology deals with forms and relations of posi- tion, it demands a careful selection of terms, and a methodised * I have introduced the hypothesis of a vertebrate neural mouth (cast aside in the course of my examination of the subject), because I believe it will be found to involve relations of importance in the anatomico-physiological in- vestigation of the pre-stomal and post-stomal portions of the vertebrate and annulose cephalic nervous masses. 84 ON THE MORPHOLOGICAL RELATIONS nomenclature. All terms involving more or less than their morphological application demands, must be avoided. Terms derived from other departments of the science, and having therefore an established technical meaning, have invariably produced misconception, when transferred for morphological purposes. Influenced by these considerations, and satisfied that the annulose and vertebrate types of organisation, although fundamentally distinct, present parallel forms of structure, and must consequently be closely linked together in morpho- logical inquiry, I have to suggest a more extended and pre- cise system of nomenclature for this department of the science. In the annulose and vertebrate types of organisation, the body of the animal consists of a linear ^3 133 of segments. To the constituent segment, with its diveig' '<* appendages, I apply the term somatome (rf/Aa, repvu). For the purpose of avoiding circumlocution, and of sup- plying a term for a generalised conception, and thereby facili- tating morphological description, without encroaching on zoological nomenclature, I denominate a segmented animal, whether annulose or vertebrate, an entomosome an entomo- somatous animal (gVo//,os, ,