ONLY forma nal THE LIBRARY OF THE UNIVERSITY OF CALIFORNIA LOS ANGELES A STUDY HISTOLOGICAL CHARACTERS Periosteum and Peridental MEMBRANE. BY G. V. | BLACK, M.D., D.D.S. L PROFESSOR OF PATHOLOGY IN THE CHICAGO COLLEGE OF DKNTAL SURGERY. WITH 67 ORIGINAL ILLUSTRATIONS. CHICAGO: W . T. KEENER 96 WASHINGTON STREET. 1887. COPYRIGHT, W. T. KEENER, 1887. H/tl PREFACE. The contents of this volume appeared in serial form in the Dental Review. In reviewing the matter for publication in book form, I find that the subject matter proper for a preface is included in the preliminary chapter and at other points in the progress of the work. I have concluded therefore to let it remain as written, believing that it will serve the reader fully as well, or better, than to bring it together upon this page. This volume is almost entirely a record of my own personal observations, written in the personal or lecture style. A division into chapters has been made for the con- venience of the reader. The volume is now offered to the profession with the hope that it may in some measure supply the want that has been felt -for a more thorough study of the histolog- ical characters of the periosteum and peridental mem- brane. G. V. B. Jacksonville, Sept. 1, 1887. LIST OF CONTENTS. PREFACE CHAPTER I. Preliminary 1 CHAPTER II. Tissue elements and their distribution; Development; Matrix; Cells; Fibroblasts; White fibrous tissue; Areolar tissue; Yellow elastic tissue; Cellular elements of the fibrous mem- branes; Cartilage and bone; Relationship of the connective tissues 6 CHAPTER III. Methods of the preparation of the tissues 17 CHAPTER IV. The periosteum; Histological components of the periosteum; Outer layer; Internal layer; Non-attached inner layer, residual fibers, attached inner layer; Elastic fibers, blood vessels, nerves .... 22 CHAPTER V. Cells of the periosteum; The osteoblasts; Functions of the osteoblasts; Bone corpuscles; Osteoclasts 37 CHAPTER VI. Formation of bone; Subperiosteal formation of bone; Subperiosteal formation of Haversian canals; Lamination of bone; Removal of residual fibers; Formation of secondary Haversian canals; Intra-menibranous formation of bone 45 CHAPTER VII. Growth of bone under tendinous attachments and strong fibrous Burste; Intra-cartalaginous formation of bone; Ossification in the epiphysis; Ossification in the diaphysis; Chondroclasts and the absorption of cartilage; Formation of the periosteum beneath the perichondrium 55 CHAPTER VIII. The peridental membrane; Principal fibers of the membrane; Arrangement of the fibers: The dental ligament; The gingiva; Physical functions of the membrane 71 CHAPTER IX. Interfibrous elements of the peridental membrane; Blood supply; Sensory function; Nerve supply 84 CHAPTER X. Lymphatics of the peridental membrane; Hard formations within the membrane 90 CHAPTER XI. Osteoblasts and alveolar wall; Movements of the tooth in its alveolus; Relations of the growth of the alveolar processes to the lengthening of the face 96 CHAPTER XII. The cementum and cementoblasts; Lamella? of the cementum; Incremental lines; Growth of cementum continuous; Fibers of the cementum 102 CHAPTER XIII. Irregularities in the growth of the cementum; Hypertrophies Ill VI LIST OF CONTENTS. PAGE CHAPTER XIV. Absorptions occurring in the alveolus; Absorption of the roots of the temporary teeth; Absorption not dependent upon the vitality of the tissue being absorbed; Condition of the bone corpuscles during the progress of absorption; Irregulari- ties of absorption; Absorbed areas in dentine always repaired by deposits of cementum; Absorption of the roots of permanent teeth; Absorptions of the alveolar wall; Cirvical absorptions; Detachment and reattachment of the principal fibers of the peridental membrane 118 LIST OF ILLUSTRATIONS Fig. 1. Embryonal connective tissues. Fig. 2. The same a little more developed. Fig. 3. The cells developed into fibroblasts. Fig. 4. White fibrous tissue. Fig 5. Old white fibrous tissue. Fig. 6. Coarse white fibers showing mode of division. Fig. 7. Coarse white fibers breaking up into fine fibers. Fig. 8. Cross sections of coarse white fibers. Fig. 9. Reticular fibers, showing mode of division and the multipolar cells. Fig. 10. Cross sections of reticular fibers. Fig. 11. Connective tissue cells from which reticular fibers are de- veloped. Fig. 12. Network of elastic fibers from the point of reflection of the mucous membrane of the lip from the gum. Fig. 13. Network of elastic fibers teased out from elastic tendon. .Fig. 14. Elastic fibers showing their disposition to curl up when cut or broken. Fig. 15. Cross sections of elastic fibers. Fig. 16. Tissue of the dental pulp. Fig. 17. Non-attached periosteum from the femur of a kitten. Fig. 18. Periosteum from the shaft of tibia of pig. Fig. 19. Periosteum from lowei end of femur of a kitten, penetrating fi be rs , osteoclasts . Fig. 23. Attached periosteum from beneath the attachment of the mus- cles of lower lip. Fig. 21. The more usual form of the attached periosteum. Fig. 22. Network of elastic fibers from the coarse fibrous layer of peri- osteum. Fig. 23. Bone, with portion of the inner layer of attached periosteum and penetrating fibers. Fig. 24. Bone, showing a solid subpenosteal growth and the manner of forming secondary Haversian systems. Fig. 25. Margin of growing bone on which the osteoblasts are very much crowded. Fig. 26. Cross section of growing bone showing the Haversian canals and the plan of their subpenosteal formation. Fig. 27. Absorption of bone under the attached periosteum. Fig. 28. Intra-membranous formation of bone. Fig. 29. Growth of bone under the attachment of tendo-Achillis. Vlii LIST OF ILLUSTRATIONS. Fig. 30. Epiphytal intra-cartalagenous formation of bone. Manner in which absorption occurs. Fig. 31. Epiphysal intra-cartalagenous formation of bone. Fig. 32. Central section of head of tibia showing relations of diaphysal and epiphysal formation of bone. Fig. 33. Changes which occur in diaphysal intra-cartalegenous forma- tion of bone. Fig. 34. Ibid, supplement to Fiir :;:}. Fig. 35. Cross section of rib of young kitten showing the cartilage remaining in the newly formed bone. Fig. 36. Lengthwise section of incisor tooth with its membrane and alveolor process. Fig. 37. Cross section of the root of a temporary tooth with its mem- brane and alveolar process. Fig. 38. Cross section of cuspid tooth (adult) with its membrane and alveolar process. Fig. 39. Fibers of peridental membrane passing from the cementum to the alveolar wall. Fig. 40. Cross sections of central and lateral incisors near the gingivae, showing the tissue intervening between the teeth. Fig. 41. The peridental membrane from a perpendicular section of the tooth and alveolus of a pig. Fig. 42. Fibers emerging from the cementum and breaking up into fasciculi Fig. 43. A group of fibers emerging from the cementum and radiating fanlike. Fig. 45. Portion of alveolar wall, and portion of the peridental mem- brane, showing the osteoblasts. Fig. 46 Very large fibers of peridental membrane with inter-fibrous tissue Fig. 41. Lymph folicle, or node, from peridental membrane. Fig. 48. Lymph ducts crowded with lymphoid cells Fig. 49. Calcospherite-like spherule in the tissues of the peridental membrane. Fig. 50. Cementum and portion of peridental membrane. Fig. 51. Perpendicular section through the rim of the alveolar wall. Fig. 52. Diagramatic representation of the movement of the teeth in their alveoli. Minimum movement. Fig 53. Ibid Maximum movement Fig. 54. Cementoblasts isolated to show their forms. Fig. 55.' Cementoblasts in situ with cross sections of the principal fibers of the peridental membrane. Fig. 56. Horizontal section of cementum showing cross sections of its fibers. Fig. 57. Perpendicular section of the cementum of the pig, showing its fibers. Fig. 58. Cementum of pig from a dried section Fig. 59. Hypertrophy of cementum. Xodule on the side of the root of a lower molar. LIST OF ILLUSTRATIONS. IX Fig. 60. Hypertrophy of cementum from the side of the root of cuspid tooth. Fig. 61. Apex of root of upper bicuspid with hypertrophy of cementum. Fig. 62. Absorbed area of root of temporary tooth partly refilled by cementum. Fig. 63. Absorption of alveolar wall. Osteoclasts. Fig. 64 Absorption of alveolar wall. Fig. 65. Partially absorbed root of lower molar repaired by deposit of cementum. Fig. 66. Pit-like absorption in the side of a root in process of repair by deposit of cementum. Fig. 67. Apex of the root of a cuspid tooth, showing areas of absorp- tion repaired by deposits of cementum. Fig. 1. Embryonal connective tissue in an early stage of develop- ment, showing the cellular elements imbedded in the ground substance. Fig. 2. The same, a little more developed, showing the cellular ele- ments lengthening in a common direction. Fig. 3. The cells developed in spindle forms, fibro blasts with long filaments extending from either end. Fig. 4. The developed white fibrous tissue. Fig. 5. Older white fibrous tissue, in which the cells are no longer seen, and showing the wave-like course of the fibers. Fig. 6. Coarse white fibers, made up of bundles of the fine, and showing the mode of division by the splitting off of a portion of the fibers of the bundle. Fig. 7. Coarse fiber breaking up into fine fibers. Fig. 8. Cross sections of coarse fibers showing some of their various forms. Fig. 9. Reticular fibers, showing the mode of division and the multi- polar, or irregular star forms of the cells at the divisions. Fig. 10. Cross sections of the reticular fibers, showing some of their forms. Fig. 11. Connective tissue cells from which reticular fibers are developed. Fig. 12. Network of elastic fibers from the point of reflection of the mucus membrane of the lip from the gums. Fig. 13. Network of elastic fibers teased out from elastic tendon, and showing the usual mode of division. Fig. 14. Elastic fibers, showing their disposition to curl up when cut or broken. Fig. 15. Cross sections of elastic fibers, showing their forms as seen in a group passing between coarse white fibers. Fig. 16. Tissue of the dental pulp, in which the development of the cells is not followed by any considerable formation of fibers. Fig. 17. Non-attached periosteum from the shaft of the femur of the kitten. B. Bone. 0. Layer of osteoblasts. In the central portion of the figure they have been pulled slightly away from the bone, displaying the processes to advantage. It will be observed that the fibers of the periosteum do not enter the bone. a. Inner layer of fine white fibrous tissue (osteogenetic layer) showing the neuclei of the fibroblasts and a number of developing connecting tissue cells, which probably become osteoblasts. c. Outer layer, or coarse fibrous layer, in which fusiform fibroblasts are also rendered apparent by double staining with hema- toxylin and carmine, d. Some remains of the reticular tissue connecting the superimposed tissue with the periosteum. Fig 18. Periosteum from the shaft of the tibia of the .pig, length- wise section, showing the complex arrangement of fibers in the coarse, or outer fibrous layer that sometimes occurs under muscles that perform sliding movements upon it B. Bone. Layer of osteoblasts The tissue has been pulled slightly away from the bone in mounting the sec- tion, and part of the osteoblasts have clung to the bone, some have clung to the tissues, while others are suspended midway, their processes cling- ing to each. a. Layer of fine fibers. Inner or osteogenetic layer of the periosteum, b. First lamella of the coarse or outer fibrous layer, the fibers of which are, in this case, circumferential, exposing the cut ends. It will be observed that there are ten lamellae in the make-up of the outer layer, the lengthwise and circumferential fibers alternating. The ones marked/, and i, are very delicate ribbon-like forms, which have shifted from their normal position in the mounting of the section, so as to pre- sent their sides to view instead of their ends, thus displaying their struc- ture to advantage. The illustration shows how readily separable these lamellie are. I. Heticular tissue. Fig. 19. Periosteum from the lower end of the femur of the kitten at a point where the enlarged end next the joint is being trimmed down for the elongation of the shaft, showing the fibers of the periosteum in- cluded in, or entering the bone, forming its attachment, the absence of osteoblasts and the presence of osteoclasts by which the outer portions of the bone are being removed. B. Bone. c. Osteogenetic, or inner layer of periosteum, d. Outer layer, a part of which seems to have been torn away E. A few circumferential fibers, f.f.f. Osteoblasts lying in the lacunae of Howship, or excavations in the bone made by these cells. Fig. 20. Attached periosteum from beneath the attachment of the muscles of the lower lip of the sheep, a. Bone. B. Osteoblasts, with the fibers emerging from the bone between them. c. Inner layer with fibers decussating and joining the inner side of the coarse fibrous layer in opposite directions. This is rather an unusual form of this layer of the periosteum. D. Coarse, fibrous layer. E. Attachment of muscular fibers. in ; ' *n- "' I '' -m& *- ' -1; &lsj?3 -/ ' *'; 3 aw Fig. 21. The more usual form of the attached periosteum. A. Bone, showing the residual fibers (penetrating fibers of Sharpey) within its sub- stance and passing out between the osteoblasts B, and breaking up into fine fibers, which form the internal layer of the periosteum. These are also seen protuding from the broken margins of the section at g.g.g. D. Blood-vessels which are cut across. They occur mostly in the inner layer, very close to the under side of the outer layer. A number of them are seen. H. Small nerve bundles. F. Attachment of muscular fibers. It will be noted that the Haversian canals at li.1i. h. h., and at other points, are filling up with bone that has no residual fibers. Fig. 22, Network of elastic fibers from the coarse fibrous layer from a section of the same series, as Fig. 21, after dissolving out the coarse fibers with caustic potash. High power. Fig. 28. Bone, with portion of inner layer of attached periosteum, and penetrating fibers. The section is cut across the Haversian canals, and it shows the manner of the formation of these in the surface of the growing bone at a. a. by the upward growth of spiculse of bone which then spread out and join with others, thus bridging over and forming canals. At b. b. b. b. four Haversian canals are seen lined with osteo blasts. Around each of these, fresh bone is being deposited, which may be recognized by a slight difference in shade, but especially by the fact Unit the bone corpuscles lie in a different position from others in their neighborhood, and the fact that this bone has no residual fibers. It should be noted that this formation of canals immensely increases the area upon which osteoblasts may build. Fig. 24. Bone, with a more solid growth of surface, and with osteo- blasts much crowded between the fibers of the periosteum as ther emerge from the bone. Only a part of the inner layer of periosteum is shown. (t. a. Osteoblasts several layers deep between the fibers of the periosteum. b. b. Spiculse of bone growing up into the periosteum, apparently fol- lowing the line of a particular fiber. C. A Haversian canal that seems to have been excavated in the bone, and is being filled by deposit of new bone on its walls. This new deposit of bone is distinguished by a some- what lighter shade, and the difference in the direction of the long axis of the bone corpuscles, and the absence of residual fibers. Osteoblasts ap- pear in this portion of the canal. The margins of the secondary forma- tion, show the bay-like forms usual in the absorption of bone. Above the line drawn at E, no secondary bone is found, and osteoclasts, g. g, are seen instead of osteoblasts. In this portion the excavation is going on. In this way the bone, with residual fibers, is removed and bone de- posited in which these do not appear. f ... - 5 Fig. 25, 12th in. immersion obj. Higner eye piece. Margin of growing bone upon which the osteoblasts are very much crowded, a, Osteoblasts reaching to the surface of the bone by extending process-like prolongations, b, A cell that seems to be flattening down upon the sur- face of the bone, c, Bone corpuscles, the processes of which are seen radiating in the bone matrix. Processes are also seen extending into the bone from some of the osteoblasts. Fig. 26, 1-2 in. obj. Cross section of a young growing bone, show- ing the Haversian canals and the plan of their subperiosteal formation. a, Outer layer of periosteum, b, Inner layer of periosteum, c, c, SpiculfB of bone growing outwards into the tissue of the inner layer of periosteum, d, Other and older spiculse spreading out at their sum- mits, forming portions of arches, e, Other spiculse, the arches of which are about closing to form Haversian canals. /, Complete Haversian canals, many of which are seen in the illustration. Fig. 27, 1-8 in. obj. Absorption of bone under attached periosteum. a,, a, Osteoclasts lying in deep excavations in the surface of the bone. b, b, Surface of bone, showing the fibers of the periosteum implanted in it. Residual fibers appear in the bone. It will be noted that these fibers are removed with the bone by the absorptive process, c, e, Masses of fetal tissue filling the areas formed by the absorption. Fig. 28, 12th inch immersion obj. Intra-membranous formation of bone. An island of bony deposit, a, a, Bone corpuscles, b, b, Osteo- blasts. It will be seen that these lie between the fibers of the membrane, so that in certain positions the osteoblasts lie with their ends to the form- ing bone. And for the most part the long axes of the bone corpuscles have a similar direction. /V,- ? ;?/ . lli'f if ill 4 1 i| IN a V- X , .-'i :'.''. V 7 . -^', v^vi); Fig. 29, 1-4 in. obj. Growth of bone under the attachment of the Tendo Achillis in a young lamb. A, Fibers of tendon partially con- verted into fibro-cartilage. The cartilage cells are seen mostly between the tendon fibers. B, B, and c, c, c, Canals advancing from the bone beneath into the tendon. D, D, D, Bone deposited upon the walls of the canals forming Haversian systems laid upon, or among the tendon fibers. E, Portions of the tendon fibers still remaining deep among the Haversian systems of bone. Fig. 30, 12th in. immersion obj. reduced. A Single canal as shown at b, fig. 31, very much enlarged, a, a, Cartilage, b, b, Tissue of. canal, c, Blood vessel, d, d, Bone, e, e, Osteoblasts. /, /, Chondroclasts. In both these figures the bay-like excaeations of the absorption cells are seen in the canals, and at the margins of the bone de- posited in these. Fig. 31, 1-4 in. obj. Epiphysal intra-cartilaginous formation of bone from head of tibia of young lamb, a, a, Cartilage, the cells of which have fallen into rows, but have become scattered between the let- ters a, and b, b. b, b, Haversian canals advanced from the bone into the cartilage. It should be noticed that these are lined with chondro- clasts where the absorption of cartilage is in progress, and with osteoblasts when bone is being deposited. C, Blood vessels, d, d, d. Bone, which is extended into the cartilage by the filling of the canals formed by absorption as shown at e. -/,.^. />' # *TP ^'"' -^ r Fig. 32. Low power. Central section of the head, and portion of the shaft of the tibia from young kitten, showing diaphysal iutra-cartila- ginous formation of the bone at d, and the beginning of the epiphysal at h. a, Cartilaginous head of bone, b, b, Periosteum, c, c, Layer of subperiosteal bone. e. Periosteal notch ; the point to which the sub- periosteal formation of bone extends. /, Beginning of change in the cartilage cells where they form rows, y, Line of absorption of the cartilage. At d, the darkened portion reaching up to the line g, shows the portion occupied by the bone marrow, and the light portions the bone formed. Fig. 33, 1-8 in. obj. The changes which occur in diaphysal intra- cartilaginous formation of bone, a, Cartilage unchanged. At B, the cells have become smaller and have fallen into rows. At (J, the cells are enlarged in their short diameters, or in the direction of the length of the shaft of the bone. At D, the growth of the cells has reached its limit. The matrix begins to calcify. At E, the capsules of the cells are opened by the advance of the absorbent tissue. F, Area of the formation of bone. g. Apparently some glutinous remains of the cell body clinging to the walls of the capsule, h, Small, round cells mar- row cells, p, p, p, Remains of the cartilage matrix, j, Osteoblasts applied to the remains of cartilage matrix, but no bone is seen. K, K, K, Osteoblasts and a layer of bone deposited on the remains of cartilage matxir. m, in, m, m, Blood vessels, n, Capsule which seems to have been just opened and the marrow cells seen in the act of crowding into it. o, Fusiform cells. Many of these appear in this portion of the fig- ure, and seem peculiar to this location. Fig. [34. Supplement to fig. 33, taken from another portion of the section and showing the marrow cells applied closely to the walls of the capsules next to be opened, a, Cartilage. b, Fusiform cells filling closely the last capsule opened in that row. c. c, Round, marrow cells filling other capsules in the same manner, d, Unabsorbed remains of cartilage matrix. . Fig. 35, 1-8 in. obj. From a cross section of a rib of a young kitten at a little distance (boneward) from the change from cartilage to bone, showing the large Haversian canals with the remains of the cartilage matrix enveloped in the bone formed, a, a, a,, a, Remains of cartilage matrix which, in the figures, is left white, b, b, b, b, Bone deposited on remains of cartilage matrix, and generally covered with Osteoblasts, but at c, c, c, c, and other points, osteoclasts are quite plentifully distributed. While in one part bone is being deposited, in another it is being removed, and in the end all the cartilage matrix disappears. Fig. 36, 2 in. obj. Lengthwise section of small incisor tooth of kit- ten with its membrane and alveolus. The portion included in the illus- tration is one-fourth in. long, a, a, Crown of tooth and dentine, b, Pulp chamber and root canal, c, Cementum. d, d, d, d, Alveolar walls. e, Apical space and apical foramen. f,f,f,f, Body of perideutal mem- brane, showing particularly the arrangement of its principal fibers, their direction, etc. g, g, The cervical portion of the peridental membrane, showing the relation of its fibers to the gingivus 7i, the tangled mass of fibers forming the gums k, and the periosteum n, n, of the outer surface of alveolar wall, h, h, Gingivus. j,j, Epithelium, k, k, Coarse fibrous tissue of the gums. I, I, I, Bloodvessels traversing the peridental mem- brane. A section showing the smallest number of these was selected, for the reason that the fibrous arrangement is less distorted. * m, Saculus of permanent tooth. The fibers of the peridental membrane become con- tinuous with those of the periosteum at n, n. o, Periosteum, p, Attach- ment of labial muscles. The intention of the illustration is to give a full view of the arrangement of the fibers of the peridental membrane, and the relations of the tooth, membrane, and alveolar wall. Fig. 37, 2 in. obj. Cross section of the root of a temporary incisor with the peridental membrane and alveolar walls, at about the middle of the lower third of body of the peridental membrane, showing the direction of the fibers of the membrane, and the position of the blood-ves- sels, a, The dentine, b, Cementum. c, Pulp. Its blood-vessels are shown. d, d, Alveolar wall, septi between the teeth, e, e, Peridental membrane. The direction and arrangement of its fibers have been carefully repre- sented; also the position and relative size of its blood-vessels. /, Thin portion of the anterior alveolar wall, g, Hypertrophy of the cernentum. Fig. 38, 2 in. obj. Cross section of cuspid tooth with peridental membrane and alveolar wall cut through the thickened rim at the gin- gival portion of the alveolar wall, from a man forty years old. The membrane was very thin and firm, and a large piece of the anterior wall of the alveolus adhered to the tooth when extracted. It therefore repre- sents an extremely thin membrane, while fig. 37 represents one that may be regarded as thick, a, a, Peridental membrane, b, b, Cementum. c, c, Alveolar process, d, d, Dentine. It will be observed that most of the blood-vessels of the peridental membrane lie in depressions in the alveolar wall. Fig. 39, | in. obj. Fibers of the peridental membrane passing from the cementum a, to the alveolar wall b. The section is from the root of a first molar of a man about seventy years old. The point chosen for this illustration includes a portion of a strong band of solid fibers c, which pass unbroken from the cementum to the bone. More generally, the fibers, after emerging from the cementum, break up into finer fibers or fasciculi, as at d. This form of the fibers is better shown in fig. 42. Fig. 40, 2. in obj. Cross section of the central and lateral incisors bdow (toward the crowns) the rim of the alveolar wall, or through the necks of the teeth, showing the tissue of the septum and of the gums anteriority, a, Portion of central incisor, b, Lateral incisor, e, Pulp chamber of lateral incisor, d, d, Cementum of central incisor, e, e, Ce- mentum of lateral. /, Fibers of the peridental membrane extending from tooth to tooth continuously. These are fixed in the cementum of each tooth, and form the tissue of the septum, g, g, Fibers of the peri- dental membrane, which join with the coarse fibrous tissues of the gums //, }>. ./',,/, Epithelial covering of the gums. Fig. 41, in. obj. Peridental membrane from perpendicular section of a tooth of the pig, stained with nucleus tinting dye. a, Cementum. b, Bone, e, Blood-vessels cut diagonally, d, Nerve bundle, e, Lym- phatics. A number of these are seen near the cementum. The principal fibers are transparent, while the interfibrous tissue is stained. The cellu- lar elements appear in rows between the principal fibers, which are large and strong near the bone, and only partially break up into fasciculi in the central part of their length. Fig. 42, 12th in. obj. (reduced.) Fibers emerging from the cementum and breaking up into fasciculi. From the peridental membrane of a molar of an aged person. This represents the more usual form of the principal fibers, as seen in old age in man. They pursue a somewhat wavy course, and generally the identity of the individual fiber is lost. They are inserted into the bone in compact bundles similar to those of the cementum. Fig. 43, 12th in. obj. (reduced.) A group of fibers emerging from the cementum and radiating fan-like. On either side, the principal fibers are absent for a little space, which is filled with indifferent tissue. From the apical space (at the apex of the root) of a bicuspid of an old person. a- &-'/. - " '' ; '''' 'y/ Fig. 45, 12th in. obj. (reduced.) From section including a portion of the alveolar wall, and portions of the peridental membrane, showing tin- osteobla- fttS^ rlf/ H v- N ' *i* y *\ S/ % ^ ? % ' - -'," ' ' --" : * "> ^ ------ Fig. 50, 12th in. obj. (reduced.) Cementum and portion of the peri- dental membrane from the sheep. From a cross section of the tooth. a, Cementum. B, Cementoblast lying between the fibers, which latter break up into fasciculi immediately after leaving the cementun. c, c, Cross section of the lymph follicles or nodes. D, Fibroblasts. E, Blood vessels. These are accompanied by a large amount of interfibrous, or indifferent connective tissue. F, Nerve bundle. G-, Fasciculi of fibers pursuing a direction different from the main trend of the principal fibers. Fig. 51, | in. obj. Rim of the alveolar wall, from a perpendicular section, a, Haversian bone, which is left without stippling to render it more apparent, b, Subperiosteal bone, showing residual fibers, c, Per- iosteum, d, Extreme gingival margin of the alveolar wall, e, Fibers of tbe peridental membrane. /, Bone formed by the osteoblasts of the peri- dental membrane, g, g, g, Points at which the absorption of bone is in progress. Figs. 52 and 53. Diagramatic illustration of the movement of a central incisor during the growth of the alveolar process between the age of twelve aud twenty-one years. The broken lines represent the tooth and its alveolus at twelve years of age, and the solid the same tooth at twenty-one. Fig. 52 represents the minimum movement, while fig. 53 represents the maximum movement, as ordinarily observed. The figures are let- tered alike. The growth of the process is represented by the movement from a, a to b, b. The tooth is carried forward with this growth, and the alveolus is tilled with new bone from the line c, to the line/. a ' f ^ lit -:-- - c Fig. 54, 12th in. obj. Cementoblasts isolated to show the peculiar irregular forms of these cells. Fig. 55, 12th in. obj. Cementoblasts in situ, with cross sections of the principal fibers of the peridental membrane of the pig, from a section cut horizontal to the surface of the cementum and including these cells. 1 1 will be seen that the Cementoblasts fill all the space not occupied by the principal fibers. (In figure 57 e, the Cementoblasts are seen as they appear in section perpendicular to the surface of the cementuni.) Fig. 56, 12th in. obj. Section of cementum of pig cut horizontal to and near the surface of the root of the tooth, showing cross sections of the included fibers, b. Thin margin of section, from which the fibers have fallen out of their alveoli, c, A little thicker portion in which the fibers remain. It will be noticed that from shrinkage the fiber is a little small for its alveolus, so that it is slightly separated from one side, a, Cement corpuscles Fig. 57, i in. obj. Perpendicular section of the cementum of a pig, showing the included fibers of the peridental membrane, e, Margin of cementum showing fibers passing from the cementum to the peridental membrane, and the layer of Cementoblasts with other cells in the neigh- borhood. /, Lymphatics, d, d, Fibers protruding from broken margin of section, a, Dentine, b, Junction of dentine and cementum. Fig. 58, 12th in. obj. Cementum of pig from the dried section, a, Dentine, b, Lacunae of cementum with canals anastomosing with each other, c, Imperfectly calcified fibers. It will be noticed that a few of the dentinal tubes pass through into the cementum. r ? i iifpwwptw) Fig. 59, 1 in. obj. Hypertrophy of the cementum on the side of the root of a lower molar near the neck of the tooth. From a lengthwise section, man. a, Dentine, b, Cementum. c, Fibers of peridental mem- brane. From b to c the cementum is normal, and the incremental lines fairly regular, but at d, one of the lamclUe is greatly, thickened. At e,. this lamella is seen to be about equal in thickness with the others. The next two lamella: are thin over the greatest prominence, but one is much thickened at g, and both at h. These latter seem to partially fill the valleys which were occasioned by the first irregular growth. Fig. 60. 1. in obj. Hypertrophy from root of cuspid, man, in which the irregularity is confined to the first lamella, a, Dentine, b, Thick- ened first lamella, c, Subsequent lamella), which are seen to be fa'rly regular. Fig. 61, 2 in. obj. Apex of root of an upper bicuspid tooth with ir- regularly developed cementum. a, a, Dentine, b, b, Pulp canals. The lamelke of cementum are marked 1, 2, 3, etc. d, d, d, Absorption areas that have been refilled with cementum. It will be seen that the apices of the roots were originally separate, but became fused with the deposit of the second lamella of cementum, and that in this the irregular growth began and was most pronounced. It has continued through the subsequent lamellae, but in less degree. It will also be noticed that the absorption areas, d, d, d, have proceeded from certain lamella 1 . That between the roots has broken through the first lamella and penetrated the dentine, and has been filled with the de- posit of a second lamella. Other of the absorptions have proceeded from lamella. 1 , which can be readily made out. The small points, e, seem to have been filled with the deposit of the last layer of the cemeutum, while others have one, two or more layers covering them. mam i L, ' -~ 2* -y y Fig. 62, i in. obj. Cross section of the root of a temporary incisor tooth of the pig, showing a large area of absorption which is partly filled in with cenientum. a, Dentine, b, b, Cementum. c, c, Area of absorption. It will be noticed that in this area all of the cementum and a considerable portion of the dentine has been removed, d, d, Cementum that has been laid down upon the surface of the dentine and cementum alike, e, e, Peri- dental membrane. /, Portion of bone forming the wall of the alveolus that has grown forward into the area of absorption, g, g, Osteoclasts which are removing these bony projections. The bone which has been advanced here to take the place of the absorbed area is being removed again in compliance with the rebuilding of the cementum, which is in progress. Fig. 63, in. obj. Portion of the anterior alveolar wall of an incisor that is being absorbed, a, a, Portion of the inner layer of the per- iosteum, b, b, Bone forming a portion of the anterior wall of the alveo- lus. It will be observed that it contains a number of Haversian canals, h, li. c, c, A portion of the peridental membrane, d, d, d, Osteoclasts which are in the act of removing the bone, thus widening the al- veolus, e, Space from which a large osteoclast has probably fallen dur- ing the preparations of the section. It will be noticed that where the Osteoclasts are removing the bone, the fibers of the peridental membrane are detached and some little space is occupied by tissue of a fetal type, but in the spaces between the groups of Osteoclasts the fibers are firmly attached to the bone. At /, there seems to be a little new bone formed to which fibers are attached. In this way bone seems to be re- moved, part by part, and the attachment of the membrane maintained. Fig. 64, | in. obj. Portion of the alveolar wall of a cuspid tooth of an old person, showing absorptions a, a, Portion of the peridental membrane, b, b, Portion of bone that seems to have been built on to supply an area of previous absorption, e, A recent absorption area. At /, three Osteoclasts are seen. It will be noted that the fibers of the peri dental membrane are detached throughout this area of absorption and the space is occupied by tissue of a fetal type. It should also be noted that the Haversian systems of the bone had been cut into by the previous absorption, removing portions of the rings of the Haversian systems. Residual fibers are seen in the bone b, but there are none in the Haver- sian bone c. \r**y- - --- -^z~ - ~- m SSK - i //s f -Z*s m .,,.-; -^bi^ _. : ^ : : "^-S 'C ^ . . -/ ? . y i "*..-.> & \ /: .s- ^i M fc...; .- .-; ;''.v*:s v* Fig. 65, in. obj, One half of the apex of the root of a lower molar. From a dry section, a. Pulp canal, b, Dentine, c, Cemenlum. A number of absorptions have occurred at d. Absorptions have pro- ceeded from the second lamella of the cementum and have penetrated the dentine to a considerable depth. These have been refilled with a some- what irregular deposit of cementum. Along the line e, a very consider- ble absorption has cut away the entire apex of the root, removing not only the cementum, but evidently a considerable portion of the dentine as well. From the appearance of the incremental lines, this seems to have occurred contemporaneously with those pointed out at d. The ex- posed dentine has been again covered with cementum, which is fairly regular, though its incremental lines are not clear. /, An absorption that seems to have been in progress at the time of extraction. Fig. 66, i in. obj. From a section of a bicuspid with its alveolus, showing a pit-like absorption upon the side of the root in which the re- deposit of the cemeutuni has begun, a, Dentine, b, Cemeutum. c, Per- idental membrane, d, Bone forming the wall of the alveolus, e, Ab- sorbed area of cementum. It will be noticed that a new deposit of ce- mentum has begun the filling of the area, and that the soft tissue in the area of absorption is of a cellular type. The bone also shows the effects of absorption in the cutting away of portions of the rings of the Haver- sian systems at /, while at g the presence of osteoclasts shows that ab- sorption is in progress at that point. Fig. 67, & in. obj. Cross section of the immediate apex of the root of a cuspid tooth, showing large areas of absorption, a, Root canal, b, e, ff, and j show extensive absorption areas that have been refilled with cementum, while c, d, Ji, and k show smaller absorption areas that have occurred later. Some of these areas show the included fibers of the per- idental membrane plainly, while others do not, probably for the reason that the section is not parallel with them. At /, the original or regular deposit of cementum reaches the present surface. The plane of the section is not such as to show the incremental lines, and therefore the relation of the absorptions to these cannot be seen. THE PERIOSTEUM AND PERIDENTAL MEMBRANE. CHAPTER I. PRELIMINARY. In the study of histology there have been great ad- vances within the last few decades. This advance has been along special lines to which attention has been strongly drawn by the results of individual effort, or in which the needs of the suffering public have directed in- vestigation. Cohnheim and Strieker, with numerous co- laborers, have done much to unravel and make plain the formerly mysterious tissue changes which occur in in- flammation. By the investigations of numerous workers the tissue forms and modes of growth of the various tumors have been made so clear, that even the young worker in pathological anatomy may readily recognize their various forms, and classify properly those that may come under his lens. The more difficult special tissue forms of the eye and ear have been so plainly unfolded by workers in these fields that it is no longer a question as to the forms of the elements found, but the discussion is carried to the domain of the more intimate and special physiological function of individual groups of cells which are recog- nized by all. The very complex structures of the brain, spinal cord, and the various ganglia of the nervous sys- tem have been searched so closely that the discovery of form elements yet undescribed seems almost impossible. And as it is with these, so it is with a large majority of 1 2 PRELIMINARY. the form elements of the human body. Yet there are many special fields opening up for further discovery and waiting for laborers. In this work each advance in discovery has brought with it a corresponding advance in technique. New and better means of bringing difficult and hidden form ele- ments into view have been so rapidly brought forward that one who has been out of the work for but a few years will, on entering the histological laboratory of to- day, find himself confronted by apparatus and re-agents, much of which will seem new and strange ; and will find that these have modified the views of tissue elements with which he had been familiar, and have brought them into bolder relief, developing finer elements of structure than had been possible by the older methods of pro- cedure. That which had been known becomes better and more intimately known ; and this better technique calls for re-working in the formerly worked out mines of histological inquiry for the finding of the finer grains of information missed by former laborers. Each field in histology seems to be worked over and pondered over anew, as new pathological factors have fastened the attention of specialist or general practi- tioner. This is the case whether the new factor be based upon some new fact discovered, or theory pro- pounded ; for each thought that gives promise of devel- oping truth must be tried and tallied with the form elements with which it is associated. It is considerations such as these that have prompted me to undertake anew the study of the periosteum and peridental membrane. Fifteen years ago I went over the subjects pretty closely, but at that time there seemed to be no special call for more definite information in regard to them. Upon the peridental membrane there had not been much written, and there did not seem to be much interest in the subject among the dental specialists. PRELIMINARY. 3 Since then, however, attention has been strongly called to the structure of this membrane from several directions almost simultaneously, and an intense interest awakened. These are, first, the efforts that have been expended in the study of its destructive diseases, which was stimu- lated primarily by the late Dr. Riggs of Hartford ; sec- ondly, by the greater and more general interest recently felt in the correction of irregularities of the teeth, in which changes in this membrane and the relations of the parts which it unites are brought about ; third, by the greater interest that has been manifested by the masses of the dental profession in the retention of pulpless teeth, and roots which have lost their crowns, and which are dependent upon the continued health of the peridental membrane under modified conditions ; fourth, by the re- vival under varied forms of the ancient methods of replanting and transplanting teeth, the success of which is supposed to be dependent, in whole or in part, upon the reconstruction of the peridental membrane, or its re- attachment to the teeth; and, fifth, by the singular fact that has of late been noted more accurately ; that a large proportion of the teeth thus replanted with seeming suc- cess, are finally lost by absorption of their roots ; a matter which seems to depend upon some mal-condition of the tissues of the peridental membrane. All of these considerations call earnestly for an intim- ate knowledge of the histology and physiology of this membrane as the basis for the formation of correct views of its pathology and recuperative powers when subjected to disease or serious injury. In order that I might obtain correct views for presentation, I have gone back to the tissues themselves for information and have made a re- study of the subject de novo, availing myself of the new methods of procedure, and preparing such a number of sections from various sources as would seem to give every possible view of the subject. In this study it has 4 PRELIMINARY. not seemed judicious to confine my labors to the peri- dental membrane, either in the study or in the presenta- tion, but to unite with it the study of the periosteum for the purpose of having a broader field of comparison. This is at once suggested by the natural kinship of these tissues, and has been rendered the more necessary by previous views that have been entertained as to the dis- tinctions between them, or their identity. Indeed, the relations of these membranes are such that the perios- teum must be studied in order to arrive at correct views in regard to the structure and function of the peridental membrane, which will clearly appear as we proceed. They are alike in many of their features while presenting points of sharp dissimilarity, and by studying them to- gether each becomes better understood. The task is an unusually difficult one for several reasons. First, it is impossible to obtain suitable sections for the examination of these tissues without first decalcifying the bones and teeth ; for we must study them in their normal relations to the parts with which they are associated. The acids to which they must be subjected in the process of decal- cification are not without effect upon the tissues. This is injurious in a large degree, and robs them of that freshness so necessary to the gaining of good views of their constituents. Again, the selective stainings that are so valuable in histological determinations depend upon the finer chemi- cal qualities of certain constituents of the tissues, their cells, or fibers, which cause certain of these to absorb a dye or color while others do not, thus distinguishing them.. The necessary subjection to acids in decalcifica- tion disturbs these finer chemical relations seriously, so seriously as to render the use of some of the finer stain- ing agents unavailing, and causing much annoyance and imperfection in the use of others. Again, in the study of most of the tissues a little PRELIMINARY. , 5 shrinkage in the process of hardening for the purpose of making sections is of little or no consequence, for all being soft they will presumably shrink in the same degree, and their relations will not be disturbed; but in the mem- branes we are to study we have soft tissues combined with bone, and teeth and their mutual relations must be main- tained. If shrinkage occurs in the softer portions these relations are disturbed and the object defeated. CHAPTER II. TISSUE ELEMENTS AND DISTRIBUTION. Before proceeding with this study it will be well to- review the more elementary histology of the class of tis- sues to which these membranes belong ; to lirst learn of what tissue elements they are mostly composed, and the character of these elements individually ; and afterward we shall be enabled to study them more intelligently in their combinations and peculiar forms in special localities. These membranes belong to what is termed the con- nective tissue group, and in structure are very nearly related to many other parts; so much so, indeed, that in most of the works on histology a description of the group as a whole has been considered sufficient without separ- ate descriptions of the special membranes, or with a sim- ple mention of some of the more important structural peculiarities. This would seem to be sufficient to the ordinary student of histology who often has the structures under observation, but it seems that to those who depend mostly on reading for their information in regard to such subjects, which up to the present time includes the greater number of both medical and dental practitioners, this does not serve the purpose when attention has been strongly called to a particular one of these. If one attempts to look up the special subject of the periosteum or peridental membrane in any or all of the current his- tological works, he will find the descriptions short and rather vague ; indeed that the literature of the subject is- very incomplete. Yet if these descriptions, short as they are, be taken together with a good practical knowledge of the histological characters of the elements of the group- TISSUE ELEMENTS AND DISTRIBUTION. 7 of structures to which they belong, a comprehensive idea of them will be gained. Still it must be admitted that more especial description is needed in the light of the recent interest awakened in the peridental membrane. Furthermore, additional studies of the periosteum, especial- ly from the pathological standpoint, are very much needed, and these should be preceded by further studies of its regional histological characters, especially differences in the internal layer and the varying modes of its attach- ment to the bone. Previous studies of the periosteum have related almost solely to its bone-forming powers giving little or no consideration to the special elements which serve purely physical functions or distinctions be- tween these. This large group of fibrous membranes is usually made to include structures which, though seemingly widely separated, are closely connected in their structural pecu- liarities. That is to say, though they may seem to serve widely different purposes, or, better, are connected with widely different organs, they are all emphatically fibrous in their structure and differ only in the peculiarities of their fibrous arrangement, in preponderance of the white or elastic varieties, and in the number and character of the cells which may be contained within the fibrous net- work. Again the purposes subserved by these different fibrous membranes when closely studied, are found to be as similar as their structure. They are all coverings for other structures, and form their connections with neigh- boring parts, and, while in themselves they are indifferent tissue, they are generally made subservient to functioning tissues by conveying bloodvessels and nerves, and holding in some part of their netword embryonal cells for the supply of the needs of the tissues which they envelop or connect. DEVELOPMENT. The connective tissues are developed in a soft trans- parent homogeneous material which has been known as 8 TISSUE ELEMENTS AND DISTRIBUTION. ground substance, basis substance, gelatinous substance or matrix. This material is in large proportion in the prim- itive or developmental state of this tissue, both in the fetus and in the early development of it as it occurs in the healing of wounds in the adult. Within this matrix the cells lie imbedded, and in this state it is usually termed gelatinous tissue. In this matrix the cells may exist in such great numbers as to obscure the ground substance, or they may be but sparsely distributed, and their devel- opment may be studied step by step as the adult tissues are assuming their forms, and through those changes by which certain of the fibrous elements are derived from them. In a few of the organs of the adult this tissue seems but partially developed, notably in the dental pulp (see fig. 16), the ground substance remaining in large proportion, and the cells being developed with but slight inter-mixtures of the fibrous elements. These have been termed myxomatous tissues. But generally the tissues undergo such development as to completely change their apparent character. The ground substance disappears more or less completely, giving place to fibers of various forms. Among these, two varieties, differing essentially the one from the other appear, known as the white and the yellow, or the inelastic and the elastic fibers. The former is in much the larger proportion, and its develop- ment is traced very directly from the primary cells found in the basis substance. In fig. 1, I present an illustration of the tissue taken from beneath the epithelium of the abdominal wall of a human fetus in the sixth week, and in fig. 2, a specimen from the same locality from a little older fetus. (The umbilical cord is usually recommended for obtaining views of embryonic tissues.) In fig. 1, the cells are round, oblong or irregular in form and the cell contents slightly granular, and presenting either no clearly defined nucleus, or it appears but faintly, or at least it has not the prorni- TISSUE ELEMENTS AND DISTRIBUTION. 9 nence seen in the epithelia. In fig. 2, the cells are gen- erally assuming a lengthened form in a common direction, and some of them present pointed extremities, yet no true fibers are present. In fig. 3, the cells are illustrated in a more fully devel- oped state, in which the points are drawn into long slender filaments. These may often be found in the sub- cutaneous tissue of the fetus, lying side by side and end to end with their filaments joined together, apparently, in such relative position that the full length of the filaments of two cells lie side by side, as in the two lower cells in fig. 3. Sometimes these fibers seem to be fused into one* As the development proceeds this appearance is changed by the development of numerous fibers between the cells ; the cells meanwhile becoming smaller. As to the precise mode of the formation of these fibers there is still some difference of opinion among histologists. One view re- gards them as developed from the ground substance in the immediate neighborhood of the cell, and another, that the fiber is shed out from the cell itself is the direct product of the cell. One can hardly trace this develop- ment as it proceeds without feeling a conviction that the fibers arise, at least, under the immediate supervision of the cell. I shall, therefore, call such cells fibroblasts. This fibrillation proceeds until the ground substance has disappeared and given place to a fibrous tissue which pre- sents the appearance represented in fig. 4. As the tissue grows older the cells are separated more and more widely, and become smaller, until finally in the older tissues they are represented only by thin scales lying among the fibers. Many, and often almost all of them, disappear entirely. This disappearance is often quite complete in the more compact fibrous tissues, especially the tendons. In the developed tissue the fibers are generally not straight un- less put upon the stretch, but pursue a wave-like course, as shown in fig. 5. 2 10 TISSUE ELEMENTS AND DISTRIBUTION. These fibers are very small, and are usually gathered together in bundles in which the individual fibers may seem to have but slight connection with each other, and form broad, flattened, wavy belts of loose texture, running parallel or crossing each other in various directions, as in the peridental membrane, or may be formed in close, com- pact bundles, that assume the form of large fibers (coarse fibers fig. 6), running nearly parallel, but interlocking with each other, as in the outer layers of the periosteum, or may cross each other in every conceivable direction, leaving larger inter-spaces or meshes (areolse) between them, as in the areolar tissue, or may be compacted into a dense, tangled mass, as in the gums. In some of these forms the fibers are cemented together into bundles by an intervening substance. The individual fibers are never seen to branch or divide, and we may often search the tangled nets of the coarse fibers or bundles in vain to find them dividing, but in some localities these are found abundantly, as in the gingivse. These branchings are, I believe, always effected by the splitting off of a portion of the fibers, which form a bundle, or coarse fiber, as represented in fig. 6 (from a silver nitrate preparation). The smaller bundles which split off in this way sometimes join and form a part of an- other coarse fiber, and by these divisions and junctions form nets through which fibers running in different direc- tions may pass, or they may inclose cellular elements. This kind of branching occurs perhaps only in the softer forms of the coarse fibers. Occasionally, when the tissue is passing from a more firm to a looser texture, the more solid, coarse fibers are seen to break up and spread out in finer fibers, as represented in fig. 7. These coarse fibers are seldom round. They are often seen to form bundles interlocking with each other ; often in compact masses. These, when seen in cross sections, present exceedingly irregular forms and sizes (fig. 8). TISSUE ELEMENTS AND DISTRIBUTION. 11 Fine sections of the tissue of the gums, when deli- cately stained with silver nitrate or osmic acid, give a great variety of views of these. In this position the coarse fibers are very closely interwoven, and every field will present cross sections differing in outline and config- uration of the cut ends of the fibers. In some positions, however, we find branching fibers of a different type. The cells, in their development, instead of assuming the tapered spindle forms, with pro- cesses at either end, present irregular star forms, sending out three or more filaments, as represented in fig. 11. In some positions these cells are seen to remain in this form without further fibrillation, as in the dental pulp ; but in others, notably in the framework of the lymphatic glands, they form by their 'fibrillation an intimately branched net- work, as represented in fig. 9. These are known as reticular fibers, and form reticular tissue. In these the star-shaped cells are seen at the junction of the branches, and in the mature forms seem to lie upon them as a flat- tened scale, which may be removed by brushing. These fibers, like those previously studied, are not round. The shapes, as shown in cross sections, present indefinite variation, with a tendency to elongated forms, as illustrated in fig. 10, showing the fibers to be irregu- larly flattened. The development of the yellow or elastic fibers has not been traced so successfully as the white, and there is still much uncertainty regarding the manner of their origin. Krause regards them as being developed from cells in a manner similar to that of the reticular fibers, except that elastin is formed instead of the glue-giving substance of the white fibers. Boll and others have also traced their formation from cells. But a large number of those who have examined the subject have failed to trace the devel- opment of these fibers from cells. Others have thought that elastic fibers are developed 12 TISSUE ELEMENTS AND DISTRIBUTION. by the formation of granules of elastin in the basis sub- stance, and the union of these, end to end. The same material is also found in the form of a very thin, elastic, and apparently perfectly homogeneous membranes, which are supposed, according to this view, to arise by the union of the granules of elastin in the form of sheets, which be- come united into a continuous membrane. The elastic fibers are found in almost all parts of the soft tissues of the body, except the epithelial structures. In another form this substance may be demonstrated here also, serving as a connecting substance for the epithelium. If a very thin section of the stratified epithelium be treated with a 33 per cent, solution of caustic potash, by the plan discussed later for the demonstration of elastic fibers, the epithelial cells will gradually disappear, leav- ing a delicate net of elastic material, which accurately represents the former junctions of the cells. A few liga- ments are composed of elastic fibers almost as pure as the ligamentum nuchse of the ox, and ligamentum subflava of man ; but in most places they are but scantily distributed. Wherever found, they present the same characteristic form of network. The fibers divide dichotomously and form junctions freely, and in this form are interwoven with the white fibers of the areolar tissues and the fibrous membranes ; and wherever we find these of loose texture, we find large intermixtures of the yellow fibers. I have represented in fig. 12, a portion of these nets as seen at the points of reflection of the mucous membrane of the lips from the gums. It is a little unusual, in the fact that it represents nodal points from which several fibers radi- ate, while usually they divide only dichotomously, as rep- resented in fig. 13. The point of reflection of the mucous membrane from the gum tissue at the labial side of the teeth, is a very good place to study them. Here the tissue is of a very loose structure, and the mucous membrane is united to TISSUE ELEMENTS AND DISTRIBUTION. 13 the parts beneath by a fine network of elastic fibers. Carmine or hematoxylin stainings, mounted in glycerine, serve the purpose best when the networks are sought ; but for examining cross-sections of these fibers as they occur entwined among the coarse white fibers, osmic acid or silver nitrate stainings, mounted in balsam, give bet- ter results (fig. 15). In fig. 13, I have represented the fibers as they appear when teased out from elastic tendon. Elastic fibers, like the other varieties, are seldom round. In fig. 15, I have illustrated these forms as seen in cross-section in a silver nitrate staining, in a group noticed passing between some coarse white fibers. Elastic fibers show a peculiar disposition to curl at the ends when cut or broken, which 1 have represented in fig. 14, giving examples taken from the position mentioned above. Here we will often see the short pieces cut off in thin sections, very much curled. The cellular elements of the fibrous membranes, other than those already described, are mostly peculiar to the position, rather than to the fibrous tissue, and belong to the tissue invested rather than to the fibrous investment, and their consideration belongs to the regional descrip- tions. The leucocyte is found among the meshes of these membranes very generally, and other cells have been described as especially belonging to them ; particularly a round, nucleated cell larger than the leucocyte, and cer- tain forms of the branched corpuscles. In some positions these latter appear abundantly, notably in the membranes of the eye. It seems probable that some of these are developmental types destined for some use in the neigh- borhood, rather than belonging specifically to the connec- tive tissues as such. There are, however, young cells present undergoing development in perhaps all of the tissues of young animals, and possibly in the old, that, in the regeneration or augmentation of the tissue, pass through 14 TISSUE ELEMENTS AND DISTRIBUTION. the phases already described. And it is also probable that many of the peculiar forms occasionally seen are cells that have become stationary, have begun to retrograde, or have, from peculiarities of environment, assumed modi- fied forms. Fatty tissue consists of connective tissue cells, filled with oil, which usually lie heaped together in little groups, or may form great masses by aggregations of these. It is most abundant in areolar tissues of loose texture, but is occasionally found in the fibrous mem- branes. The fibrous membranes act very largely as a depot of supplies to the tissues which they invest. They bear the bloodvessels and nerves, and in some cases they receive, partially, as in the periosteum for the bones, and in others wholly, as in the peridental membrane for the cementum, the pabulum from the blood to be transmitted through their meshes to the point of assimilation. The local characteristics of the individual membranes are continually modified by the deflection of their fibers this way or that, to give place for the passage of blood- vessels and nerves, and for the investment of them. These deflections are often of such a character as to mislead the observer if only one or two. sections are examined. In these forms, and inclosing in the meshes formed by its fibers, varying numbers and forms of cellular elements, this tissue is distributed throughout the body. It is con- tinuous everywhere, and has been described by different writers under a great variety of names, according to the local peculiarity of the tissue and the positions in which it is found. It is fo.und under the mucous membranes submucous tissue ; under the serous membranes sub- serous tissue; under the 'skin subcutaneous tissue ; and about the bloodvessels it forms a continuous membranous sheath, or investment, and in this way gives them sup- port and protection. In the same way it forms the TISSUE ELEMENTS AND DISTRIBUTION. 15 investment of the nerves neurilemma ; and incloses each muscle in a distinct sheath myolemma ; and dip- ping in between the muscular fibers, surrounds each one individually sarcolemma ; and serves to connect them with their tendons, or with the periosteum. It invests the glands, holding their lobes in position, and, following the ducts into the substance of the gland, forms an invest- ment for each lobule, and within this substance the blood- vessels that supply the gland ramify. It forms the support for the organs of the hollow viscera peritone- um pleura ; it invests the brain dura mater arachnoid membrane, and forms the investment or ma- trix for its functioning cells neuroglia ; it incloses the heart in a closed sac pericardium and forms the investment of the eye sclerotica. In strong membran- ous sheets fascia it binds down the muscles, and holds them in position ; it forms the investment of the bones periosteum and serves to attach the roots of the teeth to their alveoli peridental membrane. In a still more condensed form in which the fibers lie parallel with each other, it forms the tendons which connect the muscles with the bones, and the ligaments which connect the bones together. This tissue also stands in very close developmental relations with still other and seemingly very different tissues. Cartilage and the bones are developed directly from a connective tissue matrix, and seemingly the one is developed from the other, though close examination seems to reveal the fact that the development of the one dis- places the other wholly or in part. The bones, at least, are developed from specialized cells the osteoblasts, which seem endowed with a special bone-forming power. These cells are, however, developed from connective tissue cells, or at least from the cells that, from all that has as yet been learned of them, are the same as the em- 16 TISSUE ELEMENTS AND DISTRIBUTION. bryonal connective tissue cells. This point will be exam ined more particularly later. It appears also from the teachings of comparative his- tology that one of these tissues may be substituted by another of equivalent value. That which in one animal appears as ordinary connective tissue may in another be of quite a different reticular type ; and that which is rep- resented by cartilage in one may be substituted by bone in another. These changes are often icmarked also in the developmental stages of the same animal. Thus in mammals the greater part of the skeleton is first repre- sented in cartilage, which is afterwards replaced by bone, while a few of the bones, as the cranial, are first repre- sented as fibrous membranes, in the midst of which the bones are formed. This is called the inter-membranous formation of bone. Three modes of the formation of bone are usually recognized; the inter -cartilaginous, inter-membranous, and the sub-periosteal. Further than this these tissues have other relation- ships from a physiological point of view. Their signifi- cance in the action of the healthy body is of a more subordinate kind ; though they make up an enormous proportion of it. They represent, as is usually said, tissues of lower vital dignity (Frey), and seem in a degree subordinate to the more proper functioning tissue for which they form an extended framework in the meshes or cavities of which the muscles, vessels, nerves, gland cells and organs lie imbedded. The name then of connective tissue seems to be en- tirely appropriate. If we farther reckon the muscular tissue with this group, which seems proper according to most histologists from its developmental relations though it is widely specialized, it may aptly be termed the tissue of support and motion, while the tissues of the epithelial type constitute the tissues of function and pro- tection. CHAPTER III. METHODS OF THE PREPARATION OF TISSUES. Perhaps it would be well, before going farther, to indicate briefly the methods I have employed in the preparation of the tissues from which my studies and illustrations of those to be described have been made. These have been taken, for the most part, from young and small animals, such as the cat, lamb, pig, dog, etc. The human fetus, and also tissues taken from the adult, have been employed in sufficient amount to make reasonably good comparisons, but the difficulty of obtaining these sufficiently fresh to give the best results, is quite obvious. The time between the death of the animal and the im- mersion of the tissue in the fluids by which it is prepared for cutting, should be counted by minutes, never by hours. For this purpose I have used Miiller's fluid and chromic acid, giving the preference to the former, and have usually added the acid for decalcification, after the first day. It has been considered important that very small bones be used, in order that the time of exposure to acids in the process of decalcification be as short as possible. It is exceedingly difficult to cut large bones into sufficiently small pieces, without disturbing the relations of the soft portions of the tissue, especially in the loosely attached portions of the periosteum. The injurious effect of acids has been closely studied, and it has been found that the element of time is, within certain limits, more important than the strength of the acid solution employed ; -that is to say, a tissue decalcified in one day with a three per cent, solution of nitric acid, and then thoroughly de- acidulated by copious ablution, will come under the lens 3 17 18 METHODS OF THE PREPARATION OP TISSUES. in better condition than if exposed to one-half per cent, for five or six days. The use of alcohol in hardening has been avoided as far as possible, on account of the shrinkage which it in- duces. Indeed, it has been limited to the dehydration of the tissue for the purpose of impregnation with the im- bedding material, in cases in which this is demanded. Some sections of each class of tissue have been made without dehydrati'on, or any form of impregnation, for purposes of comparison and the formation of conclusions as to the changes induced by the different materials used for these purposes. By this mode we are unable to obtain sections sufficiently thin and regular for general study, but may obtain scraps that will reveal the tissue charac- ters for comparison. Such studies demonstrate that all of the modes of impregnation yet used for the purpose of cutting sections, injure the tissues in some degree, and that this injury is very closely associated with the time the tissue is allowed to remain in the imbedding material. Of these I have used gum arabic, celloidin, bayberry tal- low (the concrete expressed oil of Laurus hobilus, or bay- berry tree), paraffin, and paraffin modified by additions of cosmoline. The finest sections may be cut in paraffin. The disposition of this material to curl up before the knife, is readily avoided by laying a piece of fine tissue paper wet with alcohol upon it, and cutting under this. This paper also serves well to transfer the sections to fluids. The necessary subjection of the tissue to alcohol for dehydration, then to warm chloroform in the impreg- nation of the tissue, and the removal of the paraffin after cutting, is not without evil result. In this respect the bayberry tallow is better, as the use of chloroform is avoided, warm alcohol being sufficient both for impregna- tion, and solution and removal of the tallow after cutting. Each of these have given me better results, as to the final Condition of the tissue, than the celloidin ; but, in order METHODS OF THE PREPARATION OP TISSUES. 19 to obtain good results, the time the tissue remains in the imbedding material must only be counted by minutes, never by hours ; and if, after its removal, and placing the tissue in water, it does not swell out to its normal propor- tions in every part, which failure may be detected after sufficient experience by its appearance, it should be cast aside and a new effort made. The gum arabic method is suitable only for very small bits of tissue, on account of the time necessary for hardening large masses. Tissue may be bound up, or shrunken in any of these processes for a very short time, without losing its resiliency, or power of resuming its original condition, but if it is con- tinued beyond a certain time, this is lost in a greater or less degree. Careful additions of acetic acid to the water will often assist in the restoration of the normal condi- tion of the tissue. The ordinary microtome has been used for cutting sections. The staining has been by carmine in its different forms, Picrocarmine, hematoxylin, osmic acid, and chloride of gold. Double stains of carmine and hematoxylin, and pigmenting (see below) have been made use of. Sections from each portion of tissue cut have been studied, mounted in glycerine jelly, plain, also plain after acetic acid, and in each of the above stains, and then these studies repeated in similar mountings in balsam. The aniline dyes have been tried in tissues in which acids have been used to decalcify bones, but have not given me good results. Pigmentation should be explained, as I do not know af the use of the process by others. It is done in two ways, making a diffusive or selective pigmentation as de- sired. Place the sections in osmic acid solution (one per cent.), and let them remain from half an hour to an hour. (1st.) Transfer to distilled water for half a minute, just long enough to remove the osraic acid from the surface, and at once place in a solution of hematoxylin, as pre- pared for staining a thin solution is best and allow 20 METHODS OF THE PREPARATION OF TISSUES. them to remain until they have assumed a deep smoke or soot color, which will require but a few minutes. (2d.) Wash thoroughly in distilled water from half an hour to an hour, then transfer to solution of hematoxylin as before. The change to the soot color will be a little slower. Any purple color acquired from this solution may be removed by acetic acid without affecting the pigment. The sec- tions may now be prepared and mounted in any manner desired, and will be found very transparent to transmitted light, provided the pigmenting has not been carried too far. In (1st) the pigmenting will effect all the tissues alike, is diffusive, but in such a way that all of the ele- ments come fairly into view. In ("2d) the pigmenting is selective, the osmic acid resisting removal by water is re- duced as pigment by the hematoxylin. This pigmenting rests on the fact that a mixture of osmic acid and hema- toxylin throws down an amorphous black deposit, and this is obtained in the tissue in such a fine state of division as to resemble a stain when the highest powers of the micro- scope are used. Some portions of the tissue hold the osmic acid at least do not give it up to water very readily hence the selective pigmenting of the tissues that are well washed after removal from the acid, before being submitted to the hematoxylin. In this way, ordi- nary epithelium may be made to resemble natural pig- ment cells, the cell body being pigmented deeply, while the nuclei and cementing substance remain transparent. A word as to the illustrations. These are all made from tissues freshly prepared for the study of this subject, and are done with as much care as to accuracy of repre- sentation as I have been able to bestow. The manner of the representation of the tissues generally emploj^ed, is in a large degree conventional, and my illustrations are no exception to the rule. That which I have made out to my own satisfaction, I have endeavored to represent clearly, avoiding the representation of either shadows or METHODS OF THE PREPARATION OF TISSUES. 21 suppositions. I therefore make no claim that the pictures are exact representations of individual fields in my sections, but are rather what I make out to be the actual forms of the tissue elements and their relations to each other, after having made the best study of them that I am able to do at the present time. CHAPTER IV. THE PERIOSTEUM. The periosteum forms the immediate covering of the bones. It is continuous at all points except those surfaces covered by the articular cartilages and the attachment of the ligaments and tendons. It is not, therefore, continuous from bone to bone, ex- cept in those united by suture, as the cartilages men- tioned uniformly clothe the ends of those united by joints. Each of the long bones, and most of the short ones also, has its individual periosteum, which encloses it as in a sack, and is closely adapted to all parts of its surface. If the flesh is carefully removed from any of the long bones the periosteum will be seen to present a smooth, white, lustrous appearance, much like the surface of a tendon, over a large part of the surface, but at certain points which correspond with the attachment of muscles, or fascia, it will be left more or less ragged and dull, for at such points the superimposed tissues are firmly adherent and must be cut away with the knife. At all other places the tissues separate from it easily and smoothly, indeed, are not attached, or are attached only by a very slight network of reticular or elastic fibers which break away readily and, to the naked eye, leave no sign of their pres- ence. If now we slit up the periosteum lengthwise the bone, along a smooth portion, and insert the handle of the scalpel beneath it, it will be found readily separable from the bone over the greater part of its surface. Indeed, the attachment seems to be but little more intimate than was that of the tissues to the outer surface. However, if the 22 THE PERIOSTEUM. 23 detachment be closely followed it will be seen that at many, or perhaps only a few points, fibers adhere to the bone, and are broken. These are, in the main, very small blood vessels that enter the bone from the periosteum, but occasionally a few fibers of the periosteum enter the bone also. In the progress of the detachment a point is arrived at finally where this easy separation ceases abruptly, and the periosteum becomes firmly adherent to the bone. It is now found, in the effort to continue the detachment, that the periosteum is a very thin, tough, inelastic membrane that is torn with difficulty, but it is impossible to continue the separation from the bone otherwise than with the knife, and the extreme thinness of the membrane renders this difficult. An examination of these adherent points reveals the fact that they are, first: points at which some of the tissues are attached to the outer surface of the periosteum, as muscles or fascia ; second, near the ends of the bones where the periosteum approaches the articular cartilages ; third, wherever it approaches the insertion of tendons or ligaments ; fourth, wherever mu- cous membranes, or the skin, seems adherent to the bones beneath, as at the entrance of the meatus auditorius, the gums, mucous membrane of the nose, etc. At all such points the periosteum is as firmly adherent to the bone as if it formed an integral portion of it, and serves as the medium or* attachment for the superimposed tissues. Through this medium many attachments of muscles, fascia, etc., are effected, and these points of attachment will intercept and prevent the separation of the periosteum from the bones at many points. This feature of the an- atomy of the periosteum has not yet been studied in detail. Yet its importance in the management of diseases of the bones, especially the suppurative diseases, when pus is likely to find its way beneath the loosely attached per- iosteum, must be apparent to every surgeon. While I 24 THE PERIOSTEUM. can not now undertake this part of the subject in extenso^ I propose on another page to consider very closely the character of the attachments of the periosteum at differ- ent points. Histologically , the periosteum is composed of fibrous tissue, in the meshes of which are found certain cellular elements. It presents for examination : 1st. An outer layer of coarse white fibrous tissue. 2nd. An inner layer of fine white fibrous tissue. 3rd. Elastic fibers. 4th. Pentrating fibers, or fibers of the periosteum that, in the growth of the bone, are included in its substance. (Fibers of Sharpey.) 5th. Osteoblasts, or a layer of cells that lie between the periosteum and the bone. 6th. Osteoclasts cells that absorb bone. The white fibrous tissue is everywhere disposed in two layers, an inner and an outer ; or a layer of coarse fibers forming the outer portion, and a layer of fine fibers form- ing the portion next to the bone. The yellow or elastic fibers are found mostly intermingled with the coarse fibrous layer. They are usually very difficult of observa- tion, and do not, as a rule, appear in sections as ordinarily prepared . OUTER LAYER. The size and arrangement of the coarse fibers in the formation of the' outer layer is exceedingly variable in different regions of the osseous system. On the long bones they are generally smaller than upon the short, while I have found the largest fibers about the bones of the face. The rule is that the periosteum, as a whole, is thicker and stronger at exposed points where the bones are near the surface, and is more delicate when deeply covered with other tissues. Hence we find it thin, and its fibers correspondingly delicate on the shafts of the long bones, especially such as the femur, humerus, etc. THE PERIOSTEUM. 25 In these positions the coarse fibers of the outer layer are small, and for the most part run parallel with the long axis of the bone. (See fig. 17.) The fibers are usually very much flattened, and the fine fibers of which they are formed, not very firmly bound together. Indeed, they are often disposed in ribbon-like layers, with the flat sides horizontal to the surface of the bone, and the edges of these are often joined in such a manner as to form a con- tinuous sheet of fibrous material. This is especially the case when the periosteum is deeply covered with muscles which perform sliding motions on its surface. In such places this portion is often made up of a number of lamel- lae thus formed, which are very loosely joined together, so that by careful manipulation it may be separated into a number of complete lamellae. The fibers which constitute these layers do not all run in the direction of the long axis of the bone, but some are interposed which cross these at right angles, or in the direction of the circumference of the bone, as shown in fig. 18, in a section cut lengthwise, from the tibia of the pig. This example shows five layers of circumferential fibers, and those marked / and i, have shifted from their position in mounting the section in such a way as to present the sides of short sections to view, in- stead of the ends, and serve well to show how the fine fibers are joined into ribbon-like forms. The figure, as a whole, illustrates how readily the different layers are separable, though, as combined, they are calculated to give great strength, at the same time accommodating sliding movements readily. I have endeavored to represent every portion of it just as it happened to lie in the preparation. This may be re- garded as an example of the more complex arrangement of the coarse fibers, or outer layer, in the non-attached periosteum. The disposition of the fibers is usually much more simple, presenting fewer running in a circumferen- tial direction until, finally, none whatever can be found. 4 26 THE PERIOSTEUM. This simpler form I have represented in fig. 17, from a lengthwise section from the femur of a kitten. Every gradation between these may be found. For this illus- tration a point has been selected where the outermost fibers have been broken by the needle in detaching the superimposed tissue. Some of the fibers beneath are also a little separated, and in the central part the layer of osteoblasts is pulled partly away from the bone, display- ing their processes to advantage. It will be seen that the fine fibers, a, cease abruptly, giving place to the coarse fibers of the outer layer c. By comparing this illustra- tion with fig. 21, and noting the difference in the size of the osteoblasts (for the illustrations are drawn with dif- ferent powers) some idea will be gained of the difference in the size of the coarse fibers in different regions. In drawing fig. 17, the ^-inch immersion lens was used, while in fig. 21 the J-inch dry was substituted. These fibers (fig. 17) are round or irregularly flattened, and show none of the ribbon-like forms seen in fig. 18. It is the form of this layer most commonly met with on the shafts of the long bones, though the gradations between these two figures are sufficiently common. In both of these figures I have illustrated the delicate reticular tissue by which the periosteum is very loosely attached to the super- imposed parts. As the ends of the bones are approached the perioste- um is thinner, and often the coarse fibrous layer is found lying almost flat on the bone, most of the inner layer having disappeared, and at many points the osteoblasts are not to be seen. (Fig. 19.) At frequent intervals, however, sometimes continuously for a space, osteoclasts (/././.) have taken their place, and are trimming down the surface of the enlarged ends. In this region the fibers of the periosteum enter the bone and in this way form the firm attachments noticed at their ends. (Fig. 19.) This happens to such an extent that, in pursuing the study THE PERIOSTEUM. 27 of sections cut lengthwise the shaft of the bone, up to the articular cartilage, one is impressed with the idea that the whole of the periosteum has sunk beneath the surface of the bone. As this occurs the fibers of the outermost parts of the coarse fibrous layer often seem to unite into a fibrous sheet which is inserted finally at the margin or fringe of the articulat cartilage, or into the cartilage itself. On the bones of the face and other positions where the periosteum lies near the surface of the tissues, the outer layer is composed of very large, white fibers, with which a small quantity of yellow elastic fibers is mingled. The white fibers form an intimate network, being closely in- terwoven with each other. (See figs. 20 D, and 21 E.) Sections cut in almost any direction will show longitudinal fibers, but a disposition to run in the direction of the pull or strain of muscles or other tissues attached to the peri- osteum may be seen ; otherwise the direction will have a tendency to follow the long axis of the formation of the bone. In either case a considerable number take a trans- verse or a diagonal direction, passing through the meshes formed by the principal fibers. None of these fibers take a direction perpendicular to the surface of the bone, but they are so disposed that a fiber that may be on the inner surface of the layer at one point, may at a little distance arrive at the outer surface. In this way the fibers seem to be plaited together, (fig. 21 E), sometimes in a very compact layer only a few fibers in thickness, and some- times the fibers are so disposed as to form several lamellae, held together by occasional, or it may be very frequent, passage of fibers from the one layer to the other, or by a network of elastic fibers only. (Fig. 22.) Usually, even in cases of considerable thickness of this layer, coarse fibers may be traced that in their longitudinal course gradually approach one or the other surface. The thickness of this layer is very variable. Occasion- 28 THE PERIOSTEUM. ally it is only the thickness of two or three coarse fibers superimposed on each other ; rarely the coarse fibrous, layer is condensed into a single membranous sheet, to which the overlying tissues are attached. On the other hand, I have seen the thickness of J-inch in the human subject ; however, I am not sure that the latter was entirely normal. The thinner portions are often those to which muscles are attached. Indeed, the statement is made by Krause (Allgemeine und Microscopische Anato- mic, p. 68) that this layer is sometimes wanting at the- points of attachment of muscles. Although I have made many cuttings through such points, I have never found this layer absent except when the muscle was attached to the bone by well-defined tendon, in which case none of the elements of the periosteum whatever remain, but the fibers of the tendon pursue their course uninter- ruptedly into the surface of the bone. The characters described above are present in the coarse fibrous layer of the periosteum wherever it is found, without exception. At a few points it is blended with other fibrous tissues, especially with the mucous membranes and skin, as it is seen in the gums, and at the entrance of the opening of the external ear, and other points at which the skin is rigidly adherent. In these cases, if we proceed from the surface of the bone out- wards, the first coarse fibers are always disposed as in the periosteum at other points, i. e., lying horizontal to the sur- face of the bone ; but after passing a few of these, the hori- zontal direction of the fibers is sometimes gradually, some- times abruptly, lost, and the character of the tissue changes to the tangled fibrous forms of the skin, the gums, areolar tissue, or whatever may be the superimposed fibrous tissue. Often, however, the periosteum remains entirely dis- tinct from the superimposed tissue, and is united with it only by a scanty network of elastic fibers which allow of THE PERIOSTEUM. 29 free sliding motions of the one tissue upon the other. All grades of connection, from this latter to the intimate commingling of the coarse fibers, may be found in different places. Many of the smaller muscles, and larger ones that have their attachments by a broad base, are attached directly to this layer of the periosteum. In case of the muscles, the sarcolemma of each individual mus- cular fiber is attached directly to these coarse fibers. (Figs. 20 and 21.) In a few cases fine fibers may be seen traversing the layer of horizontal fibers of the periosteum in a perpendicular direction, seeming to be condensed ex- tensions of the sarcolemma as shown in Fig. 21. Occa- ionally these pass entirely through the coarse fibrous layer, and then appear to be continuous with the fibers of the internal layer. The fasciae are attached to the perios- teum by their fibers blending, or becoming continuous with those of its external layer. INTERNAL LAYER. The internal layer is of an entirely different character from the outer, both in the nature of its fibers and in their arrangement. It also presents great diversity of arrangement. In the consideration of this layer it will be convenient to divide it into attached and non-attached, as it presents notably different characters in its fibrous structure, and in the relation of its fibers to the bone which it clothes. The non-attached inner layer of the periosteum is separated from the bone almost completely by an inter- vening layer of polygonal or flattened cells, the osteo- blasts. (Figs. 17 and 18). None of its fibers pass into the bone ; while in the attached periosteum those of the inner layer do pass into it, or seem to spring out of it. (Figs. 21, 23 and 24.) It is composed of the finest and most delicate white connective tissue fibers, with which there are no coarse white, or yellow elastic fibers asso- 30 THE PERIOSTEUM. elated. On the short bones these fibers seem not to be disposed in any particular direction, or upon any specific plan that I have been able to detect. They decussate freely in every direction. On the long bones the fibers of this layer are more generally parallel to the long axis of the bone, as illustrated in fig. 21, though not uni- versally so. In all young animals these have in their meshes a considerable number of young connective tissue cells in various stages of development, in addition to the fusiform nuclei of the white fibrous tissue or fibroblasts. In the main the fibers lying next to the layer of osteo- blasts have a course horizontal to the bone ; but in the short bones, or in the neighborhood of attachments, this is changed to a direction more inclined towards the coarse fibrous layer, and the particular band or group we attempt to follow will become intermingled with others and lost. At another point immediately adjacent, the fibers are seen cut across either directly or diagonally ; but even among these will be seen those that are horizontal to the plane of the section. While there seems to be no uni- formity in the direction of the fibers, the fibrous appear- ance is maintained, giving the impression of an intimate intermingling rather than of a network. This appearance may be much modified by the manner in which the sec- tion is prepared for observation. If it be with a good selective stain this layer in young animals may appear distinctly cellular, the fibers being much hidden, while the cells are made prominent. If on the other hand the fibers be rendered prominent by diffusive carmine stain- ing, osmic acid, or pigmenting, the tissue will give the impression that it is almost wholly fibrous. The various plans of preparation should be employed in its study. The fibers do not seem to branch and anastomose as in a net, but rather to decussate with the utmost freedom, rarely forming groups or bands of any considerable num- ber running in a common direction. However, it is THE PERIOSTEUM. 31 apparent that in the portion next to the layer of osteo- blasts they are more inclined to a direction horizontal to the surface of the bone ; while in the portions next to the coarse fibrous layer their general direction has become perpendicular, or more or less inclined to the sur- face of the bone. In the long bones the fibers of this layer in the non- attached regions very generally lie horizontal to the sur- face of the bone throughout its thickness, as is shown in figs. IT and 18, and run in the direction of its long axis. The tissue is loose in texture and somewhat embryonal in its character immediately adjacent to the layer of osteo- blasts, but becomes more prominently fibrous as the bone is receded from. Its attachments on either side are very loose and easily broken up so much so that it is diffi- cult to keep the parts in position while mounting the sections. In those sections in which the relations of the parts are a little disturbed by spreading apart, we often obtain the best displays of the tissue elements, and it can be seen that the osteoblasts have processes which pass in among the fibers lying next to them, and also into the bone, forming a sort of attachment to it, which is, how- ever, very easily broken up. This is well shown in figs. 17 and 18. This latter form is common to the shafts of the long bones, and is almost universally present in the non-attached regions, which may in general be expected, except in the region of the attachments of muscles, fasciae, ligaments, or the approach to the ends of the bones. - In such positions the form of the attached periosteum is assumed. In the attached portions of the periosteum the fibers of the internal layer exhibit a definite arrangement. This presents certain variations at different points, but these are only modifications of a definite plan. Here the fibers are not separated from the bone by the layer of the osteo- blasts, but spring directly out of the bone itself, and the 32 THE PERIOSTEUM. osteoblasts are seen to be disposed between the fibers, as in figs. 20, 21, 23 and 24. Perhaps a more correct state- ment would be that the fibers spring out of the bone between the osteoblasts. At some points the former statement would be the more correct, for the reason that the fibers occupy the greater amount of territory, so that the osteoblasts are crowded into various forms to accommodate them. Every grade, from an occasional fiber passing out of the bone between the osteoblasts, to an increase in numbers and size which represents the insertion of the tendon, in which no osteoblasts are present between the fibers may be found. In the attached portions then, the fibers of the inner layer of the periosteum spring directly out of the bone. In order that this may be well seen it is absolutely neces- sary that extremely thin sections be cut parallel with the fibers as they emerge from the bone, and in general this will also give a good view of the arrangement of the fibers of this layer of the periosteum, for the fibers pur- sue the same general course until they reach the inner surface of the coarse fibrous layer. Each of these fibers, after passing out of the bone, or immediately after rising above the osteoblasts between them, breaks up into a tuft of very fine fibers ; indeed, in many sections it is shown that that which in the main appears as rather a coarse fiber as it makes its exit from the bone, is really a compact bundle of very fine ones. These, on separating, spread out fan-like, and intermingling and decussating freely with others, take their way perpendicularly, or inclined somewhat to the surface of the bone, to the inner surface of the coarse fibrous layer to which they are attached. The arrangement of the fibers as they pass from the bone to the coarse fibrous layer varies greatly in different positions. The most common form seen is that in which all of them pass at more or less inclination to the perpendicular, and join the coarse fibrous layer at an THE PERIOSTEUM. 33 acute angle, as shown in fig. 21. Yet every angle from about 45 to 90 degrees may be met with. Occasionally, however, we see them joining the coarse layer in inverse directions, decussating with others as shown in fig. 20. It is quite rare that the fibers join the coarse layer at right angles. In many instances their decussation in this layer is much more limited, and they pass quite directly from the bone to the coarse layer, forming a very regular sheet of fibers that are almost parallel. This layer has no elastic fibers, or at least they must be rare. Some observers state that these are found here, but I have repeatedly made the examination in the manner detailed below, without finding them. ELASTIC FIBERS. Elastic fibers form a network in the coarse fibrous layer that is very difficult to see without special preparation. This is partly on account of the fineness of the fibers themselves, but more especially owing to their relations to the coarse ones. In fine sections stained diffusely with carmine they may be imperfectly seen as white lines, but they are studied to best advantage by dissolving out the white fibers on the stage of the microscope. If this is done with sufficient care their arrangement can be quite accurately made out. This is done as follows : Place the section on the slide in water, lay on a cover glass, and carefully dry the slide at its edges ; now fasten the cover securely at two points, preferably next the edges of the slide, with a little gutta-percha dissolved in chloroform, with balsam, or with wax. Now having placed the slide on the stage of the microscope in such a position that it will be inclined from end to end (it may lie flat if pre- ferred), lay on a piece of blotting paper cut to fit the circle of the cover glass (a square cover glass may be used), and lay it on the highest end of the slide in such a position that it will touch all of the higher edge of the 5 34 THE PERIOSTEUM. cover glass not covered by the gutta percha. Also lay a piece of blotting paper on the opposite end of the slide, so that it will touch the margin of the cover glass. Here a central point of contact is sufficient. Thus prepared, saturate the upper bit of blotting paper with a strong solution of caustic potash (33 per cent, is best). This will gradually pass through under the cover and be absorbed by the paper below. A fresh drop should be added every few minutes continuously for several hours. The white fibers will first swell and become more transparent, and the elastic fibers meantime will come into view. Finally all of the white fibrous tissue will slowly melt down and disappear, and the only tissue left on the slide will be the elastic fibers and some remains of the bone. This process may be checked at any stage by substi- tuting distilled water for the potash solution, and if this is followed by glycerine, and glycerine jelly, a permanent mount of the object can be effected. It must be borne in mind that the solution of the tissue can not be stopped at once, and the particular stage desired for the prepara- tion must be anticipated. The washing with distilled water must be continued for a considerable time to remove all of the potash. If the process of the solution of the tissue be closely watched it will readily be discovered that the elastic fibers form a network in which the coarse fibers of the periosteum are inclosed, or that the elastic fibers are en- twined about the white in such a manner as to prevent their separation, or, if they are somewhat separated by a strain, will bring them back by their elasticity. I have illustrated such a network in fig. 22, taken from a section from the lower jaw of the same series as that represented in fig. 21. They are not uniformly distributed in the coarse fibrous layer, but seem to be most plentiful where muscles are attached to a rather thick outer layer, and the regions of the attachment of the mucous membranes. THE PERIOSTEUM. 35 Along the shafts of the long bones I have usually found very few, and these seem not to penetrate the periosteum deeply but are, indeed, unusually joined to its surface, and serve to make a very loose attachment of the super- imposed tissue. The inner layer of fine fibrous tissue of the periosteum is generally destitute of elastic fibers. Only once have I seen a few of these penetrating to the surface of the bone. Frequently I have seen a few fibers passing some distance into this layer, but generally they are confined to its outer margin. The blood-vessels of the periosteum are quite numerous, and present considerable variations in different regions. On the shafts of the long bones the larger vessels usually run in a direction parallel to the long axis of the bone, and lie between the periosteum and the superimposed tissues, or on the surface of the periosteum. These branch laterally, and anastomose in such a manner as to form a tolerably continuous network. This network receives here and there branches from the superimposed tissues. In some situations, especially in the attached portions, tfyis network lies immediately beneath the coarse fibrous layer, or in the outer part of the internal layer, in many instances as nearly between them as is possible. (Fig. 21 D.) However, in those situations in which the coarse fibrous layer is thickened by the formation of two or more lamellae, the network of blood-vessels is often found be- tween these, a circumstance which has given rise to the statement by various authorities that the blood-vessels of the periosteum are found mostly in the outer layer. In my observation there has been much more irregularity in the blood-vessels of the periosteum of the short bones, which, I may say, would naturally be expected, both as to the position of the individual layers, and the regularity of the network formed. From the network of vessels thus formed in any of these positions frequent capillary 36 THE PERIOSTEUM. branches are given off, also occasional larger vessels, which pass down through the fibers of the internal coat and enter the Haversian canals of the bone. In the at- tached forms of this coat, these branches very generally follow the direction of the main trend of the fibers of this portion of the periosteum, and in a few localities they are quite numerous, especially about the bones of the face, and notably over the surfaces of the alveolar processes. In the portions of the periosteum, with which the fibers of the mucous membranes, or the skin, are intimately blended, the position of the blood-vessels is notably irregular ; indeed, they seem to pertain rather to the super- imposed tissue than to the periosteum, and send frequent branches through the latter to the Haversian canals of the bone. Occasionally I have noted a plexus of vessels in the in- ternal layer very close to the layer of osteoblasts, but these are very small and infrequent. The nerves of the periosteum are generally few in num- ber ; however, a considerable number of the larger ves- sels are accompanied by a small bundle of nerves, which are probably distributed mostly to the blood-vessels them- selves. They enter the bones with most of the larger branches of the blood-vessels. At some points, nerves passing through the periosteum to enter the canals of the bone are very frequent. These are points where the nerves are required by organs situated within the bone. The supply of the peridental membranes renders them frequent in the periosteum of the alveolar processes. CHAPTER V. THE CELLS OF THE PERIOSTEUM. The cellular elements of the periosteum consist of de- veloping connective tissue cells destined to form osteo- blasts, osteoclasts and fibroblasts. The fibroblasts are such as are destined to reconstruct or augment in num- bers the fibers of this membrane and have been suffi- ciently considered. However, I may say that a consider- able number of connective tissue cells are found that seem not to show specific character. They seem not to be pro- ceeding regularly to the development of fibrous material nor to be allying themselves to either of the other two forms, and are probably cells that have missed their des- tiny and therefore have developed, irregularly. By care- ful search a variety of such may be found. They are mostly round or oval nucleated forms, but occasionally irregular star-shaped forms present themselves. Such cells seem to have no function to perform in connection with this membrane or in the locality in which they are found ; they are not sufficiently numerous and regular in their distribution for me to suppose that they perform some undiscovered function which renders their presence necessary. Hence the supposition that they are cells which have missed their destiny and finally disintegrate and disappear. In the progress of our study of the other cell-forms, the function of which is obvious, we shall find sufficient evidence of faulty action, or of over-activity in certain directions, which is yet within the range of what may be termed physiological errors on the part of the elementary forms. These are errors in direction of growth, or removal of tissues, which are checked before 37 38 THE CELLS OF THE PERIOSTEUM. they become so pronounced as to be regarded as patho- logical; as, for instance, in the case of absorption of bone beyond the needs of the time and its reconstruction after- ward. By English writers the osteoblasts are usually reckoned as belonging to the periosteum, while some of the German authors have classed them as belonging to the bones, and designated them as the cambium layer. So far as they are connected with the periosteum at all, their place is between the periosteum and bone in the non-attached forms, and upon the bone between the pene- trating fibers in the attached forms. However, the num- ber of embryonal cells that are found among the fibers of the periosteum in the immediate vicinity of the bone, gives the impression that this portion of the tissue is the place of the development of the osteoblasts, and that these cells are destined to become such. The most plausible supposition is that these embryonal cells are leucocytes that have wandered in here from the blood streams, not by any manner of chance, as this expression might indi- cate, but through the control of some unseen power which causes these cells to congregate where they are needed for building up of new tissues, or the repair of injuries to the old ; and to develop into the necessary forms for this purpose, whether it be for the formation of fibrous tissues, the formation of bone, the absorption of bone, or for whatever else may be needed which is in the power of the connective tissue cell to perform. The osteoblasts are polygonal cells which lie upon the surface of the bone and usually clothe it as epithelium clothes the mucous membranes. They vary greatly in size, so much so, indeed, that no measurement will give a very accurate idea of them. They are also placed very differently in relation to the bone in different positions and under varying conditions. In case of young bones that are rapidly growing they are often very much crowded together, and thus compressed into a great variety of THE CELLS OF THE PERIOSTEUM. 39 forms. Occasionally they are very much elongated, as, for instance some of the cells in fig. 25, taken from a cross section of the tibia of a young kitten. Here it will be seen that some of the cells reach the bone only by ex- tending a process-like elongation between the neighboring cells (a) while others seem to be flattening down upon the surface (b). In my studies it has seemed to me that only those cells which are attached to the bone should be con- sidered as osteoblasts. They are undoubtedly developed from the embryonal cells of the neighborhood, but it is not until the time of their attachment to the bone that their destiny can be definitely determined. Therefore, we can hardly say that more than a single layer of these cells is ever found upon the bone in any case. More than one layer is often made to appear by cutting sections diagonal to the surface of the bone. The more usual forms of the osteoblasts appear in figs. 17 and 18, where there are not too many to conveniently cover the surface ; and by the slight shrinkage that is almost inevitable in histological preparations, they are made to stand slightly apart. The processes of these cells appear prominently in figs. 17 and 18. These are very difficult of observation, and it is only under especially favorable circumstances that they appear ; however, they are seen so frequently in favorable positions as to lead to the supposition that all osteoblasts that are so far devel- oped as to come to lie upon the bone possess them. These cells are found also lining the Haversian canals, and the interior of the hollow bones at all points that present augmentation by growth. They are therefore not peculiar to the periosteum. In the case of old persons and animals, when the growth of the bones has ceased, the osteoblasts are lessened in numbers, and have changed their forms in such manner as to lie upon the surface of the bone as thin flattened scales, which often can not be seen upon the margin in sections cut perpendicular to the 40 THE CELLS OP THE PERIOSTEUM. surface ; but in such sections they will appear whenever a Haversian canal is so cut as to present the flat sides of the cells to view, especially if stained with a good nucleus tinting dye. In this condition the cells seem to be inac- tive. In the study of young bones many regions of in- activity may be met with in which the osteoblasts present this appearance. The function of the osteoblasts is clearly the formation of bone. There is no growth of bone without their pres- ence. It is true that calcifications of tissue occur in various places without the presence of osteoblasts, and to the naked eye these may closely resemble bone ; but upon microscopic examination they are found not to present the tissue forms of bone. These tissue forms are directly the product of the osteoblasts. The precise manner of the formation of bone is not agreed upon, two theories still being entertained. These may be briefly stated. The one view regards the osteoblasts as forming the matrix by aggregating themselves together upon the surface of the bone. This matrix thus formed is in turn converted into bone by becoming infiltrated with lime salts. All bone is shown by certain processes of chemical solution, to be composed of delicate laminae laid the one upon the other horizontal to the growing surface, whether this be the surface of the bone proper, or the surface of the Haver- sian canals. It is supposed, according to this view, that these laminae are made up from the different layers of consolidated osteoblasts. In this process certain of the osteoblasts persist, or are included in the formed bone without calcification, and thus become the bone cor- puscles. There are many objections to this view. One of the most potent is the fact that the osteoblastic layer is very rarely found in a condition of even semi-consolidation. The cells do not approach the loss of individuality neces- sary to the formation of a continuous sheet of matrix. THE CELLS OP THE PERIOSTEUM. 41 In reasonably good preparations they always appear as individualized cells. Furthermore, we are not able by any treatment of bone yet devised, to render the outlines of such cellular elements of its matrix apparent. These objections to this view has been pointed out by a number of prominent histologists. Another view is that the osteoblasts shed out from themselves the material that forms the bone by some pro- cess closely akin to secretion, if it be not this in fact. It seems probable that this process of secretion is per- formed by all of these cells that lie against the bone, and that the process is not continuous, but presents alterna- tions of activity and rest. This will account for the lamellation observed in bone more perfectly perhaps, than the supposition previously mentioned. This kind of lamel- lation is also observed in the structure of the shells of shellfish, the formation of which is generally agreed to be by a process of secretion. In the formation of bone by this process, certain cells seem to become matured and flattened down against the surface, and to sink beneath it. As a matter of fact, the bone material is built up over them and they become encapsuled, and are then known as bone corpuscles. They lose bulk in this pro- cess, so that the bone corpuscle is usually smaller than the original osteoblast. It is difficult to see the processes of the bone corpuscles in moist specimens, but they are plainly apparent in sections of dried bone, in which the canaliculi, which were occupied by them, are filled with air. The cells that sink into the bone in this manner, while not entirely regular in number and distance from each other, do present a kind of regularity which serves to give the impression of rows around the Haversian canals, and along the borders of sub-periosteal bone (in cross sections of the long bones). These rows bear a pretty distinct relation to the lamellae of the bone, as would naturally be expected if either of these explana- 6 42 THE CELLS OF THE PERIOSTEUM. tions of the process be adopted. The osteoblasts in flattening down very generally lie lengthwise upon the long bones, therefore the resulting bone corpuscle lies in the same manner with its broadest diameter to the form- ing surface, whether this surface be that of the wall of a Haversian canal, or the surface of the bone. Therefore, in cross sections of the long bones we get cross sections of these cells, so that they present a somewhat different appearance from that seen in the lengthwise sections. The processes of the bone corpuscles are very numer- ous, and radiate in every direction through the bone matrix forming junctions with each other. (See fig. 25 c.) Each individual bone corpuscle with its processes seems to preside over a specific area of bone matrix, and the impression might be entertained that this individual corpuscle had formed this area. This impression is also much strengthened when in the study of irregular for- mations, globules of bone are found, each showing a single bone corpuscle near its center; or perhaps several of these lying together with the area of each more or less clearly visible. In studying these, it is often difficult to escape the conviction that each osteoblast that so matures as to become a bone corpuscle really forms the area of bone with which it is immediately surrounded. How- ever, the study of the forming surface will serve to dispel this idea and admit the assistance of osteoblasts not yet so fully matured. Again, a close study of the processes of the bone corpuscles shows that their general direction is perpendicular to the forming surface of the bone (fig. 25), so much so that with low powers a striation in this direction often becomes prominent. Much of this is due to the processes reaching far into the bone before the encapsuling occurs. In those portions of bone formed under an attached periosteum, particularly if the penetrating fibers are numerous and large as shown in figs. 20, 21, 23 and 24 the THE CELLS OF THE PERIOSTEUM. 43 bone corpuscles do not lie with their long axes horizontal to the surface of the bone, but in a line parallel with the penetrating or residual fibers. This is explained by the fact that the osteoblasts are held, or lie between the fibers in such a way as to present their short diameters or ends to the surface of the bone, which position they retain. It serves as a mark designating the portions of the bone formed under a periosteum of this character even when the fibers themselves can not be seen. This applies to all those forms of the attached periosteum in which the penetrating fibers are large and thickly set. When the fibers are more sparsely distributed the osteo- blasts and the resulting bone corpuscles, may lie in the same relative position to the forming surface, as in case of the non-attached forms. The osteoclasts, myoplaxes or giant-cells, present various forms, vary indefinitely in size, and are usually multinucleated. (See figs. 19 /, /, /, 24 g and 27, a, a.) Occasionally, one may be recognized with but a single nucleus, and I have seen them containing as many as twenty-four. From four to ten is a more common num- ber. The general inclination is to the round or oblojig form. They are very rarely branched and present no processes. Such forms of cell may be found in other localities, and we can only recognize them definitely as osteoclasts, when found in contact with bone, or some of the hard tissues undergoing absorption. In such posi- tions, they uniformly lie in little bay-like excavations in the surface, known as the lacunae of Howship. They conform in certain measure to the depth and size of the excavation in which they lie, which fact seems to argue that most of their growth has occurred in this position. I often see very small ones in small excavations and large ones in correspondingly large excavations. But in ab- sorption of greater extent, such as in the hollowing out of the shafts of the long bones, we often find very large cells 44 THE CELLS OF THE PERIOSTEUM. lying on the surface of the bone without any lacunae what- ever. I may say, however, that the number of such cells that are sometimes seen in the tissues of the bone marrow, detached from the bone, but in the neighborhood of extensive absorption, has given me the impression that possibly these cells may in some degree possess amreboid movement during life, and therefore, a limited power of migration. The function of these cells is sufficiently obvious. They dissolve the bone with which they are in contact, probably by the secretion of a solvent fluid, making room for themselves, and in this way remove the surface of the bone, i. e., cause its absorption. In this way the en- larged ends of the bone are trimmed down to the size of the shaft (in the elongation of the bones during growth), and the central cavities are hollowed out. Channels are burrowed through and new bone again deposited, thus re- moving the old and filling in with new. In this work the osteoblasts and the osteoclasts are continually replacing each other, the osteoblasts building and the osteoclasts tearing down ; and by the joint action of these, both the formation and the conformation of the bones are affected. CHAPTER VI. FORMATION OF BONE. Histologists have usually described three modes of the formation of bone. These relate to the conditions under which the bone is formed, and are the subperiosteal, intra-cartilaginous and intra-membranous. The subperi- osteal is not a de novo origin, but a growth superadded to previously formed bone, or laid down upon the surface of cartilage. This has been in a measure considered while describing the functions of the osteoblasts, but certain points should be elucidated. The surface of a growing bone is not smooth and compact, but is continually thrown into convolutions by the upward growth of spiculse, or upon long bones, of long ridges more or less sharp, arranged parallel with the long axis and which often ris- ing into the tissues of the periosteum, form arches by spreading laterally and joining with like ridges on either side, as shown in figs. 23 a, a, and 26 c, . In the study of complete sections, it is found that this growth is mostly in the direction of the length of the bone. Indeed, this is very apparent in the illustration, for, it will be noted, that at .5, the cells are very much flattened, so that in the lengthwise section they appear banana-shaped with rather a disposition to enlarge at one end ; and, in the enlargement from B to (7, they become somewhat rounded, mostly by gaining in breadth. At also the capsules that enclose the indi- vidual cells are more and more separated in the direction of the forming bone. This represents the growth of the shaft of the bone in length, for after the osseous sub- stance is once formed, it does not increase in dimensions by interstitial growth. The increment is always to the ends, first in cartilage, then by the process of growth rep- resented in the illustration. In the region of D, it will be seen that the nuclei (the transparent portion of the cell fills the capsule) are diminishing in size and becom- ing rather ragged in outline. This is undoubtedly a mark of degeneration in the cell, and it will be noted that the growth of the cells ceases from about this point. They become passive, and take no further active part in the processes that are going on ; unless it be a slight advance toward disintegration, as indicated by the progressive diminution of the nuclei. Occasionally a globular form will be seen occurring in the central part of the nucleus at this time, that closely resembles the marrow cells 9 66 INTRA-CARTILAGINOTJS FORMATION OF BONE. which appear so abundantly after the capsules of the car- tilage cells are broken into by the absorptive process ; but I have never seen more than a single one of these in a cell, and must suppose that this is either a nucleolus, or, that it is an accidental dropping together of material of the disintegrating nucleus. In the region between D, and E, that portion of the mass that forms the walls of the capsules, in which the cells are imbedded, is under- going the process of calcification, or infiltration with lime salts. At least, this is the general opinion of those who have examined the subject with reference to this point. My own examinations do not enable me to determine it. The whole of the cartilage, from the region B down, is much more transparent than the cartilage in which the changes have not yet begun, and this difference is ren- dered much more prominent by pigmenting. In this pro- cess the cell bodies remain absolutely transparent as represented in the illustration. This is entiiely different from the epiphysal cartilage while undergoing this change. In these the whole of the cartilate takes the pigment in a marked degree, and this is true when the two forms are included in the same section, as I have often had them toward the end of the process of ossifica- tion. They also react differently to other stains. This fact seems to show plainly that there is some chemical difference in the structure, to which this difference of reaction is due, but as yet I am ignorant as to what this difference may be. The most interesting part of the process is that taking place at E. Here we find that the walls of the capsules, facing toward the central part of the length of the shaft, are successively disappearing before the advance of a growth of fetal tissue, and that the remaining or lateral walls of these same capsules become so many tubes in which this growth advances. Some of these, indeed, are also broken down, merging two into one, frequently INTRA-CARTILAGINOUS FORMATION OF BONE. 67 making larger tubes. But for a space the greater num- ber of them remain. This occurs, not in a few of the rows of cells that form the shaft of the cartilage, but in all of them together, generally forming very nearly a straight line through, or as seen in sections, across the shaft of the cartilage. That is to say, presenting a solid advance which includes the whole thickness as represented in Fig. 33. There are no radiating canals, as seen in the absorption of the epiphysal cartilages, or in the absorp- tion of tendons, ligaments and bursse. (Compare with Figs. 29 and 31.) But before speaking further of the process of absorp- tion, let us examine the tissue that is taking the place of the cartilage. At h, are seen the round cells (marrow cells) that are very generally advanced to fill the capsules from which the cells seem to escape, as soon as the cap- sules are opened. These are seen everywhere in the mass of fetal tissue, and they are often so abundant as to ren- der the observation of the other cellular elements diffi- cult. Furthermore, they are liable to be scattered over the other parts of the section, in the course of the prepa- ration, and lead to confusion, unless special care is taken. On the right hand of the figure some of the tissue has been lost, but, in the other portions, it will be seen that these round cells are filling the capsules opened. At JV, one seems to have been just opened, and these cells seem in the act of crowding into the aperture. At 0, are pointed out fusiform or oval cells, applied closely to the remaining walls of the capsules which, it will be observed, extend to the lower end of the figure, and are marked with the letter p at various points. At m, w, m, TW, are seen the cellular elements and fibers of the blood vessels, which are extended into each one of the opened tubes. /, Points out osteoblasts applied to the remaining walls of cartilaginous matrix, upon which no bone has yet been deposited. These are seen also in other parts of the 68 INTRA-CARTILAGINOUS FORMATION OF BONE. figure. No deposit of bone is seen usually, until the space of several cartilage cells beyond the point of absorption has been reached, but at K, K, JT, K, is seen deposited on the walls of the tubes a layer of bone which is in turn covered with osteoblasts. The new bone is deposited upon the remains of the cartilage, partially fill- ing up the tubes formed by the opening of the capsules of the cartilage cells. We may now return to the absorption area, repre- sented at E. In this absorption I have been unable to identify a single well marked choiidroclast, applied to the opening of the capsules of the cartilage cells. In Fig. 33 all of the capsules opened are partly destitute of cells, i.e., have not yet filled up with the advancing cells, but in Fig. 34 I supplement this defect, by choosing for illustra- tion a few capsules which the fetal tissue fills compactly. Here we find both fusiform and marrow cells applied to the boneward face of the capsules, sometimes the one, sometimes the other, or they may be mixed together. These fusiform, eel Is have uniformly a well marked nuc- leus of irregular outline, instead of the pale round form seen in the chondroclasts and osteoclasts, and we see apparently the same cells applied to the remaining walls without witnessing any evidence of solution. The absorp- tion cells appear in great abundance a little further away, removing portions of the tube walls and enlarging the channels. (Fig. 35.) The agents of solution in this case are probably the small cells. It is well known that the leucocytes develop this power in a marked degree in other localities. They are the agents of solution of sponge, in the sponge-graft, of animal membrane sutures, ligatures, and other foreign substances. They are also the principal agents of absorp- tion, when this process occurs in connection with inflam- mation. Furthermore, the absorption cells are undoubt- edly developments from the primary connective tissue INTRA-CARTILAGINOUS FORMATION OP BONE. 69 cells, which these round cells represent. They require time to make their growth, and during this period of growth are exercising their peculiar function, as has been shown on a former page. It may, therefore, be assumed that in the absorption we are now considering, the amount of tissue removed at one point being only the thin wall of these capsules, is too small for the devel- opment of chondroclasts that will be capable of satis- factory differentiation from others by microscopic exami- nation. As already indicated, the remaining walls of the alveoli of the cartilage cells become the nidus for the deposit of bone, at a point removed, by the length of a few cells, from the point of absorption. It will be noted also that the greater portion of the matrix of the cartilage still remains, this having already been reduced to a very small amount, by the progressive enlargement of the cartilage cells, as illustrated in fig. 33. At a distance of a few cell-lengths further, the absorption of this remain- der of the cartilage matrix, together with that of the greater part of the bone first deposited, is in active pro- gress. This is best seen in cross sections, fig. 35. If these are double stained with hematoxyliri and carmine, the remains of the cartilage will be purple, while the bone deposited upon it will be red, which distinguishes them sharply and quite beautifully, and at the same time the cellular elements are well shown. In following up serially cross-sections prepared in this way, and receding bone-ward from the point of the beginning of bone form- ation, it will be found that the Haversian canals are enlarged and decrease in number, and in this process all or nearly all of the remains of the cartilage is removed. Indeed, in the central part of the shaft only a little bone is formed, and this is all removed after a time, to form the cavity. Along the circumference the bony formation is stronger, and is merged with the subperiosteal bone ; but 70 INTRA-C ART IL AGIN OUS FORMATION OF BONE. even this is also removed in time. In all of the central portion of the length of the shaft it is not reformed, or if so, it is only to be removed again ; but toward the ends of the bone it is replaced with more mature Haver- sian bone. The processes of bone formation and of its absorption are going on simultaneously in a very close proximity. I have illustrated this in fig. 35, from a cross section of the rib of a young kitten, at some little distance boneward from the point where ossification begins, d, Represents a few Haversian canals cut across. 5, J, Point out the bone, and a, the remains of the cartilage matrix, which, when there has been no absorption of the bone formed, lies centrally in the irregular rings of bone. Osteoblasts appear over a large part of the surface, but at some points absorption is in progress; the osteoclasts are indicated by the letter c. By the absorption overbal- ancing the deposit of bone, the space is gained for the bone marrow. In all of these varying phases of bone formation, it will be noted that the active agents are the osteoblasts. These seem to be developed in the inner layer of the peri- osteum, or with equal facility in the tissue that fills the Haversian canals, or the endosteum. They are therefore not peculiar to the periosteum, but belong rather to the surface of the bone, whether this surface be an external or an internal one. CHAPTER VIII. THE PEEIDENTAL MEMBRANE. The peridental membrane comprises that tissue which intervenes between the root of the tooth and the bony walls of its alveolus. It has received various names from time to time, as alveolo-dental membrane, dental perios- teum, alveolo - dental periosteum, pericementum, etc. The office of this membrane may be regarded as threefold functional, physical and sensory. It is functional in so far as it is the place of the development of the osteoblasts, which build portions of the alveolar walls, and the cementoblasts, which build the cementum. These cells seem to be received into the fibrous meshes of this mem- brane from the blood streams as leucocytes or amoeboid cells and here undergo their development, or that differ- entiation which fits them for the building of bone on the one side, and the building of cementum on the other. During this development they become allied to their respective places, i. e., the surface of the bone and the surface of the cementum. The physical function is the fixation of the tooth in its position, a passive function which is performed by the fibrous elements. These fibers, which I shall designate as the principal fibers, form the bulk of the tissue of the membrane, and their ends are fixed in the cementum of the tooth's root on the one side, and in the bone which forms the walls of the alveolus on the other, and are thus stretched across the intervening space in various direc- tions, and in such a manner as to swing the tooth in its socket. The sensory function is supplied by an abundance of nerves which enter the membrane from every direction 71 72 THE PERIDENTAL MEMBRANE. through the walls of the alveolus, at the apical space, and by way of the gingival border below* the rim of the alveolus. Besides the osteoblasts and cementoblasts, the mem- brane presents various cellular elements: such as fibro- blasts for the augmentation or renewal of its fibrous tissues ; osteoclasts for the removal of the walls, or por- tions of the walls of the alveolus for the accommodation of changes in the position of the tooth, or of the cementum for the change of the form of the tooth's root. These lat- ter seem to be developed as occasion requires, but are very generally present somewhere within the alveolus. Besides the cells mentioned there is always a considerable number of undeveloped cells within the meshes of the fibrous tissue in young subjects, but not very many in the old. There is also a set of lymphatics which are peculiar to this membrane. They occur in great abundance immediately surrounding the cementum in young sub- jects, but are much diminished in numbers in the old. In many parts of the membrane there is seen an indif- ferent inter-fibrous tissue. It is a tissue composed of cells and fibers, not possessing very marked characters, intervening between the principal fibers in many places, especially where these are large, and making up the bulk of the membrane in certain localities where these are absent, and accompanying the blood-vessels and nerves. The form of the membrane is such as to closely invest the root of the tooth and fill its alveolus, but it does more than this, for it invests the tooth lower down than the lowest border of the alveolar wall. The membrane may conveniently be divided into three divisions: the apical, that portion surrounding the immediate apex of the root, * In the descriptions which follow, the tooth will be regarded as a cone of which the end of the root is the apex and the crown, the base. Therefore toward the apex of the root is npward, and toward the crown is downward, whether the tooth is in the upper or lower jaw. THE PERIDENTAL MEMBRANE. 73 or occupying the apical space fig. 36 e ; the body of the membrane, which fills the alveolus from the apical space to the lower border or rim of the alveolar wall a; and the cervical or gingival portion, or that portion immediately surrounding the neck of the tooth below the rim g. The thickness of the membrane varies very much in different individuals, and in different teeth in the same individual. It is thickest in the child, and it becomes thinner (normally) as age advances until forty, or per- haps sixty years has been reached. In fig. 37, I give a very accurate outline of a cross section of the alveolus with its contents from a lamb (temporary tooth), cut at about the middle of the lower third of the body of the membrane ; and in fig. 38, another from the cuspid tooth of a man forty years old, cut a little closer to the gingival border, so as to include the thickened rim of the alveolar wall. These are drawn as enlarged by a two-inch lens (using a camera lucida), and then reduced one-half, and illustrate very fairly the extremes which occur, normally, in the thickness of this membrane. Such blood-vessels as could be clearly seen with this low power are shown in their proper positions and dimensions. It will be seen that these are usually midway between the alveolar wall and cementum, in the central part of the membrane, in the young subject ; while in the old they are more gene- rally close to the bone, indeed very many of them lie in grooves in the alveolar wall. The direction of the fibers of the membrane in the position of the sections is indicated as perfectly as is prac- ticable with this low power of the microscope. Variations in the thickness of the membrane are presented in its different parts, but these seem to follow no rule whatever, except that it may be that the apical portion is generally somewhat thicker in young subjects. With this exception, the differences in thickness seem to be mere irregularities in the contour of the alveolus, which is constantly under- 10 74 THE PEEIDENTAL MEMBRANE. going change by absorption and rebuilding of bone. The general form of the membrane is better seen in fig. 36 from a lengthwise section of an incisor tooth of a young kitten. This tooth, though very slender, is so small (only three-sixteenths of an inch long) that it gives a better opportunity for a full length illustration than the larger teeth of man. The elements of the membrane are the same, however, both in form and arrangement in relation to the root of the tooth and its alveolus. My principal object in presenting this illustration has been to give a correct outline picture, including the entire root with its alveolar walls, in which the direction of the fibers should be correctly indicated in all of its parts. For this pur- pose I have selected a section in which the fewest number of blood-vessels appeared, and in which there is, there- fore, the least distortion of the fibrous arrangement. On the lingual side, there is some modification of the form of the alveolus occasioned by the nearness of the crypt of the permanent tooth, a portion of the sacculus of which is seen at m. This has caused the thickness of the membrane to be diminished in its neighborhood. Farther toward the crown, and also toward the apex of the root, the membrane is thicker. A close study of the illustration, with the aid of the description accompanying it, will give a good idea of the general form and arrange- ment of the membrane. THE PRINCIPAL FIBERS OF THE MEMBRANE. Those fibers which are fixed in the cementum and from thence stretch across, and are fixed in the alveolar wall, or into some other tissue, as the fibrous mass of the gums, and thus serve to maintain the tooth in its position, I shall term the principal fibers of the peridental mem- brane. These are of first importance in the study of this membrane, for with the exception of some deviations from the usual course of these for the accommodation of the THE PER1DENTAL MEMBRANE. 76 blood-vessels and nerves, the other elements are so dis- posed as not to interfere materially with their arrange- ment. The structure is at the same time so very complex that we need to bring to our aid every available device for gaining a clear comprehension of the arrangement of its elements. To this end the arrangement of the prin- cipal fibers should be first studied, and afterwards the character of the fibers themselves, and following this the inter-fibrous elements. ARRANGEMENT OP THE FIBERS. Beginning with the gingival portion, we find the prin- cipal fibers firmly fixed to the cementum, literally spring- ing out of it, and passing diractly out, or but slightly divergent, from all the surfaces of this part of the tooth. The manner of the fixation of these fibers in the cementum will be studied in detail later. On passing out from the cementum they may retain the solid form (fig. 39) or split up into fasciculi of finer fibers (fig. 42). In the latter case, which is the more common, they show some disposition, in many localities, to gather into loose bundles, the elements of which pur- sue a common course. But more generally perhaps the bulk of the fibers lie parallel with each other, deviating only to give place to blood-vessels and nerves, or the larger groups of lymphatics. Upon the labial and lingual surfaces of incisors these, after passing out some little distance from the tooth, are lost in the coarse, tangled, fibrous tissue of the gums. This is fairly well seen in figs. 36 and 40, g. g. Usually there is a fairly strong fibrous bundle turning down into the gingivus (fig. 36, 7i), especially on the labial side. Nearer the border of the alveolar wall the fibers pass on under the gum tissue proper, and are continuous with the outer layer of the periosteum of the outer surface of the alveolar walls. As these pass the margin of the alveolus, fibers, springing 76 THE PERIDENTAL MEMBRANE. out of the bone, first decussate with, and then become mingled with them, thus forming a very firm support to the gingivus. This bundle has been termed the dental ligament. As we pass around the teeth toward the lateral sur- faces a disposition of the fibers to bend away laterally is noticed (fig. 40), and before we have fully reached the lateral surfaces the fibers may be traced continuously to the neighboring tooth, following a somewhat curved course, and passing the lower margin of the alveolar wall. Between neighboring teeth the fibers pass directly, or at a slight inclination from one tooth to the other, being fixed into the cementum of each (fig. 40, /). In the cen- tral part of their course many blood-vessels are seen, which cause more or less deflection in the course of individual bundles of fibers. If the horizontal section, including two teeth, is cut very close to the margin of the alveolar walls the fibers will be found to break up into bundles near the ' central portion, and many of them pass out of the section, while a portion continue on from tooth to tooth. The arrangement of the fibers on the lingual side does not differ materially from that of the labial as shown in fig. 40. The gingivus, or free border of the gum (fig. 36, A) is covered with a moderately thick but very dense epithelial coating, surmounted upon the fibers emanating from the cementum of the neck of the tooth and the dense tangled mass of fibrous tissue forming the gums. Considerable importance has been given to that portion of the epithe- lium of the gingivus lying next to the neck of the tooth, which is composed of softer and more delicate cells than other portions. I will return to this point later. The fibers of the lower portion of the body of the membrane run nearly directly across from the cementum to the walls of the alveolus, which they enter. Those entering at the rim of the alveolus usually have an incli- THE PERIDENTAL MEMBRANE. 77 nation upward (toward the root of the tooth) as shown in the illustration, but a little farther upward they ruu squarely across, following nealy a straight course. It is here that the largest and strongest fibers of the peridental membrane are found, and we can often trace individual fibers entirely across from the cementum to the bone, even in young subjects, both in lengthwise and cross sec- tions. It is the region from which the sections for figs. 37 and 38 were taken. As we pass farther toward the apex of the root the trend of the fibers in passing from the cementum to the alveolar wall becomes more and more downward (toward the crown), and at the same time a greater disposition to form into fasciculi or loose bun- dles is noted. In young subjects, when the membrane is thick, some of these bundles are very long, reaching for a considerable distance along the root to be attached finally to the alveolar wall. This disposition to form into fasciculi is seen most prominently perhaps, well up toward the apex of the root, where a greater portion of the alveolus is occupied by different tissues. Here fan- like fasciculi radiating from the cementum bone quite common, standing out as broad bands of fibers pursuing a straight course from the cementum to the bone, as if put upon the stretch ; as shown on the lingual side near the end of the root of the tooth in fig. 36. Finally in the apical space (fig. 36, e) the disposition of the fibers is extremely irregular. Indeed in young subjects the tissue here has often more the appearance of embryonic tissue, in which there are few fibers developed, except those accompanying the blood-vessels, which lat- ter are large and often divide into a number of branches, some entering the apical foram to supply the pulp of the tooth, and others passing down in the peridental mem- brane. In older subjects fibers are developed here which pass pretty directly from the root to the bone in radiating fasciculi. 78 THE PERIDENTAL MEMBRANE. This is in brief the arrangement of the principal fibers of the membrane, as seen in well prepared sections. How- ever, many sections, when large numbers are examined, will come under the lens, which show wide variations from this arrangement. First, if the lengthwise section is cut a little to one side of the center, perhaps very few fibers will appear ; or one not well skilled in the examination will fail to make them out as they lie among the cellular elements, for the reason that they are cut across at more or less of an angle. Especially will this be the case if the section is mounted plain in glycerine, or if it be well stained with a good nucleus-tinting dye. In either case the cellular elements will be rendered prom- inent, and the fibers, which remain transparent, will be hidden from view. I have many sections in which no fibers could be made out, but from the fact that they are so thick that the cells of the inter-fibrous tissue, which lie between them, appear in rows (fig. 41). Those prepared in the same manner, but which are a little thicker, so that the cells lie upon the fibers as well, show no appearance of fibers whatever. The same class of sections, however, stained diffusely with carmine, or pigmented, show the fibers prominently. Secondly, many lengthwise sections follow blood-vessels which traverse the membrane in this direction. These often are surrounded by more or less indifferent fibrous tissue. These fibers may lie parallel to the course of the vessels, and it is manifest that where the line of one of these happens to be followed, the mem- brane will appear, or rather will actually be divided into two parts, one of which will be attached to the cemen- tum, and the other to the alveolar wall. It will be seen at once that unless the elements seen are well understood, a very erroneous conclusion may be arrived at, that of a double membrane. One would suppose from reading our literature that such had actually been the case. With increasing age the cementum is thickened, the THE PERIDENTAL MEMBRANE. 79 walls of the alveolus are strengthened, the thickness of the peridental membrane diminished, and all its fibers shortened by being included in the cementum on the one side, and in the bone on the other. In this case the fibers generally appear to pass more directly from the cemen- tum to the bone in all of the upper portion of the alveolus; yet the general trend, as illustrated in fig. 36, is fairly maintained. If this arrangement of the fibers be studied with ref- erence to the physical functions of the membrane i. e., that of maintaining the tooth in its position during the strain of its normal usage, it will be found that it is the very best that could be devised for the purpose. The tooth is swung in its socket in such a manner as best to resist a strain upward upon its crown, and save the tissues of the apical space from injury, while the fibers running squarely across in the lower third of the body of the mem- brane prevent displacement laterally. The fibers of the peridental membrane are wholly of the white or inelastic connective tissue variety. There are no elastic fibers, or, at least, I have not been able to find any remaining after dissolving out the white fibers with alkaline solutions. The form of the principal fibers, though in many respects bearing a close conformity to the fibers of the internal layer of the attached periosteum is peculiar to this membrane. Indeed, in many localities no difference could be observed, if the examination were confined to the immediate surface qf the alveolar process. The fibers of this portion are, however, in the main larger than those of the periosteum and rather less thickly placed. While in many localities they break up into fine fibers almost immediately after passing out of the bone, as is the case in the inner layer of the attached periosteum, in others they continue far out into the membrance as strong, seemingly, solid cords, with perhaps finer fibers and cellular elements running in a different direction, 80 THE PERIDENTAL MEMBRANE. interwoven between them (fig. 46). In thin sections cut parallel with the fibers and stained with a good nucleus- tinting dye this arrangement gives the tissue a very char- acteristic appearance. The fibers are, in this case, per- fectly transparent and invisible, and the cellular elements, which lie between them, appear disposed in rows as shown in fig. 41. Sections from the same series diffusely stained, or pigmented, show the fibers prominently. The appearance of the fibers varies very much in dif- ferent cases, and even in the same case in different modes of preparation and staining. For instance, fibers that appear as solid cords when stained with hematoxylin, may appear as fasciculi composed of very fine fibers, when stained diffusively with carmine. By this means we learn that the most compact of these coarser fibers are really condensed bundles of fine connective tissue fibers. In the peridental membrane these, the individual fibers, are often as compact as any that I have seen from the strong- est tendons, but these coarser fibers are not themselves gathered into bundles as in the tendons. Hence the fibrous arrangement here is not similar to that of a tendon or ligament. While the fibers in many localities, espe- cially next to the bone, are large and strong, each one stands somewhat apart from its neighbors with other ele- ments intervening, which is not the case in the tendon or ligament. Therefore while the passive function of this membrane is that of fixation of the tooth in its position and of the same nature as that of a ligament, it has not in any of its parts the structure of a ligament. The fibers passing out from the cementum are some- what smaller and more thickly placed than those spring- ing from the alveolar wall, but otherwise have the same character. In young subjects the parallel arrangement of these is somewhat interrupted near the cementum by the lymphatics which lie between them in great abundance. These fibers springing from the cementum on the one THE PERIDENTAL MEMBRANE. 81 hand and from the bone forming the walls of the alveolus on the other, stretch across the intervening space in the directions indicated in fig. 36, but there is something more in the arrangement. While in some cases individual fibers are maintained as such, and can be traced from side to side, as shown in fig. 39, the rule is that the larger fibers springing from either source break up into fasciculi of very fine fibers as shown in fig. 42, and their individu- ality is lost by commingling with others. The fasciculi are, however, continuous from the bone to the cementum. The central part of the membrane therefore seems, and is actually composed of finer fibers than either its cemental or osteal margin. The fibers springing from the cemen- tum very generally break up into fasciculi almost im- mediately. It is only near the cervical border of the membrane or opposite the rim of the alveolus that we see them generally continuing as solid fibers for any consid- erable distance. However occasional fibers, or a few together may be found here and there in any portion of it which do continue from side to side, especially near the apex of the root where there are" often found individu- alized groups of such. Those arising from the bone and especially those near the rim of the alveolus often con- tinue as solid fibers through one-third or even one-half the thickness of the membrane, giving off only occasional small fibers, but near the central part they generally break up into fasciculi and their identity is lost. In the thick membranes of young subjects there is usually a very distinct vascular region near the central portion, or midway between the bone and the cementum. It is in this region or zone that the principal blood-vessels and nerve-trunks are found. This causes much irregu- larity in the course of the fibers of this region, for the fasciculi are deflected from their course in passing the vessels. Besides these deflections we often find consider- able bundles of fibers, especially in the middle portion, 82 THE PERIDENTAL MEMBRANE. or high up on the root, pursuing a course very different from the general trend, and these pass between the fas- ciculi and have the effect of modifying their course. In cross sections of the contents of the alveolus these are seen cut across. As age advances the appearance of the tissues of the membrane is considerably changed. Most of the cellular elements disappear, and the fibers appear more promi- nently. These latter are very much shorter, and it is easier to follow them through from the cementum to the bone. In many regions there is no appearance of inter- fibrous tissue whatever, and fasciculi or bands of fibers cut parallel to their length often appear prominently. In fig. 39, 1 have represented such a band of fibers seen pass- ing from the cementum a, to the alveolar wall b. The illustration is taken from a perpendicular section of the roots and alveolus of a first molar of a man seventy years old. The fibers of the lower portion of the figure c, pass entirely through the membrane without breaking up into fasciculi. This occurs only occasionally in rather small bands of fibers lying parallel or nearty so. The more general form of the fibers is that represented at d, in the same figure where they break up into fine fibers soon after leaving the cementum, as in figs. 42 and 43. In passing the sections about under the lens, bringing different por- tions of the membrane successively into view, a great va- riety of appearances will be noted. Wherever the section is parallel with the length of the fibers they will be seen emerging from the bone and cementum, and generally breaking up, as shown in fig. 42, into fasciculi that then pursue a wavy course,- usually more or less obliquely toward the other side. Not very infrequently strong groups will be found arising from either bone or cemen- tum that spread out fan-like, as seen in fig. 43, some of which may be traced through the membrane while others pass out of the section or are lost by mingling with other THE PERIDENTAL MEMBRANE. 83 fibers. In rambling over the membrane with the micro- scope many points are found at which there appears to be no attachment whatever. This in many instances, is from the fact that the section is not parallel with the fibers at that point, which can often be definitely made out by the presence of fibers cut obliquely. But at other points, and these are not few, certainly no attachment has existed. Indeed the principal fibers may be absent and the fibers of the indifferent tissue may lie flat upon the surface of the cementum or bone for a considerable space. Their course being parallel with the surface. At some points the cause of the detachment is evidently absorp- tions of the alveolar wall or of the surface of the cemen- tum, and the principal fibers may be seen to have been severed. The osteoclasts are found frequently, and the roughened surface tells plainly of their action, even at this advanced age. It has become plain to me after a long study of this point that the attachment of the fibers is continually changing. They seem to be loosened and remain so for a time, but they are again attached, or new fibers are developed. Some other part is loosened and again attached, so that in passing around the root of a tooth of an old person these non-attached points are con- tinually coming into view. This will be studied more in detail under absorptions within the alveolus. As has been said, the interfibrous tissue is much di- minished in old age. At many points none whatever can be seen ; at some points, however, there is so much of this that it might be mistaken for a young membrane. In run- ning along the surface of the cementum occasional groups of cementoblasts appear with undeveloped cells in their neighborhood. The same appearances of local activity are met with along the bony wall also. CHAPTER IX. INTER-FIBROUS ELEMENTS OP THE PERIDENTAL MEMBRANE. Other than the blood-vessels and nerves, the principal interfibrous elements are an indifferent tissue, and the various forms of cells. The principal fibers are accom- panied by fibroblasts, which belong to them, and are ren- dered prominent by any nucleus-tinting dye. Fig. 50, D. But aside from these there is among the principal fibers a very considerable number of fibroblasts, accompanied by very fine fibers, which pass between the principal fibers and often pursue an independent direction. Fig. 46. This I have termed the interfibrous or indifferent tissue. It seems to pervade the entire membrane, and is found wherever the principal fibers are absent, or are coarse enough for it to be distinguished. In figure 46 I have represented this tissue with a high power. The illustration is taken from the margin of bone near the rim of the alveolus, where the principal fibers are very large. The interfibrous tissue is seen to be ordinary fibrous con- nective tissue containing the usual fibroblasts. In this instance its course is diagonal to the principal fibers. This tissue is well seen in many regions of the membrane, but when it is mingled with the principal fibers of the vascular region its identity is necessarily lost, except where it forms an investment for the vessels and nerves. Fig. 50, E and F. Parts of the membrane here and there are made up seemingly of this tissue, the principal fibers being absent. Fig. 49 d. This is most frequently seen high up on the root or about its apex, and marks espe- cially those regions of the membrane that I havedesignat- 84 INTER-FIBROUS ELEMENTS. 85 ed in previous pages as non-attached. In general, when standing alone, it gives the appearance of indifferent tis- sue. In the young subject its fibroblasts are a marked feature of the membrane when stained with a good nucleus-tinting dye, but in the old these become very thin scales, and do not take stains well, so that it is difficult to distinguish them except with high powers. The tissue then appears loosely fibrous, and the fibers, while pursu- ing no very definite direction, have a general tendency to lie horizontally to the cementum, or parallel with its margin, as seen in lengthwise sections. It does not seem to attach itself to the cementum or bone, as do the prin- cipal fibers. The fibrous investment of the blood-vessels and nerves, additional to the tissue properly belonging to their walls, seems to belong to this tissue. In young sub- jects this is often very abundant (fig. 50, E and F), form- ing masses accompanying the vessels, and causing devia- tions in the course of the principal fibers. In older sub- jects this accompaniment of the blood-vessels mostly dis- appears, and in sections their walls look comparatively thin. BLOOD SUPPLY OF THE PERIDENTAL MEMBRANE. The blood supply of the peridental membrane is very bountiful in the young subject, and though it is much diminished with the thinning of the membrane as age ad- vances the vessels remain fairly abundant. In the young subject there is a very well marked vascular area lying centrally between the cementum and alveolar wall, or often rather closer to the cementum. This is most reg- ularly seen in cross sections. Through this portion the fibers are deflected from their regular course in many parts to give space to the larger arteries, veins and nerve bundles. Fig. 50, E. and F. The larger arteries enter the alveolus mostly at the apical space, or rather one or two ve'ssels enter here, and immediately break up into 86 INTER-FIBROUS ELEMENTS. smaller ones. One or two of these enter the root canal to supply the pulp of the tooth, while the others from four tq six or eight pass down along the sides of the root to supply the peridental membrane. In their passage down the membrane these divide into many branches, a considerable number of which enter the Haversian canals of the alveolar wall, or receive branches from that source. This kind of connection between the circulation of the tissues outside of the alveolar wall and the peridental membrane is very rich in young subjects, and although the bone becomes much more dense with advancing age it is still fairly well maintained. Seemingly for this reason there is not much diminution in the size of the main arteries passing down from the apical space to the gin- givus, though they are much increased in numbers. We may therefore say very justly that the blood supply of this membrane is received largely through the walls of the alveolus. Some vessels are continuous, however, from the apical space to the gingivus. I have a few sections from the incisor teeth of the dog cut lengthwise, inject- ed, that show arteries traversing the membrane from apex to gingivus without break, but giving off and receiv- ing branches from the alveolar wall throughout their course. Many of these branches can be traced through the alveolar wall to their connection with the larger ves- sels of the gum-tissue. These vessels during their course in the peridental membrane give origin to a fairly rich capillary plexus that supplies its tissues. It is rare to see a vessel of any size close to the cementum. This portion of the tissue seems to be supplied almost solely, but very richly, by the smaller capillaries. The passing and re- passing of the vessels through the alveolar wall is well seen in sections, and shows many of the larger ones near the bone and within its canals. With the thinning of the membrane as age advances the vessels are found lying very close to the bone, and in case the membrane is very INTER-FIBROUS ELEMENTS. 87 thin many of them lie in grooves in the bone. This is best seen in cross sections. (Fig. 37.) Veins accompany, or perhaps stand a little apart from, most of the larger arteries. At the rim of the alveolus the vessels of the peridental membrane anastomose very freely with those of the gum, and this gives a pretty rich gingival plexus. From this arrangement of the circulation of the blood in this membrane it will be seen that it is not readily robbed of its blood supply by accident. In case of alve- olar abscess involving the apical space, the blood supply from that source is cut off, but that through the alveolar wall and by way of the rim of the alveolus is ample ; or even in case the supply from both the apical space and by way of the rim of the alveolus is cut off simultaneously, the remaining body of the membrane will be supplied through the alveolar wall, and will not suffer from want of blood. An inflammation involving one part does not necessarily endanger another. The sensory function of the peridental membrane is supplied by nerves entering it in company with the blood- vessels, and from all the sources of blood supply men- tioned under that head. The principal bundles, how- ever, enter by way of the apical space, and then divide, a portion entering the apical foramen for the supply of the pulp, while the others pass down the sides of the root supplying the peridental membrane. A considerable number enter through the walls of the alveolus by way of the Haversian canals, each containing from four to ten or more nerve fibers. These traverse the membrane, giving off smaller bundles which are lost in the tissue, until the gingival border is reached, where, in company with those of the gum tissue, a rather rich plexus is formed. Specialized nerve terminations have not been found in this membrane in sufficient numbers to show that they are essential. I have seen a few Pacinian corpuscles near 88 INTER-FIBROUS ELEMENTS. the gingival border, and rarely some other knob-like terminations. Generally, however, none of these are found. The bundles of fibers sub-divide into single fila- ments which are lost in the tissues,' and probably termin- ate mainly as naked fibers. Through this supply of nerves the perrdental mem- brane becomes the organ of touch for the tooth. The enamel, the portion of the tooth exposed, has not the sense of touch. This may be demonstrated by experiment in many ways. One of the simplest of these is per- formed as follows : Take any small instrument and touch ,with it the enamel of any tooth. It will be found that the lightest touch is felt distinctly by the patient. Now place the finger on the opposite side of the tooth and make firm pressure, and while this is maintained again touch the exposed part of the enamel with the instru- ment. It will be found that under these conditions the touch will not be felt. Now by varying the pressure with the finger it will be found that in order for the touch of the instrument upon the enamel to be felt it must be suffi- cient to overcome the pressure brought to bear by the finger. A slight movement of the tooth must be pro- duced so that it may effect the peridental membrane, without this no sense of touch is manifested. This is different from the temporary semi-paralysis that may be produced by firm continued pressure, or by a blow. In order for this to be effective it must be pretty severe or long continued. For comparison this may be tried upon the hand or fingers. This simple experimentation readily demonstrates that the sense of touch in the tooth is very different from that of the skin. The sense of touch in the finger nails will be found similar to that of the tooth. Normally, the sense of pain is not easily aroused in the peridental membrane. The office of fixation of the tooth, and maintaining this against the heavy pressure normally brought to bear upon it, demands the capability of with- INTER-FIBROUS ELEMENTS. 89 standing heavy strain and blows without complaint, and at the same time without limiting, in the absence of such a strain, the acuteness of the sense of touch. The mem- brane does not, however, on this account, bear mutilation without pain, but is, perhaps, as painful as .the average of the tissues, and in its inflamed state it becomes exceed- ingly sensitive to very slight pressure, as is uniformly witnessed in acute pericementitis. Its rich supply of blood-vessels and nerves renders it capable of rapid recovery from injuries of almost any kind. Indeed, there is no tissue of the body that shows a more marked ten- dency to recover from severe injuries. These sensory functions are not destroyed by injury to any particular portion of the membrane. I have carefully tried the sense of touch in teeth after having removed all of the contents of the apical space, i. e., after soreness had so far abated that the sense of touch was not abol- ished by the sense of pain, and found the sense of touch was, as far as could be ascertained, normal. That its sensitiveness to painful impressions is not abated by the destruction of the nerves entering by way of the apical space, is sufficiently obvious to all who have had to do with large acute alveolar abscesses producing extensive destruction of the tissues of the apical space. It follows, therefore, that the nerves entering the mem- brane through the walls of the alveolus are sufficient for the maintenance of the sensory functions. CHAPTER X. LYMPHATICS OF THE PERIDENTAL MEMBRANE. The peridental membrane has a very peculiar system of cells closely resembling those of the lymphatics. In young subjects these are found in great profusion lying among its fibers close to the cementum. I know of no other system of cells similar to this anywhere within the bodies of men or of the lower animals. They seem as distinctly specialized as the agminated glands or Peyer's patches of the small intestine. I therefore regard them as peculiar to this particular portion of the peridental membrane. They occur mostly in the form of rows of cells insinuated between the fibers of the membrane. They are never far from the cementum, but not in contact with it, except in some isolated cases observed in the pig. These rows of cells anastomose freely with each other and form a network over the whole of the root of the tooth. Their number is so great that I have counted from one hundred to two hundred of them cut across in the cross section of the root and alveolus of an incisor tooth of ordinary size. Fig. 50, C, C. These rows of cells vary very much in the numbers of cells in- cluded in their make-up. Sometimes a cross section will show only one or two cells lying together. Again, and more commonly, five or six that form a rounded group, and more rarely, especially near the gingivus, where they are generally larger and more numerous, there will be quite a body of them giving with high powers a gland- like appearance. I have represented one of these in fig. 47, using for the purpose the one-twelfth inch objective, in which its relations to a small capillary vessel are shown. 90 LYMPHATICS. 91 Very often the cells lie between the fibers in such a way as to show, in cross or lengthwise sections, rows run- ning outward from the cementum. This is especially well seen in the pig. These often seem to be single rows of cells, or they may consist of two or three rows lying side by side. In either cross or lengthwise sections the islands of cells seem to be entirely detached from each other, especially if the sections are very thin. But in sec- tions cut horizontal to the surface of the cementum at such a distance as to include them, they are seen to be in the form of chains that anastomose with each other, like a network. In fig. 48 I have represented a group of these, using the one-eighth inch objective. This is very readily seen with low powers if the section, cut in the manner indicated above, be double-stained with car- mine and hematoxylin. In this case the lymph cells take the hematoxylin and the fibrous tissues are stained red, and with low powers, the first impression will be that of a fine capillary injection. Higher powers will reveal the true character of the tissue. The individual cells are like those of the lymphatic glands. They show a circular or polygonal outline, and the central portion takes the staining agent strongly. In the larger groups it is easily seen that they are enveloped in a very delicate limiting membrane. This limiting mem- brane is not so easily seen about the smaller groups or rows of cells. However, by following one of these carefully* which I regard as a very delicate lymph duct crowded with lymphoid cells, I have been able in many instances, to connect it with the smaller veins or capillaries in the form of the perivascular spaces peculiar to the lymphatics of other regions. Owing to the extreme difficulty of obtain- ing nitrate of silver stainings of this membrane, it is spe- cially difficult to make out these points quite satisfactorily. Klein seems to have shown that nodes of lymph cells develop within the lymph sacks or enlargements of the 92 LYMPHATICS. lymph ducts, which he designates as endolymphangeal, and also outside, but in contact with these, which he terms perilymphangeal nodes. These are, however, en- dolymphangeal, as distinguished from the peiilymphangeal glands or nodes. In fact, these seem to be lymph canals that are packed with lymphoid cells rather than true lym- phatic glands. The cells are very well seen in plain glycerine mountings, especially after acetic acid, and the groups may readily be made out with the half-inch object- ive, but as they lie crowded among the other tissues higher powers are necessary to differentiate them. These cells are more abundant in the omnivora than in other animals that I have examined, and the pig is an especially good subject for their study. They are very well seen in the herbivora, also, but seem not so abundant in the carnivora. They seem to diminish in numbers as age advances, though this point has not been studied suf- ficiently. In one membrane from a man, forty years old, the number seems to be much diminished, though groups of them were seen in almost every field. In another from a man about seventy, only a few groups of the cells were found. It seems probable that they disappear, for the most part, with advancing age. In this they agree with specialized lymphatics elsewhere, such as Peyer's patches of the small intestine, and a few that have been noted in other positions. One circumstance, aside from the histological interest, has directed my attention quite strongly to these cells. In extracting a cuspid tooth a large piece of the anterior por- tion of the alveolar wall broke away, adhering to the root of the tooth, and gave me the opportunity of making sec- tions for the study of its membrane. Phagedenic perice- mentitis was destroying the membranes of some of the other teeth, but about this one no pockets were observ- able, though there was some slight redness of the gingivus. On microscopic examination, I found that some of the LYMPHATICS. 93 lymphatics near the gingival border of the membrane were in a state of suppuration, while some others did not take staining agents well. This condition followed the lymph chains in the direction of the apex of the root to a distance that surprised me, considering the very slight signs ot disease visible before operating, and seemed espe- cially confined to these cells. Examination of them for micro-organisms was not thought of in time. This case hints quite strongly that these lymphatics are the seat of this very peculiar affection. It seems that it is also these glands that are first affected in salivation with mercury, when, as physicians say, " the gums are just touched," and the teeth become sore, when pressed together. Also, when the teeth become sore from other causes that may be regarded as constitutional, i. e., from some agent in the blood that affects these glands. Formerly, it was suggested by Serres, who is quoted by Salter, that the inner portion of the epithelium -that portion clothing the border of the gingivus folded in against the tooth acted the part of a gland. This part of the epithelium is softer than other portions, and the gland-like action noticed here under the influence of iodide of potassium, mercury, and some other remedies, evidently led to this conclusion, which, from clinical ob- servation, seemed to me to be justified. (See American- System of Dentistry, vol. I, p. 955.) But since I have made a more critical study of these lymphatics, it has be- come clear that the results were derived from them which had been attributed to the inlying epithelium of the gingivus. I find the lymphatics to be larger and much more numerous just in that neighborhood, and while I have found no such thing as a duct leading to the gingival aperture, the glands lie in very close proximity to it. . Furthermore," a portion of the connective tissue in immediate conjunction with the tooth is not covered by the epithelium. In other words, there is no attachment of the epithelium to the 94 LYMPHATICS. root of the tooth. It seems to be through this space that the cells so-called salivary corpuscles found under the free border of the gingivus, pass. These may be found at any time under the healthy gingivus, and their numbers are augmented with every irritation of the membrane. Indeed, close clinical examination makes it apparent that there is a slight secretion at this point that is not quite satisfactorily explained even yet by microscopic study of the part. HARD FORMATIONS WITHIN THE PERIDENTAL MEMBRANE. There are occasionally found, in the tissues of the peri- dental membrane, especially in elderly persons, certain hard formations that resemble the calcospherites so fre- quently found in the tissues of the dental pulp. I have seen more of these about the roots of the molars than elsewhere, but have also found them along the sides of .the roots of the bicuspids. Occasionally I have seen these built into the substance of the cementum, especially in hypertrophies. In fig. 49 I present an illustration of one of these, rather a small one, from the membrane of a bicuspid, which presents their usual appearance very fairly. They are composed of concentric rings of lime salts united by a basis substance which appears identical with the phlebo- liths of varicose veins, and calcospherites of the dental pulp. They do not, however, present exactly the same features of either of these. They are much larger than the calcospherites of the dental pulp, and the incremental bands or layers are much thicker. Neither do they pre- sent the nodular forms composed of numbers bound together in one mass, so common to either of the before- mentioned bodies. They are usually seen like the one in the figure, as isolated spherules, many of which are large enough to be readily seen with the naked eye. In several instances I have seen two spherules united, but LYMPHATICS. 95 this is unusual. The larger ones, as they appear in sec- tions, after being decalcified, of course, usually show cracks radiating from the center toward the circumfer- ence. This may have occurred in the cutting, though I have no means of determining it. I only know that the smaller ones usually show nothing of this kind. In several instances I have seen cementum built upon the larger ones, and fibers attached, showing that they may become a nidus for an irregular or nodulated hypertrophy. I have also in my collection hypertrophies which show these forms in their substance. Further than this, I know nothing of the origin or significance of these bodies. In the peridental membranes of old people there is a considerable number of pigment granules found. They occur isolated, or in groups, oftenest about the walls of the blood-vessels, but also a part from these. They are intensely black, rather small, and seem to be amorphous. They remind one very much of the pigment so generally seen in lung tissue. They are not present in the periden- tal membrane of 3 r oung persons. Nothing is certainly known of their origin or significance. The idea that they arise from extravasations of blood might be sug- gested, but this seems improbable. CHAPTER XI. OSTEOBLASTS AND ALVEOLAR WALL. The osteoblasts of the peridental membrane are found on the inner surface of the walls of the alveolus in abun- dance in young subjects. They lie on the bone between the principal fibers (figs. 45 and 46), and there are gen- erally many young cells in the neighborhood, filling in between the fibers if they are large and solid as in fig. 46, or in the meshes of the finer fibers when they break up close to the bone as in fig. 45. But in this respect the utmost variety will be found. Many localities, even in young subjects, will be found almost destitute of these cells, while others, at only a little distance perhaps, will be crowded with them. In aged subjects they are gen- erally absent, or are represented only by very thin flat- tened scales, lying close against the bone, that are very difficult of observation. But even in these cases occa- sional areas will be found in which the osteoblasts appear, covering the bone as in the young, only less profusely. These are undoubtedly areas of activity, points at which bone is being built up to accommodate some change in the position of the tooth. This will be discussed farther under the head of absorptions taking place in the alveolus. The building of bone occurs on the inner walls of the alveolar processes in that growth which fits them about the roots of the teeth. These additions are made in the same manner as subperiosteal bone is built up under the attached periosteum, to which the reader is referred. The peridental membrane is very thick in young sub- jects, and the alveolus correspondingly wide. Bone is deposited upon the inner walls of the alveolar process as 96 OSTEOBLASTS AND ALVEOLAR WALLS. 97 the membrane is reduced in thickness. Indeed after the alveolar process is once formed the subsequent deposit of bony matter is mostly on the inner side, filling in the en- larged space through which the crown passed in the pro- cess of eruption, to conform it to the root of the tooth. In this growth of bone new canals seem not to be formed by the growth of processes which arch over, as in sub- periosteal growths. Nearly all the canals formed open into the alveolus very nearly in the direction pursued by principal fibers of the peridental membrane. (See Fig. 36.) Many of these approach the alveolus so obliquely that in cross sections such canals appear. In lengthwise sections, however, their true character is sufficiently ap- parent. The bone is therefore built up in the first in- stance in the same manner as solid subperiosteal bone, but with canals running in the direction of the growth, or at an angle inclined to that direction. This growth of bone shows the residual fibers very plainly in many of its parts, for the fibers of the peridental membrane are in- cluded in this in the same manner as the fibers of the at- tached periosteum. This I have attempted to illustrate in Fig. 51, from a perpendicular section through the rim of the alveolar wall, choosing the extreme point of the alveolar process that represented by ?>, Fig. 53 on the labial side ; c?, Fig. 51 represents the extreme point of the rim of the alveolar wall. /, /, The subperidental bone which is closely filled with residual fibers from the large fibers of the peridental membrane, b. Subperiosteal bone, which is usually small in amount, and on the labial side, is confined mostly to the immediate rim of the alveolar wall ; for. on the labial side there is more often found ab- sorption of bone, thinning the alveolar wall as it is built up on the inner side. The Haversian bone is left without stippling that it may be more plainly marked, and is pointed out by a. g, g, g, Are points at which absorption of bone is in active progress, e, Points out the fibers of 98 OSTEOBLASTS AND ALVEOLAR WALLS. the peridental membrane. This bone, forming the alveo- lar wall, it will be seen, is first built up solid as under the firmly attached periosteum. There is, therefore, no differ- ence in the building of bone here and elsewhere, except that the included fibers are larger, which gives the bone quite a characteristic appearance. This bone is very soon invaded by absorbents, and canals are burrowed through it, which is followed by the deposit of systems of Haver- sian bone, thus removing the fibers, as shown in the fig- ure. This process follows very closely the building of the bone, so that there is not at any time a very consider- able amount of the alveolar wall that shows residual fibers. This is well shown in Fig. 51, in which I have left the Haversian bone without stippling to distinguish it more clearly. At maturity the bone has become so changed by this process that the residual fibers are con- fined to the immediate surface, and almost the entire mass of the alveolar wall is seen to be made up of secondary Haversian systems. In old subjects these show all along the inner border the effects of absorptions and rebuild- ings of bone that have occurred from time to time for the accommodation of changes in the positions of the teeth. This matter will be discussed in detail later. A description of the origin of the alveolar process be- longs rather to embryology, and I shall not enter the dis- cussion of that part of the subject here. The growth of the alveolar process, after the tooth has taken its place in the arch, presents some peculiar features. This growth is, in a large degree, contemporaneous with the develop- ment of the tooth's root, whether it be a temporary or permanent tDoth. The socket at this time is usually much too large for the root, and the peridental membrane is correspondingly thick. This is necessarily the case in the first instance, for the accommodation of the fully formed crown of the tooth. After the tooth has taken its position the alveolus grows smaller by the deposit of bone on its OSTEOBLASTS AND ALVEOLAR WALLS. 99 inner wall, until it is brought more nearly to the size required by the root which it is to support. This occurs very rapidly as the tooth is taking its position in the arch. There is. however, a movement of the permanent tooth, after it has taken its position in the arch, to which I wish to call special attention. This takes place largely during the very noticeable change which occurs in the features about the age of puberty, but is in progress from the time the permanent incisors have taken their places until ma- turity. I have illustrated this movement diagramatically in figs. 52 and 53. In each figure an incisor tooth is rep- resented in dotted lines with the rim of the alveolus at a, a. e, Represents the apex of the root, and the dotted line o the inner wall of its alveolus ; while the space be- tween the lines c and d shows its thick peridental mem- brane. This represents the position of the tooth and its alveolus at the age of ten or twelve years. The tooth and alveolus drawn over this with solid lines represents the same tooth in the position it will have assumed at the age of twenty-one or two years. The growth of the alveo- lar process has carried the tooth in the direction of its length about the distance represented by the length of its crown, or that part of the tooth covered by enamel, as represented in fig. 53, which is the maximum movement that I have observed, while the minimum movement is about one-half the length of the crown, as represented in fig. 52. This movement seems to be rather greater in men than in women, but it presents considerable varia- tion. I should say that the various points of growth of the bones of the face are possibly not determined yet with sufficient accuracy for fixed points to be established that will be without objection. The measurements I have used have been from the anterior spinous process of. the superior maxillary bones (figs. 52 and 53, J), to the cut- ting edges of the superior central incisors. This measure- ment, made at ten or twelve years of age and at maturity, 100 OSTEOBLASTS AND ALVEOLAR WALLS. indicates the movement shown in the diagrams. This is a large factor in the elongation of the face. The move- ment in the lower jaw seems to be about the same as that in the upper, though it can not be so definitely determ- ined. The principal growth concerned carrying the teeth forward for the elongation of the arch, is^ as is well known, at the back part of the maxillae, carrying the an- terior portions forward to make room for the molars. The growth of the alveolar process, which carries the tooth with it, as shown in 52 and 53, is almost entirely from the osteal side of the peridental membrane, or upon the inner side of the alveolar wall. The elongation is made, it is true, upon the rim of the alveolus, the portion represented in fig, 51 growing in a line almost parallel to the length of the tooth from the points a, a, in figs. 52 and 53, to the points 6, 6, and in the meantime all of the space between the wall (inner) of the former alveolus c, and that of the final alveolus /, is filled in by growth of bone from the osteal side of the peridental membrane. This is all built in originally with the character of bone represented at/, fig. 51. and in figs. 45 and 46, and is re- moved by absorption and replaced by Haversian bone, as represented at a, fig. 51. The plan of this removal and rebuilding is more particularly described in fig. 24, and on page 000, to which the reader is referred. In this way there is a continuous activity in growth and reconstruc- tion of the alveolar processes during this time, in which the tooth itself, except its cementum, is passive, the dentine and enamel having previously completed their growth. The movement represented in these figures is seen to be almost wholly in the direction of the long di- ameter of the tooth, but there is some movement of the crown of the tooth forward in the direction of its short diameter. This is accompanied by a tilting of the crown forward, as shown. I have often found absorption in pro- gress about the point A, and observation seems to indicate OSTEOBLASTS AND ALVEOLAR WALLS. 101 that a reduction occurs as represented from the line h to g. However, f i om the want of a fixed point from which to measure, it seems almost impossible to determine the amount of the movement in this direction. The tilting of the crown forward is readily determined, however, by taking the relative positions of the tooth to a perpendic- ular line. I do not know that any previous writer has discussed this subject, and I have not now sufficient data at hand for the full presentation of it. Yet it is of great import- ance in connection with the formation of the dental arch, and serves to illustrate the necessity of retaining it com- plete during the formation of the features. It also has an important bearing on the subject of the correction of irregularities. 1 will have more to say of it after having considered the cementum. CHAPTER XII. THE CEMENTUM AND CEMENTOBLASTS. The cementoblasts or cement builders are to the cementura what the osteoblasts are to the bone. They are the cells concerned in the formation of the matrix, and the deposit of lime salts, which enter into the forma- tion of the cementum. These are cells of rather large size and of peculiar form, and are found lying between the principal fibers of the peridental membrane and upon the surface of the cementum. While functionally they hold the same relation to the cementum that the osteo- blasts hold to the bone, they have no resemblance to the osteoblasts in form. The osteoblasts are polygonal cells inclining to the round form, and their longest diameter is often directed away from the bone upon which they lie, as has been said upon another page. I have never seen the cementoblasts presenting these forms, but on the contrary, they are always distinctly flattened cells with one of their flat sides resting upon the cementum. They are, indeed, in the form of somewhat thickened scales, of very irregular outline. This irregularity of outline seems to be due to the position they occupy among the principal fibers of the peridental membrane as these latter pass out from the cementum. There is usually a central mass, which is seen to con- tain a regularly formed nucleus, and from this central portion irregular projections extend among or between the fibers of the neighborhood. The cells, with their projections, are so placed that they occupy all the surfaces of the cementum, except 102 THE CEMENTUM AND CEMENTOBLASTS. 103 that occupied by the fibers that emerge from it. A better idea of their form can be gained by examination of the illustrations, figs. 54 and 55. In the first of these I have isolated several cells, and it will be seen that the form of the projections from the cell body is such as will fit in between the fibers. In the other illustration the fibers are shown cut across and left white, so that their outline may be better seen. These illustrations are taken from sections cut horizontal to the surface of the cementum, and are double stained with hematoxylin and neutral carmine, which gives a diffusive red stain to the fibers, while the cells are of a deep blue. Sections cut in any other direction will fail to give a correct impression of the form of these cells, but the sections cut perpendicular to the surface are valuable as illustrating fairly the thickness of the cells. In such sections the cementoblasts are seen in parts only. In a given focus of the lens, isolated parts of the same cell may appear as small cells separated by fibers, and it is practically impossible to connect them and gain definite information of their form from such sections alone. The projections among the fibers of the membrane spoken of above are not in any proper sense processes from these cells, but are to be regarded as portions of the cell body which takes this form on account of the presence of the fibers. I have made out true processes proceeding from these cells in but few instances, but enough to show that they exist upon a considerable number, if not all, passing into the cementum upon which the cells lie. However, they are evidently not so numerous nor so regular as the pro- cesses of the osteoblasts, or if so they are much more difficult of observation. I have never seen processes ex- tending from these cells in a direction from the cementum out into the tissue of the peridental membrane. I think it probable that such processes exist, but it is imprac 104 THE CEMENTUM AND CEMENTOBLASTS. ticable to display them by stretching the tissue away from the cementum, attached as it is by strong fibers, in any manner similar to that represented in figs. 17 and 18, in case of the non-attached periosteum. In the growth of the cementum some of the cemento- blasts are included in its substance, and persist as cement corpuscles in the same manner as the osteoblasts are in- cluded in the bone as bone corpuscles. The number and relative positions of these are, however, extremely irregu- lar in those animals that have a thin cementum. About the necks of the human teeth and the teeth of the car- nivora, there are usually no cement corpuscles, but at points where the growth of cementum is thicker, they ap- pear in considerable numbers ; and toward the apex of the root, where the deposit of cementum is considerable, they may appear in profusion. That regularity of occur- rence which is noted in bone corpuscles, is not seen in the cement corpuscles. On the contrary, they appear in groups or in patches, while perhaps considerable areas are destitute of them. In some of the herbivora, and notably in the pig, they appear with more regularity, figs. 57 and 58. The cement corpuscles have processes corresponding to those of bone corpuscles, but presenting great irregu- larities. Some may show none whatever, others a few that may be very short or very long. While others again have a great profusion that radiate in every direction, branch and anastomose with each other and with those of neighboring cells, forming an intricate network. Many of the corpuscles show processes passing in one direction only and that is usually toward the surface of the cementum. The cementum is deposited upon the dentine and covers the root portion of the tooth. There is never an attach- ment of the soft tissues with the dentine upon its outer portion. Under some conditions the soft tissues may, in- THE CEMENTUM AND CEMENTOBLASTS. 105 deed, lie in apposition with the dentine upon its surface, but there is no physiological union of the two structures. The physiological connection of the dentine is with the dental pulp, and upon the pulpal side of the structure. When the soft tissues lie in contact with the opposite side, whether during development or afterward, the physiological process is either the deposit of cementum upon the dentine, or absorption of the dentine. The deposit of cementum is in the form of lamellae, layers, or strata, and covers the root over its entire sur- face. These lamellae are thin, normally, toward the neck of the tooth, and thicker, progressively, as the apex of the root is approached, the difference usually being very considerable. In normal conditions the number of lamel- 103 is about the same on all parts of the root, which gives a much thicker cementum at the apex than at the cervical portion of the root. The first of these, or at least the first part of the first lamellae, is usually hyaline or irregularly granular and ordinarily contains no cement corpuscles, or at least but few. The next lamella, especially high on the root portion, presents these corpuscles very generally, and they continue irregularly through the successive lamellae, provided always that the individual lamellae be of considerable thickness. Very thin lamellae, whatever their position, are usually destitute of corpuscles, while the thicker ones contain them. These lamellae seem to represent periods of activity in the deposit of cementum, each lamella being the result of a single period of activity. If we extract a tooth soon after its eruption and examine its cementum, we shall usually find it very thin and containing but one or two lamellae. A tooth from a person who has reached matur- ity will present a larger number and the cement will be thicker than in that of a child of twelve or fourteen years, but not nearly so thick as the cementum upon the roots of teeth from old people ; nor will it contain so many 106 THE CEMENTUM AND CEMENTOBLASTS. lamellae of cementum. These layers are subject to the greatest irregularity, both in the thickness of the single ones and in their number. Neither do they present much regularity at a given age in different persons. In all these respects there is the utmost irregularity. The individual lamellae of cementum are divided by lines that may be very distinct, or but imperfectly seen. The mode of preparation makes much difference in the distinctness of these lines. Sections cut from decalcified teeth and mounted plain (without staining), in glycerine, show them very fairly, but they are rendered more distinct by tinting slightly with a diffusive carmine stain. These lines I will call, as Salter has done with good reason, the incremental lines of the cementum. This is appropriate from the fact that each one marks the divisions between the lamellae that are laid upon the root, the one upon the other. Each successive lamellae is younger than the preceding one, as we pass from the surface of the den- tine outward. In subperiosteal growth of bone, incremental lines oc- cur similar to those in cementum, but they are rarely per- manent, for, as has been said, subperiosteal bone is changed by the burrowing out of the bone first formed, and the deposit of Haversian systems in its stead. Nothing of this kind occurs in the cementum. It has no Haver- sian systems. In all of my examinations of this structure, I have not in any instance seen anything that could be called a Haversian system as these are known in bone. I have seen many canals that seem to represent small blood- vessels included in its structure, especially near the apex of the roots or between roots that have become fused by deposits of cementum, but these have never had about them deposits resembling the Haversian systems of bone. In normal conditions the lamellae of cementum, when once deposited, are permanent. They may indeed be re- moved, or burrowed into, as I shall describe later, by ab- THE CEMENTUM AND CEMENTOBLASTS. 107 sorptions beginning at the surface and cutting through the successive layers, but they bear no resemblance to the burrowing for the formation of Haversian canals in bone. Such absorptions are always refilled by a true surface de- posit of cementum, if filled at all. See fig. 61, a, a, a. A correct understanding of these facts is important to the study of hypertrophies and absorptions of the cemen- tum, which I shall introduce later. Furthermore, the cementum must, I think, be regarded as continuously growing, in the sense of not ceasing at maturity. It is very evident that its growth does not cease with the maturity of the tooth, nor with the maturity of the person. We find pretty uniformly a thin cementum upon the teeth of the young, and a thick cementum upon the teeth of the old ; and when a great number are examined from persons of known ages, it will be found that there is a continuous increase in thickness and in the number of in- cremental lines. But in such examination great varia- tions from any given rule will be noted. One set of sec- tions cut from the lower molar of a man, about seventy years old, shows on the sides of the roots forty- two lamel- lae easily distinguishable and counted with a half inch lens. While over the apex of the root, which presents some hypertrophy, there are a few additional lamellae. The incremental lines are not always regular in their distribution over the tooth's root. Sometimes a lamella is laid down that covers only a part of the root and two lines merge into one. This seems to show that there has been a local activity of deposit over part of the surface, that has not extended to the entire root. Some of the incremental lines seen toward the apex of the root where the cementum is thicker may disappear as the neck of the tooth, where the cementum is thinner, is approached. Again, regions will be found in which it is evident that certain lamellae of the cementum have been removed by absorption. 108 THE CEMENTUM AND CEMENTOBLASTS. FIBERS OF THE CEMENTUM. As I have said the fibers of the peridental membrane spring out of the cementum. These fibers pass through all of its lamellae to the first one laid on the dentine and part way through that, no matter what the thickness may be. In most localities in the human cementum these fibers are not continuous, but are broken at some of the incremental lines. At some such points they have cer- tainly been detached by absorption, but in most instances this cause of detachment can not be made out satisfactor- ily. On account of this frequent breaking it is not gen- erally possible to follow individual fibers from the peri- dental membrane entirely through the cementum, even in sections cut parallel with them, though they may be seen in all its lamellse. In the pig the fibers are much larger and less thickly placed than in man. This renders the tracing of individual fibers from the membrane into this substance comparatively easy (Fig. 57). In the pig, also, there is a great thickness of cementum, compara- tively, formed in a few months, and this presents but a few incremental lines at which the fibers are broken. We can, therefore, follow individual fibers through its entire thickness in sections cut parallel with them. In man, the fibers are so much broken at the incremental lines that it is only now and then that we are able to find individual fibers traversing its whole thickness. Much of the cementum of man, especially that about the necks of the teeth, when so stained as to show them clearly, seems almost as if made up of fibers. These are usually small, placed close together, and run pretty squarely outward, pursuing a straight course, (Fig. 59, 5, c,) but farther up on the root, where the cementum is thicker, they are often found curved in various directions, and many times we shall notice an abrupt change of direction at an incremental line. Some spaces or patches will be noticed in which the fibers seem to be absent. THE CEMENTUM AND CEMENTOBLASTS. 109 These fibers have been noticed by various writers, and not a few have spoken of them as the fibers of Sharpey, while others, Salter and Abbott, seein to have mistaken them for canaliculi similar to those of dentine. This error can scarcely be avoided if the examination has been con- fined to the dried specimen, for it seems that many of the fibers are but imperfectly calcified, and in drying suffer shrinkage to such an extent as to give that appearance. I have a number of sections in my collection that show this. These are the principal fibers of the peridental mem- brane included in the cementum in its growth, and fur- nish the means of making firm hold of the peridental membrane upon the root of the tooth. They are white connective tissue fibers, the ends of which are included in the matrix of the cementum sufficiently to make them apparent when the lime -salts are removed, but when both are calcified, they can not be demonstrated except in cases in which there is imperfect calcification of the fibers, as has been mentioned above. A very beautiful demonstration of these fibers may be had in the cross-section of them, i. e., in moist sections of the cementum cut horizontal to its surface. If these be very thin, stained, and mounted in balsam, they will show the fibers cut across especially well. In this case there will generally be such a shrinkage that a part of the circumference of the fiber will be parted from its matrix, showing it plainly ; and by close focusing the whole outline of the fiber may be clearly seen. In some very thin parts of sections the fibers may drop out of their alveoli, leaving openings. This was the case in the sec- tion from which fig. 56 was made. In many very thin sections parallel with the fibers, we may see about broken edges the fibers protruding from the margin, as is shown in fig. 57, d, d. This is much as I have illustrated the residual fibers of bone as doing in fig. 21. 110 THE CEMENTUM AND CEMENTOBLASTS. The clearness and regularity of the appearance of these fibers of the cementum in my preparations make it a matter of great surprise to me that they have not been before described by writers on dental histology. I can only account for its oversight by the fact that very few- studies of the peridental membrane have been made, and these seem to have been only casual, and thus, the con- nection of the fibers of the two structures have escaped notice. In this way the appearance of fibers in the cementum has been passed as something not understood, or they have been wrongly interpreted. However, most of the studies of this structure have been made from dried sections in which the fibers could not be dem- onstrated. CHAPTER XIII. IRREGULARITIES IN THE GROWTH OF CEMENTUM, Hypertrophies of the cementum have been under dis- cussion for many years and generally they have been re- garded as pathological phenomena. I think, however, that the careful student must admit that, in the vast numbers that occur, there are comparatively few in- stances in which the pathological character of these is fairly made out. They have been regarded as connected with all manner of aches and pains. I wish now to call attention to a mode of study of these, which, if followed, will, I think, dispel most of these notions. Not that I wish to affirm that in no case a hypertrophy of the cementum may be related to a process of disease, but rather to show that this is not necessarily the case and as a matter of fact is very rarely so. They are to be regarded rather as irregularities than as pathological phenomena. I have already said that the cementum is to be regard- ed as continuously growing in the sense that its growth continues to old age. It may be found augmenting in thickness in persons seventy years old and the process be perfectly normal. I wish also to further emphasize the fact that the manner of the growth is by interrupted ac- cretion, or in periods of activity and rest. The inter- vals of inactivity are probably very great sometimes, but the examination of the cementum of any con- siderable number of persons at thirty years of age, and comparisons with a similar number at fifty years, will show that there has been a pretty regular increase in the thickness and in the number of lamellae of the cementum. If those of fifty are again compared with those of seventy, 111 112 IRREGULARITIES IN GROWTH OF CEMENTUM. a farther increase in thickness and number of lamellae will be manifest. This growth takes place at irregular intervals of time, which is expressed in this lamellation. The lamellae are laid the one upon the other successively and the outer ones are of course the last in the order of growth. When a tooth presents through the gum and has taken its place in the arch, its cementun will generally present but one layer ; but if it has been brought into use for a time it is likely to present two or three, one formed contemporaneously with the root and one probably when it was first brought into contact with its antagonist or possibly while it was being protruded after the growth of the root was accomplished. It seems probable also from examinations I have made, that there often several la} r ers of cementum deposited during the movements of the teeth connected with the lengthening of the face which was illustrated in Figs. 52 and 53. At any rate differ- ences in this regard are observed, whatever be their cause. As the tooth grows older new lamellae are laid down. It must be admitted that the study of these lamellae has not as yet been sufficient for us to form any definite idea as to their relation to the age of the individual after the first two or three have been laid down. But however this may be, it will be found upon examination that every case of irregularity in growth will be connected with one or more of the lamellae, and the relative time of the irregu- larity of growth to the deposit of the individual lamellae can be made out. On applying this mode of study to the irregularities of growth in my collection, I find a great variety. They are connected with the lamellae in all sorts of ways. Some belong to a single lamellae, others include several, while others again include all of the series from the" first to the last, each one being thicker in the hypertrophied portion than elsewhere. Now it is perfectly evident that such a IRREGULARITIES IN GROWTH OF OEMENTUM. 113 hypertrophy, as this latter, lias been forming with each successive growth of the cementum from the first to the last, while those that are confined to one or a few lamellae have begun and ceased with the deposit of these. There is no such thing as interstitial growth of the cementum, and no thickening of the lamellae can occur after another is deposited over it. Among these hypertrophies confined to one or a few lamellae, the greatest variety will be found. I have speci- mens from teeth just erupted showing hypertrophy of the first and only lamellae yet deposited. But these are more rare than those connected with the second or third. It seems to be with the latter that the greater number of the irregularities are connected ; though a goodly number will be found beginning with those deposited later ; and some are connected with the last one, even in very old persons. These last have of course occurred late in life while the others have occurred at an earlier age. The greater number of the irregularities in the deposit of the cementum are probably connected with some especial strain upon the tooth, and their causation probably cor- responds with that of the absorptions which are yet to be studied. We generally find these combined in the same tooth and occurring at about the same time. That is to say, the absorptions of the cementum are shown in the lamellae that lie next beneath those that show the con- dition of hypertrophy but are generally upon another portion of the root, which may be contiguous or upon the other side. I frequently see these latter that have cut away the first two lamellae, penetrated the dentine to some depth and have been refilled with cementum in con- nection with the deposit of the third or fourth lamella. Now these facts have prompted this thought ; the tooth makes its growth and presents its crown to its antagonist. At first the cusps of the one do not strike fairly into the sulci of the other. This causes a lateral strain upon the 114 IRREGULARITIES IN GROWTH OF CEMENTUM. peridental membrane as the tooth is forced to one side sufficiently for the proper adjustment of the cusps. A portion of the membrane is put upon the stretch and probably the cementoblasts are stimulated to increased deposit of cementum during this interval. This results in an irregularity of growth which may be in connection with a single general lamella of cementum, or it may be only a partial lamella confined to one part of the root. At the same time absorption may have occurred in an- other part as upon the opposite side, removing some por- tion of the layers previously formed, or forming irregular openings throughout the whole thickness of the previous formation and penetrating the substance of the dentine. These latter are now refilled with cementum with the next lamella deposited, and afterward the deposit may take place regularly over both the hypertrophy and the absorp- tion area, and these will be found covered with a number of regularly formed lamellae. Such a theory seems very weak, however, when con- fronted with thickenings like the one shown in fig. 60, which is confined to the first layer, while the subsequent ones are very regularly formed. This was a thickened portion on the side of a root of a cuspid tooth. It can not be stated positively that this was all formed before there was a contact with its antagonist, but its deposit was certainly continuous with the layer formed contempora- neously with the development of the tooth. I have found such thickenings of the first layer in teeth not yet fully developed upon which there was as yet but the one layer of cementum deposited. This seems to show that these irregularities do not depend wholly upon extraneous influences. Other instances will be found in which on some part of the root there will be a thickened -portion confined to a single layer belonging to a much later date, as the one illustrated in fi^. 59. This was on the distal side of the IRREGULARITIES IN GROWTH OF CEMENTUAL 115 root of a molar near the gingival border, and so far as could be made out without a history of the case, the con- ditions point to an irregular strain upon the tooth as a cause. The crown of the adjacent bicuspid had been broken away a number of years previously, apparently, and this tooth had leaned forward over the remaining root. Upon the mesial side of the anterior root there were several absorptions affecting the lamellae next be- neath the one hypertrophied upon the distal side. Ap- pearances indicate that this occurred at an age of up- wards of fifty years. Other cases occur in which there is an increased thick- ness in each successive layer over the same spot. These are found mostly about the apex of the root upon one side, or covering the entire apex in the form of a rounded knob. They may become thinner gradually toward the neck of the tooth or cease abruptly. In the latter case absorption areas will generally be found around the border of the hypertrophied portion. I have illustrated such a case in fig. 61, from a hypertrophy of the root of a superior bicuspid. It will be noted that in this case the roots were originally separate, and that they became fused together with the deposit of the second lamella of the cementum ; and that this lamella presents the greatest thickness, while those deposited later are progressively thinner; therefore a large part of this deposit must have occurred early in life. Connected with this, areas of ab- sorption have occurred at d, d, d, which have narrowed the root at that part, increasing the nobbed appearance of the apex. It will be seen that these absorption areas have been refilled with cementum in connection with the deposit of certain lamellae. I have seen a number of cases of hypertrophy similar to the one last described, that I supposed resulted from the loss of an antagonist and a consequent partial protru- sion of the tooth from its socket. But most of these 116 IRREGULARITIES IN GROWTH OF CEMENTUM. showed, when sections were made, that the thickening had begun very early in the .history of the tooth. The second and third lamellae being the thicker, necessarily excluded the loss of the antagonist as the cause. Other cases occur, in which the increased growth belongs to the lamellae last deposited, and in these the loss of the antag- onist would seem to be a probable cause. Our knowledge of the subject is not yet sufficient for the satisfactory determination of the cause of these irregularities in any case, but the suppositions given may lead to further study and thought, and lead to something more satisfactory. In the meantime it seems evident that the anomaly should not be considered as a pathological state, but rather as an irregularity of development. Yet these enlargements, when considerable, may impinge upon the surrounding tissue in such manner as to induce conditions of a patho- logical nature. Another point of interest should be noted in this con- nection. It is a well-known fact that cementum and bone never unite. At least no well authenticated case is on record. In reptiles and fishes the osseous union of the teeth with the bones is the normal condition. With this fact before us, and considering the great similarity of cementum and bone, it seems quite remarkable that such a union should not sometimes occur. In the study of this subject I often find an exceedingly thin peridental mem- brane dividing the hypertrophied cementum from its alve- olus. But there is always some soft tissue. I do not remember of any case occurring high up on the root about which the membrane was unusually thick. The rule is that it is thinner, than about the parts not hyper- trophied. The bone forming the alveolus is also apt to be more than usually cancellated. When cementum in its growth approaches cementum the case is entirely different. On coming together fusion occurs whether the roots belong to one tooth or to differ- IRREGULARITIES IN GROWTH OF CEMENTUM. 117 ent teeth. In this way the roots of neighboring teeth be- come fused together in a considerable number of instances. Sometimes this seems to have occurred contemporaneously with the development of the teeth, and the subsequent thickening of the cementum obliterates the point of junc- tion to such an extent as to give the appearance of a single root with two crowns. But many of the cases seen have evidently occurred comparatively late in life. I have seen a number of specimens in which it seemed that the fusion of the roots had occurred on account of the teeth having been forced out of position, especially in molars, which had inclined forward after the loss of the next tooth anterior to them, and the roots pressed back- ward in such a way as to come in contact with the roots of a posterior tooth. Again spherules of calcific material occur in the peridental membrane. As has been noted, cementum may be deposited upon these, and this will fuse with the cementum of the root of the tooth. These facts taken together seem to show that, while cementum and bone are so very similar in structure, there is a radical difference in the specialized cells by which they are formed, which prevents them from coalescing in their functional activities. Yet these cells are developed within the meshes of the same membrane, the fibers of which span the space from the one hard formation to the other. CHAPTER XIV. ABSORPTIONS OCCURRING IN THE ALVEOLUS. The absorptions occurring in the alveolus are of much interest and practical importance to the practitioner. They are very frequent, occur under various conditions and circumstances, and may be of any extent, from the slightest erosion of the surface of the root of the tooth, or of its alveolar wall, to the complete removal of either or both. It is by absorption that the roots of the tempo- rary or milk teeth are removed to give place to the per- manent or adult teeth. And so far as microscopic study of the subject can determine, it is. by precisely the same plan that the roots of permanent teeth are occasionally absorbed, either in part or completely. So far as has yet been determined, it is this same process of absorption that is the great enemy with which we have to contend, in the various operations of replanting, transplanting and im- planting natural teeth. The subject of the absorption of the roots of the tem- porary teeth does not properly come within the scope of this work, except incidentally for comparison with other absorptions. A study of the physiological errors that occur in the absorption of the roots of the temporary teeth will do much to explain some things that seem very strange in the absorptions which occur in the alveoli of the adult teeth. By physiological errors, I mean, as has previously been said, an action of the tissues which is purely physio- logical in form, but going beyond the needs of the time and perhaps calling for a counter-action on the part of the adjacent tissues for its correction ; but not going to an extent that can properly be classed as pathological. 118 ABSORPTIONS IN THE ALVEOLUS. 119 In the consideration of the soft tissues such errors are not readily detected, because all traces of them is soon effaced ; but in the study of the bones, and especially of the teeth, where these errors remain written indelibly in the structure in which they have occurred, possibly many years before, we may, after sufficient observation, trace their progress and subsequent correction with almost the same certainty that we can trace a wellworn pathway through the wooded hills. The process of absorption has been spoken of, its pe- culiar cells illustrated and described, and its effects upon the hard tissues detailed, in the previous pages. It is generally performed, we may say always, when any con- siderable mass of hard tissue is to be slowly removed, by the specialized cells known as osteoclasts. How these cells perform this function is not yet perfectly clear. It seems that they elaborate and evolve from themselves a substance which dissolves the hard tissues with which they may be in contact. Some observers, as Krause, re- gard this substance as being lactic acid, while many others seem unwilling to express an opinion. The action upon the hard tissue is certainly different from that of lactic acid, in that there is very little softening of tissue upon which it acts farther than the portion actually liquefied and removed. The surface, being absorbed, is thrown into elevations and depressions by the form of the cells acting upon it, but the surface of each of these depressions will be found to be clean, smooth and hard, and when dried will glisten like a polished surface. The osteoclasts are not attached to the surface of the bone or tooth by any mechanical means whatever ; they simply lie agairist the surface and are detached with the least movement. They act, however, only when lying in con- tact with the surface. Any intervening substance what- ever will prevent their action. Therefore, the formation of an abscess with pus lying about the end of the root 120 ABSORPTIONS IN THE ALVEOLUS. of a temporary tooth, so long as it lasts, is a bar to the absorptive process. This may act in two ways. 1st. The presence of the pus may separate the cells from the tooth's root. 2d. The pathological condition may pre- vent the physiological action of the cells. The process of absorption is always to be regarded as physiological, but the error of direction and extent may be so great as to constitute a pathological condition, as when the root of a permanent tooth is wholly, or in a great part, re- moved by this process. The tissue acted upon in absorption is always passive. On this point there seems to have been a difference of opinion, some writers supposing that the absorption of bone was performed in part by the bone corpuscles. There may be some forms of disease of the bones in which this is the case, as claimed by Cornil and Ranvier ; but certainly there is no such thing in the physiological absorptions. The root of a tooth that has lost its pulp, and consequently the vitality of its dentine, will be absorbed as readily and as completely as the living tissue provided always that the tissues in contact with the root be in a physiological condition. I have frequently noted the absorption of the root of a temporary tooth after the healing of alveolar abscess ; but, if the abscess continues, the absorption will generally fail in part or entirely. For the performance of absorption, then, it is required that the physiological action of the cells be not seriously impaired. At the same time, the clinical history of cases seems to show that a moderate degree of irritation or inflammatory action may hasten, or even be the condition of the beginning of many of the absorptions. It is not yet clearly made out that the absorption of bone in condi- tions of inflammation is always the same process as that which occurs physiologically, but I will say that in all the absorptions within the alveolus which I have yet exam- ined, the process has been identical with the physiological ABSORPTIONS IN THE ALVEOLUS. 121 removal of the roots of the temporary teeth ; but is mani- fested in directions and in forms that are often erratic in the extreme. I have examined very closely the condition of the bone corpuscles in the immediate neighborhood of areas of absorption in various regions and conditions, and have never seen any evidence whatever that they took part in the process. I have, in a number of instances, found the bone corpuscle uncovered by absorption and their pro- cesses removed up to the body of the cell, and yet no change could be discovered in the condition of the cell itself. There is certainly no enlargement of the chamber in which it lies. It seems to be entirely passive. Pre- cisely the same is true of the cement corpuscles. The dentine is also removed, and the dental fibres cut away without the least change occurring, either in the remain- ing parts of the fibrils, or the dentine of the neighborhood. All of this illustrates the fact that these tissues when once formed become passive agents. Not that all of their parts have become inert material devoid of life, but they are for the most part composed of formed material, in which physiological activity is reduced to a minimum. Many of the irregular phases of the absorptive process might be illustrated by the examination of the roots of the temporary teeth. Perhaps very few of these are regularly removed proceeding from the apex of the root to the crown. Indeed, the more common form is for the absorption to begin some distance down on the side of the root, cutting a deep cleft. Then it will begin at some other point and do the same thing, and at another, and so on. These will finally merge into the great gap in the substance of the root, and the process will perhaps proceed more rapidly in the destruction of the remaining portion. We have no evidence that during this time the ab- sorptive process produces any inconvenience to the young animal, or the child. It is not until the tooth is materially 16 122 ABSORPTIONS IN THE ALVEOLUS. loosened by the loss of its root that inconvenience is felt. But during the earlier part of this process it seems to proceed with much uncertainty and indecision (if such terms are admissible), for we find many instances in which the absorption bar- proceeded for a time and then ceased not only ceased, but the work of repairing the breach has been undertaken by the building in of new cementum. I offer an illustration of such a case, taken from the temporary tooth of a pig, in fig. 62. In this case a large breach extending far into the dentine had been made in the side of the root, nearly midway its length, by absorp- tion, and at f the bone had grown forward toward the absorbed area. Now a change occurred. Cementum is again deposited for the repair of the breach, and this is laid down over the cut ends of the dentinal canals, upon the dentine, covering it over smoothly and evenly in this case, though it is not always done so regularly. It will be noted that the gap in the dentine is not repaired by a new formation of dentine. Such gaps are always repaired by cementum, if repaired at all. In many cases there is a much greater deposit of cementum of repair than in this, but this one is sufficient to show that cementum may be laid down upon the dentine denuded of its cementum, which is a point of no mean importance in these days of the study of the various forms of replantation, and of the amputation of roots of teeth. Fig. 65 illustrates the same thing as occurring upon the root of a permanent molar. Passing now to the permanent teeth, I will first notice the absorptions occurring in the alveolar wall. These are very numerous, and may be studied by preparing sections of any of the teeth of the adult ; but the best studies will be had from the alveoli of teeth that are at the time un- dergoing change of position from any cause, such as the loss of a neighboring tooth, continued pressure, or the in- cisors (and I suppose the molars also) during that change ABSORPTIONS IN THE ALVEOLUS. 123 of position which occurs during the lengthening of the face, which was illustrated and described in chapter XI. Under any of these circumstances changes in the alveolus and the attachment in the principal fibers of the peri- dental membrane occur, and these seem to call for ab- sorption and rebuilding of bone. In fig. 63 I present an illustration of this, taken from the middle portion of the anterior wall of an incisor. The upper portion of the il- lustration is toward the crown of the tooth. This illus- tration shows especially well the method by which the fibers of the peridental membrane become detached and reattached during movements of the tooth in its alveolus. No very considerable absorption areas are seen, but groups of osteoclasts appear at very frequent intervals, as shown at d, d, d, which lie in the lacunse of Howship, absorbed into the surface of the bone. At all such points the fibers are detached. Indeed, these fibers seem to disappear with the appearance of the osteoclasts, but wherever the bone is not covered by these cells the fibers are found to be in position. At/ it will be noted that a portion of new bone has been built on to the old, in which the ends of the fibers are secured. In this way, it seems, absorptions and changes in the alveolus may occur slowly, or even with considerable rapidity, and sufficient attachment of the principal fibers of the membrane be maintained to hold the tooth securely while its position is being changed. Parts of the fibers are cut away and some portions of the bone removed, then the fibers are reformed and built into the wall of the alveolus by a new deposit of bone about their ends. These changes are not confined to young animals, or young persons, but may be found in progress in the old as well, but are generally more irregular. I have not had the opportunity of examining a case in which the artificial movement of the teeth, as in the cor- rection of irregularities, has been made, but from what I have seen I suppose that the absorption and rebuilding 124 ABSORPTIONS IN THE ALVEOLUS. occurs in precisely the same way. However, in the rapid movements that are often made in these cases, there must be a solid line of absorption along one portion of the al- veolus (that pressed against) detaching the fibers en masse, while the fibers on the other side are lengthened. Hence, the tendency of the tooth to return to its old posi- tion until time enough has elapsed for a sufficient refor- mation of its alveolus and the reattachment of its fibers. In adults evidences of changes in the alveolar wall may be found about almost any tooth (so far as my ob- servation has extended) that has changed position from the loss of neighboring teeth. In fig. 64 I present an illustration from the alveolar wall at the posterior surface of a bicuspid that had moved backward slightly from the loss of the crown of the second bicuspid. The bone, 6, 6, seems to have been built in to supply an area of absorp- tion that was considerably more than the needs of the actual movement of the root. That this has been an ab- sorption is clearly shown by the Haversian systems of the bone being cut into and portions of their rings removed, as is shown all along the line. At e, a recent absorption has occurred, and from the presence of three osteoclasts (*) it is seen to have been in actual progress at the time of the death of the individual. Such absorptions as this latter are not infrequent in the alveolar walls. They seem to occur without any cause that I have been able to trace, though it is probable that they are stimulated by some slight movement of the tooth, and have proceeded beyond the needs, and are again refilled by the deposit of bone. In a large number of examinations very many spaces will be found at which there seems to be no attachment of the membrane to the bone, and yet the appearance of residual fibers within the bone shows plainly that the fibers have previously been attached here. In these' cases there is sometimes evidence of absorption of the surface ABSORPTIONS IN THE ALVEOLUS. 125 of the bone, sometimes not, but it seems most probable that the fibers have been removed by this process, though this may occur from some process not yet noted. Precisely the same thing occurs along the surface of the cementum, sometimes evidently from absorption of the surface of the cementum, but sometimes such absorptions cannot be demonstrated. Absorptions of the cementum are not so frequent as those of the alveolus. In fig. 65 I present an illustration exhibiting the evi- dences of absorption of portions of the root of a lower molar. In absorptions of the cementum in cases in which it has not been so great as to obliterate the lamellae we may do much in the way of fixing the time of the occur- rence relatively to the laying down of the individual lamellae, in the same way that we can fix the relative time of the formation of hypertrophies of the cementum described in chapter XIII. These absorptions are found to have broken through certain of the lamellse and ex- tended, perhaps as those shown at d, fig. 65, considerably into the dentine. .They are afterward repaired by the deposit of cementum, and the lamellse of cementum sub- sequently laid down are seen to pass over them without material disturbance. In all such cases we know that the absorption has occurred very early in the history of the tooth, otherwise it would have broken through the lamellae deposited later. In the study of the subject we shall find these beginning with any of the lamellse of the cementum, from first to last, as the absorption has occurred early or late in life. In fig. 66 a pit-like absorption has extended from the surface through all of the lamellse of the cemen- tum except the first, almost reaching the dentine. This was from an old man, and was evidently very recent, for the process of repair seems just begun and is apparently in active progress. The greater number of absorptions that I have studied seem to have begun in the second or third distinct lamellae, 126 ABSORPTIONS IN THE ALVEOLUS. and have probably been contemporaneous with the first use of the tooth, at a time when it is forced a little to this side or that for the filling of its cusps into the sulci of the opposing tooth. At e, in fig. 65, an absorption of much greater extent is shown. This seems to have cut away the entire apex of the root. Absorptions as exten- sive as this are much more rare than those previously noted, but close observation of teeth extracted will within a few years reveal a goodly number of such. They are found in teeth that seem to have rather short, thick roots, often with an irregular surface. Sometimes these will be found upon microscopic examination to be recent absorptions in which the dentine is exposed. Again, they will be found covered with a fresh deposit of cemen- tum. In the greater number of cases a close study of the lamellae of the cementum will give a clue to the time of the absorption. For this purpose it is necessary that the section be carried directly at right angles with the lamellae, for otherwise they will not appear distinctly. It is therefore practically impossible to study every part of a root. But generally enough sections can be had from lengthwise cuts to give a good idea of it. In fig. 65 a study of the lamellae of the cementum shows that the absorption which shortened the root at e occurred early in the history of the tooth, and that it was promptly recovered with cementum. The incremental lines do not appear very plainly in this part, hut they lead into it in such a way as to leave no doubt. In other cases that I have examined, that were outwardly similar, and which might be illustrated, the absorptions have occurred late in the tooth's history, the absorption having broken through the greater number of the lamellae, or have been recent, as the absorption at/, fig. 65, in which there seems to have been no effort at repair. From the examinations that I have made I am led to the opinion that absorptions of this nature in the roots of ABSORPTIONS IN THE ALVEOLUS. 127 the permanent teeth do not remain long without the occurrence of the reparative effort, if -the tissues are in a condition for this effort to be made. It may also be stated that, if the tissues are in a condition to produce absorp- tion, they will also be in a condition to make the repair, provided no impairment has occurred in the meantime. Fig, 66, from a section cut from the immediate apex of the root of a cuspid, shows something of the extent and completeness of these repairs. A class of absorptions precisely similar to that illus- trated in fig. 66, is of rather frequent occurrence near the gingival margin of the cementum. I have called atten- tion to these heretofore, and at various times, in the con- sideration of caries of the teeth, and especially in the appendix to " Formation of Poisons by Micro-organisms," page 168, and in the "American System of Dentistry," vol. I, p. 777. These absorptions are very generally of the form of that illustrated in fig. 66, and when they occur very close to the attachment of the membrane at the gingival border, are liable to become uncovered by the shrinkage of the soft tissues and afford lodgement for micro-organisms, and thus are a predisposing cause of caries. I have often noted quite broad absorption areas at this point which seem to remove that portion of the cementum which laps upon the enamel, producing a marked groove. This is occasionally more extended, cutting considerably into the dentine, and in case it becomes exposed, gives the opportunity for the girdling of the tooth, in whole or in part, by caries becoming implanted in it. I have seen several instances in which the tooth was almost severed from its root by these cer- vical absorptions. One lower molar in my possession had an absorption beginning upon the mesial surface, that invaded the pulp cavity. In another case now under ob- servation such an absorption so weakened a lower incisor that the crown broke away. A number of similar cases 128 ABSORPTIONS IN THE ALVEOLUS. might be mentioned. These might be mistaken for caries, if the condition of the surface, and the tissues filling the space, were not carefully observed. But the condition is so different in the two cases that a mistake should not occur. Of course, after caries has once invaded the part, there is no means of knowing whether an absorption began the breach or not. From the studies previously cited it seems that the detachment and reattachment of the peridental mem- brane in parts here and there is continually occurring. Not only is this the case where there has been appreci- able absorption of the cementum, as in the cases illus- trated, but a study of the fibers included in the cemen- tum shows unmistakably that they have been broken at many of the incremental lines when absorption cannot be demonstrated. In these cases the constant reappearance of the fibers in the lamellae subsequently deposited shows that the plan of the reattachment is by new deposits of cementum upon the old. In this new deposit the ends of the fibers are imbedded, making a firm hold. This occurs equally well if the new deposit be upon the denuded dentine, as when it is upon the cementum. This being the constant method in this class of cases, I must now suppose that in the various modes of planting natural teeth, the manner of attachment to the root is the same. That is to say, the attachment of the tooth depends upon the production of a lamella of cementum covering the root. This lamella of cementum is laid down upon the root by the tissues in contact with it. It does not seem to depend upon the vitality of the cementum upon which it is deposited. It does not grow from the cementum, but from the soft tissues from the cemento-blasts. If this lamella of cementum is once perfectly formed, there would appear to be no reason why it should not endure, but the apparent difficulty is to obtain that perfect la- mella of cementum ; and the absorptions continue little ABSORPTIONS IN THE ALVEOLUS. 129 by little, proceeding from the many imperfect points, un- til the root is destroyed. This appears from studies now made. Future investigations may reveal new factors not yet noted. I have now finished the task I set myself to perform a practical histological study of the periosteum and peridental membrane. The task has been difficult in many respects, and has required an amount of labor much greater than was expected in the beginning. Although I had much available material, I have thought it best to make new preparations of all the tissues. These have all been gathered, and the work done since the first of October of last year. As the work progressed it was found that a number of series of sections were required for study in special directions, which greatly increased the labor. All of the illustrations are made from freshly prepared material. The work is now before the profes- sion, and by the profession its value must be judged. Many phases of the subject are new. Very few studies of these tissues had been made by previous observers. Therefore, extended references do not seem to be called for. Indeed, the literature does not furnish them. Hy- pertrophies and absorptions of the cementum have been studied by John Tomes, Chas. Tomes, C. Wedl, Salter and others, and among these some very brief examinations of the peridental membrane appear. Among the works on general histology there is some brief mention of the characters of the periosteum and peridental membrane, and several have mentioned the presence of residual fibers (fibers of Sharpey) in the cementum. Such notices have, however, been too sparse to give much information on the subject. However, after studying these papers, the reader will do well to review any and all of these that may be within his reach. INDEX. A. Absorption at the gingival margin 127 a predisposing cause of caries 127 bone corpuscles passive in areas of 121 cells development of 68 detachment of the fibers of the peridential membrane by 128 irregularities . of 121 of bone 48, 44 of the roots of the temporary teeth 118 of the roots of the temporary teeth prevented by disease. 118 of the roots of the temporary teeth not prevented by death of the tooth's pulp 120 of the alveolar wall 122 passive condition of tissues acted upon by - 120 relation of irritation to 120 repair of breaches made by 125, 127 roots of teeth shortened by 126 the process of 119 Absorptions occurring within the alveolus 118 Acids effects of, on tissues 4 " on selective stainings 4 Apical space 73 fibers of the 77 Alveolar wall, absorptions of the 122 evidences of changes in the, in adults 124 Haversian canals of the 97 manner of the growth of the 98 movements of the teeth during the growth of the. .. 98 relations of the growth of the, to the elongation of the face 100 B. Basis substance _ 8 Blood vessels of the periosteum , 35 of the peridental membrane 85 Bone, beginnings of the deposit of sub-periosteal 64 conversion of articular cartilage into 57 diaphy sal formation of 57, 62 epiphysal formation of 57, 58 first deposit of, in cartilage 68 formation of 45 formation, osteoblasts the agents of 70 formed under the attached periosteum 42 growth of the shaft of , in length 65 S'owth of, under tendonous attachmen ts 55 aversian systems of 46 131 132 INDEX. Bone, intra-membrmous formation of 16, 52 intra-cartilaginous formation of - 57 lammellae of 46 length of, not increased by interstitial growth .. 65 modes of the formation of T... 16, 45 penetrating fibers of 46 removal of the penetrating fibers of 47 subperiosteal formation of 45, 57 two distinct modes of replacement of cartilage with. 57 Bone corpuscles ". 41 processes of 42 position of the, in bone _ 43 ' relation of the, to the surface of the forming bone.. 46 Boll 11 C. Calcospherites in the peridental membrane 94 Cartilage, absorption of 59,64, 68 calcification of the matrix of 66 cells 63 changes in epiphysal, preparatory to the formation of bone 58 changes in dhphysal, preparatory to the formation of bone 62 changes in the cells of 63 condition of nuclei of, cells before absorption 65 continuous growth of articular 62 destiny of the, cells 60, 61 division of the cells of 63 deposit of bone upon 59 infiltration of , with lime salts ... 59 manner of the absorption of diaphysal 66 opening of the capsules of, cells by absorption _. 66 passive condition of cells of, before absorption 65 pierced by capillaries 64 pigmented ... 66 special reaction of, to stains 66 Caustic potass, used in demonstrating elastic fibers 34 Cells, development of, in ground substance - 8 cartilage 63 cartilage, disintegration of neuclei of 66 degeneration of cartilage 65 development of absorption 69 marrow 64 marrow, in regions of absorption of cartilage 65 Cellular elements of membranes 13 of the periosteum 37 of the peridental membrane 72 Cement corpuscles 104 processes of the 104 Cementoblasts 102 different from osteoblasts 102 processes of the 103 relations of the, to the fibers of the peridental mem- brane 103 relations of the, to growth of cementum... 104 sections for displaying the form of the.. 103 INDEX. 133 Cementum 102, 104 continuous growth of the - 107, 111 deposit of, in lamellae ^ 105 development of the lamellae of the . .'. 112 fibers of the 108 fibers of the, demonstrated in cross section 109 fusion of, with cementum. 117 hypertrophies confined to one or a few lamellae of the... 113 hypertrophies of the - Ill inclusion of blood vessels in the 106 incremental lines of the _. 106 irregularities in the growth of the Ill knob-like thickenings of the 115 modes of study of irregularities in the growth of the 112 no Haversian systems in the 106 non-union of , with bone 116 theory as to the cause of irregularities in the growth of the 113 Chemical relations of the tissues, with regard to stainings 4 Chondroclasts 61 development of 69 Cohesion _ _ 1 Connective tissue, primary _. 8 Connective tissues, develo'pmental relations of the 15 ' ' appropriateness of the name 16 D. Dentine, physiological connections of the 105 Development of connective tissue 7 " of elastic fibers 11 Ducts of the lymphatics of the peridental membrane 91 E. Elastic fibers 11 development of . . 11 distribution of _ 12 manner of demonstrating the 33 of the periosteum 33 Elastin connecting the epithelia . 12 " granules of 12 " homogeneous membranes of _ 12 Elongation of the face during the growth of the alveolar walls 99 F. Face, movements of the teeth during elongation of the 99 Fatty tissue 14 Fibers, arrangement of, in the peridental membrane 75 bundles of 10 coarse, seldom round 10 coarse, in cross section - 10 detachment of the, of the peridental membrane 123 development of 9 development of yellow elastic .. 11 134 INDEX. Fibers, inter-locking of 10 " manner of branching 10 " meshes formed of 10 " of the cementum 108 ' ' of the cementum demonstrated in cross section 109 ' ' principal, of the peridental membrane 74 " osteogenetic 50 14 principal, of the peridental membrane included in the ce- mentum 109 4< reticular 11 " relations of , to forming bone 50 " varieties of 8 " white inelastic -. 8 " yellow elastic 8, 11 Fibrilation... 9 Fibroblasts 9 Fibrous elements derived from cells 8 Fibrous membranes, functions of the 14 histology of the v. 6 " local characteristics of the 14 names of the 14 " relations of the, to cartilage and bone 15 Fibrous tissue, substitutions of 16 Formation of secondary Haversian systems in bone . - 47, 48 Fusion of cementum with cementum 123 G. Gelatinous substance 8 " tissue 8 Giant cells 43 Gingivus, the 76 Ground substance 8 Growth of bone on inner surface of alveolar wall 96 under tendonous attachments _ 55 under articular cartilage 57 Gum, border of the, described 76 H. Hard formations within the peridental membrane 94 Haversian canals of the alveolar wall 97 " formation of, by the removal of bone 47 " formation of, in tendonous attachments. 55 " relations of the penetrating fibers of bone to the .. 47 Haversian systems of bone 46 " secondary 47 Histology of the fibrous membranes 6 Howship, lacunae of 43 I. Illustrations, how made 20 Impregnation of tissues for cutting sections 18 for cutting sections in bay berry tallow. 18 ' for cutting sections in celloidin 18 ' ' for cutting sections in gum arabic 18 " " for cutting sections in paraffin 18 INDEX. 135 Incremental lines of the cementum 106 Intra-membranous formation of bone ., 52 Intra-cartalaginous formation of bone 57 of bone, diaphysal 62 of bone, epiphysal 58 Irregularities in the growth of the cementum .' Ill K. Krause 11 Klein _.. ' 91 L. Lacunae of Howship 43 Lamellae of the cementum 105 relation of numbers of the, to the age of the individual 105 represent periods of activity of growth . . 105 Ligamentum nuchea... 12 Ligamentum subflava 12 Localization of the sense of touch for the teeth, experiments 88 Lymphatics of the peridental membrane .72, 90 double stainings of the .... 91 ducts of the 91 in different animals _ 92 individual cells of the ..... 91 limiting membrane of the . 91 probable connection of the, with destructive percementitis 92 Lymph nodes of the peridental membrane 91 Lymph cells of the peridental membrane 91 M. Matrix 8 Marrow cells - .. 64 Membrane, limiting, of the lymphatics of the peridental membrane 91 Membranes, cellular elements of. 13 " subordinate to functionary tissues 16 " subordinate to relations of the 16 Methods of the preparation of tissues 17 Movements of the permanent teeth in their sockets during elonga- tion of the face 99 Mueller's fluid 17 Myoplaxies 43 Myxomatuous tissues.. _ 8 N. Nerves of the periosteum 36 " " " peridental membrane 87 " terminations in peridental membrane 88 Notch-pereosteal 57 136 INDEX. O. Organ of touch of the teeth -- 88 Osteoblasts 38, 102 description of the - 38 development of, on the surface of cartilage 63 ' forms of the, in old persons 39 ' functions of the -- 40 in the Haversian canals ... 39 ' opinion as to where the, belong 38 place of the 38, 39 suppositions as to the way bone is built by the 40 ' the only agents of bone formation 70 ' and the alveolar walls - 96 Osteoclasts, ameboid movements of the 44 ' at the ends of the long bones 26 description of the 43 functions of the 44 ' lacunae of Howship formed by the 43 Osteogenetic fibers '. ..- 50 Osteogenetic substance. 50 P. Pain, sense of, in the peridental membrane 88 Penetrating fibers of bone 46 " " " calcification of the... 51 " " " " removal of the 47, 52 Perichondrium.. 63 " changed to periosteum. 64 Peridental membrane, attention called to the 3 and periosteum, kinship of the 4 and periosteum, difficulties in the study of the 7 arrangement of the fibers of the 75 blood supply of the 85 cellular elements of the 72 changed appearance of the tissues of the, in old age 82 components of the - 72 diminished thickness of the, in old age 79 divisions of the 72 direction of the fibers of the 73 direction of the fibers of the body of the 77 detachment and re-attachment of the 128 facicular arrangement of the fibers of the. .80, 82 fibers of the.- 74 fibers of the, inelastic 79 fibers of the lower border of the 76 fibers of the apical space 77 form of the 72 form of the principal fibers of the 79 functions of the 71 indifferent tissue of the 84 inter-fibrous elements of the 84 lymphatics of the 12, 90 nerve terminations in the . , 88 INDEX. 137 Peridental membrane, office of the 71 physical functions of the 71, 79 physical functions of the fibers of the 79 pigment granules in the 95 principal fibers of the 71, 74 relation of the cementoblasts to the fibers of the 103 sensory functions of the 71, 87 sensory functions of the, not destroyed by in- jury to any one portion 89 the, the organ of touch for the tooth 88 thickness of the 73 variations in the arrangement of the fibers of the 78 " variations in the appearance of the fibers of the 78, 80 " vascular region of the 81 Periosteal notch . 57 Periosteum, blood vessels of the 35 cells of the, not showing specific character . . . . 37 cellular elements of the.. 37 embryonal cell among the fibers of the 38 gross examination of the 22 histological character of the _ 24 nerves of the 36 previous studies of the. .. . 7 where the, is adherent to the bone 23 where the, is separable from the bone 23 Periosteum, internal layer, appearance with selective stains 30 ' ' appearance with diffusive stains. . . 30 " arrangement of the fibers of the, on the long bones 30 " arrangement of the fibers of the, on the short bones 30 " attached forms of the, described 31 " attached and non attached forms of the. 29 ' ' character of the fibers of the 29 " de novo development of the 64 " destitute of elastic fibers.. 35 " in attached regions of the long bones. .. 31 " in non-attached regions of the long bones 31 ' non-attached form of the, described 29 " plan of the fibers of attached, form of the 32 " " relation of the fibers of the, to the bone. 32 external layer of the 24 " " arrrangement of the, for sliding movements of tissues upon it.25, 29 " " arrangement of the, on the shafts of the long bones 26 " " " arrangement of the, at the ends of the long bones... 26 " " arrangement of the, on the bones 'of the face 27 " " attachment of muscles to the 29 " " " attachment of facese to the 29 " " character of the coarse fibers of the 25 " " complex arrangement of the fibers of the 25 1 8. 138 INDEX. Periosteum, external layer of the lamellae of the 25 " " " " ribbon-like layers of the 25 " " ' " simpler form of the . . 26 " " " " sometimes absent 28 " " " " sometimes blended with other structures . . 28 " " " ' sometimes united to other tissues by elastic fibers - " " " " where thick and where thin 24 Phleboliths 94 Physiological errors .. ..37, 118 Pigmentation, plan of. 19 Pigment granules in the peridental membrane 95 Preliminary . . . . 1 Preparation of tissues, acids in the IT methods of the -... 17 Mullers fluid in the 17 time as an element in the 17, 19 injurious effects of acids in the 17 use of alcohol in the 18 Processes of the bone corpuscles 42 " " cement corpuscles 104 R. Replantation of teeth . 3 Residual fibers of bone 49 " " functions of the 49 " " of the alveolar wall 97 Reticular fibers 10 Riggs, Dr., of Hartford 3 Roots of teeth shortened by absorption 126 S. Salter. 93, 129 Salivary corpuscles 94 Sensory function of the peridental membrane 87 Serres - 93 Sharpey's fibers. 49 Shrinkage of tissues 4 Space, the apical 73 Staining tissues, plans of - 19 Strieker 1 Subperiosteal formation of bone 45 T. Technique, advances in.. 2 Tendinous attachments growth of bone under 55 Tendo-achillis, growth of bone under attachment of . 55 Tissue elements and their distribution. 6 Tomes, John ... 129 Tomes, Charles 129 Transplantation of teeth 3 Two modes of replacement of cartilage by bone 57 W. Wedl 129 Y. Yellow elastic tissue . . 11 UNIVERSITY OF CALIFORNIA LIBRARY Los Angeles Tl-i- *- * University of <*Momla SOUTHERN REGIONAL UBRARY 405 from which It was ,^o' t \ i^r-ry Form L9-116m A 000414479 6