me) a ee pO ye ne ee Pe a Received Accession No, 3. 2 @ 2) ae ee ae ag 6 zt *,* No book or pamphlet is to be removed from the Lab- oratory without the permission of the Trustees. SUE i THE AMERICAN JOURNAL OF ANATOMY EDITORIAL BOARD CHARLES R. BARDEEN, University of Wisconsin. HENRY H. DONALDSON, Wistar Institute of Anatomy. THOMAS DWIGHT, Harvard University. JOSEPH MARSHALL FLINT, University of California. SIMON H. GAGE, Cornell University. G. CARL HUBER, University of Michigan. GEORGE 8. HUNTINGTON, Columbia Univer sity. FRANKLIN P. MALL, Johns Hopkins University. J. PLAYFAIR McMURRICH, University of Michigan. CHARLES 8. MINOT, Harvard University. GEORGE A. PIERSOL, University of Pennsylvania. HENRY McE. KNOWER, SECRETARY, Johns Hopkins University. VOLUME V 1906 Vv THE AMERICAN JOURNAL OF ANATOMY BALTIMORE, MD., U. S. A. The Friedenwald Company BALTIMORE, MD., U. 8S. A» eee Oke iE. PIT. DV: NV. VE VII. VIII. CONTENTS: OF VOR. V No. 1. DrcempBer 1, 1905. JoHN WARREN. The Development of the Paraphysis and the Pineal Region in Necturus Maculatus . ... 1 With 23 text figures. K. T. Bett. The Development of the Thymus . . . 29 With 3 plates and 5 text figures. JEREMIAH S. Fercuson. The Veins of the Adrenal. . 63 With 3 text figures. GEORGE WALKER. The Blood Vessels of the Prostate LAIN ce bee Los peed eee, CP cn (me Pa RES Sot harsh el, ES With 2 colored plates. Bennet M. Atten. The Embryonic Development of the Rete-Cords and Sex-Cords of Chrysemys .... . 79 With 1 double plate and 6 text figures. Frepertc T, Lewis. The Development of the Lymphatic SyStcnMint have meee Js ee. fs. |. OB With 8 text figures. Frepertc T. Lewis. The Development of the Veins in the DimbesoteiabbiteBimbryostsfe., >) J. . . . ads With 1 text figure. No. 2. May 31, 1906. Ross GRANVILLE Harrison. Further Experiments on the Development Opdrertpheral Nerves ..°. 1. : . . . Dm With 5 figures. Contents IX. Apert C. EYCLESHYMER and JAMES MEREDITH WILSON. The Gastrulation and Embryo Formation in Amia Calva RTP torte \ Wee acct ee RE 133 With 4 double plates. X. CuHarwes F. W. McCuure. A Contribution to the Anatomy and Development of the Venous System of Didelphys Marsupialis (l.).—Part II. Development 163 With 1 single and 4 double plates and 27 text figures. LIST OF MEMBERS OF ASSOCIATION OF AMERI- CAN ANATOMISTS. . . 2.2 . . MXID-XOGm No.3. Junv 25, 1906. XI. Franxiin P. Maur. A Study of the Structural Unit of the Liver Ue rae, tag Dae 227 With 74 figures and 7 tables. XII. Apert C. EycresHymer. The Development of Chroma- tophores in Necturus oa . 309 With 7 figures. XIII. Smnry Kirin, $8. M., M. D. On the Nature of the Granule Cells of Paneth in the Intestinal Glands of Mammals Pe ee 315 With 5 figures. XIV. CuHaries L. Epwarps and Ciarence W. Hawn. Some Phases of the Gastrulation of the Horned Toad, Phryn- osoma Cornutum Harlan ; 301 With 15 text figures. No. 4. . September 1, 1906. XV. Rosert BENNETT BEAN. Some Racial Peculiarities of the Negro Brain 353 With 16 figures, 12 charts, and 7 tables. XVI. BSVLT. x VT: erX, Contents ; Vv FRANKLIN P. Matni. On Ossification Centers in Human Embryos Less Than One Hundred Days Old. . . . . 483 With 6 text figures and 7 tables. J. L. Bremer. Description of a 4-mm. Human Embryo. 459 With 16 text figures. CHaries R. Srockarp. The Development of the Mouth and GillsinmBdellostoma Stoutt j5), tv2 ©. \. Beasi-5ily With 36 figures. PROCHEDINGS OF THE, ASSOCIATION OF AMERICAN ANATOMISTS. NINETEENTH SES- SION, August 6-10, 1905. TWENTIETH SESSION, December27 28. and 29 VIO ne ek eee ote eee eek me Lt oe mt! ij = fn 7 ; ( yey } é { . | 4 ; F at 7 : hm) #) F 90 Ge bi t > eles : "e i 4 ‘ | ft . | | F a ie . oe ae ” A ; | | | | . | iw y f wns Ae - ’ ia , rai» | ce - and Ve ie iF 7 i " | ‘ NM a nn) ad - ns ay ry \a et ; j y tb i , 1 : ’ Map 7 ; - : | | b } t 7 f ee Ay (8G NCR Sarai a : = 7 7 . ae a aL w os ia’ PES DEVELOPMENT OF THE PARAPHYSIS: AND THE PINEAL REGION IN NECTURUS MACULATUS. ~~ BY JOHN WARREN. Demonstrator of Anatomy, the Anatomical Laboratory, Harvard Medical School. WITH 23 TEXT FIGURES. The presence of the paraphysis in Necturus was noted by Prof. C. S. Minot in his article “ On the Morphology of the Pineal Region, based on its Development in Acanthias ” (28), and a brief description of certain stages given. C. L. Herrick (15, Pl. VIII, Fig. 1, 3, 4) gives a brief account of the adult paraphysis, and shows it in the above figures, where it is named “ Preparaphysis.” Osborn (31, Pl. IV) shows the para- physis in an adult brain in comparison with the brains of other am- phibia. Kingsbury (21) describes briefly the adult paraphysis as well as a few of the earlier stages, and also gives an account of the epiphysis and the plexuses. I have found, however, no detailed account of all the - stages in the development of the paraphysis and the pineal region. This term is used here in the same sense as in Minot’s article, quoted above. The greater part of the specimens studied for this article were taken from the Embryological Collection of the Harvard Medical School, and the numbers of each section used are given. Other specimens were pre- pared specially for this purpose. In some cases where the plane of sec- tion was uneven, two or more sections were used in drawing the figures in order to show all the structures, which should appear in the median line. Fig. 1 is a median sagittal section through the brain of an embryo of 8-9 mm. I am indebted to a colleague for the drawing of this section, as this stage is wanting in the collection. In the roof of the fore brain three arches are seen. From before backward these are the paraphysal arch, P. A., the post-velar arch, P. V. A., and the epiphysal arch, Hp. A. The first two are separated by the velum transversum, V, which marks the limit between the two subdivisions.of the fore brain. Hence the paraphysal arch belongs to the telencephalon, the other two to the AMUERICAN JOURNAL OF ANATOMY.—VOL. Y. 1 2 Paraphysis and the Pineal Region in Necturus Maculatus diencephalon. The epiphysal arch is bounded by two angles, which rep- resent the position of the future supra and posterior commissures. ‘The velum transversum is a simple infolding of the brain roof, and consists of two distinct layers, one caudad and one cephalad, the space between them being filled by a loose mesenchymal tissue, which later contains numerous blood vessels. This figure is practically identical with Minot’s figure of acanthias of the same stage (28, Fig. 1), and is, therefore, of great importance in showing the homologies of these parts in elasmo- branchs and amphibians. It is probable, as Minot states, that these arches occur in most of the vertebrate series. The term post-velar arch, introduced by Minot (28), is much better for purposes of description than the terms “ zirbelpolster ” of German writers, and the “ dorsal sack ” or “ postparaphysis ” of American authors. TGS ale Fic. 1. Embryo of 8-9 mm. Sagittal section, X 63 diams. Fic. 2. Embryo of 10 mm. Harvard Embryological Collection, Sagittal Series, No. 269, Section 39, * 63 diams. Fig. 2 represents the roof of the diencephalon and telencephalon of an embryo of 10 mm. The two layers of the velum are nearer together and in the region of the epiphysal arch are seen the first signs of the epiphysis, #. This structure is a small rounded diverticulum, which arises from the cephalic end of the arch. It is hollow and opens into the cavity of the fore brain. 9 Fig. 3 is a similar section of an embryo of 12 mm. The velum is a trifle longer and the epiphysis a little larger than in the preceding figure. Immediately cephalad to the velum a very small evagination in the paraphysal arch can be seen, P. ‘This is the first sign of the paraphysis, and it appears distinctly later than the epiphysis. The latter overlaps its short stalk both caudad and cephalad, and at this stage the stalk is still hollow, though its cavity was obliterated in this section. John Warren 3 Fig. 4 is a section of an embryo of 13 mm. The yelum is again a little longer and its caudal layer is now distinctly thinner than its cephalic layer. The paraphysis is now a well-marked narrow diverticulum ex- tending dorsad from the paraphysal arch parallel to the velum. The paraphysal arch just cephalad to the opening of the paraphysis has been + HIGeos Fic. 3. Embryo of 12 mm. Harvard Embryological Collection, Sagittal Series, No. 49, Section 58, X 63 diams. Fic. 4. Embryo of 183 mm. Harvard Embryological Collection, Sagittal Series, No. 598, Sections 71 and 75, * 63 diams. forced downward to a slight degree, as there is relatively more space between it and the ectoderm than in the previous figures. The epiphysis is about the same size as in Fig. 3, and its opening into the brain is clearly seen. Fig. 5 is a section of an embryo of 12.4 mm., which is, however, further advanced than that of Fig. 4. The velum, the post-velar arch, and the epiphysis are about the same, but the paraphysis is distinctly longer, and Fic. 5. Embryo of 12.4 mm. Harvard Embryological Collection, Sagittal Series, No. 675, Section 57, * 63 diams. Fie. 6. Same as Fig. 5, X about 120 diams. has become a narrow tube. The brain roof cephalad to it has descended still more into the cavity of the telencephalon and the opening of the paraphysis is much nearer the tip of the velum. Fig. 6 is the same section as Fig. 5, only drawn on a higher scale to show the histological details. The walls of the paraphysis and velum consist of a single layer of cells, with large oval nuclei and without very distinct cell boundaries. 4 Paraphysis and the Pineal Region in Necturus Maculatus These cells are, of course, continuous with those which form the brain wall in this region. The same is true of the epiphysis, but the walls seem thicker, as the organ has been cut somewhat obliquely. Close to the paraphysis two vessels can be seen, a larger one cephalad and a much smaller one caudad, Ves. ‘The vessels lie in intimate relation to this structure, and it is important to note their relation at this early stage, because as development progresses the relation between paraphysis and blood vessels becomes more and more intimate. Fig. 7 is a section of an embryo of 15 mm. The most striking feature here is the increase in size of the paraphysis, which has become a long tube with a lumen extending its entire length, and at its distal end a lat- eral diverticulum has appeared. The roof of the fore brain has now descended to such a degree that the opening of the paraphysis is on a level with the tip of the velum. The velum itself has lost its cephalic layer, and consists of one layer only, which, however, is much longer than the velum in Fig. 5. If Figs 4, 5, and 7 are compared it will be seen that Fic. 7. Embryo of 15 mm. Harvard Embryological Collection, Sagittal Series, No. 79, Sections 85 and 89, * 63 diams. the distal end of the paraphysis is practically at the same distance from the ectoderm in each case.. As the paraphysis has developed during those stages into a long tube, its growth must have occurred by a downward extension of the neighboring parts into the cavity of the fore brain. This is practically the same process described by Minot in Acanthias. It is also shown by the great increase in distance between the roof of the telencephalon and the ectoderm from Fig. 4 to Fig. 7. The opening of the paraphysis in Fig. 3 is nearly ona level with the base of the velum, and as the down growth of the parts takes place the opening of the para- physis and the paraphysal arch descend, apparently pushing the cephalic layer of the velum ahead of them. Therefore the single layer of the velum in Fig. 7 really corresponds to the original caudal laver, plus the cephalic layer, which has been forced down ahead of the opening of the paraphysis. In studying Fig. 7 it might seem as if the posterior wall of the para- physis corresponded to the cephalic laver of the velum. This, however, is AI oh n Warren 5 not the case, as can be seen in a wax reconstruction of the parts, Fig. 8. This is a reconstruction of the brain of an embryo of 14.5 mm. The tops of the hemispheres, 7, have been removed to give a clear view of the paraphysis, P, which otherwise would be more or less covered in by them. The paraphysis appears as a straight tube in the median line and caudad to it is seen a broad partition, V, extending the whole width of the dien- cephalon. This is the velum, consisting of one layer only, which répre- sents the two originally distinct cephalic and caudal layers. The down growth of the parts in order to provide room for the development of the paraphysis has formed a deep angle in the roof of the fore brain. This Fic. 8. Wax model of brain of embryo of 14.5 mm. Harvard Embryo- logical Collection, Sagittal Series, * 120 times. angle is bounded caudad by the velum and cephalad or ventrad by the narrow roof of the telencephalon (paraphysal arch) immediately cephalad to the paraphysis. As the hemispheres develop, they grow at first in a dorsal direction and occupy the space left by the formation of this angle, so that the paraphysis is practically buried between the hemis- pheres in front and the velum behind, Fig. 10. The growth of the paraphysis must, therefore, be regarded as having an important effect on the development of the fore brain at this stage. Up to this stage the development of the velum has been in a ventral direction towards the floor of the fore brain, but now it begins to grow in quite a different direction. In Fig. 7 a distinct bulging of the velum is 6 Paraphysis and the Pineal Region in Necturus Maculatus seen, which is extending caudad at nearly a right angle to its previous line of growth. If the roof of the telencephalon be closely examined a slight bulging will be seen just cephalad to the opening of the paraphysis. These two outgrowths into the fore brain mark the beginning of the choroid plexuses, which, therefore, have in their origin a very intimate and definite relation to the opening of the paraphysis, one arising caudad and the other cephalad to it. The epiphysis at this stage has increased considerably in size, and the cavity in its stalk is now permanently oblit- erated. The body of the organ overlaps the stalk a little behind, and is beginning to grow well forward of it. The posterior commissure, P. C., appears here for the first time, a distinct interval in the roof of the brain lying between it and the stalk of the epiphysis. Fie. 9. Embryo of 17.5 mm. Harvard Embryological Collection, Sagittal Series, No. 540, Sections 113-115, & 63 diams. Fig. 9 is a section through the brain of an embryo of 17.5 mm. The paraphysis has increased in length, and from its distal end, which is somewhat enlarged, small tubules are given off. The whole tube is tipped somewhat forward. The choroid plexus is now well developed, and con- sists of two distinct parts, one dorsal and one ventral. ‘The dorsal part corresponds to the velum, which has grown caudad as far as the mid brain and has absorbed a large part of the post-velar arch. The ventral part is developed from the original paraphysal arch, and is growing towards the floor of the fore brain. Burckhardt (3) refers to these plexuses as “nlexus medius” and “ plexus inferioris,” respectively, and Mrs. Gage (13), who studied them in Diemyctylus, where the anatomical conditions closely resemble those of Necturus, names them the “ diaplexus” and “ »prosoplexus.” Prof. Minot has suggested the terms diencephalic John Warren 4 plexus for the dorsal part, and telencephalic plexus for the ventral part, and I shall use these terms, as they express more clearly the exact origin of each plexus. The diencephalic plexus, D. Plx., appears as a large wedge-shaped mass covered by a thin layer of cells, and consisting of a loose connective tissue in the interstices of which numerous blood corpuscles can be seen. The telencephalic plexus, Yel. Plx., has the same general characteristics as the diencephalic. The epiphysis has become fiattened and more elon- gated, and is attached by a narrow stalk to the brain wall. The supra commissure, S.C., is seen just cephalad to the stalk of the epiphysis, which is prolonged forward above it. I was unable to obtain any sagittal series between 15 and 17.5 mm., but in a transverse series of 16.5 mm. the first traces of this commissure can just be made out, and therefore it Fie. 10. Wax model of brain of emhryo of 18 mm. Harvard Embry- ological Collection, Frontal Series, No. 850, X about 75 diams. probably appears between 16 mm. and 17 mm. as a rule, but at these early stages there is a good deal of variation in the development of all these parts. The posterior commissure is rather larger than in the previous stage. Fig. 10 is the drawing of the model of the brain of an embryo of 18mm. This model is intended to show the circulation of the paraphysis at this stage. The distal end of the paraphysis, P, is surrounded by a venous circle, from either side of which veins, Ves., run outward and back- ward just caudad to the hemispheres, H, to terminate in the internal jugular vein, J.J. V. This vein is passing backward external to the fifth, V, and seventh, VJ, cranial nerves. Fig. 6 showed the intimate relation of the paraphysis to these vessels at 12.4 mm., and when the sections of this series were followed out it was found that here the vessels sur- rounded the tip of the paraphysis. It seems that as the paraphysis devel- 8 Paraphysis and the Pineal Region in Necturus Maculatus ops it forces its way into the veins lying over this part of the fore brain, and the tubules, as they are given off at later stages, force their way into these veins, Fig. 15, forming the sinusoidal type of circulation described by Minot (29) and Lewis (25). From the venous circle shown in Fig. 10 smaller vessels run down along the sides of the paraphysis and anasto- mose with the vessels of the choroid plexuses. A vessel also runs back to the epiphysis, and a larger one forward between the hemispheres. The circulation of this region appears at this stage to be mostly venous, as I could trace the arteries only to their point of entrance in the anlage of the skull, and the return circulation probably occurs by means of a minute capillary network over the surface of the brain. Fig. 11 is a section through the brain of an embryo of 26 mm. The E. 12 Sh SS gg Fig. 11. Embryo of 26 mm. Harvard Embryological Collection, Sagittal Series, No. 377, Sections 125 and 126, X 63 diams. paraphysis here is much more developed. It inclines somewhat forward, and from its wide central lumen a number of tubules are given off in every direction. The epiphysis and the commissures show but little change. The striking feature of this figure is the great development of the plexuses. The diencephalic plexus, D. Plr., has grown through the mid-brain nearly to the hind-brain, and the telencephalic plexus, Tel. Piz., has grown downwards into the depths of the cavity of the fore brain towards the infundibular recess. Fig. 12 is a transverse section of an embryo of 26 mm., corresponding approximately to the line A-B, Fig. 11. The section passes through the epiphysis, #, and the supra commissure, S.C., just beneath it. Then through the diencephalic plexus, D. Plx., and that part of the cavity of the diencephalon between this plexus and the roof, Dien. 'The section John Warren 9 then passes through the paraphysis at a point where two small tubules are given off, then through the telencephalic plexus, Tel. Plx., the telen- Fic. 12. Embryo of 26 mm. Harvard Embryological Collection, Trans- verse Series, No. 376, Section 89, X 63 diams. (See line A-B, Fig. 11.) cephalon, V'el., the lateral ventricles, 1. V., and the foramina of Munro, Ff. M. In this section the plexuses of the hemispheres, L. Pla., are seen. They arise on either side of the origin of the telencephalic plexus, and é AG == }y NN Jf “pf ro é A ( ~ : XQ Fic. 18. Embryo of 26 mm. Harvard Embryological Collection, Frontal Series, No. 378, Section 188, X 63 diams. (See line C-D, Fig. 11.) oT pass outward at right angles to it through the foramina of Munro into the lateral ventricles. Fig. 13 is a frontal section age an embryo of 26 mm., corresponding 10 -Paraphysis and the Pineal Region in Necturus Maculatus closely to the line O-D, Fig. 11. The section passes through the para- physes, P, and a large lateral tubule, and then through the entire length | veg | ) LP lapse Fig. 14. Same Series as Fig. 13. Section 108. (See line #-F, Fig. 11.) of the diencephalic plexus, D. Plz., the distal end of which is here en- larged and has reached to the hind brain, H. B. Fig. 14 is of the same Fig. 15. Same as Fig. 11. X about 150 diams. series as Fig. 13, and corresponds approximately to the line #-F, Fig. 11. It passes through the telencephalic plexus, Tel. Pla., the plexus of the John Warren . idl hemispheres, L. Plz., and the lateral ventricles, L. V. It shows clearly how the plexuses of the hemispheres arise from the telencephalic plexus and pass at first outward and then forward through the foramina of Munro towards the cephalic extremity of the lateral ventricles. Figs 15 is a high power drawing of Fig. 11, magnified 150 diams. The wall of the paraphysis consists of a single layer of cells with large oval nuclei, and these cells are continuous with the cells covering the choroid plexuses, but the latter are flatter and form a thinner layer. On either side of the paraphysis two large vessels are seen, ves., the epithelial cells of which lie directly against the wall of the paraphysis. The little tubules seem to be forcing their way into these vessels, which are branches of the vessels seen in Fig. 6 and Fig. 10. The vessels also pass down into the choroid plexuses. Fig. 16 is a section of an embryo of 31.4 mm. “Oy O.Ch. Fic. 16. Embryo of 31.4 mm. Harvard Embryological Collection, Sagittal Series, No. 537, Sections 119-122, * 63 diams. The general arrangement is practically the same as in Fig. 11, except that all the parts have progressed somewhat in their development. The distal end of the paraphysis has begun to grow distinctly more cephalad, and the whole structure is much larger than at 26 mm. The choroid plexuses are more extensive, and from the diencephalic plexus a prolongation is ex- tending downwards towards the telencephalic plexus. This latter has pretty well filled up the depths of the third ventricle, and from it pro- longations dip down into the recesses in the floor of the fore brain. The two commissures are practically the same as they were at 26 mm., and 12 Paraphysis and the Pineal Region in Necturus Maculatus though the epiphysis is a little larger it has been displaced considerably caudad, as this part of these sections was unluckily somewhat injured. _Fia. 17. Brain of adult necturus. Sagittal Section, * 88 diams. Fig. 17 is a section through the brain of an adult necturus. This drawing is magnified 38 diams. only, as it was too large to draw on the same scale as the preceding figures. The paraphysis, P, forms a very complex structure extending far for- ward above and between the hemis- pheres. It consists in a general way of a proximal and a distal part. The former is broad and thick, and ex- tends forward and upward. It then turns forward at quite a marked angle to form the distal part, which is narrow and.tapering. The central canal in the proximal part is very large and irregular, but in the distal! portion much narrower. From all parts of this canal a large number of tubules are given off, which extend in every direction, and _ between which lies a confused mass of blood- vessels. One sees here a large vessel ventrad to the organ, and a smaller dorsad to it, the same relations as appear at 12.4 mm., Fig. 6. From these vessels branches pass into the choroid plexuses. Fig. 18 is a transverse, section of an adult brain corresponding ap- proximately to the line A-B, Fig. 17. This is drawn on the same scale as most of the preceding figures, 63 diams. The paraphysis, P, is seen in the median lne between the hemi- spheres. It shows a distinct central cavity, with many tubules running out in every direction, between which is a mass of blood-vessels of all sizes. Below a portion of the telen- cephalic plexus and the plexus of the hemispheres are seen. John Warren 14 Paraphysis and the Pineal Region in Necturus Maculatus Fig. 19 is from a wax reconstruction of the adult paraphysis on a scale of 120 diams., made from the same series as Fig. 18. The angle between the proximal and distal parts is quite striking, and is much more marked in Ichthyophis (Burckhardt, 4, Fig. 1), but of course this division into proximal and distal parts is really a purely arbitrary one. This model gives a good idea of the complex structure of the organ. The tubules are of all shapes and sizes, often convoluted and anastomosing with each other. The spaces between them, which the vessels occupy, are quite large and striking. Fic. 19. Wax model of paraphysis of adult necturus, same series as Fig. 18, X about 120 diams. Fig. 20 represents a small portion of the paraphysis of Fig. 17, mag- nified 560 diams., and shows clearly the relation of the tubules to the vessels. In the centre of the figure is a tubule, 7, dividing into two branches, 7’, T?. Surrounding these tubules on every side are sinusoids, st., whose flat endothelial cells are seen lying directly against the epithelial wall of the tubules with no connective tissue between them. We find here in order first a sinusoid, then a tubule; then another sinusoid and another tubule, and finally a sinusoid. The wall of the tubules consists of a single layer of cells with large oval nuclei and very indistinct cell boundaries. The nuclei contain masses of granules arranged very irregu- Jokn Warren 15 larly. There can be no question about the glandular nature of the para- physis, and its circulation is evidently sinusoidal. The choroid plexus, Ch. Pla., Fig. 17, appears as a confused mass of GING * Clsiaoyeo =" 7 SDS Fic. 20. Small portion of adult paraphysis, same section as Fig. 17, X 560 diams. vessels covered by a thin layer of cells. This mass completely fills up the cavity of the fore and mid brains, and may in some cases appear in the hind brain, Fig. 23, though there seems to be considerable variation Fig. 21. Wax model of epiphysis of adult necturus. > 280 diams. in the caudad development of this part of the plexus. The two parts of the plexus overlap each other, and are also closely interlaced. The epiphysis, H, is still attached to the brain by a very narrow stalk. The body overlaps the stalk somewhat-behind, and then is prolonged forward as an oval flattened body above the roof of the diencephalon, and 16 Paraphysis and the Pineal Regign in Necturus Maculatus its cavity seems to be divided more or less into compartments. Fig. 21 represents a wax reconstruction of an adult epiphysis seen from -above. It is irregularly triangular in shape with a broad base and a blunt apex. Its surface is grooved more or less by vessels which lie against its walls. Fig. 22 is the same model with the top removed. ‘The interior is more or less subdivided by incomplete septa. At its apex there is a small cavity ‘Fic. 22. Same as Fig. 21, with top of epiphysis removed. bounded behind by a partial septum, then comes a large chamber, which divides into two passages running back towards the angles at the base. Between these two passages appears a comparatively solid area, inter- rupted, however, to some extent by small spaces, which communicate with each other and the larger chambers. This solid area lies over the stalk of the organ. The supra commissure appears to be comparatively small, D.PIx. E Fig. 23. Brain of adult necturus. Viewed from above. X 7 diams. while the posterior is large and forms a deep groove in the roof of the brain. Fig. 23 is a view of the brain of an adult necturus showing the relative positions of paraphvsis and epiphysis. The tufted extremity of the diencephalic plexus can be seen in the fourth ventricle. If Fig. 1, the embryo of 8-9 mm., is compared with Fig. 17, the adult, one sees that the paraphysal arch has been wholly taken up in the formation of the telencephalic plexus, the plexus of the hemispheres, and John Warren lye the paraphysis. The velum and the greater part of the post-velar arch have been absorbed in the formation of the diencephalic plexus. A portion of this arch, however, persists and forms that part of the roof of the diencephalon between the diencephalic plexus and the supra. com- missure. The epiphysal arch has formed the epiphysis. The paraphysis is a structure common to all vertebrates either in the adult or embryonic condition (Selenka, 34, Francotte, 11), but previous observations on mammals leave much to be desired. It always arises from the telencephalon cephalad to the velum transversum, and its opening is placed between and dorsad to the foramina of Munro as emphasized by Dexter (5). In the cyclostomes, Ammocoetes (Kupffer, 24), and Petromyzon (Burckhardt, 3), the paraphysis appears as a small sac-like diverticulum lying ventrad and close to the enlarged distal end of the epiphysis. In elasmobranchs, Minot (28) and Locy (27) found that the paraphysis in Acanthias appears at quite a late stage as a small outgrowth from the paraphysal arch and, owing to the small size of the post-velar arch and the compression of the velum, it comes to lie immediately cephalad to the epiphysis. In ganoids, Kupffer found in Accipenser that the para- physis appears first as a small outgrowth which later becomes a somewhat sacculated vesicle (23, Fig. 19). Hill (18) and Eycleshymer and Davis (9) studied the paraphysis in Amia. Here it begins as a simple vesicle, which increases rapidly in size and gives off diverticuli from its central cavity. In teleosts (Burckhardt, 3) the paraphysis appears late and remains in a rudimentary condition. In the dipnoi, Burckhardt (3) de- scribes the paraphysis in Protopterus as a wide outgrowth giving off small diverticul. ) In amphibia the organ becomes highly differentiated and its appear- ance in the adult brain is very striking. It appears as an elongated body lying above and between the hemispheres, and extending cephalad for a varying distance in various forms, Fig. 23. Osborn (31, Pl. 4) shows a view of the brains of Siredon, Necturus, Proteus, and Siren. The paraphysis has the same general form in each of these, but it is somewhat larger in Necturus. The paraphysis of Triton and Ichthyophis (Burck- hardt, 4) has the same characteristics. In the latter the paraphysis ap- pears in sagittal section as a hammer-shaped organ extending forward above the hemispheres. (4, Fig. 1). In Rana the paraphysis has the same position as in Necturus, but is smaller. On removing the top of the skull in Necturus the paraphysis is seen lying beneath the pia surrounded by the blood-vessels which cover this part of the brain. It appears to the naked eye so vascular and also in sections so intimately related to the 2 18 Paraphysis and the Pineal Region in Necturus Maculatus choroid plexus that it is not astonishing that it was at first regarded as a portion of this plexus. According to Minot (28) the paraphysis of Rana is characterized by the character of its epithelium, its tubular struc- ture and its apparently sinusoidal circulation. This is practically similar to the conditions found in Necturus. In Menopoma Sorensen (36) describes the paraphysis as a solid vas- cular mass, and in Ichthyophis Burckhardt (3) describes it as an elaborately folded structure of a glandular character. In Amblystoma, Kycleshymer (8) shows that the organ gives off tubules and has a digit- ated appearance. In Diemyctylus (Mrs. Gage, 13), in an embryo of 10 mm. the paraphysis closely resembles that of Necturus at 18 mm. (Minot, 28, Fig. 13), and in the adult it is a long tube giving off many tubules in close relation to vessels. Herrick (15) calls the paraphysis of an adult Necturus the “ pre- paraphysis ” and says it consists of an irregular central chamber with complicated diverticuli in close relation to vessels. This description corresponds closely with Fig. 17. The model of the adult paraphysis, Fig. 19, shows the complicated arrangement of the tubules, many of which anastamose with each other, and the spaces between the tubules are filled by blood-vessels. Fig. 6 shows how the paraphysis at 12.5 mm. is beginning to invade a large vessel lying over it on the surface of the brain. This vessel at this point is much enlarged. Fig. 10 shows this relation much clearer and also that these vessels in relation to the paraphysis are tributaries of the internal jugular vein. Fig. 15 shows the relation of the paraphysis to these vessels at 26 mm. and that the vessels pass into the choroid plexuses both dorsad and ventrad to the organ. The little tubules can be seen grow- ing out into the vessels. Fig. 17 shows how these relations between vessels and tubules in the adult become much more intimate, and the vessels corresponding to those in Fig. 15 are seen passing into the choroid plex- uses dorsad as well as ventrad to the paraphysis. Schdbel (33), who studied the circulation in the brain of certain amphibia, of which Necturus was one, shows that in the adult two large vessels pass outward just caudad to the hemispheres to empty eventually in the internal jugular vein. These vessels surround the paraphysis and anastomose with two or three large vessels running forward between the hemispheres. This is practically the same arrangement shown in the model in Fig. 10. He does not mention the paraphysis but refers to it as a large venous plexus. Rex (32) also has studied the veins in the amphibian brain, and his preparations are practically the same as Schobel’s. He refers to the paraphysis as the “ nodus chorioideus ” and says that it is a sort John Warren 19 of meeting point for the-veins of the fore and mid brains. He shows beautifully in his injections how veins pass both dorsad and ventrad to the paraphysis to enter the plexuses, and how closely these vessels are related to the tubules of this structure. Mrs. Gage shows practically the same arrangement in Diemyctylus As regards the arteries Schobel shows that they are much smaller than the veins, and describes a small vessel passing caudad to the hemisplieres to pass eventually into the plexuses. The intercrescence of the tubules of the adult paraphysis and the veins is shown clearly in Fig. 20, each vessel and tubule lying back to back with no connective tissue between them. In view of all these facts it seems evident that the circulation of the paraphysis is sinusoidal. According to the above descriptions, the development of the paraphysis into a complicated, glandular organ, which is also very vascular, seems to be a striking characteristic of the amphibia. In lacertilia the paraphysis of Anguis fragilis has been studied by Francotte and of Lacerta vivipara by Francotte (10, 11, 12) and Burckhardt (3). The latter shows the paraphysis in an embryo of 13 mm. as a narrow tube with a slightly expanded distal extremity, much as that of Necturus of 15 mm. Francotte describes the paraphysis of Lacerta vivipara as a long tube giving off a mass of tubules which les under the parietal eye, and resembles the epiphysis of birds (11, Fig. 14; 12, Fig. 24). In Anguis (10, Figs. 15 and 19) the paraphysis forms a long narrow sack, with somewhat convoluted walls, which curves back over the post-velar arch to end in close relation to the parietal eye. The conditions in the lizard are essentially the same (10, Fig. 31). In Phrynosoma coronata Sorensen (35, Fig. 2) describes the paraphysis as a long, narrow tube, immediately cephalad to the epiphysis. In the ophidia Leydig (26, Fig. 6) shows the paraphysis of an embryo of Vivipara urcini near birth as a large, wide tube with no convolutions or diverticul and practically the same conditons in a young “ Ringel- natter ” and Tropidonatus natrix (26, Figs. 5 and 2). Among the chelonia Voelzkow (39) has described the paraphysis in Chelone imbricata as at first a wide tube much convoluted, which later decreases somewhat in size. (Figs. 21 and 22.) Its distal end inclines caudad close to the epiphysis. In Chelone mydas Humphrey (20, Fig. 7, Pl. IL) shows the paraphysis as a long tubular structure, giving off small tubules, and in an embryo of Chelydra it appears as a large, wide sack, from which tubules arise. It is in closer relation to the epiphysis than in Chelone mydas or imbricata. In Cistudo Herrick shows a model of Sorensen (15, Fig. 5, Pl. VI) of the paraphysis, which is a wide tube with convoluted walls and tubules. 20 Paraphysis and the Pineal Region in Necturus Maculatus In the crocodilia Voelzkow (39) has described the paraphysis. of Crocodilus madagascarensis grand and Caiman niger spix. In the former the paraphysis is at first a wide tube which becomes convoluted and much longer and narrower. In the latter the paraphysis forms a larger tube and the convolutions and tubules are more complicated. In both cases the organ reaches its greatest development in embryonic life and retro- grades later, though more so in the crocodile. He was unable, however, to follow the development in the caiman as far as in the crocodile. Owing to the thickenings in the brain wall the organ is crowded some- what caudad against the post-velar arch. In birds the paraphysis is relatively rudimentary. Burckhardt (3) shows the paraphysis in an embryo of the crow as a small diverticulum not unlike that of Petromyzon. Dexter (5) worked out in detail the development of the organ in the common fowl, and showed that it ap- peared at first as a small diverticulum. The walls become much thick- ened and in a chicken of 10 days it is a small, oval structure, about 150 p in its greatest diameter, with very thick walls (5, Fig. 5). Selenka (34) has described the paraphysis in the oppossum, but as far as I am aware little is known of the development of the paraphysis in mammals, though Francotte (11) has observed it in human embryo of twelve weeks. From the cyclostomes to the amphibia the paraphysis shows a steadily progressive development, and the various forms through which it passes, from the simple diverticulum of Petromyzon to the elaborate gland of the urodela, are illustrated in a general way by the stages of its develop- ment in Necturus. In the vertebrates above the amphibia the paraphysis retrogrades and practically retraces its steps through the reptilia and birds to mammals, reaching in the chick essentially the same form in which it started in Petromyzon. Its development, therefore, may be indicated by a curve, which ascends steadily from the cyclostomes, reaches its height in urodela, and descends through the reptilia and birds to mammals. The epiphysis is present in nearly all vertebrates. It is stated to be absent in the alligator (Sorensen, 36 and 37), and in the caiman and crocodile (Voelzkow, 39) and in Torpedo (d’Erchia, 7). The epiphysis of Necturus as compared with the paraphysis is relatively poorly developed and in this respect resembles the epiphysis of other urodela (Mrs. Gage, 13). In Diemyctylus Mrs. Gage found that the epiphysis was entirely cut off from the brain and that its cavity was nearly obliterated. In Ichthyophis (Burckhardt, 1 and 4) the epiphysis is a small, pear-shaped organ attached to the brain by a narrow solid stalk. Herrick (15) in Menopoma, describes the epiphysis as an irreg- John Warren 21 ular number of vesicles attached to the brain by a narrow opening. Ac- cording to Kingsbury (21) the structure in Necturus consists of an aggregation of closed vesicles, forming an oval, flattened body, and there is no connection with the brain. The cavity of the epiphysis commun- icates through its stalk with the cavity of the diencephalon up to 15 mm., when the cavity in the stalk becomes obliterated. The stalk persists and was present in all the adult brains which I examined, but in some cases it was so small that it could easily be overlooked. The reconstruction of an adult epiphysis, Fig. 22, shows that the cavity of the organ forms a large chamber subdivided to a certain extent by incomplete septa. A much more solid area is seen towards the caudal extremity, which is placed just over the stalk. The same characteristics I have observed in another model made from a different brain. One gets the idea that the epiphysis consists of a series of vesicles in studying sagittal sections a little to one side of the median line, as for instance in Fig. 17, where the epiphysis was displaced a little to one side. . There has been such a vast amount written on the origin of the epiphysis and the pineal or parietal eye and their homologies that it seems superfluous to add anything more here. In a very general way, however, there seems to be some sort of proportion in the relative development of the paraphysis, epiphysis, and the parietal eye. In urodela where there is no parietal eye and a small epiphysis, the paraphysis reaches its highest degree of development. In those forms where the paraphysis is rudi- mentary or relatively slightly developed the parietal eye is present or else the epiphysis is relatively highly developed. Compare, for example, the figures of Burckhardt (3) of Petromyzon, Minot (28) of Acanthias, Burckhardt (3) of Trout, Leydig (26) and Voelzkow (38) of reptilia, and Dexter (5) of the fowl. Rana, however, seems to be a marked ex- ception to this statement, as there the paraphysis, epiphysis, and pineal eye are all present and well developed, and the same may be said for Lacerta (Francotte, 10 and 11) and Sphenodon (Dendy, 6). As the paraphysis and epiphysis are glandular structures they have probably some sort of compensatory function and where one is highly developed the other is relatively rudimentary or even absent. Compare in this respect also Torpedo with Acanthias and the crocodile and alligator with the chick. As a rule the stalk of the epiphysis is placed immediately caudad to the supra commissure, in all cases I believe, except in the toad, where there is a distinct interval between it and this commissure (Sorenson, 36). In Necturus there is an interval in the roof of the brain between the stalk and the posterior commissure. This portion of the roof of the brain was 22 Paraphysis and the Pineal Region in Necturus Maculatus described by Kupffer (23) as the “ schaltstiick,” and according to him it is best developed in amphibia. Burckhardt (3) maintains that it occurs in all vertebrates from Petromyzon up, but according to Kupffer it is absent in Accipenser (23, Fig. 19), and it is also wanting in Acanthias (Minot, 28, Fig. 10) and in the fowl (Dexter, 5, Fig. 9). The velum transversum is probably characteristic of all vertebrates. Minot (28). In Petromyzon the velum appears as a small transverse fold, and the post-velar arch is well marked. The plexus development is, however, very slight. In elasmobranchs the velum of Acanthias forms a long, narrow, transverse fold, and the post-velar arch is so small that the origin of the velum seems to be close to the supra commissure. The caudal layer of the velum is distinctly thinner than the cephalic (Minot, 28, Fig. 6). This is also seen in Torpedo (d’Erchia, 7, Fig. 12), and in Necturus, Fig. 6. The velum later on has the character of a choroid plexus, but the plexus of the hemispheres is very rudimentary (Minot, 28). In Notidanus Burckhardt (3) shows a long, narrow velum, a short post-velar arch, and a small telencephalic plexus. The plexus of the hemispheres, however, is absent. In Accipenser (Kupffer, 23, Fig. 19) the velum is long, well developed and folded to a certain extent, and the post-velar arch is quite extensive. In ganoids (Studnicka, 38) the membranous roof of the brain serves as the tela choroidea of higher types. In this class of vertebrates according to Burckhardt (3) the plexus of the hemispheres is lacking, but the telencephalic plexus is well developed, and in teleosts the former is also wanting, but the latter present in a reduced form. In amphibia all the plexuses are highly developed, and in Necturus they are of marked extent (Kingsbury, 21). The velum in Necturus appears at first as a transverse fold in the roof of the brain separating the diencephalon from the telencephalon. This fold develops at first ventrad and then caudad through the mid brain as far as the hind brain. This great growth of the velum forms the diencephalic plexus. The post-velar arch, which at first is wide and well marked, is practically absorbed by the overgrowth of the velum, and a small portion only persists in the roof of the diencephalon between the origin of the dien- cephalic plexus and the supra commissure, Fig. 17. The telencephalic plexus develops from the paraphysal arch immediately cephalad to the paraphysis, the opening of which therefore is surrounded by these two plexuses. They fill up the cavity of the third ventricle and mid brain, and the diencephalic plexus may appear in the hind brain (Osborn, 29). This seems to vary in different cases, and in the majority of brains which I was able to examine the extremity of this plexus did not actually extend John Warren 23 into the hind brain. In Fig. 23, however, this extremity appears as a marked tuft in the fourth ventricle. ‘The plexuses of the hemispheres arise on either side from the origin of the telencephalic plexus and pass into the lateral ventricles, extending nearly to their cephalic extremities. In Lacerta vivipara (Francotte, 12, Fig. 24) the post-velar arch has beén much compressed from before backward so as to form a deep narrow angle. At the apex of the angle the folds of the diencephalic plexus are seen. The velum is smooth and apparently is not included in the formation of the plexus. In Anguis fragilis (Francotte, 10, Figs. 19 and 15), the post-velar arch does not seem to be so much compressed, and the plexus formation somewhat greater. As he says, however, the development of those parts in Lacerta is practically the same as in Anguis. According to Burckhardt the telencephalic plexus is much reduced in size, consisting merely of small folds, but the plexus of the hemis- pheres is well developed (Burckhardt, 3). In the turtles Humphrey (20) found that the velum of Chelydra is but slightly developed, and no diencephalic plexus is formed. All the other plexuses are telencephalic in origin. Herrick (15, Fig. 5, Pl. VI), shows in Cistudo a well-developed telen- cephalic plexus and a diencephalic plexus represented by many folds in the caudal layer of the velum and the post-velar arch. In Chelone im- bricata Voelzkow (39, Figs. 19 and 22) shows at first a well marked velum and a wide post-velar arch. In later stages the velum and prac- tically all the arch are thrown into folds to form the diencephalic plexus. The telencephalic plexus is also well developed. In the serpents much the same arrangement can be seen. The velum (Leydig, 26, Figs. 2, 5, and 6) forms a prominent fold, and it and the post-velar arch form a very vascular plexus. In the crocodilia (Voelzkow, 39, Figs. 7, 11, 18, 15), the velum and the post-velar arch are at first well marked, but the parts later become so compressed from before back- ward that the arch forms a deep acute angle in the depths of which plexus foldings are seen. ‘The caudal layers of the velum, however, takes no part in the plexus formation. In birds, Dexter (5) found that the velum of the fowl is small and the post-velar arch broad at first. This becomes compressed so as to form an acute angle much as in the crocodilia. The cephalic limb of this angle and all the velum is converted into the choroid plexus. In birds the plexus of the hemispheres is very well developed, but the telencephalic plexus is practically absent. In fishes the plexus development is quite simple, in many cases being merely the thin membranous roof of the third ventricle; in others, how- ever, this is much folded and vascular (Sorensen, 35). In certain forms 24 Paraphysis and the Pineal Region in Necturus Maculatus there is a telencephalic plexus, but the plexus of the hemispheres is absent or rudimentary (Burckhardt, 3). In amphibia there is a great overgrowth of all the plexuses, especially of the diencephalic plexus, which here reaches its highest development. In reptilia the plexus of the hemispheres is well developed, but the telencephalic plexus is reduced in size (Burckhardt, 3), and the diencephalic much more so. In birds the plexus of the hemispheres is highly developed, the telencephalic plexus practically absent, and the diencephalic plexus, while very similar to that of reptilia, approaches nearer to the tela choroidea of higher mammalia. Osborn first named the supra-commissure and worked out its homol- ogies. According to him (30) the urodela are distinguished from the anura by the frequent extensive development of this commissure, which is large in Amphiuma, smaller in Necturus, and much reduced in Rana. It appears in Necturus a little later than the posterior commissure, as is usual in most cases, as far as I am aware, except in Ammocoetes, where it appears shortly before the posterior commissure (Kupffer, 24, Fig. 5). It is found in all the chief types of vertebrates, and is usually smaller than the posterior (Minot, 28). It is developed from the diencephalon, while the posterior belongs to the cephalic limit of the mid brain. CONCLUSIONS. 1. The paraphysis appears first in an embryo of 12 mm. It is de- veloped from the telencephalon immediately cephalad to the velum trans- versum as a small diverticulum, which becomes eventually a complicated gland with anastomosing tubules. The gland is very vascular, and has a sinusoidal circulation. 2. The epiphysis appears first in an embryo of 9-10 mm., and is de- veloped from the diencephalon. It is always attached to the brain by a small solid stalk, and the cavity is partially subdivided by incomplete septa. 3. The velum transversum grows at first ventrad and then caudad as far as the hind brain, forming in this way the diencephalic portion of the choroid plexus. The post-velar arch, which is at first quite extensive, is almost entirely absorbed in this extensive growth of the yelum. 4. The telencephalic plexus arises from the roof of the telencephalon, and fills up the depths of the cavity of the third ventricle. The opening of the paraphysis is surrounded by these two plexuses. 5. The plexus of the hemispheres arises at a right angle from the telencephalic plexus just cephalad and ventrad to the opening of the paraphysis. | John Warren 25 6. The supra-commissure appears first at 16-17 mm. It lies imme- diately cephalad to the stalk of the epiphysis and is comparatively small. 7. The posterior commissure appears first at 15 mm., and there is a marked interval in the roof of the diencephalon between it and the epiphysis. I wish in conclusion to express my acknowledgments to Prof. Minot for his kind advise and interest in the preparation of this article. BIBLIOGRAPHY. The following are the principal articles consulted, but of course do not form a complete bibliography of this subject: 1. BurcKHARDT, R.—Die Zirbel von Ichthyophis Glutinosus und Protopterus Annectens. Anat. Anz., Bd. VI. 2. Die Homologien des Zwischenhirndaches bei Reptilien und Vogeln. Anat. Anz., Bd. IX, 320-324. 3: Der Bauplan des Wirbeltiergehirns. Morpholog. Arbeiten, IV Bale Heft. d3ie 4. Untersuchungen am Gehirn und Geruchsorgan von Triton und Ichthyophis. Zeitschr. f. Wiss. Zoologie, Bd. 52. 5. Dexter, F.—The Development of the Paraphysis in the Common Fowl. American Journ. Anat., Vol. II, No. 1, 13-24. 6. DENpy, A.—On the Development of the Pineal Eye and Adjacent Organs in Sphenodon (Hatteria). Quart. Journal Micros. Soc., Vol. 42, 111. 7. D’Ercuis, F.—Contributo allo studio della volta del cervello intermedio e della regione parafisaria in embrioni di Pesci e di Mammiferi. Monitore Zoologico, VII, 118 e 201. 8. EYCLESHYMER, A. C.—Paraphysis and Epiphysis in Amblystoma. Anat. Anz., Bd. VII. 9. EYCLESHYMER, A. C., and Davis, B. M.—The Early Development of the Paraphysis and Epiphysis in Amia. Journal of Comp. Neurology, Vole t. 10. FRANcoTTE, P.—Récherches sur le dévéloppement de L’épiphyse. Arch. de biologie, T. VIII. ile Note sur lil parietal, l’épiphyse, la paraphyse et les plexus choroides du troisiéme Ventricule.' Bull. de l’acad. royale, ete., d. Belg., 3 Serie, T. 27. 12. Contribution 4 l'étude de l’e@il parietal, de l’épiphyse chez les Lacertiliens. 13. Gace, 8S. P.—The Brain of Diemyctylus Viridescens. Wilder Quart. Cent. Book, 1898. 14. Gaupp, E.—Zirbel, Parietalorgan und Paraphysis. Ergebn. Anat. Entwick.- Ges., VII, 208-285. 15. Herrick, C. L.—Topography and Histology of the Brain of certain Rep- tiles. Journ. of Comp. Neurology, Vol. I, 37; Vol. III, 77-104, 119-138. Topography and Histology of certain Ganoid Fishes. Journ. of Comp. Neurology, Vol. I, 162. 16. 28. 29. Paraphysis and the Pineal Region in Necturus Maculatus . Herrick, C. L.—Embryological Notes on the Brain of a Snake. Journ. Neurology, Vol. I, 160-176. . Hix, C. L.—The Epiphysis in Teleosts and Amia. Journ. of Morphology. Vol. IX, 237-268. . His, W.—Zur allgemeinen Morphologie des Gehirns. His. Archiv, 1892, 346-383. . Humpurey, O. D.—On the Brain of the Snapping Turtle. Journ. of Comp. Neurology, Vol. IV, 73-108. . Kayessury, B. F.—The Brain of Necturus Maculatus. Journ. of Comp. Neurology, Vol. V. The Encephalic Evaginations in Ganoids. Journ. of Comp. Neu- rology, Vol. VII. . KUPFFER, C. vy.—Studien zur vergleichenden Entwicklungsgeschichte des Kopfes der Kranioten. Hefte I. Derselbe. Hefte II. . Lewis, F. T.—The Question of Sinusoids. Anat. Anx., Bd. XXV, No. 11. . Lrypie, F.—Zirbel und Jacobsonsche Organe einiger Reptilien. Archiv f. Mikrosk. Anatomie, Bd. 50. . Locy, W. A.—Contribution to the Structure of the Vertebrate Head. Journ. of Morphology, XI. Minot, C. S.—On the Morphology of the Pineal Region, based on its Development in Acanthias. American Journ. of Anatomy, Vol. I, No. 1, 81-98. On a Hitherto Unrecognized Form of Blood Circulation without Capillaries in Organs of Vertebrates. Pro. Boston Soc. Nat. Hist., Vol. 29, No. 10, S. 185-215. . OsBorN, H. F.—Preliminary Observations on the Brain of Menopoma. Proceed. Phil. Acad., 1884. Contribution to the Internal Structure of the Amphibian Brain. Journ. of Morphology, Vol. II, 51-86. . Rex, H.—Beitrage zur Morphologie der Hirnvenen der Amphibien. Morph. Jahrb., XIX, 295-311. . SCHOBEL, Jos.—Ueber die Blutgefaésse des Cerebrospinalen Nervensystems der Urodelen. Archiv f. Wissen. Mikros., Bd. XX, 87-91. . SELENKA, E.—Das Stirnorgan der Wirbelthiere. Biolog. Centralbl., Bd. X, 323-326. . SORENSEN, A. D.—The Roof of the Diencephalon. Journ. of Comp. Neu- rology, III, 50-58. Comparative Study of the Epiphysis and the Roof of the Dien- cephalon. Journal Comp. Neurology, IV, 153-170. Continuation of above. Vol. IV, 153-170. . STUDENICKA, F. Cu.—Beitrage zur Anatomie und Entwicklungsgeschichte des Vorderhirns der Cranioten. . VOELZKOow, A.—Epiphysis und Paraphysis bei Krokodilien und Schild- kréten. Abhand. der Senchenburgischen Naturforschenden Gesell- schaft, Bd. XX VII, Heft. II. John Warren route - ABBREVIATIONS. A. @—Anterior commissure. Ch. Pla.—Choroid plexus. Dien—Diencephalon. D. Plex.—Diencephalic plexus. E.—Epipbhysis. Ep. A.—Epiphysal arch. F. B.—Fore-brain. F.M.—Foramen of Munro. ° H.—Hemisphere. H. B.—Hind brain. Hyp.—Hypophysis. I. J. V—tInternal jugular vein. L. Pla.—Choroid plexus of lateral ventricle. L. V.—Laterai ventricle. M. B.—Mid-brain. O. C.—Optic commissure. Tel. Pla.—Telencephalic plexus. Tel.—Telencephalon. P. G.—Posterior commissure. P. V. A.—Post-velar arch. f P. A.—Paraphysal arch. P.—Parapbhysis. S. ¢.—Superior commissure. Si.—Sinusoid. T.—Tubule. Ves.—Vessel. V.—vVelum transversum. THE DEVELOPMENT OF THE THYMUS. BY EE. T. BELL; B:.S:;, M.D: Instructor in Anatomy, University of Missouri. With 3 PLATES AND 5 TEXT FIGURES. This paper is intended mainly as a contribution to our knowledge of the histogenesis of the thymus in mammals. Special attention is given to the origin and development of the corpuscles of Hassall, since their mode of formation has never been satisfactorily described in mammals and their significance in all forms is in dispute. An attempt is also made to show in detail the changes that occur during the transformation of the thymus from the epithelial to the lymphoid condition. This work was begun at the suggestion of Dr. D. D. Lewis at the University of Chicago. The greater part of it has been done at the University of Missouri. Special acknowledgments are due Dr. C. M. Jackson for valuable criticism and suggestions. I wish also to thank Mr. Charles H. Miller of the University of Chicago for his kindness in sending me material. MATERIAL AND METHODS. As material for the greater part of my work, I have used pig embryos from 8 mm. to full term (26 cm. to 30 cm.). These are especially suit- able for such work since they may be procured in abundance from the large packing houses at almost any stage of development. For special purposes I have studied a few specimens from human foetuses, and from the cat, rat, and guinea pig. The smaller pigs used (8 mm. to 27 mm. ") belong to the collection in the anatomical laboratory at the University of Missouri. These were stained in bulk with alum-cochineal and mounted in serial sections. In the later stages, which were prepared specially for this work, the ventral half of the cervical and anterior thoracic regions was usually cut out and embedded from pigs from 3 cm. to 8 em. On specimens from 8 cm. to 30 cm., I dissected out the thymus and used such parts as were desired. 1The crown-rump measurement is used in all cases. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 30 The Development of the '’hymus All pig material was fixed in Zenker’s fluid, embedded in paraffin, and mounted in serial sections from 3» to 10 thick. Except those of the young stages (8 mm. to 27 mm.) the sections were stained on the slide. Most of them were stained with hematoxylin or iron-hematoxylin and counterstained with Congo red. For special purposes many other stains were used. To demonstrate the delicate protoplasmic threads of the syncytium during the later stages of the lymphoid transformation, I stained by the iron-hematoxylin method but omitted the final decolorization in iron- alum. Protoplasm is stained deep black; nuclear structure is poorly shown, but the finest cytoplasmic processes may be seen. For the demonstration of connective tissue fibrille in the syncytium, I found the method recommended by Jackson (13, 8. 39) most satis- factory. e¢. Midis, LMie'5 | Ik Abioy-Ge UE 2. Text Figure 1. Cranial view of third gill pouch (thymic anlage); X 38; pig embryo, 11 mm.; ec, ectoderm; 7, lumen; nt, nodulus thymicus; ph, con- nection to pharynx; sp, sinus precervicalis. TEXT FIGURE 2. Ventral view of thymic anlage; X 33; pig embryo, 15 mm.; ec, ectoderm; 7, lumen; nt, nodulus thymicus; ph, connection to pharynx; Sp, Sinus precervicalis. To determine the relation of the blood-vessels to the corpuscles of Hassall, I put a young kitten under deep anesthesia and injected a large quantity of a strong aqueous solution of Prussian blue into the aorta through the common carotid artery. ‘The heart continues to beat even after an amount of fluid twice as great as the total volume of the blood has been injected. An injection made in this way is under a slightly increased blood pressure and easily reaches the finest capillaries. There is therefore a thorough injection with little danger of rupturing delicate blood-vessels. ORGANOGENESIS. My observations on this phase of development are not sufficiently com- plete to warrant a full discussion. This term will be used to include those changes that occur in the thymus during its passage from an epithelial to a characteristic lymphoid structure. HE. T. Bell 37 be an accumulation of small round nuclei. At about the same period blood-vessels and connective tissue grow into the epithelial anlage.” His (12 b), 80, and Stieda (26), 81, claimed that the corpuscles of Hassall are the only remnants of the epithelial anlage, that the lymph- ocytes, reticulum, ete., are of mesenchymal origin. Maurer (17 a), 86, described the leucocytes as arising directly from the cells of the epithelial anlage in the thymus of teleosts. In the amphibian thymus (17 b), 88, he thinks that the leucocytes are probably of mesen- chymal origin. He was unwilling to conclude that they arose from the epithelium because he could not find transition forms. In lizards (17 ¢), 99, he records that even before the separation of the epithelial anlage of the thymus from the pharynx, changes begin. The peripheral cells are closely crowded together and show many mitoses. There arises between the central cells, or is formed in vacuoles in their protoplasm, a fluid which accumulates until the nuclei surrounded by a thin zone of protoplasm are connected only by protoplasmic threads. A loose medulla is thus formed which looks lke a cellular reticulum. The cortex is still sohd. The lymphocytes are formed from the epithelial cells; none come from with- out. Later, blood-vessels and connective tissue grow in. He believes that the reticulum is of mesenchymal origin in all forms. Maurer (17 d), 02, still holds that in amphibians the lymphocytes are probably of mesenchymal origin. Hermann et Tourneux (11), 87, find that in man and other mammals the epithelial anlage of the thymus is gradually converted into leucocytes and reticulum cells. Vacuoles appear during the transformation which seem to be formed by the absorption of large cells. In a sheep embryo of 130 mm., the clear epithelial cells have all disappeared, giving rise to small round cells and reticulum cells. Prolongations of connective tissue, each containing a blood-vessel, grow into the anlage during the transformation. They are not sure that all the thymic elements are epithelial in origin, being especially in doubt about the origin of some of the reticulum cells. Gulland (8), 91, describes the development of the tonsil in the rabbit. Leucocytes first appear in the connective tissue around the thymus. Later they appear in the connective tissue around the tonsil. They infiltrate the tonsillar epithelium. No leucocytes are of epithelial origin. After studying the tonsil he examined the thymus in a few specimens and concluded that the same process of leucocyte infiltration occurred there. He does not give the details of their infiltration, and did not see any of the transition forms of nuclei in the thymus at that period. Prenant (22), 94, made a careful study of the development of the 1S) ioe) The Development of the Thymus thymus in sheep embryos. His results are as follows. At 25 mm. the gland is composed of distinct polyhedral cells with nuclei of only one kind. A few mitoses and an occasional direct division are to be seen. At 26 mm. mitoses are numerous (ore nucleus in fifty). Nuclei are reg- wlarly rounded or elliptical and some small nuclei occur juxtaposed to large nuclei. At 28 mm. many mitoses are present and irregular spaces have appeared. ‘These spaces are not blood-vessels nor parts of the thymie duct but vacuoles. Some nuclei, noticeably small and darkly colored, lie close to the large, clear nuclei and seem to be budded off from them. Some nuclei (rare) are broken into three or four chromatic bodies. Embryos of 40 mm. have undergone in great part the lymphoid transformation. All transitions are found between the large, pale ellip- tical nuclei of clear reticular structure and the small, deeply colored rounded nuclei whose sap is strongly stained. These last are certainly lymphocytes and constitute an immense majority of the cellular elements. Large, clear nuclei are found joined to small dark ones—nuclear couples. At 85 mm. the medulla appears; the cortex corresponds to the entire’ thymic mass of preceding stages. The cortex contains a great many lymphocytes separated by islands and rows of pale nuclei. There are about thirty lymphocytes to one pale nucleus. Mitoses are numerous in the cortex. In the medulla at this stage, the large clear, and small dark, nuclei are about equal in number, and mitoses are rarer than in the ‘cortex. In later embryonic stages a clear peripheral zone is present where cell proliferation takes place. Mitoses are now more numerous in the medulla than in the cortex. It is probable that a certain number of the epithelial cells persist as reticulum cells in the fully-formed organ. J. Beard (3 a), 94, (3 b), gg, thinks that the function of the thymus is to form the first leucocytes. He finds that in the skate the epithelial cells are converted early into lymphocytes which emigrate into the blood. There are many breaks in the gland where the lymphocytes escape in masses. The thymus is the only source of leucocytes until the other lymphoid organs are formed. Ver Eecke (28), 99, finds that in the frog the epithehal thymus is invaded by lymphocytes and connective tissue. The epithelial cells are not destroyed but merely dispersed by the mesenchymal elements. He alls the resulting tissue lympho-epithelial. This idea of the comming- ling of the two tissues had already been advanced by Retterer. Nusbaum and Prymak (20), or, on teleosts, agree with Maurer that the lymphocytes are of epithelial origin but disagree on the details of their formation. They find that the epithelial anlage is at first composed of cells with distinct boundaries. It is not different from the epithelium Be cS Bell 39 of the pharynx. Before any blood-vessels or connective tissue have in- vaded the organ, changes begin in.the central part. These changes con- sist in the breaking up of the cytoplasm so that the cells become branched and connected by delicate processes. These processes finally break apart leaving a nucleus surrounded by a thin layer of protoplasm— a lymphocyte. The peripheral epithelial layer multiplies rapidly, forming nuclei somewhat smaller and darker than their own. These nuclei be- come gradually changed into the nuclei of lymphocytes and break away from the other cells. All transitions are present between the large, clear epithelial nuclei and the lymphocytes. Blood-vessels and connective tissue grow in from the outside. It appears from a survey of the literature that, of those who have studied the origin of lymphocytes in the mamalian thymus, His, Stieda, and Gulland have advocated the idea that they invade the gland from without, and that the original epithelial anlage persists only as remnants, the corpuscles of Hassall. They also consider the stroma of mesenchymal origin. On the other hand, Kolliker, Hermann and Tourneux, and Pren- ant, have described the lymphocytes as derived directly from the epithelial cells of the anlage. Hermann and Tourneux and Prenant ascribed a similar origin to part of the reticulum. Neither His, Stieda, nor Gulland made a detailed histological study of the changes that take place in the thymus during the transformation. They did not see the vacuolization of the cytoplasm, the changes in the epithelial nuclei, ete.—processes which undoubtedly occur. Gulland made nearly all his observations on the tonsil and then from a superficial examination of the thymus concluded that the process is the same there. The conclusions of these men are therefore not to be compared on this point with those obtained by the thorough and careful work of Prenant. On amphibians, Maurer hesitatingly agrees with His, and Ver Hecke accepts the mesenchymal origin of the leucocytes; while on fishes Maurer, Beard, and Nusbaum and Prymak believe in the epithelial origin of lymphocytes. Maurer’s work on reptiles is in agreement with his work on teleosts. As to the origin of leucocytes in the lymphoid organs of the alimentary canal, opinion is divided. Retterer, v. Davidoff, Rudinger, Klaatsch, and others have described the leucocytes as arising from epithelium and being invaded by mesenchymal elements forming adenoid tissue. Stohr, Gulland, Tomarkin, and others describe them as penetrating the epithe- ~ lum from without. I shall now discuss my own observations on the lymphoid transform- ation in the thymus of the pig. From a very early stage (11 mm.), the 40 The Development of the Thymus epithelium of the third gill pouch is a syneytium. No cell boundaries exist. The nuclei, large and irregular in shape, are embedded in a com- mon mass of cytoplasm. In the thymus at 20 mm. I find a syncytium of dense cytoplasm embedded in which are large nuclei of irregular shape and size. No distinct types of nuclei are present yet; all stain with medium intensity. A few mitoses are to be seen. In a section of the mid-cervical segment at 3.7 cm. (Plate I, Fig. 1), I find evidence that the lymphoid transformation has begun. The syn- cytium is composed of coarsely reticulated cytoplasm much looser in texture than that of the preceding stage. It contains a few irregular spaces (s s) which are evidently of the nature of vacuoles. These may be formed, as Maurer suggests, by liquefaction of the cytoplasm. There is no reason to suppose that cells degenerate and form them as Hermann and Tourneux believed. Three types of nuclei may be distinguished ; large pale nuclei (/ pn) large dark nuclei (J dn), and small dark nuclei (lymphoblasts) (db). Transition forms occur between these types. The large dark nuclei are intermediate forms between the pale nuclei and the lymphoblasts. A few mitoses (m) occur. No blood-vessels are present inside the anlage but they may be seen between the buds just outside. At this stage, the head and the thoracic segment have areas that are somewhat farther advanced than this. The intermediary and cervico-thoracic cords show no changes. At a later stage than the above (Plate I, Fig. 2), in the thoracic segment of a 4.5-cm. pig, «he spaces of the syncytium (s s) have in- creased greatly in number and size. The anlage is now a cellular retic- ulum. The large pale nuclei are somewhat less numerous than the dark nuclei and many have become angular, adapting themselves to the nodes of the syncytium. They contain less chromatin than in the preceding stage. Large dark nuclei and lymphoblasts are present; the lymphoblasts are much more numerous than in the preceding stage. A very few small dark nuclei are completely separated from the syncytium. These are lymphocytes. There are no lymphocytes in the connective tissue around the thymus or in the blood at this stage. I did not examine the tonsil or spleen at any stage. A few small blood-vessels are to be seen; their walls consist of endothelium only. There are more mitoses than at the preceding stage, but none happened to be present in the area shown in the figure. During mitosis, at all stages of develop- ment, except the early epithelial condition, the chromosomes are so closely packed that it is very difficult to distinguish them individually. In a section through the mid-cervical segment of a 7-cm. pig (Plate I, Fig. 5), we see a stage somewhat later than the one shown in EH. T. Bell 41 Fig. 2. In various parts of the section lymphocytes (/) are completely formed. The great majority of the small round nuclei are in the lympho- blast (Jb) condition, i. e., they are not yet completely separated from the syncytium. There are a few lymphocytes outside the thymus in the interlobular tissue in this region; around the head and the thoracic segment at 7 cm. they are numerous, these parts being in a later stage of transformation. I have never seen lymphocytes outside the thymus, ' where there were none inside it; but they appear outside shortly after they are formed here. Those formed next the interlobular septa seem to pass out very early. Of course the lymphoblasts, which are distinguishable from the lymphocytes only by being imbedded in the syncytium, are to be seen in the thymus long before any appear outside. At the stage shown in Fig. 5, a great many nuclei are in mitosis. [ have not seen at any stage, the amitoses and nuclear couples described by Prenant for the sheep. In some parts of the section comparatively large solid epithelial areas occur. These are found as often in the central as in the peripheral part. Many of the pale nuclei are smaller than those shown in Fig. 2. The blood-vessels are somewhat larger and more numerous than those at 4.5 cm. It is to be noted that the epithelial anlage does not at any stage become converted entirely into small round cells as many observers have stated. Distinctly pale angular reticular nuclei can always be seen. In the mid-cervical segment at 8.5 em. (Plate I, Fig. 4), a great many lymphocytes (/) are formed. These lie between the persisting epithelial cells which are now arranged in irregular cords and islands. In these epithelial masses, lymphoblasts may still be seen indicating that the formation of lymphocytes is still in progress. Many of the pale nuclei are now small. The heavy hematoxylin stain in this case makes the nuclei darker than they would appear with an ordinary stain. A few nuclei are in mitosis. This figure shows also the first appearance of the medulla (md). The medulla is formed directly, as shown in the figure, from persisting parts of the epithelial syncytium. Certain centrally situated masses of this syncytium undergo changes of such a nature that they stain readily with cytoplasmic stains such as Congo red. Im sections stained with hema- toxylin and Congo red, the medulla is first recognized as a_ brightly colored area situated usually about the center of the lobule. These epithelial masses that give rise to the medulla seem to increase in size about the time of the change in staining capacity. The first differenti- ation of the medulla is chemical rather‘than morphological, for there are other persisting epithelial masses even larger than it in the same section 42 The Development of the Thymus that do not react in the same way with the cytoplasmic stains. The medulla appears in the head and the thoracic segment at 7.5 em. to 8 cm. All the gland except this small central area forms the cortex. Blood- vessels now reach all parts of the gland, but are still few in number. I cannot distinguish any wall except the endothelium on those actually inside the gland. In a 9.5-em. pig, the medulla is larger. It contains pale nuclei of various sizes, large dark nuclei, and lymphoblasts. Its spaces are smaller than those of the cortex. The early stages in the formation of the cor- puscles of Hassall appear as soon as the medulla begins to form. The epithelial cords in the cortex have become less conspicuous, but are still forming lymphocytes. A few nuclei are in mitosis. Many blood cap- illaries may now be seen penetrating the gland from the periphery. These vessels run in the epithelial masses and have a wall of large endothelial cells which gives them the appearance of radiating cords. When these vessels first appear, as at this stage, they have only an endothelial wall. The blood-vessels grow in as small capillaries which, after their entrance, increase in size and branch; they do not break in as large vessels surrounded by mesenchymal tissue. I am fairly sure that aside from the endothelial cells few or no mesenchymal cells come into the thymus. Around the greater part of the periphery of the gland is a solid zone of syncytium two or three nuclei deep which is in trans- formation like the epithelial cords inside. This zone, described by Pren- ant as a zone of proliferation, grows rapidly, as the frequent mitoses indicate. Its inner boundary is forming lymphocytes and reticulum cells. In a 14-em. pig, the lymphoid transformation is practically at an end except in the medulla. The peripheral zone of proliferation has dis- appeared. The cortex has about the same structure as at 24 cm., as previously described. In the medulla, lymphoblasts, large pale nuclei, and the large dark intermediate types are still present. ‘There are a few mitoses here. It is very probable therefore that the formation of lym- phocytes is still in progress in the medulla. The medulla at 24 cm. shows a similar structure except that there are fewer lymphoblasts. These facts persuade me to regard the medulla as a center for lymphocyte formation at least as late as birth. Connective tissue fibrillee begin to appear in the gland along the large blood-vessels and the interlobular septa as early as 10.5 cm. They are only a little farther in at 16 cm.; but near full term they are present in nearly all parts of the stroma. (See Plate I, Fig. 6.) The above account may be summarized as follows: In the pig the epithelial syneytium of the thymic anlage becomes loosened up by the hh. T. Bell 43 formation of vacuoles in it. These vacuoles increase in number and size, converting the anlage into a cellular reticulum. While this vacuoli- zation is in progress, the nuclei, which at first are of one kind with a medium amount of chromatin, differentiate into large clear, large dark, and small dark (lymphoblast) forms. The large dark nuclei probably divide by mitosis and form the lymphoblasts. The lymphoblasts grad- ually break loose from the syncytium, passing into its spaces and becoming lymphocytes. Shortly after lymphocytes begin to be formed, some of them pass out of the gland into the surrounding connective tissue. The lymphoid transformation begins in embryos of 2.5 cm. to 3 cm. and con- tinues in the cortex until 12 cm. or 13 em. In the medulla it is not com- plete at birth. Since the thymus increases greatly in size during this period the epithelial syncytium must grow rapidly. Lymphocytes are constantly being formed at the expense of the growing syncytium. A peripheral zone of proliferation is present from about 8 cm. to 12 em. The medulla is formed as a chemical differentiation of certain centrally situated areas of the epithelial syncytium. ‘The histological changes occur earlier in the head and thoracic segment than in the mid-cervical segment and very much earlier than in the cords. The reticulum of both cortex and medulla is practically all of epithelial origin. Some branched cells around the blood-vessels in the cortex may be of mesenchymal origin. My reasons for regarding the lymphocytes as of epithelial origin are as follows: A. The lymphoblasts are true epithelial nuclei, because (1) there are numerous transition forms between them and the large dark nuclei which later cannot be regarded as invading lymphocytes; (2) they are closely embedded in the syncytium and show no evidence of having eaten their way through the protoplasm; (3) they are present from a very early stage and increase in number as development proceeds; (4) they are present before blood-vessels invade the gland and have no constant rela- tion to blood-vessels or to the surface of the gland that indicates an inva- sion from either of these directions; (5) they are present before lympho- cytes appear in the connective-tissue around the thymus. B. Some observers admit that the small dark nuclei (lvmphoblasts) are of epithelial origin but do not admit that they form lymphocytes. The considerations that lead me to believe that the lymphoblasts do form the lymphocytes are: (1) the small dark nuclei (lymphoblasts) show every possible relation to the syneytium from being completely embedded in it to lying free in the syncytial spaces. A comparison with later stages shows that this appearance is not due to poor fixation or to the an The Development of the Thymus adherence of the nuclei to the reticulum; (2) the first free nuclei often appear in the center of the gland when there are no other free nuclei in the periphery at that level; (3) there is good evidence that lymphocytes emigrate from the thymus in large numbers. If we examine the thymus of a 7-em. pig in serial sections we find that the lymphoid transformation is less advanced in the mid-cervical segment than in the head. In the mid-cervical segment there are a few lymphocytes in the interlobular tissue. In the lower end of the head where there are more lymphocytes inside the gland, lymphocytes pack the interlobular tissue and form a thin zone around the periphery of the gland. In the middle of the head where the transformation is far advanced, lymphocytes pack the inter- lobular tissue and form a thick zone around the entire gland. Indeed, in some sections, there are more lymphocytes in the zone outside than are present inside the gland. If this zone of lymphocytes be passing into the gland, it is not easy to understand why it is formed from within out- wards, and why it is thickest where the greatest number of lymphocytes are already present inside. No satisfactory suggestion has yet been made as to why lymphocytes should thus suddenly pour into the thymus at a time when if present at all elsewhere they are rare. They do not come to break up the thymic epithelium, for that is already a reticulum before free cells are present (Fig. 2, Plate I). Where lymphocytes invade intestinal epithelium as in the tonsil they eat paths through it leaving spaces. The epithelial reticulum of the thymus is not formed in that way. On the other hand it is not difficult to believe that this zone of lymphocytes is formed by cells passing out the periphery of the thymus and that the gland thus contributes a great number of lymphocytes to the organism ; (4) I have not been able to find lymphocytes in the connective- tissue around the thymus before they are present inside. An invasion by way of the blood-vessels may be excluded, since the thick zone of lympho- cytes formed around the gland shows that these cells either enter or leave it through the preiphery. THE CORPUSCLES OF HASSALL. These bodies were first mentioned by Hassall (10) in 46. He speaks of them as being composed of mother cells which enclose the newly- formed daughter cells and nuclei. He thought the central mass was formed by the outer enclosing layers. He found bodies which he regarded of the same nature in fibrous coagulations in the heart. Virchow (29), 51, in a discussion of endogenous cell formation, com- pares Hassall’s corpuscles to carcinoma pearls. He had about the same HB. T. Bell 45 conception of the nature of the corpuscles as Hassall. ‘This oft-quoted comparison was therefore not based upon a deep insight into their nature. Ginzburg (9), 57, did not advance beyond Hassall’s conception that the central mass is formed by the peripheral layers. Paulitzky (21), 63, described the center of the corpuscles as homogen- eous or granular. They sometimes contain an elliptical nucleus, some- times fat droplets. The larger ones have in the center several nuclei’ or cell-like forms. The central part is formed from masses of epithelial cells. Connective tissue cells grow around them and are transformed into epithelial cells forming the peripheral part of the corpuscle. The term “ concentric corpuscles ” was introduced by Ecker (6), who described them as arising directly from gland cells by fatty meta- morphosis. He distinguished (1) simple corpuscles, round vesicles with thick concentric hulls, containing inside a fatty opalescent mass, and (2) compound corpuscles, which consist of several vesicles with a common hull. The peripheral layers of a corpuscle consist of flattened cells. His (12 a, 12 b), 60, 80, described the corpuscles as consisting of an outer striated shell, probably composed of nucleated cells, and contain- ing lymphocyte-like cells inside. He supposed them to be the original cells of the epithelial anlage which become entangled in the reticulum in some way. Their rapid growth in their narrow confines causes the con- centric form. Ei Cornil et Ranvier (5), 69, considered the corpuscles as arising from the endothelium of blood-vessels and compared them to the spheres of their “Sarcome angiolithique.” This suggestion of a vascular origin, made by Cornil et Ranvier, was elaborated by Afanassiew (1a), 77. Afanassiew held that the corpuscles of Hassall arise from the endo- thelium of the smaller veins and capillaries. The endothelial cells in- crease in size, become cubical, and later fill the lumen of the vessel. During the proliferation of the endothelium, the blood-vessels break up into segments which are now nearly solid cords. These cords are at first connected to each other and to blood-vessels, but they soon break apart. The surest proof that the corpuscles are of vascular origin is that ery- throcytes may be found inside them. Vascular injections, however, do not go into a corpuscle except in a very early stage, since the lumen is soon obliterated by the endothelial plugs. The corpuscles are formed entirely by the endothelial cells. Afanassiew worked on embryos of man, the rabbit, and the calf. Stieda (26), 81, in sheep embryos, describes the epithelial mass of the 46 The Development of the Thymus thymic anlage as being broken up by ingrowing adenoid tissue. From 50 mm. to 60 mm., there are no large epithelial cells; but later at 100 mm. he finds in the adenoid tissue large cells 9 w to 15 » in diameter, isolated or united in groups, whose protoplasm colors light-red with carmine. These large cells have a concentric structure. Some of them are enclosed by large cells whose cytoplasm does not color with carmine, giving rise to a yellowish mass of irregular form and stratified appearance. In older embryos (250 mm.), the cellular masses are numerous but the large colored cells are rare. ‘The yellowish masses are groups of the large cells which have undergone a transformation like that of the stratum corneum of the epidermis. Stieda considers the large colored cells which form the corpuscles as remnants of the epithelial anlage, although he admits that for a long period during development he found no trace of them. He explains the formation of the corpuscles in accordance with Cohn- heim’s hypothesis that most tumors arise from unused tissue remnants. Ammann (2) 82, made most of his observations on human fcetuses. He describes the corpuscles as arising from connective tissue. ‘The cor- puscles are cellular in structure and are formed of one, two, or three cen- tral cells around which a variable number of cells, increasing with age, are arranged like the coats of an onion. The corpuscles are formed from reticulum cells and leucocytes. Growth consists in the apposition of cells from without. The life of a corpuscle consists usually of four stages: (1) Stadium der Transparenz; (2) Stadium der colloiden Entartung ; (3) Stadium der Verkalkung; (4) Stadium des Zerfalls. The nucleus of a reticulum cell or leucocyte increases in size at the expense of the cell body. Its increase in size establishes the concentric form. The corpuscle undergoes colloid and usually calcareous degeneration. Fat droplets, cholesterin crystals, and colloid granules are found together in the degenerating corpuscles. Breaking up in this way makes absorption possible. No epithelial remnants are to be observed. No erythrocytes are found in the corpuscles. In four cases of atrophic thymus gland which yet contained lymphoid tissue Ammann found corpuscles in all stages of development. He also found that the corpuscles are formed most rapidly when the thymus is at the height of its development. From these facts he concluded that they are not connected with the involution of the thymus as Afanassiew thought. He thought that their formation is due to a physiological de- crease in the intensity of growth of the medulla, due to the rapid growth of the cortex. : Watney (31), 83, agreed with Ammann that the corpuscles arise from connective tissue cells. Bode bas tae AY Monguidi (18), 85, distinguished true and false concentric corpuscles— the latter being only sections of blood-vessels. Hermann et Tourneux (11), 87, gave a description of the structure and formation of the concentric corpuscles about like that given by Ammann except that they regard the reticulum cells from which the corpuscles develop as of epithelial origin. Gulland (8), g1, regarded the corpuscles as epithelial remnants and compared them to the epithelial pearls of the tonsil. Maurer (17 c), gg, described the corpuscles as epithelial in origin. His description of their formation is however different from that of His. All the cells of the epithelial anlage at first assume a lymphoid character. Later, some of these cells reassume their epithelial nature and then form the corpuscles. His conclusions for teleosts and amphibians are similar to the above results which he obtained from the lizard. Ver Eecke (28), 99, for the frog, describes the leucocytes and con- nective tissue cells as invading the thymic anlage and separating the epi- thelial cells. The epithelial cells, separated by the mesenchymal elements, lie at first in groups or singly. They go through a cycle of two phases, a stage of growth, and a stage of involution. In the former stage, they increase to three or four times their original size and their cytoplasm differentiates into circular layers like the coats of an onion. The majority are monocellular. Some cells grow together making a more complex multicellular type. There are some intermediate forms, cells with a dense dark protoplasmic body, indistinct striations, and a nucleus partly or completely hidden in a precocious degeneration. In the stage of in- volution, which sets in early, the cytoplasm degenerates by the formation of vacuoles containing a hyaline liquid. The liquefaction may be in the form of a diffuse vacuolization, a large central vacuole, or a peripheral vacuole circular in section. The nucleus loses its affinity for stains, be- comes deformed, breaks up, and finally disappears. The corpuscles are finally absorbed. They never contain erythrocytes. The cells do not de- generate to form a corpuscle. The liquefaction forms an internal secre- tion which is forced out by the muscle tissue in the reticulum. Entirely different results on amphibians are reported by Nusbaum and Machowski (19), 02. These investigators revive the old idea of Afan- assiew, accepting his results except that they think the adventitia as well as the endothelium of the blood-vessels takes part in the formation of the corpuscles. They find erythrocytes in the corpuscles. These erythrocytes either gradually shrivel and disappear, or they are absorbed by leucocytes or endothelial cells. The leucocytes after digesting the hemoglobin of the erythrocytes become eosinophile cells which are numerous in the thymus. 48 The Development of the Thymus Wallisch (30), 03, measured the volume of the human thymus and of the corpuscles of Hassall at various stages. He finds that the total volume of the corpuscles of a 7-mo. embryo is 4.6 mm.,’ and of those of a 6-mo. child, 174.6 mm.’ The total volume of the thymus of a 78-mm. embryo, when it has already been partly transformed into adenoid tissue is only 6.8 mm.’ Since there is no evidence that the cells of the corpuscles multiply, he concludes that they cannot be regarded merely as remnants of the original epithelial anlage. Disregarding the crude observations of the earliest investigators, there remain three distinct theories of the formation of the corpuscles of Hassall. 1. The epithelal anlage of the thymus is broken up by the invading mesenchymal elements. The separated masses of epithelial cells undergo further changes mainly of a degenerative nature to form the corpuscles. This was the belief of His and Kolliker. According to this interpretation, the corpuscles are to be regarded as remnants that have nothing further to do with the gland. Stieda, Maurer, and Ver Hecke held this view in a modified form. Stieda regarded the cells forming the corpuscles as epithelial remnants but admitted that they go through a stage in which, for a time, they lose their epithelial character. This is substantially the same as Maurer’s view. He thinks that the cells of the epithelial anlage all become lymphoid, and that some of them afterwards reassume their epithehal nature and form the corpuscles. Ver Eecke regards the cor- puscles as epithelial remnants but thinks that they are glandular in nature, not mere useless remains. 2. The corpuscles are formed from the proliferating walls of blood- vessels. This idea was suggested by Cornil and Ranvier and elaborated by Afanassiew. Nusbaum and Machowski accept Afanassiew’s view except that they believe the adventitia of the blood-vessels as well as their endo- thelium takes part in the formation of a corpuscle. ‘These investigators thought that the formation of the corpuscles is connected with the in- volution of the thymus. 3. The corpuscles are formed from reticulum cells of the medulla and grow by apposition of the surrounding cells. This view was advanced by Ammann. Ammann thought that the reticulum is of connective tissue origin. He also believed that leucocytes formed the central part at least of some corpuscles. Hermann and Tourneux accepted Ammann’s results, except that they ascribed an epithelial origin to the reticulum. (I do not know whether they accepted the origin from leucocytes described by Ammann.) Ammann thought that the corpuscles formed because of a physiological decrease in the rate of growth in the medulla. K. T. Bell 49 My own observations on the development of the corpuscles of Hassall in pig embryos, will now be considered. The medulla, as previously de- scribed, begins to form from the epithelial syncytium usually near the center of the lobule. It is first recognized by its more marked reaction with cytoplasmic stains such as Congo red. Shortly after the medulla begins to form, the earliest stages of the corpuscles may be observed. - A few corpuscles have appeared at 9.5 em. I did not find them earlier. They are all formed from the epithehal syneytium of the medulla. Before beginning this discussion I will explain the use of my terms. By a corpuscle of Hassall, I mean a modified area of the epithelial syn- cytium of the medulla, containing at some period of its development, one or more nuclei, and-whose cytoplasm has been in part or entirely trans- formed into colloid. The term colloid is applied to various substances probably of widely different chemical nature, but is fairly adapted to our imperfect knowledge. I shall use the term here in the restricted sense employed by Ziegler,’ i. e., hyaline substances of epithelial origin, that do not give the reactions of mucin. Colloid in the corpuscles of Hassall does not usually appear as solid masses in its early formation, but as fibers, granules, or sheets which are separated by more or less cytoplasm that is not yet changed. This stage I have called, “ colloid in formation” (c f). It later assumes a more solid homogeneous appearance which I call solid colloid (¢ s). Often the solid colloid stains intensely with cytoplasmic stains. 1 call this kind solid deeply-staining colloid (¢ s d). In later stages, the colloid often loses its affinity for cytoplasmic stains, staining a very pale color or not staining at all. I call this variety old colloid (0c). According to their mode of development, the corpuscles of Hassall may be classified as follows: A. Concentric Corpuscles. a. Simple. 1. Ordinary type. 2. Hpithelioid type. 3. Cystic type. b. Compound. B. Irregular Corpuscles. a. Compact type. b. Reticular type. *Gen. Pathology, 10th ed., Warthin’s translation, p. 205. 50 The Development of the Thymus A. The concentric corpuscles include those that from their earliest appearance are concentric in structure. Adopting Ecker’s classification, I distinguish simple concentric corpuscles and compound concentric corpuscles. (a) Three types of simple concentric corpuscles are to be considered. (1) The ordinary type is far more numerous than any other. The earl- lest recognizable stage is shown in Plate II, Fig. 11. A nucleus (n) of the syneytium of the medulla has enlarged to perhaps twice its ordinary volume and has lost the ability to stain in the characteristic way with hematoxylin. Its sap is clear and a few reddish stained granules repre- sent its chromatin. Around it in the cytoplasm is an indistinct uneven layer of colloid (cf). The colloid is not yet solid and is being formed in concentric fibers or sheets. A shghtly later stage is shown in Plate IT, Fig. 14 and Fig. 15 (left side of figure). Some of the colloid (¢ s) next to the nucleus is now solid. The next stage is shown in Plate II, Fig. 15 (right side of figure). These corpuscles show a thick layer of colloid (¢ s d) that stains intensely with Congo red. Just outside the deeply staining colloid, colloid in formation may be seen. The nuclei are clear, and have become smaller and irregular in outline. The colloid seems to be pressing upon them and obliterating them. The colloid transformation gradually involves the adjacent cytoplasm of the syn- eytium until other nuclei are involved. The corpuscle has now reached the condition shown in Plate II, Fig. 12. The central area (0 c) is solid, the nucleus having disappeared entirely. Another (n’) is nearly ob- literated by the colloid. Part of the central area (0 c) no longer stains intensely, and it is breaking loose by the formation of a concentric space. Several nuclei are surrounded by colloid in formation. Their long axes are nearly in a tangential direction. ‘These nuclei are clear but only moderately swollen. In the further development of the corpuscle (Plate III, Fig. 17 and Plate II, Fig. 7), the central area (c s d) increases in size. The nuclei involved in this area become obliterated probably by the pressure of the colloid and are no longer distinguishable. This central area usually splits off and may break up into many smaller masses. The peripheral part of the corpuscle increases by extension of the colloid formation into the adjacent part of the syneytium. This extension takes place in the early stages by direct progressive involvement of the immediately adjacent cyto- plasm; in later stages (Fig. 7), by the formation of concentric lamelle which cut off unchanged areas of cytoplasm. The lamellxe increase in size and number, the cytoplasm included between them is changed into colloid. They finally become closely packed, giving the characteristic and BT Bell ol well-known onion-like structure found in the fully-formed corpuscle. The nuclei that are enclosed between the lamelle gradually lose their chromatin and become flattened out. They do not swell and are not obliterated. It seems that swelling occurs only in nuclei that are sur- rounded by deeply staining colloid, and that this change is preparatory to their obliteration by or transformation into colloid. The amount of the corpuscle that breaks up to form the softer center is very variable. 'The size of the center usually seems to increase with the age of the corpuscle. Plate III, Fig. 21, shows a variation from the ordinary concentric type. ‘The central nucleus (7) stains reddish but is not enlarged. Most of the other nuclei are unchanged. All the colloid (c¢ f) is in the early fibrous and granular stage. From 20 cm. to full term many corpuscles show masses of calcareous material in or near the center. This material rarely appears in younger corpuscles (Plate III, Fig. 17, ¢7). It stains a violet blue with Dela- field’s hematoxylin. The majority of the corpuscles of Hassall belong to the ordinary type of simple concentric corpuscles described above. It is very clear that they have nothing to do with blood-vessels. They never contain eryth- rocytes nor anything resembling them. Rarely a lymphoblast or leuco- cyte is found inside the corpuscle. These seem to be usually involved in the corpuscle lke ordinary stroma nuclei during the formation of the lamelle. (Their occurrence in other types will be discussed later.) It is also clear that these corpuscles arise from the syncytium of the medulla. They are epithelial in origin, since the entire stroma of the gland is derived from epithelium, but they are certainly not remnants of the original epithelial anlage. Neither are they formed from lymphoid- like elements that reassume their epithelial nature as Maurer described for the lizard. Some of Ammann’s observations are in accord with my results. The swelling of the nucleus was noted by Ammann as the first step toward the formation of the corpuscle. {t should be noted, however, that rarely a corpuscle begins to form as a mass of colloid out in the cytoplasm and involves nuclei secondarily. I cannot distinguish his “Stadium der Transparenz ” for I cannot be sure that a corpuscle is beginning to form until some colloid is present. The formation of the colloid is associated with the swelling of the nucleus. His other three stages, “ Stadium der “Stadium der Verkalkung,” and “Stadium des > colloiden Entartung,” Zerfalls ” are easily seen. I have never seen corpuscles begin in leucocytes as Ammann described. His statement that the corpuscle grows by ap- position of reticulum cells is true in a modified sense. He thought that 52 The Development of the Thymus the outer part of a corpuscle is formed of reticulum cells that have moved up and flattened themselves out around it. The description just given shows that the corpuscles are never composed of distinct cells, and that the increase in size is due to an extension outward of the colloid formation and not to a moving in of the adjacent tissue. The concentric form of this type of corpuscle is due at first to its being formed around a spherical or ellipsoidal nucleus. The swelling of this nucleus creates a centrifugal pressure in the adjacent cytoplasm. Before or during its transformation into colloid; the cytoplasm also imcreases in quantity. That the cytoplasm increases in quantity is shown by the fact that the nuclei are fewer in the corpuscle than in any adjacent area of the syneytium of equal size. This centrifugal pressure presses the newly formed colloid into concentric lamelle. It at first turns the long axes of the nuclei tangentially, and later flattens them and makes them concave toward the center. 2. The epithelioid type of corpuscle is characterized by large areas of cytoplasm so marked off by colloid lamelle as to give the appearance of a mass of large epithelial cells. They may contain only one nucleus em- bedded in a well-defined area of cytoplasm (Plate IIT, Figs. 18 and 20). These correspond to the monocellular corpuscles that have been described for lizards and amphibians. They are rare in the pig. I have not been able to trace these very far, as they soon become indistinguishable from other forms. The only difference I have noted is that the outer colloid lamellae begin to form early, causing the peculiar appearance of a large epithelial cell. Again the epithehoid type may present an appearance such as shown in Plate I, Fig. 3. These do not seem to be formed around any special nucleus. The outer colloid lamelle form before any center has been established, marking off large cytoplasmic areas that may look like large cells. The centrifugal pressure of expansion caused by the great increase of cytoplasm in this area determines the concentric form in these corpuscles. Pure epithelioid corpuscles are very rare, but epi- thelioid areas in other corpuscles are not uncommon. The occurrence of epithelioid areas in corpuscles of the ordinary type shows that it is due to variations in a fundamentally similar process. 3. In the cystic type of corpuscle, the central part, instead of becoming transformed into colloid, undergoes early liquefaction, forming vacuoles. The central nucleus does not increase in size as in the ordinary type, but shrivels up and disappears. The corpuscle begins by the formation of outer colloid lamella—the central mass is not changed into colloid. In Plate II, Fig. 10, the central area (p m) is undergoing a diffuse liquefaction. The nucleus (7) is colorless and shrunken. In Plate IT. K. T. Bell 53 Fig. 8 (right side of figure), the central area has formed two large vacu- oles (v). On the left side of the same figure, a concentric vacuole (v) has formed, separating off a central spherical nucleated mass of proto- plasm. The nucleus of this mass of protoplasm is shrunken and the cytoplasm shows many small vacuoles. The corpuscle shown in Plate IT, Fig. 9, is probably a later stage of the form just described. The central protoplasmic mass has become converted into an ellipsoidal pale body (pm). The small circular body in this shriveled mass is probably the nucleus. Some corpuscles like the one shown in Fig. 9 are found in which the central mass has entirely disappeared. The further growth of corpuscles of this type seems to be by formation of colloid lamelle as in the ordinary type. They soon become indistinguishable from other forms. The cystic type of corpuscle is rare in the pig. This evidently cor- responds to the form in amphibia that misled Nusbaum and Machowski into reviving Afanassiew’s theory. The central masses, in Figs. 8 and 9, might readily be mistaken for red corpuscles in animals in which these cells are nucleated. But the red cells of the blood of the pig are not nucleated at this stage. I have traced a number of these corpuscles (as well as those of other types) in serial sections and have never seen any indications of a connection to blood-vessels. Nusbaum and Machow- ski (19), (Fig. 1, e, S. 116) show a corpuscle which is similar to my Fig. 9. It will be noted that the central space in neither of these figures is lined by endothelium. The early form of corpuscle shown by Nus- baum and Machowski (Fig. 1, d, S. 116) is very probably a normal blood- vessel with cubical endothelium. I have often found such vessels with cubical endothelium in the interlobular tissue of the pig’s thymus at 10 em. to 12 em. They probably may be found at other stages also. In the thymus of a kitten, injected by the intra-vitam Prussian blue method pre- viously described, the majority of the corpuscles were found to be in early stages. The injection did not penetrate any corpuscle. I had a somewhat better opportunity to study the relations of the corpuscles to the blood-vessels in a 14 em. human embryo. Here the vessels of the thymus were all very much distended with blood and the corpuscles were in early stages. No blood cells were found in the corpuscles. (b) Compound concentric corpuscles are formed whenever two or more simple concentric corpuscles begin to form so close together that they come in contact during their later growth. An early stage of such a corpuscle is shown in Plate II, Fig. 15. The colloid lamelle are formed around each center until they come in contact; they are then formed around both centers. In Plate III, Fig. 22, a compound concentric cor- 54 The Development of the Thymus puscle is shown. ‘There are three simple concentric corpuscles in it— one of them (the lowest in the figure) in a very early stage. Several lamelle are common to the older corpuscles, and one is common to all three. This arrangement of the lamella is a mechanical effect of the tension in the cytoplasm, due to the centrifugal’ pressure from the two centers. ‘The size of the separate centers in a compound corpuscle de- pends upon the stage they have reached when they come in contact. If a compound corpuscle be formed by the union of two simple corpuscles in an early stage, as in Plate III, Fig. 19, all indications of its com- pound nature are soon lost. A corpuscle originally compound may, then, in later stages, become indistinguishable from simple corpuscles. The simple corpuscles uniting to form a compound concentric corpuscle may be of any of the types previously described. B. IRREGULAR CORPUSCLES. This group includes those corpuscles which are not at first concentric. Concentric areas may appear later. According to the classification pre- viously given, I distinguish a compact type and a reticular type. (a) The compact type (Plate III, Fig. 16) first appears as a compact area of syneytium of irregular shape. It is recognizable by the colloid it contains. The nuclei are not noticeably increased in size and have no regular arrangement. Their chromatin still stains dark with nuclear stains. The colloid (cf) is not yet solid. The corpuscle has no distinct center. These corpuscles grow by direct colloid transformation of the adjacent syneytium. No distinct lamellae are formed. The colloid may remain in the fibrous condition shown in the figure (cf) or it may become solid, but it never reaches the deeply staining condition unless ¢ concentric area be established. A later stage of this type is shown in Plate III, Fig. 23. The cor- puscle is sharply marked off from the syncytium. Some of its colloid is solid. A concentric area (cs) is beginning to form. The nuclei are not markedly different from those of the adjacent syncytium. These corpuscles may become large and branched. Often one or more con- centric areas are developed after the corpuscle has attained considerable size. By the growth of these concentric areas, irregular corpuscles may become converted into concentric corpuscles. (b) The reticular type is produced by colloid formation in the or- dinary reticulum of the medulla. In the types previously described, the spaces of the reticulum are usually obliterated as the colloid formation advances; but in this form the spaces persist as a part of the corpuscle. Pure reticular corpuscles vary greatly in size, sometimes involving only E:T. Bell 55 one node of the syncytium. They are never concentric, and never form lamella. Reticular areas often occur in other forms of corpuscles. In this way leucocytes are often involved in the corpuscle, since they lie in the spaces of the reticulum. Lymphocytes often get into a corpuscle in the lymphoblast condition, being cut off by the formation of lamelle outside them (Plate III, Fig. 22). The leucocytes shut in the cor- puscle in this way during development may not degenerate. ‘They prob- ably persist and help to remove the corpuscle in its final stages of degen- eration. The amount of expansion of the cytoplasm before or during the colloid transformation is probably small in the irregular reticular corpuscles, since it does not obliterate the spaces of the syncytium. In the compact type, the spaces of the syncytium are obliterated and there is evidence of some expansive force (note the arrangement of the nuclei in the upper part of Fig. 23, Plate III). In the figure referred to, the number of nuclei in any part of the corpuscle is less than in an equal area of the adjacent reticulum. These facts indicate that there is an expansion of the cytoplasm. That this expansive force does not produce a concentric form is due primarily to the fact that there is no expansion of a nucleus and distinct center of formation as is present in concentric corpuscles of the ordinary type. The absence of the onion-like structure in irregular corpuscles is due to the fact that the colloid is not laid down in lamelle. Significance of the corpuscles of Hassall. It has been shown in the preceding pages that the corpuscles of Hassall in the pig are not epithe- lial remnants, and also that they are not formed from blood-vessels. There is no evidence connecting their development with the involution of the thymus, for they begin to form before the lymphoid transforma- tion is complete and are most numerous when the thymus is at the height of its development. I have not been able to see the decrease in the rate of growth of the medulla described by Ammann, and even if such did occur it is difficult to understand how it could cause the formation of a corpuscle. The above theories are, therefore, inconsistent with the facts of devel- opment in the pig. It seems to me that the formation of a corpuscle is not to be regarded as a process of degeneration. The fact that the for- mation of colloid is an essential feature in the development of every corpuscle is a strong argument that it is a form of secretion such as occurs in its neighboring branchial derivative, the thyroid. The fact that the corpuscles differentiate in an apparently uniform syneytium is further evidence against a theory of degeneration. Since the lympho- eyte-forming function of the thymus is probably secondary, it is not al o a The Development of the Thymus unreasonable to suppose that its primitive function was the formation of a colloid secretion such as occurs in the thyroid, and that the corpuscles are abortive expressions of this primitive function.’ GIANT CELLS. Polykaryoeytes may often be seen in the medulla. These bodies de- velop from the syncytium of the medulla. They are first noticeable as groups of small spherical nuclei in a solid area of the syneytium. These nuclei stain with medium intensity and are all very similar in size and color. ‘The area containing this group of nuclei becomes a well-defined node of the reticulum and persists as such. A polykaryocyte is, there- fore, a large node of the reticulum containing a number of small nuclei very similar in appearance. These cells often occur in groups. They are entirely distinct from the corpuscles. They are evidently similar to the polykaryocytes found in bone marrow and other lymphoid tissues. SUMMARY. The following is a resume of the development of the thymus in the pig: The thymus of the pig is probably developed entirely from the endo- derm of the third gill pouch. By a gradual process of vacuolization and liquefaction of the cyto- plasm, the epithelial syncytium of the thymic anlage is converted into a cellular reticulum. From the first appearance of vacuolization, three types of nuclei are present: large pale nuclei; small dark nuclei (lymphoblasts), and large dark intermediate forms. The lymphoblasts gradually break loose from the cellular reticulum, moving into its spaces and forming lymphocytes. Mitoses are most nu- merous at the period of the most rapid formation of lymphocytes. The medulla continues to form lymphocytes at least as late as birth. Lymphocytes appear in the connective tissue around the thymus shortly after they are formed; and lymphoblasts, which are distinguish- able from lymphocytes only by being embedded in the syncytium, are present in the thymus a long period before lymphocytes are found any- where in the neighborhood of the thymus. The cellular reticulum of the earlier stages persists in a modified form as the reticulum of both cortex and medulla. It retains more cytoplasm 7Ver Eecke (28) believes that the corpuscles in amphibians are of a glandular nature. Eins Bell, BY in the medulla. Practically all the reticulum of both cortex and me- dulla, as well as the lymphocytes, are, therefore, of epithelial origin. The corpuscles of Hassall develop from the syncytium and are, there- fore, epithelial in origin. They are, however, not to be considered as remnants of the original epithelial anlage. In development various types of corpuscles are distinguished. The ordinary type of concentric corpuscles first appears as an enlarged clear nucleus around which colloid is being formed. Before or during the formation of colloid, the cytoplasm increases in quantity, filling the spaces of the reticulum and producing a centrifugal pressure which shapes the newly-formed colloid into concentric lamella and fiattens the neighboring nuclei, making them concave toward the center. The cen- tral nuclei usually become obliterated. The epithelioid type is distinguished by its resemblance to large epi- thelial cells, this appearance being due to the formation of colloid lamelle around large areas of clear cytoplasm. The central part of the corpuscle usually remains unchanged until after some of the colloid lamellee are formed. The cystic type differs from the ordinary type only in that the central part undergoes vacuolization instead of colloid transformation. Those with concentric vacuoles may simulate blood-vessels containing nucleated red cells. Corpuscles never contain erythrocytes; neither can they be injected at any stage of development. Serial sections also show that there is no connection to blood-vessels at any stage. Compound concentric corpuscles are formed by the union of two or more simple concentric corpuscles during development. Irregular corpuscles are not concentric in arrangement, and are formed in the syncytium in an irregular manner. In the compact type of irregular corpuscles, concentric areas may form. The formation of colloid is an essential feature in the development of every corpuscle, and is not to be considered as a process of degeneration. Since the conclusion of my work and after my manuscript was given to the publishers, two articles dealing with the thymus have appeared. Ph. Stohr (Ueber die Thymus, Sitzungsberichte der phys.-med. Gesellschaft zu Wurzburg, June 8, 1905) believes that the thymus first epithelial in nature becomes converted entirely into small cells of lymphoid appearance. Later the large reticulum cells are formed from these by enlargement. The cor- puscles of Hassall are formed by the massing together and enlargement of these lymphoid-like cells. The small round cells of the gland are epithelial in origin but are to be regarded not as lymphocytes but as epithelial cells. The thymus is not a source of lymphocytes. T io 6) The Development of the Thymus The author apparently believes that none of the small round cells leave the gland though he admits that lymphocytes enter. But as mentioned above the zone of connective tissue immediately around the head at 7 cm. may contain even more lymphocytes than are present inside the gland at that time If these are all entering the gland then it is probable that most of the small round cells are really lymphocytes. This conception then does not simplify the problem but is only a theoretical compromise between the two views as to the origin of the lymphocytes. J. Aug. Hammar (Zur Histogenese und Involution der Thymusdriise, Anat. Anz. Bd. XXVII, June 17, 1905) regards the reticulum as formed from the epithelial anlage but thinks the evidence at hand insufficient to decide the question as to the origin of the lymphocytes. He finds lymphocytes outside the thymus in many animals (man, cat, chick, frog) before any are present inside the gland. The corpuscles of Hassall develop from the epithelial reticulum and undergo hyaline (colloid?) degeneration. My description of the formation of the corpuscles of Hassall differs essen- . tially from Hammar’s, in that I believe the formation of the corpuscle consists in the expansion of the cytoplasm of the syncytium and its conversion into colloid. Hammar did not recognize ‘“‘ colloid in formation,’ though he speaks of the coarse fibrillar structure of the protoplasm. He -did not describe such corpuscles as are shown in Fig. 7, Plate II. The considerations presented above in favor of the epithelial origin of the lymphocytes seem to me much stronger than those given by Hammar. His statements as to the presence of lymphocytes around the thymus before they are present inside are to be taken with some reservation inasmuch as he mentions small round cells separate from the syncytium earlier, but regards them as degenerating epithelial cells (S. 65). His figure from thé human foetus (Fig. 18, S. 66) does not seem to be strong support for his statement. Certainly many lymphocytes are present in the pig thymus when the reticu- lum is broken up as much as shown in the figure referred to. It is also to be borne in mind that the different parts of the thymus undergo the lymphoid transformation at different times and that a single section may therefore be misleading. LITERATURE. la. AFANASSIEW, B.—Ueber die concentrischen Kérper der Thymus. Archiv ie, monlkor, ANH OS, 1x6, ROY. IST Weitere Untersuchungen tiber den Bau und die Entwickelung der Thymus und der Winterschlafdriise der Séiugethiere. Archiv f. amdcar, ANNES, JBL, DOIN 5 Weir AMMANN, A.—Beitrige zur Anatomie der Thymusdriise. Basel, 1882. 2a. BEARD.—The development and probable function of the thymus. Anat. Anz., Bd. IX, 1894. The true function of the thymus. Lancet, 1899. 4. Born, G.—Ueber die Derivate der embryonalen Schlundbogen und Schlundspalten bei Séugethieren. Archiv f. mikr. Anat., Bd. XXII, 1883. 5. Cornin et Ranvrer.—Manuel d’histologie pathologique. Paris, 1869, p. 135 (cited from Ammann). 1b. 21. 22. H: T. Bell ANS) Ecxer.—Art. “ Blutgefassdritisen,’ Wagner’s Handw. der Phys., III (cited from Ammann). FRIEDLEBEN, A.—Die Physiol. der Thymusdriise. Frankfurt, 1858. GuLLAND.—The Development of adenoid tissue with special reference to the tonsil and thymus. Laboratory Reports issued by the Royal College Phys., Edinburgh, Vol. III, 1891. Gunzpurc.—Ueber die geschichteten Ko6rper der Thymus. Zeitschr. f. klin. Med., Bd. VI, 1857, S. 456 (cited from Henle und Meissner. Bericht tiber die Fortschritte der Anat. u. Physiol.). HASSALL.—The microscropical anatomy of the human body in health and disease. London, 1846 (cited from Ammann). HERMANN et TouRNEUX.—Article thymus, Dict. encycl. des Sciences Médi- cales. Troisiéme Série, 17, 1887. . His, W.—Zeitschrift f. wiss. Zoologie, Bd. X, S. 348. Leipzig, 1860. Anatomie menschlicher Embryonen. Leipzig, 1880, S. 56. Jackson, C. M.—Zur Histologie und Histogenese des Knochenmarkes. Archiv f. Anat. und Physiol., Anat. Abth., 1904. KASTSCHENKO.—Das Schicksal der embryonalen Schlundspalten bei Saugethieren. Archiv f. mikr. Anat., Bd. XXX, 1887. Kiern.—Neuere Arbeiten tiber die Glandula Thymus. Centralbl. f. allg. Pathol. u. pathol. Anat., 1898. LANGERHANS und SAveLinrw.—Beitrage zur Physiologie der Brustdriise. Virchow’s Archiv, Bd. 134, 1893. . . Mavurer.—Schilddrtise und Thymus der Teleostier. Morph. Jahrb., Bd. XI, 1886. . Schilddriise, Thymus, und Kiemenreste bei Amphibien. Morph. Jahrb., Bd. XIII, 1888. Schilddriise, Thymus, und andere Schlundspaltenderivate bei der Eidechse. Morph. Jahrb., Bd. X XVII, 1899. In Hertwig’s Handbuch der Entwickelungslehre der Wirbelthiere, Lief. 6-8, S. 131 ff., 1902. Moneuipi.—Sulla glandula timo. Parma, 1885 (cited from Prenant). Nussaum, J., und Macnowski.—Die Bildung der concentrischen Korper- chen und die phagocytotischen Vorginge bei der Involution der Amphibienthymus, ete. Anat. Anz., Bd. XXI, 1902. Nuspaum, J., und Prymax, T.— Zur Entwickelungsgeschichte der lym- phoiden Elemente der Thymus bei den Knochenfischen. Anat. Anz., Bids cEexe 19 000 PAvLitzKy.—Disquis. de stratis glandule thymi corpusculis. Habilita- tionsschr., Halis, 1863 (cited from Henle und Meissner’s Bericht tiber die Fortschritte der Anat. und Physiol.). PRENANT.—Développement organique et histologique du thymus, de la glande thyroide, et de la glande carotidienne. La Cellule, Tome X, 1894. PryMak, T.—Beitrage zur Kenntnis des feineren Baues und der Involu- tion der Thymusdriise bei den Teleostieren. Anat. Anz., Bd. XXI, 1902. 60 The Development of the Thymus 24. Scuarrer, J.—Ueber den feiieren Bau der Thymus und deren Beziehung zur Blutbildung. Sitzungsber. d. K. Acad. d. Wissensch. Math.- naturw. Kl. Wien., Bd. CII, Abt. III, 1893. 25. Scuepet, J.—Zellvermehrung in der Thymusdrtise. Archiv f. mikr. Anat., Bd. XXIV. 26. Sriepa, L.—Untersuchungen tiber die Entwickelung der Glandula Thy- mus, Glandula Thyroidea, und Glandula Carotica. Leipzig, 1881 (cited from Hermann et Tourneux). 27. Sutran.—Beitrag zur Involution der Thymusdriise. Virchow’s Archiv, Bd. 144, 1896. 28. Ver Eecke.—Structure et modifications fonctionelles du thymus de la grenouille. Bulletin de l’Académie royale de Médicine de Belgique, 1899. 29. VircHow, R.—Kritisches liber den oberschlesischen Typhus. Archiy, Bd. ay, ssl. Sh Aa 30. Watiiscu.—Zur Bedeutung der Hassall’schen Korperchen. Archiv f. mikr. Anat., 1903. 31. Watnry.—The minute anatomy of the thymus. Philos. Transact. of the Royal Society of London, Vol. 173, Part III, 1883 (cited from Pre- nant). EXPLANATION OF PLATES. All the figures were drawn with Leitz obj. 1/12, oc. 4, and camera lucida. The magnification after the reduction of the plates is about 1060 diameters. All drawings were made from transverse sections of the mid-cervical seg- ment of the thymus unless they are otherwise indicated. The following abbreviations designate the structures indicated in all the figures: c f—colloid in formation. 1p n—large pale nucleus. cl—caleareous deposit. m—nucleus in mitosis. ce s—solid colloid. md—beginning of medulla. ces d—solid colloid that stains n—nucleus. deeply. o c—old colloid. e—erythrocyte. p m—protoplasmic mass. end—endothelial nucleus. sf—fibril in syncytium. I—lymphocyte. ss—space in syncytium. lb—lymphoblast. v—vacuole. 1d n—large dark nucleus. PLATE I. Fic. 1. From a 3.7-cm. pig embryo. Stained with iron-hematoxylin and Congo red. Vacuolization of the cytoplasm and differentiation of the nuclei have begun. Fic. 2. From the thoracic segment of a 4.5-cm. pig embryo. Stained with iron-hematoxylin and Congo red. A cellular reticulum is now formed. Large pale nuclei, lymphoblasts, and the large dark intermediate forms are present. Fig. 3. Epithelioid type of concentric corpuscle. From a 16-cm. pig em- bryo. Stained with hematoxylin and Congo red. Colloid lamelle (c s d) EK. T. Bell 61 separate large areas of clear cytoplasm, causing the appearance of large epithelial cells. Colloid is being formed between the lamelle and around several nuclei. Fic. 4. From a 8.5-em. pig embryo. Stained with iron-hematoxylin (not decolorized). The medulla has appeared. Lymphocytes are present between the epithelial cords. Fig. 5. From a 7-cm. pig embryo. Stained with iron-hematoxylin and Congo red. A few lymphocytes have been formed. In the cellular reticulum are large pale nuclei, lymphoblasts, and large dark intermediate nuclei. The nuclei in mitosis are very compact. Fic. 6. From the medulla of a 24-cm. pig embryo. Stained with Jackson’s modification of Mallory’s method (ref. in text). Many fibrille are seen in the syncytium. Paar ul: Fic. 7. Ordinary type of simple concentric corpuscle. From a 16.5-cm. pig embryo. Stained with haematoxylin and Congo red. The corpuscle is well advanced in development. Concentric lamelle of colloid have been formed. The cytoplasm between the lamelle is in an early stage of colloid transformation. Colloid fibers cut transversely appear as dots. The nuclei are becoming flattened by the pressure of expansion. The central mass stains irregularly and all traces of the nuclei in that region are gone. Fic. 8. Two cystic concentric corpuscles. From a 16-cm. pig embryo. Stained with iron-hematoxylin and Congo red. On the left, a nucleated mass of protoplasm has been separated off by the formation of a vacuole annular in section. This might be mistaken for a blood-vessel containing a nucleated red cell. In this central protoplasmic mass the nucleus is shrunken and the cytoplasm vacuolated. In the small corpuscle on the right, two large vacuoles have formed. Fic. 9. Cystic concentric corpuscle. From a 14-cm. pig embryo. Stained with hematoxylin and Congo red. The central protoplasmic mass is pale and shrunken. The small circular body in it probably is the remains of the nucleus. Colloid lamelle are forming. Colloid fibers cut transversely appear as dots. Fic. 10. Cystic concentric corpuscle. From a 10.5-cm. pig embryo. Stained with hematoxylin and Congo red. The center contains no colloid and seems to be softening. The nucleus is shrunken. Fic. 11. Ordinary concentric corpuscle in a very early stage. From a 10.5-em. pig embryo. Stained with iron-hematoxylin and Congo red. The nucleus is enlarged and colloid is forming around it. A few colloid fibers may be seen in the cytoplasm for some distance from the central nucleus. Fic. 12. Ordinary concentric corpuscle. Several nuclei are involved. From a 10.5-cem. pig embryo. Stained with hematoxylin and Congo red. The deeply-staining colloid has completely obliterated the central nucleus (in the region 0 c), and nearly obliterated another (n’). Some of the colloid now stains pale (0c). Fic. 13. Ordinary concentric corpuscle.. From a 10.5-cem. pig. Stained with hematoxylin and Congo red. The central nucleus is being obliterated 62 The Development of the Thymus by the deeply-staining colloid. The neighboring nuclei are beginning to show the effect of the centrifugal pressure. Fic. 14. Ordinary concentric corpuscle in an early stage. From a 10.5-cm. pig. Stained with hematoxylin and Congo red. A band of deeply-staining colloid has been formed. Just outside this is colloid in formation. Fie. 15. Two simple concentric corpuscles which would have formed a compound concentric corpuscle. From a 10.5-cm. pig. Stained with hema- toxylin and Congo red. The left corpuscle is a little more advanced than Fig. 11. The right corpuscle shows a large area of deeply-staining colloid which has pressed the nucleus into a small irregular shape. PrATH TT: Fig. 16. Compact irregular corpuscle in an early stage. From a 14-cm. pig embryo. Stained with hematoxylin and Congo red. The colloid is not yet solid. The nuclei are not essentially different from those of the adjacent syncytium. Fic. 17. Ordinary concentric corpuscle. From a 12-cm. pig embryo. Stained with hematoxylin and Congo red. There is a large, central, deeply- staining colloid mass in which calcareous deposits (cl) have been made. The neighboring nuclei show the effects of the centrifugal pressure. Fic. 18. Epithelioid concentric corpuscle in an early stage. From a 10.5- cm. pig embryo. Stained with hematoxylin and Congo red. The outer col- loid lamella marks off a nucleated mass of cytoplasm resembling a large cell. The nucleus is undergoing the same changes as occur in the central nucleus of an ordinary concentric corpuscle. Fic. 19. Compound concentric corpuscle. From a 10.5-cm. pig embryo. Stained with hematoxylin and Congo red. This would have soon lost all evidence of its compound nature. Fic. 20. Epithelioid concentric corpuscle. From a 10.5-cem. pig embryo. Stained with hematoxylin and Congo red. Some colloid is forming outside the circular area. Solid deeply-staining colloid is forming. Fic. 21. Ordinary concentric corpuscle, showing a variation from the usual type. From a 16.5-cm. pig embryo. Stained with iron-hematoxylin and Congo red. The central nucleus is reddish but not enlarged. No solid colloid has been formed. Fic. 22. Compound concentric corpuscle. From a 16.5-em. pig embryo. Three centers are present. The pale colloid in the upper part is probably older than the deeply-staining variety. In the lower part of the figure, a young corpuscle is shown. Fic. 28. Compact irregular corpuscle. From a 16-cm. pig embryo. Stained with hematoxylin and Congo red. Some of the colloid is solid. No definite center is present but one is beginning to form (c s). The nuclei are not markedly different from those of the adjacent syncytium. THE DEVELOPMENT OF THE THYMUS. PLATE I. E. T. BELL. : { ye) lan ™ or Tee ~ = 4 AMERICAN JOURNAL OF ANATOMY--VOL Vv. E. T. BELL, DEL. THE DEVELOPMENT OF THE THYMUS. PLATE Il. E. T. BELL. AMERICAN JOURNAL OF ANATOMY--VOL Vv. E. T. BELL, DEL. THE DEVELOPMENT OF THE THYMUS. , PLATE III. E. T. BELL, AMERICAN JOURNAL OF ANATOMY--VOL Vv. E. T. BELL, DEL. THE VEINS OF THE ADRENAL. BY JEREMIAH S. FERGUSON, M.Sc., M. D. From the Histological Laboratory of Cornell University Medical College. New York, N. Y. WiTH 3 TEXT FIGURES. Within the past decade our knowledge of the functions of the adrenal giands, and of their relations to the rest of the economy, has been greatly enhanced by many careful chemical and physiological researches. Behe recent studies of Aichel (1), Wiesel (2, 3), Soulie (4), and others have placed the early development of the organ upon a fairly certain basis. These advances in the physiology and embryology of the organ have not as yet been accompanied by corresponding advances in our appreciation of its minute anatomy. Hence this branch of the subject is, at the present time, one of unusual interest. The intimate relation of the parenchyma of the adrenal to its blood- vessels, as shown by the general tendency to regard the organ as a true gland whose secretion enters its blood-vessels and leaves the organ through its efferent veins, makes it specially important that these vessels should be carefully studied and their structure and distribution accurately recorded. The exhaustive study of Flint (5), on the course of the adrenal vessels, based as it was upon carefully prepared reconstructions, leaves little to be desired along this line. The writer is, however, unable to find in the literature any reference to the minute structure of the veins of the adrenal, with the notable exception of Minot’s (6) article on sinusoids. To be sure Pfaundler (7) mentioned the occurrence, in the medulla of the adrenal, of venous vessels whose only wall consisted of endothelium. Gottschau (8) also, though omitting their description, has figured similar vessels in his Plate XVIII, Fig. 1. But as to the structure of the larger blood-vessels of the adrenal glands the literature seems to be entirely barren. The architecture of the arterial walls does not appear to offer any distinctive peculiarities, the tissues of which they consist being arranged in a manner precisely similar to that which characterizes the arteries of AMERICAN JOURNAL OF ANATOMY.—VOL. Y. 64 The Veins of the Adrenal similar size occurring in other organs. The veins, however, present distinct and remarkable peculiarities which it is the purpose of the present paper to describe. Methods and Material—The tissue used for this study has included specimens of the adrenal from twenty-one human adults, together with the casual examination of fetal adrenals of the pig and of man. The adrenals of other mammals, e. g., monkey, dog, cat, rabbit, and guinea- pig, have also been more or less carefully studied. These tissues have been fixed and hardened with many reagents, among which are Zenker’s solution, formol, Miiller-formol, alcohol, corrosive acetic mixture, Tellyesniczky’s fluid, and Flenming’s solution. The stains used were hematein by various methods, acid hematein, iron hematein, etc., and for counter staims eosin, orange, Van Gieson’s picro- fuchsin, Weigert’s elastic tissue stain, Mann’s methyl blue-eosin mixture, Congo-red, and Ehrlich’s triacid mixture. A combination of Mann’s hematein, Weigert’s elastic tissue stain and Van Gieson’s picro-fuchsin, gave the best results for the differentiation of the muscular and con- nective tissues. This method was applied as follows, and may be used after any of the above fixatives. 1. Stain 10-12 minutes in Mann’s hematein or in Bohmer’s hema- toxylin, until somewhat overstained. 2. Wash well in water. 3. Stain 10-20 minutes in recently prepared resorcin-fuchsin solution after the method of Weigert (9). 4. Wash in water. 5. Stain 1-3 minutes in the freshly prepared picrie acid-acid fuchsin solution of Van Gieson (10). 6. Wash and dehydrate in 95 per cent, or in absolute alcohol. 7. Clear, and mount. Types of Adrenal Veins.—The efferent veins of the adrenals arise in the medulla of the organ by the union of the broad capillaries of the medulla and the adjacent zone of the cortex. These capillaries form broad thin-walled vessels which have been described by Minot (6) as sinusoids. They converge toward the middle of the medulla, where they pass into somewhat larger vessels, which, for convenience, may be termed small central veins. These veins tend toward the hilum, are relatively short, and by union with one another soon form thicker-walled vessels which may be described as large central veins. These large veins pass toward the hilum, near which,they unite to form a large efferent vessel, the suprarenal vein. This last vein makes its exit from the hilum of the organ and enters either the vena cava inferior, as is the rule on the right side, or the renal vein, as frequently occurs on the left.” From this brief review of the course of these vessels it will be seen that four distinct venous types have been enumerated, and it is the purpose Jeremiah S. Ferguson 65 of the writer to show that these types exhibit well-defined structural peculiarities. Observations.—The sinusoids, after the careful description by Minot (6), will require but brief mention. These vessels possess the wall of a capillary and the lumen of a venule. A number of such vessels may be seen in Fig. 1, in the central portion of the medulla, on either side of the group of central veins. Their wall consists of nucleated endothelial plates which rest directly upon the parenchymal cells. Their lumen is several times the diameter of the- medullary capillaries. They are dis- ‘< co ee oe Pees *3 rn * Lon bs. - * d ‘~ Ge aa = Fic. 1. A group of vessels from the central portion of the medulla of the human suprarenal gland. a, sinusoids; b, small central veins. Fixation, 5 per cent formalin; stain, Mayer’s hematein; thickness, 8” ; photomicrograph, x 100. tinguished from the small central veins by the absence of connective tissue from the wall of the sinusoids. The small central veins are of the type shown in Fig. 1. The wall of these vessels consists of two coats, endothelial and connective tissue. The latter is always relatively thin, though the vessels possess a very consider- able lumen. Venules of this type of structure, Fig. 1, collect the blood from the sinusoids of the medulla. Frequently, however, the sinusoids open directly into the small central veins and venules, the connective tissue of the venous wall being occasionally continued for a very short distance upon the endothelium of the sinusoid. 5 ior) So The Veins of the Adrenal The connective tissue of the small central veins is richly supplied with elastic fibers, which are disposed in oblique and circular directions, RNa Mee a oe an Wary 2 BS Re ol CONT ite Mg ire FE a ape Wate ee Nae net ot ee Ye Nae We a = ee. ate se Fig. 2. The medulla of a suprarenal gland of man, showing a group of large central veins. The middle and lowermost veins are in transection, the uppermost vessel in longitudinal section. The series of sections shows that this last vessel is a branch of that in the middle of the figure. Fixation, Zenker’s fluid; stain, hematein and methyl-blue, Mann’s method; thickness, 10 ~; photomicrograph, x 60. occasional elastic fibers are also longitudinal. The typical small central veins contain no muscle. As they approach their termination in the Jeremiah S. Ferguson 67 large central veins a few smooth muscle fibers are found, but these are always disposed in a longitudinal direction. As soon as longitudinal muscle fibers appear in appreciable numbers the venous wall acquires the type of the succeeding variety, the large central vein. In the large central veins, as in the small, but two coats can be readily distinguished. The inner coat, or intima, in these vessels consists of a lining endothelium, which rests upon a very thin membrane of delicate connective tissue, containing many elastic fibers. The outer coat, or adventitia, is also a very thin membrane of fibro- elastic tissue, but its fibrous bundles are coarser than those of the intima, and its elastic fibers form a very close network. The outer portion of this coat contains a few longitudinal smooth muscle fibers. The great majority of these fibers, however, are arranged in the form of longitudinal ridges which project into the adjacent medullary tissue. [’rom one to five of these muscular ridges occur in the circumference of the vein (Fig. 2 and 3). Except at those points at which the muscle occurs, the venous wall is extremely thin (Fig. 3). The muscular ridges are frequently so large as to materially obstruct the lumen of the vessel (e. g., the middle vessel in Fig. 2, also the uppermost vessel, which is cut in very nearly longitudinal section), and they form so noticeable a peculiarity that their presence may be considered characteristic of this type of vessel. The writer has never failed to find these peculiar muscular ridges more or less highly developed in each of the human adrenals which he has ex- amined: he believes them to be constantly present. They are less highly developed in the suprarenal vessels of the lower mammals, but even there they may frequently be demonstrated. The muscle fibers of the larger ridges are arranged in bundles which are enveloped in fibro-elastic septa of connective tissue. All of the muscle fibers in these bundles are longitudinally disposed. This arrange- ment is well shown in Fig. 3, in which a large central vein is seen in transection at a point near the entrance of a large branch. Examination of sections somewhat higher in the series shows the union of these two vessels. In the section photographed, the branch has been longitudinally cut. The fine dark lines shown in the figure are bands of elastic fibers which are enveloped in delicate white fibrous tissue inclosing the cut ends of the bundles of smooth muscle. The tendency to form longitudinal ridges is shown in this figure by the irregular distribution of the muscle, one side of the vessel, in both the parent stem and the branch, beitg almost devoid of muscle fibers. The muscular character of these ridges is beyond doubt. 68 The Veins of the Adrenal Fic. 3. Large central veins from the medulla of the human suprarenal gland. The figure shows the distribution of the elastic tissue and the bundles of smooth muscle which are seen in transection in the larger vein and in longitudinal section in the smaller ones below. The series shows these latter vessels to be branches of the former, the section being selected to show a plane near the point of division. The smaller vessels are very ob- liquely cut and the muscle is distinctly longitudinal. Fixation, Zanker’s fluid; stain, Mann’s hematein, Weigert’s elastic tissue, and Van Gieson’s picro-fuchsin; thickness, 10 1; photomicrograph, X 37. Jeremiah 8. Ferguson 69 The writer has observed that the formation of such heavy ridges as those shown in Fig. 3, nearly always occurs at those points where the vessel branches. It is possible that, as in the case of the somewhat similar ridges in the veins of the erectile tissues (see Kolliker’s Handbuch der Gewebelehre, 6te Aufl., 1902, pages 486 and 487), these muscular pro- tuberances may to some extent serve the purpose of valves. As the large central veins approach the hilum of the organ they form still larger vessels which partake of the structure of the suprarenal vein. The point of transition from the one type to the other is variable, occasion- ally the type of the large central veins is continued to the exit of the suprarenal vein at the hilum of the organ. More frequently the primary branches of the suprarenal vein may be traced for a considerable distance into the medulla of the organ, still retaining the type of structure found in the larger vessel. The suprarenal vein presents three coats, intima, media, and adventitia. The tunica intima, in addition to its endothelial lining, possesses a thin membrane of very delicate connective tissue in which occasional branched connective tissue cells may be distinguished ; such cells are, however, very scanty. This coat also contains a delicate network of elastic fibers. The tunica media of the suprarenal vein is extremely thin, rarely ever does it exceed in thickness the tunica intima. It consists chiefly of fibro-elastic tissue, the elastic fibers forming quite a dense network. Few muscle fibers occur in this coat, nowhere are they found in sufficient numbers to form a definite layer, as in veins of similar size in other organs. Some of the muscle fibers are circularly disposed, but many of them are longitudinal. The tunica adventitia is by far the thickest of. the three coats and forms two-thirds to five-sixths of the entire vascular wall. It consists chiefly of smooth muscle fibers, all of which are longitudinally disposed. These smooth muscle fibers form characteristic coarse bundles which are distributed around the entire circumference of the vessel. The largest of these bundles may occasionally form projecting ridges as in the smaller veins, but as a rule the muscular tissue is more evenly distributed than in the central veins. Each of the muscle bundles is enveloped in a peri- mysial sheath of connective tissue, which blends with that of the tunica media. These adventitial sheaths possess a dense network of elastic fibers, in fact the greater part of the elastic tissue in the vascular wall is frequently found in the adventitia. On its outer surface the tunica adventitia is continuous with the capsule of the adrenal or with the adjacent connective tissue. This peculiar type of vessel is not strictly confined to the suprarenal 70 The Veins of the Adrenal gland, but occurs, more or less typically developed, in many of the large abdominal veins, notably in the renal veins and vena cava, into which the suprarenal veins empty. But nowhere is this peculiar venous type more strikingly developed, nowhere is the adventitia relatively so much thicker than the media, nowhere is a greater proportion of the smooth muscle of the venous wall longitudinally disposed, nowhere is there relatively less circular muscle, than in the suprarenal vein. Realizing the intimate relation of the parenchyma of the organ to its blood-vessels, and adopt- ing, if we may, the accepted physiological function of the adrenal—the formation of an internal secretion, a powerful vaso-constrictor which is poured into the blood within the capillaries and veins of the organ—the peculiar longitudinal arrangement of the muscular tissue, the valve-like protuberances at the junctions of the venous vessels, the absence of circular muscle from the walls of the veins of all sizes, and the general appearance of these vessels which are so remarkably different from the veins of most other organs, become, to say the least, extremely significant of a close structural relation, physiologically speaking, to the presence of an astringent secretion in the outflowing blood current. In this connection, one further observation is of importance. In the periadrenal connective tissue are numbers of small veins which return the abundant blood supply of the tissues of this region, most of them emptying into the phrenic veins. Many of these veins do not differ from the similar veins of other parts, but in many others the writer has ob- served that the muscle tissue is almost entirely disposed in a longitudinal direction, a condition which is quite the reverse of that found in the adipose and areolar tissues of other portions of the body. The writer also finds that many of the small veins of the adrenal, instead of opening into the central veins as is usually the case, pursue a less frequent course, penetrating the cortex and capsule of the organ, and emptying into the small veins of the surrounding connective tissue. The frequency with which this condition was associated with the occurrence of longitudinal muscle fibers in the periadrenal veins, suggests a more than casual relationship between the two conditions. SUMMARY. In conclusion, the above facts may be summarized as follows: 1. The efferent blood-vessels of the adrenals form four successive vas- cular types, the sinusoids, the small central vein, the large central vein, and the suprarenal vein. 2. Each of these types presents distinctive characteristics. Jeremiah S. Ferguson 1 3. In all four types circular muscle is either absent or noticably deficient. 4. In the large central veins prominent and characteristic muscular ridges are constantly present, and are frequently in relation with those points at which the branches of these vessels enter. 5. These peculiarities of structure may possibly bear a close physio- logical relation to the function of the adrenal as a gland that forms an internal secretion which has been shown to be a powerful vaso-constrictor and stimulant of smooth or involuntary muscle. BIBLIOGRAPHY. 1. AIcHEL.—Miinch. med. Wochenschr., 1900, XLVII, 1228; and Arch. f. mik. Anat., 1900, LVI, 1. 2. WIESEL.—Anat. Hefte, 1901, XVI, 115. 3}. Ibid., 1902, XIX, 481. 4. Soutiz.—J. de l’anat. et de la physiol., 1903, XX XIX, 197, 390, 634. 5. Frint.—Contrib. dedicated to W. H. Welch, Baltimore, 1900, 153; also in Johns Hop. Hosp. Rep., 1900, IX, 153. 6. Minot.—Proc. Bost. Soc. Nat. Hist., 1900, X XIX, 185. 7. PFAUNDLER.—Sitz. d. Akad. d. Wissensch., Wien, 1892, CI, 515. 8. GotrscHau.—Arch. f. Anat., 1883, 412. . 9 0 . WEIGERT.—Centralbl. f. allg. Path. u. path. Anat., 1898, IX, 289. . FREEBORN.—Proc. N. Y. Path. Soc., 1893, 73. THE BLOOD VESSELS OF THE PROSTATE GLAND. BY GEORGE WALKER, M.D. ‘ Associate in Surgery, Johns Hopkins University. From the Anatomical Laboratory, Johns Hopkins University. WITH 2 COLORED PLATES. As the structures of the body are being more and more carefully in- vestigated it is found that organs are composed of like structural units, which when repeated a number of times form the whole organ. In gen- eral these units are formed by the glandular structures, the blood-ves- sels, or by both, as is the case in the liver. Some eight years ago, at the suggestion of Dr. Mall, I undertook the study of the prostate gland, with the hope of finding structural units in it. In this search I was successful. Since then my work has been continued in the laboratories of Professor Born* of Breslau and Pro- fessor Spalteholz* of Leipzig, and although this communication is sey- eral years late in appearing, it should in reality have preceded those that were published in 1899. In the present study for the most part the prostate glands of dogs were used. Several cadavers were injected and the gross blood supply was studied in part from these. After the animals had been killed by chloro- form, the aorta was exposed just above the bifurcation and injected with various substances. A preliminary washing out of the blood-vessels with salt solution was practised in a few of the first injections, but this was soon discarded as it did not seem to enhance the value of the method. Carmine gelatine, followed by ultramarine-blue gelatine, as an injecting mass, gave the most satisfactory results. About 250 cc. of the carmine gelatine were injected first, the injection being stopped as soon as all of the tissues had acquired a maximum carmine hue. This was fol- lowed by the injection of ultramarine-blue gelatine, which was kept up until no more of the material would pass in. The carmine gelatine 1Walker, George: Ueber die Lymphgefaisse der Prostata beim Hunde. Arch. fiir Anatomie, 1899. 2 Walker, George: Beitrag zur Kenntniss der Anatomie und Physiologie der Prostata, etc. IJbid., 1899. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 74. The Blood Vessels of the Prostate Gland filled the arteries, capillaries, and veins; the blue passed into the arteries and arterioles, displacing the gelatine and filling them, but was stopped at the capillaries because the ultramarine-blue granules were too large to enter them. Ina specimen thus prepared the arteries appear blue, and the capillaries and veins red. This is shown in Figure 1, with colors reversed, in order to present the conventional appearance. As it was impossible to get a perfectly complete injection in one specimen, several of the best were selected and the gaps filled in, with the results as shown in Figure 1. One section, however, is remarkably beautiful and presents a picture very closely resembling that seen in this figure. In order to map out the complete network of arteries surrounding a separate lobule, I injected them with Prussian blue, then opened the urethra, and injected carmine gelatine into a prostatic duct through a very fine blunt hypodermic needle. A specimen made in this way is shown in Figure 2 where the ducts are represented in brown. The capillaries were studied in a specimen which had been completely injected with car- mine gelatine. A very thin section of this was stained with iron hzema- toxylin, and is shown in Figure 3. The basement membrane is arti- ficially tinted with yellow so as to make it visible. The technique of the injecting is rendered difficult by the fact that the situation of the gland in the pelvis is somewhat remote. In all, about 75 dogs were used before a complete circulation cycle could be seen. Cinnabar, lampblack, and various other substances were tried, but they did not prove as good as the combination of carmine gelatine followed by ultramarine-blue gelatine. When the ordinary directions for preparing carmine gelatine were fol- lowed, it always proved difficult to get a perfectly transparent substance. The trouble is connected with the neutralization of the ammonia by the acetic acid. The gelatine should be rendered practically neutral, but if the reaction is carried the least bit too far, the solution becomes cloudy. Sometimes two drops of the acetic acid are sufficient to make turbid a whole htre of the prepared carmine. After a good many trials, the following method was adopted: ‘Take 10 cc. of the ordi- nary laboratory ammonia and dilute with 40 cc. of distilled water, then determine by titration the exact amount of the laboratory acetic acid which will neutralize it. After this determination has been made, 10 grms. of pure carmine are rubbed up with 50 ce. of distilled water ; then 25 ce. of the ordinary ammonia are measured, and a few drops at a time are poured into the carmine mixture which is kept constantly rubbed up. This process is very closely watched, and the ammonia is gradually added until the carmine is completely dissolved, and the mixture becomes George Walker ra) translucent and assumes a dark red color. The amount of ammonia used is determined by referring to the vessel in which the 25 ce. have been measured. ‘The gelatine in whatever proportion it is required—according as a thin or thick solution is desired—is dissolved in the distilled water, and the carmine solution is added to it. We then calculate how much acetic acid will be required for the amount of ammonia which has been used; this is measured and added, drop by drop, to the mixture which is constantly stirred. A sufficient quantity of water is then added to bring the amount up to a litre. I found that in this way I could always obtain a beautifully clear gelatine and was never annoyed by the failures and uncertainties belonging to the other method. ARTERIES. The prostate gland derives its arterial supply from the internal iliac arteries by means of four branches; the superior vesical, the inferior vesical, a small branch from the inferior hemorrhoidal, and a small termi- nal branch from the internal pudic artery. These vessels will be found illustrated in my paper published in 1899. The superior vesical, a branch from the internal iliac, which is given off high up, divides before reaching the bladder, into two fair-sized branches; the lower and smaller branch extends downward and supplies the vesical third of the prostate ; this branch is sometimes called the middle vesical artery. The inferior vesical, which is a large branch, is practically the main blood vessel of the prostate gland, and should be called the prostatic artery for, in the majority of instances, it does not send any branches to the bladder. The major part of the gland is supplied by this vessel; it courses along the vesicorectal fascia and meets the prostate at its lower border, where it usually divides into seven branches, four of these enveloping the anterior, and three the posterior surface. The posterior are about one-half the size of the anterior branches. These vessels are situated in the capsule of the gland and envelop it as the fingers of one’s hand would do in clasping a round object. From these trunks a number of smaller ones are given off, so that a very close arterial network is formed over the surface of the gland. The branch from the inferior hemorrhoidal is not constant; in fact, it appears to be more often absent than present. When it is seen, it occurs as one or two small branches which meet the prostate in its urethral half, and extend over the surface as fine vessels which anastomose with the vesical artery. The internal pudie branch is fairly constant. It extends along the membranous urethra and plunges directly into the prostatic substance usually without giving off any branches to the surface. 76 The Blood Vessels of the Prostate Gland A slight anastomosis is occasionally seen. The vessels supplying the two sides of the gland are distinct. The only anastomosis across the median line is by way of the venous channels around the urethra. From the large superficial branches above described, smaller ones are given off at right angles, and pierce the gland in places corresponding to the divisions of the lobules (Art. Fig. 1). Here they penetrate the fibrous-tissue septa, and extend to the urethra, becoming smaller and smaller, however, as they approach it, so that in this region they are seen as very delicate terminal vessels. As they pass down, they give off branches which penetrate into the lobule and finally divide into myriads of capillaries which pass around the alveoli, and come in very close relationship with the secreting cells. From these cells they are separated simply by a delicate basement membrane composed of fine fibrils. From the superficial vessels branches are given off which enter the lobule di- rectly, that is, they do not pass first into the fibrous-tissue septa (Sup. Br. Fig. 1). On the anterior surface there are usually two branches which do not give off as many smaller ones as the rest, and consequently remain larger and extend over to the middle line, where they dip into the median fissure and supply the median side of the lobules (Med. Br. Fig. 1). The arrangement on the posterior surface corresponds to that seen on the anterior surface, in so far as the supply of the lobules is concerned. On the posterior surface toward the bladder one vessel penetrates the sub- stance of the gland and runs directly to the caput gallinaceum (Art. Col. Sem. Fig. 1). Here it divides into a fine network and supplies the erec- tile tissue of the organ. Before this vessel reaches the eminence a small trunk is given off which extends to the ejaculatory duct (Art. duct. ej. Fig. 1). The branch supplying the caput gallinaceum is usually derived from the pudic; sometimes it comes from the inferior vesical. The arterial supply in the connective tissue toward the urethra is much poorer than in the secreting portion. Here the vessels terminate in fine branches, relatively somewhat sparsely scattered. The arterial arrange- ment is shown on the red side of Figure 1. CAPILLARIES. The capillaries form a very complete and elaborate network around the alveoli of the lobule. Here, as is seen in Figure 3, they surround an alveolus in a more or less circular manner, and upon these vessels the cells rest almost directly, being separated only by the very delicate con- nective-tissue basement membrane. From this outside capillary, a fold- ing in is seen, which forms a definite loop (Cap. L. Fig. 3.) This at George Walker . ity first sight might appear to end blindly, but a more careful study reveals the two branches, which sometimes appear winding around each other, and presenting enlarged club-shaped ends. The cells rest on these as they do on the circular portion. Under the low power, the epithelial cells appear to be in direct contact with the capillaries, and it is only by the aid of the oil immersion that a very delicate connective-tissue basement membrane is seen. This is shown artificially colored as B. M. Fig. 3. This membrane contains a few elastic fibers. VEINS. On the surface of the gland are veins corresponding to the arteries which lie in the capsule. As a rule they merge into two main trunks corresponding to the vesical arteries; occasionally several small branches pass off into the middle hemorrhoidal vein. The superficial veins do not drain the blood from the whole gland, but only from the outer fourth, as is shown in Fig. 1. From the inner three- fourths of the gland the blood passes towards the centre, and into the large venous sinuses which are a continuation of the corpora spongiosa. (Co. Sp. Fig. 1). These immediately surround the urethra. The large venous trunks which collect the blood from the gland do not lie on the same plane as the arteries, but are situated in the fibrous septa some little distance removed from them. ‘These run, as do the arteries, on the outside of the lobule, and are interlobular, not intralobular. For the venous return from the caput gallinaceum there is no distinct vessel cor- responding with the artery, but there are anastomoses with the spongy plexus. The venous plexus around the urethra is, as before stated, a continua- tion of the corpora spongiosa. 'The blood from this region passes away into the internal pudice vein. Occasionally two or three small veins drain the tissues from this region, pass out of the prostate and run along the membranous urethra and off into the vesicorectal fascia. There is an anastomosis of the veins in the prostate and bladder where these organs come together, and also on the outside through the superior vesical veins. There is, of course, an anastomosis of the urethral veins through the corpora spongiosa plexus. SUMMARY. The prostate gland is supplied with blood by branches of the internal iliac arteries, viz., the superior vesicals, inferior vesicals, inferior hemor- rhoidals, and internal pudics; the main blood supply comes from the inferior vesicals. ~~ ‘© 2) The Blood Vessels of the Prostate Gland Branches of these envelop the surface of the gland and give off smaller ones, which penetrate between the lobules in the fibrous-tissue septa. The capillaries are separated from the epithelial cells only by a very thin basement membrane. There are superficial veins corresponding with the arteries. For the outer superficial fourth of the gland the return flow is towards the surface. ‘The inner three-fourths are drained by veins which empty into the venous plexus immediately around the urethra. The lobule is formed primarily by the individual gland ducts as shown in Figure 2. The main arteries surround this lobule which they pene- trate at many points. ‘The veins leave the lobule mainly at its peripheral and central (urethral) ends as shown in Fig. 1. EXPLANATION OF PLATES I AND II. Kia. 1 is from a section of a prostate gland of a dog injected with carmine gelatine and ultramarine-blue gelatine. The arteries in the section were blue, the veins and capillaries red. The section was cut free hand, about 50” in thickness, and cleared both in glycerine and in creosote. In the figure this artery is red and this vein blue. Art., Arteries; Art. Col. Sem., Artery of the colliculus seminalis; Art. duct. ej., Artery of the ejeculatory duct; Col. Sem., Colliculus seminalis; V. Pl., Venous plexus around the ' urethra. Kia. 2. Lobule of prostate from a gland which had been injected with ultramarine-gelatine blue into the artery, and with carmine gelatine into the prostatic duct. Pr. duct., Opening of the prostatic duct into the urethra; Gl. Tis., Gland tissues distended with carmine gelatine; Art., Surrounding artery. In this figure the artery is represented in red and the ducts in brown. Fic. 38. Very thin section from the prostate gland of a dog. Capillaries in red, injected with carmine gelatine. Section stained with iron hematoxylin, with artificial yellow tinting of basement membrane. Oil immersion with one inch eye-piece amplification. Cap., Capillaries; B. M., Basement mem- brane; Gl. Ep., Glandular epithelium; Cap. L., Capillary loop. PEATEM BLOOD VESSELS OF PROSTATE GLAND GEORGE WALKER rulasg* joy” 1 ‘Oia AMERICAN JOURNAL OF ANATONMY--VOL. V BLOOD VESSELS OF PROSTATE GLAND ; PLATE Il GEORGE WALKER ; Fra. 3 AMERICAN JOURNAL OF ANATOMY--VOL. Vv ty THE EMBRYONIC DEVELOPMENT OF THE RETE-CORDS AND SEX-CORDS OF CHRYSEMYS. BY BENNET M. ALLEN, Instructor in Vertebrate Anatomy, University of Wisconsin. WitTH 1 DOUBLE PLATE AND 6 TEXT FIGURES. A glance at the diagrams on the next page will at once serve to show the great difference of opinion that has prevailed in regard to the origin of the sex-cords and rete-cords of the Sauropsida. In fact, it is hard to conceive of any possible manner of origin that has not been held to be correct by some well-known embryologist. The Chelonia have remained almost untouched in the study of this problem. Only one work has appeared upon the rete-cords (Von Moller, 98), while no work has been published upon the subject of the sex-cords. Von Moller studied two turtles, one a specimen of Emys lutaria of 2.5 cm. plastron length, and the other Clemmys leprosa of 4.9 cm. plastron length. He observed no connection between the testis and Wolffian body. This caused him to remark: “Dieser Befund wird héchst auffallig, wenn mann bedenkt dass die Beobachtungen an Amphibien zeigen dass die Verbindungen zwischen Hoden und Wolffschen Giinge schon dann angelegt und vollendet werden, wenn die tibrigen Organe sich noch in der Entwickelung befinden, und wenn das Junge in der Hischale, respective in Uterus eingeschlossen ist. Die zwei von mir untersuchten Schildkréten hatten dagegen schon seit Monaten die Hischale verloren, und doch war bei ihnen noch kein einzige Verbindung zwischen Hoden und Wolffschen Ginge vorhanden, obwohl Anlagen dieser Verbindungen sich bereits vorfanden.” It is quite unfortunate that he considered these stages to be early enough for his purpose, since my work has shown the rete-cords to be formed at a relatively early stage of development in Chrysemys. Von Moller sums up his results as follows: “ Ich finde also bei diesem Thiere zwischen Hoden und Wolffschen Kérper noch keine Verbin- dungen, dagegen im Mesorchium und im oberfiichlichen Bindegewebe der Urniere solide Zellenstringe, fiir welche ich gendtigt bin einen Ur- AMERICAN JOURNAL OF ANATOMY.—VOL. V. 80 The Rete-Cords and Sex-Cords of Chrysemys Text Wig. A. Text Fries. A-D. Diagrams illus- trating various views held by authors whose writings are reviewed in this article. AD.—Fundament of the adrenal body. GER.—Germinal epithelium. M.—Mesentery. M, P.—Mal\pighian corpuscle. R.—Rete-cord. ; S. C.—Sex-cord. U. T.—Uriniferous tubule. Ww. D.—Wolthian duct. sprungsort anzunehmen, der weder in den Geweben der Urniere noch in denen des Hodens liegt denn ich weder im Stande bin einen Zusammenhang mit den gewundenen Kanilchen des Hodens nachzuweisen, noch einem solchen mit dem Epithel Bowmanscher Kapseln oder sonst mit Theilen der Urniere. Ich nehme daher an, dass sie vom Per- itoneum stammen.” No further allu- sion need be made to this article. Turning to the other groups of the Sauropsida, we find a large mass of lit- erature. To intelligently discuss this, we must use precise terms. ‘The sex- cords are those masses or cords of cells which eventually become the seminifer- ous tubules of the testis or the medul- lary cords of the ovary. The rete-cords are those structures which eventually give rise to the canals which unite the seminiferous tubules or medullary cords of the sex-glands with the ducts of the mesonephros. It is not necessary to enter into a lengthy review of the literature upon this subject. That has been thoroughly done by Born, 94, Mihalkovics, 85, Janosik, 85, Coert, 98, Winiwarter, 00, and others. A few diagrams will suf- fice to show, in a sufficiently vivid man- ner, the wide differences between the many views upon this subject as ex- pressed in the papers most worthy of note. The names associated with the differ- ent diagrams, Text Figures A-D, are those of the authors who have held views represented by the diagrams so indicated. After the name of each Bennet M. Allen . 81 author are placed the names of the forms which he studied in arriving at his conclusions. A. Tubules arise from the Wolffian duct and grow into the sex-gland fundament. Their distal portions form the sex-cords while their prox- imal portions form the rete-tubules. 70, Waldeyer—Chick (Gallus). B. According to this view, evaginations grow out from the capsule of Bowman. Distal branches from these stems pass down into the sex- gland fundament to form sex-cords, while the more proximal portions of the evaginations remain attached to the capsules of Bowman and serve as rete-tubules. Braun, 77, Platydactylus, Tropidonotus. Weldon, 85, Lacerta. Hoffmann, 89 and g2, Lacerta, Hematopsis, Sterna, Gallinula. Semon, 87, Gallus. Peter, 04, Lacerta. Braun, 77, considers the rete-sex-cords to be, in the strictest sense, segmental in arrangement. He expressly denies that the cells that con- tribute to the formation of the adrenal body are derived from branches of the evaginations from the capsules of Bowman, as asserted by Weldon, 85 and Hoffmann, 89 and 92. These two last named authors asserted that each evagination divides into a dorsal and a ventral branch, the _ former supplying the cells of the cortical portion of the adrenal body, and the latter forming the sex-cords. Semon, 87, was not so clear upon the question. He merely stated that the anastomosing cords arising from the capsule of Bowman pass into the adrenal and sex-gland fundaments, —the more dorsal to the former, the more ventral to the latter. C. Large numbers of cells migrate from the germinal epithelium into the underlying stroma. From this unorganized blastema, the sex-cords are formed, suddenly crystallized as it were. The rete-cords are formed of evaginations from the capsule of Bowman. Schmiegelow, 82, Gallus. Mihalkovies, 85, Lacerta, Gallus. Laulanie, 86, Gallus. D. According to Janosik, the sex-cords arise as direct ingrowths from the germinal epithelium. Cords of cells grow from their distal ends to the capsules of Bowman, thus forming the rete-cords. Cords of cells grow in from the peritoneum between the sex-gland fundament and the mesentery to form the cortical portion of the adrenal body. Janosik, go, Gallus. 6 oD wo The Rete-Cords and Sex-Cords of Chrysemys The following table will show the great difference of opinion held by authors working upon the same identical species. The view held is in- dicated in the same manner as above. é Lacerta agilis—Weldon (B) ; Hoffmann (B); Mihalkovies (C). Chick (Gallus)—Waldeyer (A); Semon (B); Mihalkovies (C) ; Laulanie (C); Schmiegelow (C); Janosik (D); Weldon (?). We cannot close an account of the literature upon the subject without reférring to the work of Semon, g1, upon Ichthyophis, one of the Gym- nophiona, and a paper by Semper, 75, upon the Sex-glands of the Elasmobranchs. Semon, gi, considers the nephrotome to be the ventral portion of the mesoblastic somite. This view, by the way, is also held by Brauer, o2. Semon states that after the nephrotome breaks away from the myotome and sclerotome, it still remains attached to the peritoneum (unsegmented mesoderm) by means of two bridges of cells—a lateral and a medial. The major part of each nephrotome forms a Malpighian corpuscle of the mesonephros. The lateral of the two bridges connecting it with the peritoneum becomes its peritoneal funnel (nephrostome), while the medial bridge sends out a process which divides into a dorsal branch pass- ing to the adrenal body, and irregular branches (sex-cords) non-seg- mental in character, that pass to the sex-glands, there to come in contact, in the case of the male, with the seminal vesicles, which are derived from the germinal epithelium. He holds a theory that the pronephros extends in rudiment, at least, along the entire length of the mesonephros, and that this pronephric rudiment develops into the adrenal body. He considers the dorsal branches spoken of above, to be these vestiges of the pronephros. Semper, 75, gives the most interesting account of the rete in the male of Acanthias. According to him, each of the 34 primary Malpighian corpuscles of the kidney is connected with the body cavity by a peritoneal funnel. Seven of the most anterior of these funnels lose their union with the peritoneum and take on the form of vesicles. Three or four of them now fuse together to form the “ central canal,” which lies at the base of the testis and parallel with it. From this central canal there arise a number of irregular anastomosing canals which extend into the testis and come in contact with the true sex-structures (Vorkeimketten) that have arisen from the germinal epithelium. This net-work of rete-cords he calls the rete-vasculosum. In other forms there exists a somewhat modified condition of consider- able interest. In comparing Acanthias and Mustelus, Semper said: “ Trotzdem scheint ein grosser Untershied in Bezug auf die Entstehung Bennet M. Allen 83 des Centraleanals des Hodens zwischen Mustelus und Acanthias zu beste- hen. Bei dieser Gattung wird er seiner ganzer Linge nach gebildet durch die Verwachsung der seitlich vom Segmantalgang nach vorn sich wenden- den Trichterblasen. Seithche Ausbuchtungen der letzteren bilden den basalem Theil der rete vascolosum. Bei Mustelus dagegen ist es nur der vorderste tiber die Hodenfalte hinaus vorgreifende Abschnitt des Central- canals den mann entstanden ansehen kénnte, denn nur an diesen setzen sich 2 (oder 3) Segmentalgiinge an. Der ganze iibrige viel langere Theil des Centralcanals entsteht aus den in das Stroma der Epithelfalte eingestiilpten Keimepithel Zellen.” Balfour, 78, shows that in the forms which he studied, the anterior end of the sex-gland only, was directly united to the mesonephros by means of the rete-canals. The condition in the lizard Platydactylus is, according to Braun, 77, quite similar. He considers the union to be formed in adult life by two or three rete-cords joining the anterior ends of mesonephros and testis; although he states that they are connected along the entire length of the testis in early stages. Hoffmann, 89, finds the union of rete-cords to be complete and intact along the entire length of the testis in Lacerta at the end of the first year. He did not study older specimens. Semon, 87, claims that there is a degeneration of the rete-cords at both the anterior and posterior ends of the sex-gland of the chick; but Janosik, go, denies this. MATERIAL AND TECHNIQUE. Our lakes in the vicinity of Madison abound in the little painted tortoise, Chrysemys marginata. The number of embryos to be gathered in the season is limited only by ones patience in the work of preserving them. I have prepared a large number of serial sections of the meso- nephros and sex-gland, as well as of entire embryos, comprising an un- broken chain of stages from gastrulation to adult life. As a fixative, Tellyesnitzky’s Bichromate-acetie fluid was almost ex- clusively used, as it gave most excellent results. Haidenhein’s iron-alum hematoxylin stain proved unsatisfactory for early stages of the embryos under 7 mm. length. For later stages than this it gave excellent results and was used almost exclusively. A counter-stain of Congo red was also employed. The sections were cut at a thickness of 7 p. Measurements were made of the distance between the cervical bend ‘and the tail bend (C-7’). In the later stages the length of carapace was also given. To more clearly understand the origin of the sex-cords, it will be 84 The Rete-Cords and Sex-Cords of Chrysemys necessary to first understand certain features in the development of the mesonephros. Reference to these features will be made only in so far as they concern the subject of this paper. In an early stage of develop- ment (C-7. 3.5 mm.), a section through the posterior part of the sex- gland fundament shows the mesoblastic somites to be attached to the lateral plates by the unmodified middle plate (Text Figure #). The cells of the latter are arranged in two rows, in such a manner as to leave a line of weakness between, which may be considered as a rudimentary lumen, connecting the body-cavity on the one hand with the cavity of the Text Fic. E. Transverse section through the middle of the mesonephros fundament of an embryo of 3.5 mm. C-T. length. AO.— Aorta. NO.—Notochord. EC.—Ectoderm. SO—Somatopleure. MY.—Myotome. SP.—Splanchnopleure. N.—Neural canal. WD.— Wolffian duct. NEP.—Nephrotome. mesoblastic somite on the other. In the region posterior to this, these relations become even more marked. More anteriorly, just behind the interesting region which forms a transition between the pronephros and mesonephros, the middle plate is found to be wholly broken away from the mesoblastic somites, and to be divided by transverse intervals into nephrotomes which occur in the number of three to four per somite. I found no evidence of a primary metamerism of these nephrotomes. So soon as the middle piece appeared to be broken up at all, the number of nephrotomes here recorded appeared. Special investigation along this Bennet M. Allen : 85 line, however, might show a primary metamerism, from which the above described condition was derived by further secondary splitting of the nephrogenous tissue. Hach nephrotome becomes vesicular to within a short distance of the peritoneum thus forming the primary Malpighian corpuscles. ‘The remaining portion of the nephrotome uniting it with the peritoneum becomes, in later stages, the peritoneal funnel or nephros- tome, while the uriniferous tubule arises as an outgrowth from the distal end of the nephrotome. The mesonephric peritoneal funnels are vestigial structures from the time of their origin. In later stages (C-7. 6 mm.), two sharply defined regions of the mesonephros may be distinguished from one another. In the anterior part of the sex-gland, only the primary Malpighian corpuscles are formed. Each is well developed, the glomerular invagination having already taken place. The 11th to 21st Malpighian corpuscles are con- nected with the peritoneum by peritoneal funnels (Plate I, Fig. 5), some of which are much better developed than others, there being great vari- ation among them. In the best developed among them, the end attached to the peritoneum flares open to form an actual funnel-like mouth, yet this opening is never continuous with that of the Malpighian corpuscles. The greater part of the peritoneal funnel is merely a cord of cells. In some cases even, it has lost its continuity with the capsule of Bowman. At this stage the first ten Malpighian corpuscles are without peritoneal funnels. Caudad of the 21st Malpighian corpuscle, each nephrotome shows two or three rudimentary vesicular enlargements. Each enlargement is des- tined to form a Malpighian corpuscle. The most ventral of these we shall consider as the primary Malpighian corpuscle. It is still rather broadly connected with the peritoneum. This place of union we shall consider as a rudimentary peritoneal funnel, although it has no flaring opening. In later stages, secondary and tertiary Malpighian corpuscles appear in the anterior region described above, thus making the total number per somite approximately equal to that in the posterior region. Roughly speaking, from nine to twelve Malpighian corpuscles in all, appear in each somite. Reference to Plate I, Fig. 1, will show certain of the points mentioned above. Furthermore, one can see an elongated mass of tissue that ex- tends from each peritoneal funnel dorso-mediad and which lies just lat- erad of the V. renalis revehens (vena cava). This we shall term the fun- nel-cord. They appear in both the anterior and posterior regions of the mesonephros as described above and are co-extensive with the sex-gland 86 The Rete-Cords and Sex-Cords of Chrysemys fundament, in fact they are found for a short distance anterior to it Naturally each funnel-cord lies opposite a primary Malpighian corpuscle, and likewise to the series of secondary, tertiary, etc., corpuscles formed in a vertical row above it. Each cord is made up of rather loosely arranged cells that bear a rather close resemblance to the mesenchyme cells. In fact the nuclei of these cells, the funnel cells, and the cells of the’ perit- oneum are not to be distinguished from one another. Cytoplasmic differ- ences alone appear and these depend upon the density of the tissue. In some cases a slight evagination of the capsule of Bowman is found at the point where it joins the peritoneal funnel. This evagination may take various forms and in many cases is wholly absent. Such an appear- ance may have led to the view held by some authors that these cords arise as outgrowths from the capsules of Bowman. This view would be still further justified if the peritoneal funnel were to break away from the peritoneum at a stage prior to that observed. There can be no question, however, but that the funnel-cords are outgrowths from the peritoneal funnels; in fact their bases are the funnels themselves. The distal portions of the funnel-cords lie above the vena cava in the fundament of the adrenal body, contributing the greater part of the tissue that in later stages constitutes the cortical substance of that gland. Perit- oneal ingrowths may also be seen extending dorso-laterad from the peritoneum at a point near the base of the mesentery to the adrenal fun- dament. These also contribute to the cortical tissue of the adrenal body. They are of less regular occurrence than the funnel cords, and in later stages lose their connection with the peritoneum, although they are easily distinguishable in the stage of 7 mm. C-7’. length. The sex-gland can be clearly distinguished in the embryo of 6.8 mm. C-T. length. It extends through six somites, although the last 4 of it remains in a rudimentary condition. Even in this stage it consists merely of thickened peritoneum containing scattered primitive sex-cells (Ureier). The sex-gland develops from a portion of the germinal epithelium lying between the bases of the funnel-cords and the base of the mesentery. In the embryo of 6 mm. C-7'. length, a few primitive sex-cells were already beginning to appear in this region. At this time, the V. renalis revehens (vena cava) les close above the germinal epithelhum which has not yet begun to thicken to form the sex-cords. In an embryo of 6.8 mm. C-T’. length the germinal epithelium has sent out masses of cells towards the VY. renalis revehens, and has at the same time bent outward in such a manner as to form in transverse section, the periphery of a semi-circle, the interior of which is occupied by the sex-cords. The tips of the sex- Bennet M. Allen — SY cords remain stationary and almost, if not quite, in contact with the wall of the V. renalis revehens, while their bases grow peripherally with the germinal epithelium. Mesenchyme cells between the sex-cords are few and far between. At some points, the tips of the sex-cords penetrate to one side or the other of the V. renalis revehens, and penetrate to the adrenal fundament to which they contribute. Plate I, Fig. 3 shows a wax plate reconstruction of a large part of ae sex-gland of the 7 mm. C-7. stage. In this stage the carapace has just formed. The prominent funnel-cords afford the most striking feature of the model. Their bases are attached to the peritoneum at the lateral boundary of the sex-gland. They extend in a dorso-medial direction. It will be noticed that each is connected with a primary Malpighian corpuscle. The other Malpighian corpuscles are not shown in the model. Mediad of the funnel-cords the peritoneum is greatly thickened, form- ing numerous irregular elevations and ridges between which are deep clefts and pits. These thickenings are the sex-cords. They are solid and their cells show no evidence of a radial arrangement to form a lumen. The peritoneum is far more cut up than would appear from the model. Many slight fissures separating adjacent sex-cords do not appear. In any case many of these rudimentary sex-cords are from the first, united with the funnel-cords while others anastomose freely with one another, so that all are either directly or indirectly connected with the latter. Primitive sex-cells are frequently met with in the germinal epithelium, as well as in the distal parts of the funnel-cords. Aside from the scattered primitive sex-cells, these tissues are composed of ordinary perit- oneal cells. The cells of the germinal epithelium are so crowded as to make it stain very deeply. The sex-cords are less dense, their cells being distinct and having clear, sharp outlines, thus differing from those of the sex-cords of the pig and rabbit, in which a syncytium is formed among the pure peritoneal cells. The cells of all but the most proximal parts of the funnel-cord are elongated in the direction in which the cords extend. This elongation of the cells is so marked that they resemble the surrounding mesenchyme save for the fact that their cyto- plasm is more dense thaw that of the latter. The cells are so closely associated that these funnel-cords stand out quite clearly from the sur- rounding mesenchyme. The proximal part of each funnel-cord is met by one, or sometimes two, evaginations from the capsule of Bowman of the adjoining primary Malpighian corpuscle. These evaginations are very clearly distinguish- 88 The Rete-Cords and Sex-Cords of Chrysemys able in this stage from the tissue of the funnel-cords but are in close contact with them. In earlier stages the funnel-cords are not even in contact with the capsules of Bowman, although they lie close to them. In these stages there are no evaginations from the capsules of Bowman, although a thickening of the cells of the medio-dorsal portions of them indicates the general region where these evaginations will take place. In the much earlier stages described above, 6 mm. C-7’., the primary union of Mal- pighian corpuscle, peritoneal funnel and funnel-cord has already been described. The later union of Malpighian corpuscle and funnel-cord is a secondary one, and has nothing to do with the temporary primary union. The breaking away and reuniting of these elements seems to be a useless process which I confess I am at a loss to explain. I can merely describe it. It is, however, a most easily demonstrated fact. In later stages, the evaginations from the Malpighian corpuscles closely fuse with the funnel-cords, and are not to be distinguished from them. As development proceeds, the primary Malpighian corpuscles are often drawn some distance laterad of the sex-gland, at the same time pulling the funnel-cords laterad and causing them to stretch. In these cases each funnel-cord becomes sharply bent at the point where the evagination from the capsule of Bowman meets it; it is then continued in a dorso- medial direction to the adrenal body. As shown above, each primary Malpighian corpuscle is connected with the sex-cord by a cord of tissue, formed by an evagination from the capsule of Bowman plus the basal portion of a funnel-cord. These strands uniting the mesonephros with the sex-gland are the rete-cords and constitute the rete-testis or rete-ovaril, as the case may be. Im these later stages the funnel-cords are more elongated and slender, but far more compact than in the early stages. Plate I, Fig. 4 shows the rete-cords and the relation that they bear to the sex-cords and primary Malpighian corpuscles. Here the base of the funnel-cord lies within the sex-gland and forms one of the sex-cords. This has been observed in many cases. In very many instances, however, '- the funnel-cords lie wholly outside the sex-gland, their bases being still attached at a greater or less distance from the sex-gland to the peritoneum covering the mesonephros. It will be noticed that the two rete-cords shown in this model are united to one another by a thickening of each in the direction of the long axis of the sex-gland. This represents a tendency to form a longi- tudinal canal uniting the rete-cords as in the Amphibia and to a certain extent in the Elasmobranchs, and in the lizard (Braun, 77). This Bennet M. Allen ~ 89 longitudinal canal remains incomplete, however, although it may unite several rete-cords in the manner shown. Young males taken at the time of hatching, show many of the rete- cords to have already acquired a lumen in places. The rete-cords of females at this age do not show a lumen, nor do they at any time, because they have already paused in development. They are, however, still recognizable. Up to this point no distinction of sex has been noted although well marked differences had begun to appear in the stage of 13 mm. O-7. length. Close study has yet to be made to determine the earliest evidences of sex differentiation. It is not our aim to follow the later development of the rete-cords or sex-cords. In its general features, the further development of the sex- glands of the turtle shows many points of similarity to that in the mam- mals. The sex-cords degenerate in the female forming the medullary cords while the “cords of Pfliiger” arise as a later thickening of the germinal epithehum. In the males the sex-cords lengthen, assuming a more regular form and arrangement. Their thorough anastomosis with one another allows the semen to be poured from several into a common rete-cord. The mesonephros degenerates leaving a number of the urin- iferous tubules to function as vasa efferentia. In the adult male the rete- cords are found to be reduced in number, there being nine in the specimen studied while sixteen were counted on the right side of an embryo of C-T. 8 mm. length. No attempt was made to determine how or when this reduction was brought about. It is quite probable that some rete- cords are weak and become broken by shifting of the organs in the process of growth. In any case there is no systematic degeneration of the rete-cords in any particular region or regions along the sex-gland. SUMMARY AND CONCLUSIONS. The sex-cords are formed from irregular ingrowths of the germinal epithelium. It is not until relatively late in development that they take on the semblance of cords. They are made up of ordinary peritoneal cells, together with primitive sex-cells which are also found in the peritoneum at this stage. The rete-testis and rete-ovarii are formed by the union of funnel-cords with evaginations from the capsules of Bowman. ‘The funnel-cords are derived from the peritoneal funnels of the Malpighian corpuscles. They occupy a region lying along the lateral edge of the sex-gland, and not only co-extensive with the latter, but extending a short distance anterior to it. The bases of the funnel-cords may, or may not, be included in the sex-gland to form a part of the seminiferous tubules of the testis or 90 The Rete-Cords and Sex-Cords of Chrysemys medullary cords of the ovary, as the case may be. The proximal portions of these funnel-cords go to form a large part of the rete-testis-ovarii, while the more distal portions join the adrenal fundament and contribute the major portion of the cortical substance of that organ. This leads me to briefly consider the adrenal body, although this was not within the original plan of the present work. Soulié, 02, finds that in Lacerta and the chick, the cortical substance arises wholly from cords of cells proliferated from the peritoneum mediad of the sex-gland and at the base of the mesentery. He states, however, that these cords become closely applied to the capsule of Bowman of the Malpighian corpuscle. It is difficult to understand how, arising from the base of the mesentery, they could reach the Malpighian corpuscle without growing dorsad along the medial side of the V. renalis revehens to the adrenal body fundament, and thence laterad and ventrad to the Malpighian corpuscle. It is diffi- cult to understand how they could take this course, without passing through and beyond the fundament of the adrenal body. There certainly are, 1n the turtle, cords of cells that arise as Soulié and others claim, near the base of the mesentery, and these contribute to the formation of the adrenal body; but certain sex-cords and the funnel cords contribute to it as well, and in even greater measure. Brauer, 02, also holds a view similar to that of Soulié as regards Hypogeophis one of the Gymnophiona. Poll, 03, reached similar results with the Elasmobranchs, Acanthias and Spinax. Be this as it may, I feel quite sure of my ground in the case of Chrysemys, and the work of Weldon, 85, and Hoffmann, 89, would lend color to this view, though they hold views in some points radically differ- ent from mine. In this connection it may be well to state that several of Hoffmann’s, 89, figures of the “ Sexual Strange” would serve fairly well to represent the funnel-cords as I have seen them. They certainly do not prove his contention that the cords in question, sex-cords and adrenal-cords, arise from the capsule of Bowman; although he has so interpreted them. Those who held view C, probably used insufficient material and lacked the intermediate stages between the period just before the formation of the sex-cords and those subsequent to their separation from the germinal epithelium. Janosik, 85, D, worked upon the chick. It is quite possible that future work may in large part substantiate his results for that form. My results agree with his as regards the origin of the sex-cords,: but differ from his upon the origin of the rete-tissue, although even here there may be a reconciliation between our views. In the literature upon the morphological significance of the uro-genital Bennet M. Allen — 91 system we have some melancholy examples of the futility of making rash hypotheses unsupported by a sufficient array of facts. Still it is of interest to consider the possible interpretation that may be placed upon these structures when they are viewed from the standpoint of phylogeny. I am inclined to consider the funnel-cords as modified sex-cords. The fact that their distal extremities contribute to the formation of the adrenal bodies does not conflict with this interpretation, because that is also true of undoubted sex-cords. The funnel-cords arise just laterad of the true sex-cords and in a very similar manner. The fact that they arise from the peritoneal funnel would not be contrary to this view if the R 2 eee lee : UMM HH fe AIP WD M Text Fic. F. Diagram to show essential structures of the mammalian sex-gland. M.—Mesonephros. S. O.—Sex-cord. MP.—Malpighian corpuscles. V.—Vestigial portion of genital R.—Rete-region. ridge. R. C.—Rete-cord. W. D.— Wolffian duct. S.—Sex-gland region. funnels could be shown to be mere recesses of the peritoneum, and similar to the latter in histological character. A more careful study of the origin of the sex-glands in the Amphibia is much to be desired as it might throw new light upon this question. It will be of interest to compare the results of this paper with those of a previous paper upon the same structures in the pig and rabbit. Allen, 04. The very schematic diagram of the testis of the pig (Text Figure Ff), shows the following points seen in a sagittal section passing through the genital ridge and the mesonephros. The genital ridge may be divided into three regions: (1) rete, (2) sex-gland, (3) rudimentary sex-gland ridge. The rete-cords are homodynamous with the sex-cords, being formed at the same time and in the same manner as the latter, and occupying 92 The Rete-Cords and Sex-Cords of Chrysemys the anterior third of the genital ridge, whose middle portion is occupied by the sex-gland. As the rete-cords develop, they come in contact with slight evaginations from the Malpighian corpuscles in that part of the mesonephros which lies nearest the rete region. They then grow back to the anterior portion of the sex-gland and at a relatively late period of development advance along its entire length, giving off numerous branches (tubuli recti) which fuse with the tips of the seminiferous tubules. The rete-cords of the mammals are the peritoneal ingrowths of the anterior part of the genital ridge. Speaking in terms of phylogeny they are the sex-cords of the anterior part of the sex-gland. The anal- ogous structures of the turtle, the funnel-cords, appear at intervals along the entire lateral margin of the sex-gland. It is quite probable that the mammalian sex-gland was derived from that of some reptilian group and that some now existing groups of reptiles may show sex-gland conditions from which those of the mammals were derived. No existing group is more likely to show mammalian affinities than that of the Chelonia. Nothing exactly corresponding to the funnel-cord has ever been found in the embryonic development of the mammals. It is true that Aichel, oo, has found that the cortical portion of the adrenal body of the rabbit (Lepus) arises from funnel-hke invaginations of the peritoneum near the base of the mesentery. He is very positive in his claim that these are the peritoneal funnels of the mesonephros. Nevertheless, he does not claim to have followed these funnels back to stages in which they were actually connected with the Malpighian corpuscles. The rete-tubules that may have directly united the sex-gland proper along its entire length with the adjacent Malpighian corpuscles of the mesonephros have disappeared without leaving a recognized vestige, in any of the mammals thus far studied. The rete-region of these mammals has been evolved from that part of the genital ridge which was primitively the anterior part of the sex-gland in the ancestors of the mammals.’ It is scarcely possible to be more specific as regards the nature of the rete-region of the mammals. Two assumptions are possible: one, that 1Tt will be well to note that in Chrysemys, several funnel-cords occur in a well-marked region, anterior to the sex-gland, in which the sex-cords remain vestigial. Upon closer study of some sagittal sections of the sex-gland and mesonephros of Chrysemys I have been struck with the resemblance that this region bears to the rete-region of the pig and rabbit as seen in similar sections. In Chrysemys the funnel-cords of this anterior region together with those of the sex-gland region are joined to form the central canal. This shows some points of resemblance to the portions of the rete-cords lying parallel to the peritoneum anterior to mammalian sex-gland. Bennet M. Allen ~ 93 the sex-cords have disappeared leaving only the funnel-cords, the other, that the sex-cords which primitively existed in this region have taken on the character and function of funnel-cords. It is difficult to decide this question. I can merely say that the latter assumption seems the more probable one, because often two or more rete-cords can be seen in a single transverse section to arise from more than one point of the peritoneum covering the rete ridge. In fact the strongest and most nu- merous rete-cords arise from the portion of it that lies nearest the mesen- tery. This question might be solved with certainty by a study of the conditions in the Monotremes or even in other less primitive groups of mammals. LITERATURE CITED. AICHEL, OTTO, oo.—Vergleichende Entwickelungsgeschichte und Stammes- geschichte der Nebennieren. Arch. f. mikr. Anat., Bd. LVI, 1900. ALLEN, B. M., 04.—The Embryonic Development of the Ovary and Testis of the Mammals. American Journal of Anat., Vol. III, 1904. Batrour, F. M., 78.—A Monograph of the development of the Elasmobranch Fishes. Works of F. M. Balfour, 1878. Braun, M., 77.—Das Urogenitalsystem der einheimischen Reptilien. Arb. Zool.-zoot. Institut, Wiirzburg, Bd. IV, 1877. HorrMann, C. K., 89.—Zur Entwickelungsgeschichte der Urogenitalorgane bei den Reptilien. Zeitschr. f. wiss. Zool., Bd. XLVIII, 1889. 92.—Sur le dévéloppement de lV’appareil. uro-génital des oiseaux. Verh. d. Koninklyke Akademie v. Wetenschappen te Amsterdam. Sectie 2, Deel I, No. 4, 1892. JANOSIK, J., 85.—Histologisch embryologische Untersuchungen tiber das Uro- genitalsystem. Sitz. Ber. Akad. Wien, 3 Abth., Bd. XCI, 1885. go.—Bemerkungen tber die Entwickelung des Genital Systems. Sitz. Ber. Akad. Wien, 3. Abth., Bd. XCIX, 1890. LAULANIE, F., 86.—Sur le mode d’évolution et la valeur de l’épithelium germi- natif dans le testicule embryonnaire du Poulet. C. R. Soc. de Biologie, T. 3, 1886. ; MIHALKOvics, V., 85.—Untersuchungen tiber die Entwickelung des Harn- und Geschlechtsapparates der Amnioten. Inter. Monatschr. f. Anat. Hist., isxol, Aig alkegslay MOLLER, F. v., 99.—Ueber das Urogenitalsystem einiger Schildkroten. Zeitschr. f. wiss. Zool., Bd. LXV, 1899. The most plausible theory is that the rete-region of the mammals has not been directly derived from a condition like that in Chrysemys; but that the genital ridges of both have been derived from a type in which the anlage of the sex-cords was co-extensive with that of the funnel-cords. To be more exact then, the rete-region of the mammals corresponds to the anterior end of the sex-gland of the turtle plus the modified region of funnel- cords anterior to it. ; 94 The Rete-Cords and Sex-Cords of Chrysemys ‘ Peter, K., 04.—Normentafel zur Entwickelungsgeschichte der Zauneidechse (Lacerta muralis). Normentafeln z. Entw. gesch. d. Wirbelthiere, Heft IV, 1904. Pott, H., 03.—Die Anlage der Zwischenniere bei den Haifischen. Arch. f. mikr. Anat., Bd. LXII, 1903. SCHMIEGELOW, E., 82.—Studien tiber die Entwickelung des Hodens und Neben- hodens. His u. Brawne Archiv f. Anat. u. Physiol., 1882. SEmMoN, R., 87.—Die indifferente Anlage der Keimdrtisen beim Htthnchen und ihre Differenzierung zum Hoden. Jena Zeitschr. f. Naturwiss., Bd. ~ XXI, 1887. go.—Ueber die morphologische Bedeutung der Urniere in ihrem Ver- haltniss zur Vorniere und Nebenniere und tiber ihre Verbindung mit dem Genitalsystem. Anat. Anz., Bd. V,°1890. g1.—Studien tiber dem Bauplan des Urogenitalsystems der Wirbel- thiere. Jenaische Zeitschr. f. Naturwiss., Bd. XXVI. SEMPER, C., 75.—Das Urogenitalsystem der Plagiostomen. Arb. Zool.-zoot. Institut, Wurzburg, Bd. II, 1875. SOULIE, 04.—Récherches sur le dévéloppement des capsules Surrénales chez les vertébrés Supérieurs. Journ. de l’Anat. et de la Phys., T. 39. WALDEYER, W., 70.—Hierstock und Hi. Leipzig, 1870. WELDON, W. F. R., 85.—On the Suprarenal Bodies of the Vertebrata. Quart. Journ. of Micr. Sci., Vol. XXV, 1885. EXPLANATION OF PLATE. Ao.— Aorta. P.—Peritoneum. Art.—Arterial branch passing to P. F.—Peritoneal funnel. the Malpighian corpuscle. P. C.—Posterior cardinal vein FC.— Funnel-cord. SC.—Sex-cord. M.—Mesentery. Vy. R. R—Y. renalis revehens. WM. C.—Malpighian corpuscle. W.D— Wolffian duct. Fic. 1. Transverse section of the mesonephros and sex-gland fundament of an embryo of 6 mm. C-T. length. X 190. Fig. 2. Transverse section of the sex-gland fundament of an embryo of 7 mm. C-T. length (carapace 5 mm. long). > 190. Fic. 3. Wax plate reconstruction of the indifferent sex-gland of an em- bryo of 7 mm. C-T. length (carapace 5 mm. long). This includes as much of the sex-gland as lies within a little more than two somites. X 190. Fig. 4. Reconstruction of a small part of the sex-gland of an embryo of 13 mm. C-T. length (carapace 12 mm. long). X 190. Fic. 5. Drawing of a part of a section adjacent to that shown in Fig. 1. The proximal portion of the peritoneal funnel is here better shown than in Tie ale ig i) ba Ce THE RETE-CORDS AND SEX-CORDS OF CHRYSEMYS BENNET M. ALLEN Aes AMERICAN JOURNAL OF ANATOMY--VOL. V PLATE | THE DEVELOPMENT OF THE LYMPHATIC SYSTEM IN RABBITS. BY FREDERIC T. LEWIS, A.M., M.D. From the Embryological Laboratory, Harvard Medical School. WitH 8 TExT FIGURES.? In following the transformations of the subcardinal veins in rabbits, the writer observed that a portion of those veins seemed to become de- tached from the venous system, and to be transformed into lymphatic vessels (02, p. 238). This supposition is not identical with the theory that the lymphatic system is a gland-like outgrowth of venous endothel- ium, always connected with the veins by means of the lymphatic ducts. It differs also from the older idea that lymphatic vessels are excavations in mesenchyma. In favor of this mesenchymal origin, the work of Sala, 00, is the most convincing. He observed in the chick that both the posterior lymph heart and the thoracic duct arose independently of the veins or of other lym- - phatics, and that their permanent openings into the veins were acquired subsequently. In the rabbit, as will be shown presently, there are many disconnected lymphatic spaces, but to their origin from mesenchyma there are four objections: 1st. The lymphatic spaces do not resemble mesen- chyma even when it is oedematous, but on the contrary, are scarcely dis- tinguishable from blood-vessels (Langer). 2d. After being formed, the lymphatics increase like blood-vessels, by means of blind endothelial sprouts, and not by connecting with intercellular spaces (Langer, Ranvier, MacCallum, Sabin). 3d. In early embryos, detached blood-vessels may be seen without proving that blood-vessels are mesenchymal spaces. These detached vessels are not far from the main trunks, from which they may have arisen by slender endothelial strands, yet often the connecting strands cannot be demonstrated. A similar supposition would account for detached lymphatic vessels. 4th. The endothelium of the embryonic lymphatics is sometimes seen to be continuous with that of the veins. 1This investigation, and the one which follows, were accomplished with the aid of a Bullard Fellowship, established in memory of John Ware. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 96 The Development of the Lymphatic System in Rabbits The second theory, that of the gland-hke origin of the lymphatic system, is supported by the remarkable injections of pig embryos, made by Prof. Sabin.” She considers that in mammals, this system buds from the venous endothelium at four points, forming four lymphatic ducts. The ducts are dilated to form four lymph hearts, which, though destitute of muscles, correspond with the four lymph hearts of amphibia. Starting from these hearts, lymphatic outgrowths invade the body, and those from the anterior pair unite with those from the posterior pair. Then the posterior hearts lose their original openings into the veins, but those of the anterior hearts persist as the outlets for the thoracic and right lymph- atic ducts respectively. The lymph hearts themselves are said to be- come transformed into lymph nodes (05, p. 355). According to this idea, the lymphatic vessels are true lymphatics from their earliest inception. 'They differ from other branches of the veins by their very oblique angle of entrance, and by failing to anastomose with arteries or veins. Anastomoses with other lymphatics are abundant, due to absorption of contiguous walls (Ranvier, 97, p. 74). The supposition suggested by the study of the subcardinal veins is intermediate between those of Sabin and Sala. The endothelium of the lymphatics is considered to be a derivative of that which lines the veins, since the lymphatics are at first a part of the venous system; but by becoming detached from their origins these lymphatics form closed sacs in the mesenchyma. Later they acquire permanent openings into the veins, and many connections with other lymphatics. In studying the development of the lymphatic vessels, several methods have been employed. Sala used serial sections, generally of injected embryos, and made wax reconstructions of the posterior hearts. Sabin perfected the method of injection which had been employed by Ranvier for pigs of 100 mm., so that it was applicable to those of 20 mm. By this means she studied the large jugular lymph sacs, or “ anterior hearts,” which, as Saxer discovered (p. 370), are the earliest lymphatic vessels to appear. On the basis of injections she was enabled to present the first connected account of the development of the mammalian lymphatic system. This was illustrated by a series of conventional diagrams, in which the blood-vessels are shown without details. Thus the internal 2 Ranvier described the interesting analogies, both functional and embry- ological, between typical glands and the lymphatic system. Sabin does not adopt the idea that the whole lymphatic system represents a few large glands. She does, however, describe it as arising from four blind epithelial (endothelial) outpocketings which ramify in the connective tissue, and this origin may be designated, after Ranvier, as “ gland-like.”’ Frederic T. Lewis 97 and external jugular veins are merged in an “ anterior cardinal vein,” the subeardinals are omitted, the renal and iliac anastomoses are made continuous with one another, and: the sciatic and femoral veins are reversed. Fie. 1. Rabbit, 13 days, 9.5 mm., Harvard Embryological Collection, Series 498, X 13 diams. 3, 4, and 5 indicate the position of the corresponding cervical nerves in this, as in the following figures. The veins shown are those of the left side: D. C., duct of Cuvier; Ex. M., external mammary; In. J., internal jugular; Pr. Ul., primitive ulnar. It was thought that more accurate figures might be obtained by the graphic reconstruction of uninjected embryos. The possibility of over- looking minute orifices guarded by valves, and the limitation of this method to small embryos are obvious disadvantages, but these are offset Us 98 The Development of the Lymphatic System in Rabbits by the avoidance of rupture of very thin-walled vessels and by the oppor- tunity of seeing lymphatics too small for injection. The method has been employed with the following results. Hie. 2. Rabbit, 14 days, 10 mm., H. BE. C., Series 155, = f - = — 7 ~ - * a J - 7 7 ' ‘ ; om : ys y ( \ 5 4 ‘ ' . ~ > - a 2 . ~ ! (S % sf A = 4 = ; Js = 7: 1 , ‘ y es 5 ‘ { ' : = x F, a F € © 1 } i} —_ Ls ‘ ) « F H ( ’ = 1 = i t ” ® ' t i ‘ Ay é ; : : 7 ) fy a we eal fn un _ . 3 os 2A ¢ inthe 5 ie i tev = i Oe ’ f eo 7 i ' e . * >i i » ip 4! , PLATE IV GASTRULATION AND EMBRYO FORMATION—AMIA CALVA A. C. EYCLESHYMER anp J. M. WILSON OR Streedam ad AMERICAN JOURNAL OF ANATOMY=-VOL. Vv A CONTRIBUTION TO THE ANATOMY AND DEVELOPMENT OF THE VENOUS SYSTEM OF DIDELPHYS MARSUPIALIS (L).’ Part [I], DEVELOPMENT. : BY CHARLES F. W. McCLURE. Professor of Comparative Anatomy, Princeton University. WitH 5 DouBLE PLATES AND 27 TEXT FIGURES. A number of publications have appeared, especially the monographs of Selenka, 86-7 and g1, and Semon, 94, in which have been described the arrangement of the blood vessels in the extra-embryonic vascular area of marsupials. So far as known to the writer, however, the only actual contributions that have been made to the development of the intra-embryonic venous system of this group of mammals are one by Broom, 98, and a preliminary notice by the writer, 02. The publication of the present paper (Part IL) has been unavoidably delayed, owing to the writer’s inability to obtain embryos sufficiently young to show the earliest stages in the development of the postcaval vein. These early stages have, unfortunately, not yet been obtained, and were it not for the circumstance that so little has been published upon the development of the veins of marsupials, an apology would be due for presenting what must necessarily be an incomplete account. In writing this paper the writer has fully borne in mind the danger involved of drawing conclusions from an incomplete series, and, in the case of Didelphys, the danger is especially great on account of the vari- able character of its venous system. A complete account of the develop- ment of the veins of Didelphys, especially of the variations of the post- cava, necessitates not only a complete series of embryos and pouch young, but a number of examples from each stage as well. Such an 1The publication of this paper in two parts, one dealing with the Anatomy (Part I) and the other, or present paper (Part II), with the Development of the venous system, was unavoidable and it is, therefore, to be hoped that the frequent references made in the following pages to Part I will not prove too great a source of confusion or inconvenience to the reader. Part I of this paper was published in The American Journal of Anatomy, Vol. II, No. 3, 1903. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 164 Venous System of Didelphys Marsupialis (LL) abundance of material the writer has been unable to obtain, and, there- fore, appreciates that many modifications, as well as additions, to his account may possibly be necessary before a complete history of the veins is at hand. In the following pages an attempt has been made, on the basis of the material at hand, to present an account of the development of the post- cava from a time soon after its first appearance until the adult stage is reached; also, an account of the development of the azygos veins, as well as the transformations which the umbilical and omphalomesenteric veins undergo during the different stages of development. An attempt to breed opossums in captivity proved only partially suc- cessful, the failure being due, I am convinced, to the unsuitable condi- tions which necessarily prevail in my laboratory. Most of my Didelphys material was therefore obtained outside of the laboratory, and, for this reason, it is impossible to give the exact age in days and hours of any of the embryos or pouch young studied. It has been possible, however, by means of Selenka’s, 86 and 87, figures and descriptions to approxi- mate their ages in a few cases and to establish the fact that the embryo of Dasyurus which Dr. J. P. Hill, of the University of Sydney, kindly sent me is, in point of structure, relatively younger than my youngest Didelphys embryo. According to Selenka, the interval between copulation and birth in Didelphys virginiana is about thirteen days (twelve days and twenty hours), while that between copulation and the beginning of cleavage is five days. In the following list where ages are mentioned the age has been reckoned from the beginning of cleavage. List OF MATERIAL STUDIED. 1. One Dasyurus embryo measuring about 6 mm. in length (crown- rump measurement). From a comparison of the structure and external characters of this embryo with that of Selenka’s, 86 (Fig. 3, Taf. XX VI), six days old Didelphys embryo, it is evident that the latter is slightly more advanced than the Dasyurus embryo, which, in point of structure, corresponds to a Didelphys embryo of about five and one-half days. 2. Eleven Didelphys embryos averaging 8 mm. in length. From a comparison of their measurements these embryos may be a few hours older than Selenka’s, 86, (Fig. 3, Taf. XX VI) six days old embryo, al- though in their external characters the two appear to be identical. 2 All measurements were made in this manner. Embryos and pouch young were measured by the writer after fixation. Charles F. W. McClure . 165 3. Three embryos of Didelphys averaging 11.5-12 mm. in length. These embryos were kindly presented to me by Dr. Bremer, of Harvard University, to whom my thanks are due. It is a curious fact that these embryos measure more than certain of the pouch young studied by the writer; a circumstance which shows, as suggested by Professor Minot, that opossums may vary considerably as to the degree of development attained before they enter the pouch. 4. One pouch young of Didelphys measuring 10.5 mm. in length. Harvard Embryological Collection, No. 614. 5. One pouch young of Didelphys measuring 11.5 mm. in length. Harvard Embryological Collection, No. 617. This measurement corre- sponds to that of Selenka’s, 87 (Fig. 2, Taf. XXIX), newly-born pouch young of eight days (eight days after beginning of cleavage), but is ap- parently not constant for young of this age, since the Harvard specimen, No. 614, which is undoubtedly the younger of the two, measures only 10.5 mm. 6. Five pouch young of Didelphys averaging about 14 mm. in length. %. Eight pouch young of Didelphys averaging about 15 mm. in length. According to measurements these correspond approximately to Selenka’s (87, Fig. 8, Taf. XXX) four days old pouch young (twelve days from the beginning of cleavage). 8. One pouch young of Didelphys measuring 17 mm. in length. PREPARATION OF MATERIAL. The writer has experienced no difficulties as regards the fixation of the embryonic material. Any one of the ordinary fixing agents, such as picro-sublimate, Perenyi’s fluid, or a 10% solution of formaldehyde,’ will produce good results. The fixation of the pouch young, however, is a very difficult matter. In these the epitrichium is so impervious to the penetration of fluids that the writer has been unable to find any fixing 2— take much pleasure in expressing my thanks and appreciations to the following gentlemen for the unusual courtesies they have extended to me in connection with the preparation of this paper: To Professor Charles S. Minot of Harvard University for the loan of the opossum material in the Harvard Embryological Collection; to Dr. Bremer of Harvard University for three opossum embryos and three pouch young; to Dr. J. P. Hill of the University of Sydney for an embryo of Dasyurus; to Professor Bashford Dean of Colum- bia University for a number of kangaroo pouch young; to Mr. Stephen S. Palmer of New York for funds necessary to cover the cost of several of the figures and plates in this paper, and to Professor Macloskie and Mr. Silvester of Princeton University for many helpful suggestions. *A 10 per cent solution of the 40 per cent commercial formaldehyde. 166 Venous System of Didelphys Marsupialis (L) agent that, with the usual after-treatment, will fix the tissues of the older pouch young avithout, at the same time, producing a considerable shrinkage. Although I have not yet had the opportunity of trying this method, I am inclined to believe that shrinkage can only be avoided by removing the epitrichium before the pouch young are placed in the fixing agent. Two methods of staining which proved to be most satisfactory for the study of blood vessels were a combination of Delafield’s hematoxylin and picric acid and one of bleu de Lyon and safranin. It is evident from the recent investigations of Lewis, 02, that the de- velopment of the postcaval vein in mammals cannot be adequately con- sidered without taking into account the réle played by the subeardinal veins, since he has shown that a portion of the right subcardinal in the rabbit enters into its formation. Lewis’ description of the sub- cardinal veins and his conclusions regarding the origin of the posteava in the rabbit, are given in the following quotation from his paper (page 241): “Small vessels from the mesentery pass into the cardinals. They anastomose in front of the aorta with vessels of the other side. They form a longitudinal anastomosis parallel with the cardinal vein, with which it is connected by numerous short veins, and from which it is sep- arated by a line of mesonephrie arteries. This longitudinal vessel con- nected with the cardinal vein at both ends, and bilaterally symmetrical in its early stages is the subcardinal vein.” “The cross connections between the subcardinal veins give place to a single large cross anastomosis caudad to the origin of the superior mesen- teric artery. Above this anastomosis the right subcardinal connects with the liver and rapidly enlarges; the left subcardinal becomes very small— Hochstetter says that it forms the left suprarenal of the adult. Below the anastomosis the subeardinals cease to exist as veins; they may persist as lymph spaces.” “'The vena cava inferior is a compound vessel composed of parts of the heart, the vena hepatica communis, the hepatic sinusoids, the upper part of the right subecardinal, and the lower part of the right cardinal vein.” Miller, 03, under the direction of the writer, has followed the develop- ment of the posteaval vein in birds and has likewise noted and described a system of veins in the embryo which corresponds exactly to that de- scribed by Lewis in the rabbit as the subcardinal system of veins. He also found in birds that a portion of the right subcardinal vein, as in the rabbit, enters into the formation of the adult postcava and that, in Charles F. W. McClure - 167 addition to this, the subcardinal veins persist in the adult as the left suprarenal and genital veins. The veins which Lewis and Miller have described under the name of “ subeardinals ” were, so far as known to the writer, first described in the embryos of birds and mammals by Hochstetter, 88 and 93, who re- garded them as the homologues of the revehent veins of the Wolffian bodies in reptiles. In tracing their subsequent development, however, Hochstetter found that they disappeared for the most part, and were represented in the adult by only the left suprarenal and possibly the genital veins in the chick, and by the left suprarenal vein in the rabbit. In addition to the mammals, Lewis, 04, has also recently described the subcardinal veins as met with in the selachians (Torpedo and Acanthias), amphibians (Necturus) and reptiles (Lacerta) and, in the writer’s opin- ion, has correctly interpreted the role which these veins play in the formation of the adult renal portal system. He states that in Torpedo and Acanthias, after fusing to form the genital sinus, the subcardinals make connections anteriorly with the cranial ends of the postcardinals and with the latter form the revehent veins of the adult renal portal “system. In Necturus the subeardinals fuse to form an unpaired vessel, which, after making connections with the hepatic circulation, constitutes the greater portion of the posteava. In Lacerta the subcardinals also form a large part of the postcava, although the fusion between the two veins is less complete here than in Necturus (Lewis). Lewis, so far as known to the writer, was the first investigator to in- terpret the development of the venous system of the selachians and am- phibians in the terms of the subcardinal veins, and, although I feel con- fident his interpretations are correct, at the same time a more thorough investigation of the amphibia is to be desired before any definite conclu- sion can be established. In reptiles, however, Hochstetter, and, more re- cently, my pupil Stromsten, 05, have conclusively shown that the veins which form a large portion of the postcava are the homologues of the so-called subcardinal veins of birds and mammals. To what extent the subeardinal veins may be developed in the embryos of vertebrates other than those mentioned above, it is impossible to state without further investigation. From our present knowledge of the subcardinals, how- ever, it is evident that they possess so great a morphological significance in certain vertebrates, that any interpretation of the vertebrate venous system must necessarily be incomplete without, at least, taking into con- sideration the presence or absence of these veins. There can be no doubt as to the morphological significance of the sub- cardinal veins; that their development is -primarily correlated with the 168 Venous System of Didelphys Marsupialis (1) presence of a renal portal system as is the case in selachians, (amphib- ians), reptiles and the embryos of birds. Their presence, therefore, in the embryos of mammals in which a renal portal system is usually want- ing” is most suggestive, and indicative of a “ ground-type” of venous system of which the subcardinal veins form a constituent element. It is evident, therefore, from what we at present know of the subcardinal veins that they can no longer be regarded as transitory structures of little importance, since they form an essential and important element of the embryonic venous system in a number of vertebrates, and are retained in the adult, to a greater or lesser degree, in accordance with the presence or absence there of a renal portal system. Since the subeardinal veins play such an important role in the devel- opment of the mammalian postcava (rabbit) it may be well, in order to better appreciate the conditions in the marsupials, to first give a com- parative sketch of the transformations which these veins undergo in rep- tiles, birds and the rabbit. , The figures recently published by Miller and Lewis show more clearly than has hitherto been observed the striking parallelism that exists, up to a certain period, between the development of the subcardinal system in reptiles, birds and the rabbit. In the latter stages, however, this parall- elism ceases to exist, owing to the divergence from the common ground- plan which occurs in birds and the rabbit in connection with a partial degeneration of the subcardinal veins. For convenience of description, therefore, the transformations which the subeardinal veins undergo will be considered as they occur under the following periods: I. Period of parallelism—(a) before posteava is formed, (b) after postcava is formed ; II. Period of divergence. j I. PrRIopD oF PARALLELISM. (a) Before Postcava is Formed.—According to Hochstetter, 92, upon whose investigations the following account of the development of the reptilian venous system is based (Lacerta), the veins which subse- quently become the Vy. revehentes anteriores and posteriores of the mesonephroi at first convey blood to these organs. These veins are branches of the caudal vein in Lacerta, but in Tropidonotus arise inde- pendently of this vein at the caudal end of the mesonephroi. They con- sist at first of two bilaterally symmetrical vessels (Text Fig. 1) which lie on the ventromedial side of the mesonephroi (see Hochstetter, 92, >See reference to Perameles under Résumé and General Considerations (page 223). Charles F. W. McClure — 169 Fig. 5, Plate XV), anastomose with the postcardinals, give off branches to the mesonephroi and receive tributaries from the tissue ventral to the aorta. LACERTA LACERTA PRECARDINAL -- PRECARDINAL --~ _ 2POSTCAVA SUBCLAVIAN SUBCARDINAL. - -4 oo ANT. REVEHENT SUBCARDINAL HEPATICO-SUBCARDINAL __ JUNCTION SUBCARDINAL ~-Z&- SUBCARDINAL’ ~~ =**VENOUS RING OMPHALO-— RIGHT . 25 “MESENTERIC POSTCARDINAL ARTERY POSTCARDINAL---- SUBCARDINAL - = SCIATIC CAUDAL CAUDAL ~-~- RiGee BGs LACERTA RIGHT . ANT. REVEHENT. —’ --“~---PRECAVA ae - POSTCAVA HEPATICO-SUBCARDINAL JUNCTION -. __ LEFT PARS SUBCARDINALIS- -= CROSS ANASTOMOSIS - = POST. REVEHENT -- ANT, REVEHENT ---POST. REVEHENT POSTCARDINAL- - SCIATIC CAUDAL - - Fi1a. 3. Fics. 1, 2 and 3. Diagrams illustrating the development of the veins in Lacerta. After Hochstetter. At a certain period of development the subcardinal veins of birds (chick, ninety hours) and the rabbit (twelve days and twelve hours) have recently been shown by Miller (03, Figs. 1 and 4) and Lewis (02, 12 170 Venous System of Didelphys Marsupialis (1) Text Fig. 7 and Figs. 1 and 2, Plate I), respectively, to attain a high degree of development and to consist, as in reptiles, of two bilaterally symmetrical vessels which hold the same relation to the mesonephroi and posteardinal veins as the subcardinals do in reptiles. (b) After Postcava is Formed.—In connection with the develop- ment of the postcava in reptiles the grouad-plan of the venous system, as represented by Text Fig. 1, undergoes considerable modification. The proximal or hepatic portion of the unpaired postcava in Lacerta grows caudad from the V. hepatica revehens dextra and, at a point slightly craniad of the origin of the omphalomesenteric artery, anastomoses with both subeardinal veins at a point which, for convenience of description, may be designated as the hepatico-subcardinal junction. The subcardinal veins also anastomose with each other caudad of this artery so that a complete venous ring, ventral to the aorta, is formed about the origin of the omphalomesenteric artery (Text Fig. 2). This condition is only temporary, however, since the anastomosis craniad of the omphalomes- enteric artery between the subcardinal of the left side and the hepatic portion of the postcava is not long retained, with the result that the right side of the venous ring (a portion of the right subcardinal) enters into the formation of a portion of the unpaired postcava (pars subcardinalis, Text Fig. 3). Correlated with the above changes the caudal vein (La- certa) gives up its connections with the subcardinals (Text Fig. 3) and joins the postcardinals so that the latter, after giving up their connec- tions with the ducts of Cuvier, function as the advehent veins of the mesonephroi. ‘The subcardinal veins, on the other hand, through their connection with the unpaired portion of the postcava, function as the anterior and posterior revehent veins of the mesonephroi. ‘The posterior and left anterior revehent veins open into the cross anastomosis between the subeardinals behind the omphalomesenteric artery; while the right anterior revehent vein opens into the unpaired portion of the postcava, somewhat craniad of the anastomosis at the hepatico-subcardinal june- tion (Text Fig. 3). A ground-plan of the venous system similar to that last described for reptiles (Text Fig 3) is also met with in the embryos of birds (chick, five days incubation) and the rabbit (thirteen days) as described and figured by Miller (03, Fig. 6) and Lewis (02, Figs. 3 and 4, Plate 1 and Figs. 5 and 6, Plate 2), respectively. In the case of both the birds (Text Fig. 4) and the rabbit (Text Fig. 6) the subcardinal veins have anastomosed with each other caudad of the origin of the omphalomesen- teric artery and the right subcardinal has been “ tapped” by the hepatic circulation at the hepatico-subcardinal junction. The subcardinal sys- Charles F. W. McClure 171 CHICK RIGHT ANT. REVEHENT _« POSTCAVA LEBR ~-—-- ANT. REVEHENT CHICK “POST. VERTEBRAL HEPATICO- SUBCARDINAL SIGTIONS* = POSTOAVA -4>---- aes POSTCARDINAL semis *e SUBCARDINALIS ~~ OMPHALO- ANASTOMOSIS~. _ Sea ca FT ee =-- MESENTERIC : tetas PEBARENAE x GENITAL ~. 4 CROSS ----a" ARTERY . ANASTOMOSIS POST. REVEHENT --# - ~ EXT. ILIAC EXT. ILIAC INT. ILIAC - ~ +GREAT RENAL SCIATIC POSTCARDINAL Fia. 4. RABBIT z POSTCAVA RIGHT ANT. REVEHENT ~~ {- - POSTCARDINAL HEPATICO-SUBCARDINAL JUNCTION -- -- LEFT ANT. REVEH PARS SUBCARDINALIS- - oe S : - OMPHALO - ROSS ANASTOMOSIS son Bee MESENTERIC POST. REVEHENT --- han POSTCARDINAL a Fic. 6. Fic. 5. RABBIT . AZYGOS - ‘ \ ‘ AA an) 7 at Ae ‘ POSTCAVA__ \_ | is «Sau PARS ! SUBCARDINALIS - ¢° SUPRARENAL \ CROSS ANASTOMOSIS -€ TELE RIGHT RENAL RENAL SPERMATIC SPERMATIC -- i POSTCAVA-- ~~ POSTCARDINAL EXT. ILIAC Fic. 7. Fics. 4 and 5. Diagrams illustrating the development of the veins in birds. After Hochstetter and Miller. Fics. 6 and 7. rabbit. After Hochstetter and Lewis. Diagrams illustrating the development of the veins in the 172 Venous System of Didelphys Marsupialis (L) tem is now represented in birds and the rabbit, as in reptiles, (1) by an anterior and posterior pair of revehent veins which hold the same rela- tions to the unpaired postcava and cross anastomosis between the sub- cardinals, as the anterior and posterior revehent veins in reptiles; and (2) by a portion of the unpaired postcava (pars subcardinalis) which consists, approximately, of that portion of the right subcardinal vein which is included between the hepatico-subcardinal junction and the cross anastomosis. It is evident from Hochstetter’s figures and description of the veins in Lacerta that the right side of the venous ring which is formed around the origin of the omphalomesenteric artery, and which enters into the formation of the unpaired postcava is derived from the right subcardinal vein. Such being the case, we then have in Lacerta a portion of the un- paired posteava which corresponds in its relations to the subcardinal por- tion of the postcava described above for birds and the rabbit, since the right side of the venous ring in Lacerta is composed of that portion of the right subeardinal, which is included between the hepatico-subcardinal junction and the original cross anastomosis between the two subcardinals. Miller, 03, has shown that in chick embryos the subcardinal veins may occasionally, as in reptiles, form a venous ring around the origin of the omphalomesenteric artery and has kindly permitted the writer to pub- lish his reconstruction of the same (Text Fig. 8). Although Miller did not publish this figure in his paper, he described it as follows on page 291: “ At about the stage from which Fig. 6 was taken (fifth day of in- cubation) the writer found a most interesting exception to the general plan of development of the subeardinal system in birds, which exception shows a striking combination of the conditions described by Hochstetter in reptiles and Echidna.. Anterior to the origin of the A. omphalomes- enterica and ventral to the aorta there is present a large anastomosis between the right and left subeardinals, just caudal to the point where the posteava joins the right subeardinal. Such a remarkable similarity to the conditions found in the earlier stages of reptilian development is certainly unusual.” The reference to Echidna mentioned in the above quotation does not refer to the formation of a venous ring about the artery, but to the secondary anastomosis between the subcardinals, as shown in the reconstruction. There can be no doubt as to the subeardinal character of the right side of the venous ring in Miller’s figure of the chick and, also, that it corre- sponds, in all essential details, to the right side of the ring in Lacerta. At the stages of development represented by Text Figs. 3, 4 and 6, it is, therefore, seen that the unpaired postcava, as thus far developed, con- Charles F. W. McClure 13 sists in reptiles, birds and the rabbit of two principal subdivisions which are genetically independent of each other; one of which is formed be- tween the sinus venosus and the hepatico-subcardinal junction and the other between the latter and the cross anastomosis between the subcardi- nals. The latter subdivision is formed in all three cases from a portion of the right subeardinal vein; while the former has a somewhat different OMPHALOMESENTER ARTERY POST, REVEHENT VEINS Fig. 8. Fic. 8. Reconstruction of the venous system of a chick embryo of five days incubation in which the subcardinals form a venous ring about the origin of the omphalomesenteric artery as in Lacerta. After Miller. Ventral view. origin in reptiles, birds and the rabbit which need not be mentioned here. There is one feature at this period of development, however, in which the venous system of the rabbit differs from that of reptiles and birds. In the rabbit (Text Fig. 6) the unpaired postcava is connected at its caudal end with each posteardinal vein by means of large anastomoses so that a continuous and uninterrupted channel is established between the 174 Venous System of Didelphys Marsupialis (L) hinder end of the body and the postcava. By this means the blood may flow directly to the heart without passing through the mesonephric cir- culation, as is the case in reptiles (Text Fig. 3) and the embryos of birds (Text Fig. 4 and 8) in which a renal portal system is present (see Miller, 03, Fig. 6). Il. Perrtop oF DIVERGENCE. The final changes which take place in connection with the development of the venous system, subsequent to those represented by Text Figs. 3, 4 and 6, and which lead up to the adult condition are in reptiles, birds and the rabbit somewhat divergent. In reptiles the fundamental plan of the venous system as represented by Text Fig. 3, is, with slight modifications, retained in the adult. The posterior revehent veins which remain, for the most part, separate in Lacerta and snakes and fuse to form a single vein in turtles (Stromsten, 05) function as the reyehent veins of the permanent kidneys. The ad- vehent veins, on the other hand, are formed from the caudal divisions of the postcardinals which, after giving up their connections with the ducts of Cuvier, return blood from the hinder end of the body to the permanent kidneys. In order to attain the adult condition in birds (Text Fig. 5), in which a renal portal system is absent,’ the Vv. renales magne (the revehent veins of the permanent kidneys) grow caudad from the caudal end of the postcava (pars subcardinalis) and, at the level of the external iliac veins, anastomose with the postcardinals. A continuous channel is thereby established, on each side, between the hinder end of the body and the posteava through which the blood may flow without previously passing through the mesonephric circulation (see Miller, 03, Fig. 7). The postcardinals which he craniad of their anastomosis with the great renal veins atrophy, while,those which le caudad of the same fuse at their caudal ends and persist in the adult as the so-called internal iliac veins (Miller). Unless the unpaired portion of the postcava to- gether with the internal ihac veins (postcardinals) may be regarded as representing a type of bifurcated or double posteava, it is evident that the postcardinal veins or any part of the same do not, in birds, as in the rabbit, enter into the formation of the adult postcava, since the latter ° Parker and Haswell, 97 (page 375), figure and describe the presence of a partial renal portal system in adult birds (pigeon). This system in the adult, however, differs fundamentally from that in the embryo in that the revehent veins (Vv. renales magnae) are independent formations and are not formed from the subcardinal veins. Charles F. W. McClure 175 terminates in birds at the-caudal end of the pars subcardinalis which, in addition to the portion which is developed between the heart and the hepatico-subeardinal junction, constitutes the postcava in the adult. The subcardinal system is represented in the adult bird by the follow- ing veins: The left anterior revehent vein forms the left suprarenal ; the right anterior revehent probably atrophies; the section of the right sub- cardinal included between the hepatico-subcardinal junction and the original anastomosis between the two subcardinals forms the pars sub- cardinalis of the posteava, and the two posterior revehent veiris enter into the formation of the genital veins. In birds the azygos veins, as met with in the rabbit, are not developed ; their place being taken, for the most part, by the newly formed posterior vertebral veins (Text Fig. 5) which open, on each side (chick) into the precava in common with the internal jugular and the subclavian veins (see McClure, 03, page 381). In the rabbit the fundamental plan of the venous system, as repre- sented by Text Fig. 6, undergoes a number of changes before the adult stage is reached. The section of the right posteardinal vein which hes caudad of its anas- tomosis with the pars subeardinalis of the postcava, after forming a col- lateral channel on the medial side of the ureter (Text Fig. 6), consti- tutes in the adult that portion of the postcava which lies caudad of the renal veins (Text Fig. 7). The corresponding section of the left post- cardinal atrophies with the exception of a small portion at its proximal end which usually persists as the left spermatic vein, and of a portion at its caudal end which fuses with the posteardinal of the opposite side to form the common internal iliac vein. The postcava of the adult rabbit is thus seen to be a compound vessel which is formed from four distinct sets of veins: The vena hepatica communis, the hepatic sinusoids and portions of the right subeardinal and right postcardinal veins. Correlated with the completion of the adult postcava in the rabbit a number of changes, also take place in connection with the remaining por- tions of the postcardinal and subecardinal veins. The posteardinals which lie craniad of the level of the renal veins entirely disappear with the ex- ception of the proximal end of the vein of the right side which persists as the common trunk of the newly formed azygos veins. Also, with the ex- ception of a section of the right subeardinal which enters into the forma- tion of the adult postcava, a portion of the left subcardinal which forms the left suprarenal, and possibly a portion of the right which forms the right suprarenal vein (Hochstetter, 03), the subcardinal veins are com- pletely lost at the time the adult stage is reached. 176 Venous System of Didelphys Marsupialis (1) THE DEVELOPMENT OF THE VENOUS SYSTEM IN MARSUPIALS. All of my marsupial embryos, as stated above, are too advanced to definitely determine the earliest stages in the development of the postcaval vein, as well as the condition presented by the subcardinal veins at a PRECARDINAL DUCT OF CUVIER POSTCARDINAL POSTCARDINAL AORTA LEFT ANT, REVEHENT VEIN SUBCARDINAL LEFT HEPATIC VEIN POSTCAVA RIGHT HEPATIC VEIN UMBILICAL VEIN HEPATICO-SUBCARDINAL- JUNCTION OMPHALOMESENTERIC VEIN MESONEPHRIC ARTERY MESONEPHRIC ARTERY ‘ ESONE c ANT. REVEHENT VEIN SUBCARDINAL MESONEPHRIC ARTERY POSTCAVA PARS SUBCARDINALIS OMPHALOMESENTERIC ARTERY MESONEPHRIC ARTERY EEFar RIGHT POST. REVEHENT POST. REVEHENT VEIN VEIN SUBCARDINAL SUBCARDINAL AORTA POSTCARDINAL POSTICARDINAL UMBILICAL aRTERY Fia. 9. Fig. 9. Reconstruction of the venous system of a 6 mm. embryo of Dasyurus. Ventral view. . time before the posteava is formed. There can be no doubt, however, so far as the subcardinal system is concerned, that it plays the same role in the marsupials, as thus far examined, as in the rabbit (Text Fig. 6), in which it enters into the formation of a portion of the postcava, as well as Charles F. W. McClure yer dre into that of the anterior and posterior revehent veins. This is clearly shown to be the case by the reconstructions of the venous system of the 6 mm. Dasyurus (Text Fig. 9) and 8 mm. Didelphys embryos (Text Fig. 10) in which the ground-plan is fundamentally the same as that de- scribed by Lewis, 02 (Plate I, Figs. 3 and 4), for a rabbit embryo of thirteen davs, where the right and left subcardinals have anatomosed in the median line, caudad of the origin of the omphalomesenteric artery, and the right subcardinal has been “ tapped” by the hepatic circulation. The point at which the right subeardinal vein makes connection with the hepatic circulation is designated by the writer in the following pages as the hepatico-subcardinal junction. On account of the bilateral symmetry of its subecardinal veins the 6 mm. embryo of Dasyurus undoubtedly represents a stage of develop- ment which is relatively earlier than that of the 8 mm. embryo of Didel- phys, and, for purposes of comparison with the latter, a reconstruction of its venous system has been added to the text (Text Fig. 9). THE VENOUS SYSTEM OF THE 8 MM. EMBRYOS OF DIDELPHYS. The Postcardinal Veins.—In the majority of the 8 mm. embryos of Didelphys (Text Fig. 10) the postcardinal veins can be traced as contin- nous vessels between the ducts of Cuvier, into which they open dorsally, and the caudal end of the body where they are formed, on each side, through the union of the internal and external iliac veins. Caudal to the origin of the omphalomesenteric artery each postcardinal vein joins the root of the postcava by means of a single large anastomosis. The post- cardinals which le caudad of this anastomosis with the postcava are ves- sels of large size and constitute its principal, though not direct, caudal continuation ; the latter being formed by the right posterior revehent vein (subcardinal). The relation of the postcardinal veins to the umbilical arteries is most complex and will be treated more fully in connection with another topic. It may be mentioned here, however, that the umbilical artery of each side, instead of lying ventral to the postcardinal vein as in most mammalian embryos or dorsal to the same as in Echidna (Hoch- stetter) and the 6 mm. embryo of Dasyurus (Text Fig. 9), is encircled by a circumarterial venous ring. Craniad of the anastomosis with the postcava the postcardinals are much reduced in size and slightly caudad of their union with the ducts of Cuvier each postcardinal receives a tributary which can be traced caudad for only a short distance as a continuous vessel. ‘These two trib- utaries (Fig. 31, Plate II and Text Fig. 10) which le lateral or dorso- 178 Venous System of Didelphys Marsupialis (L) lateral to the aorta and ventral to its segmental branches, appear to be formed through a longitudinal anastomosis between branches of the post- cardinals and undoubtedly represent a portion of the future azygos sys- tem of veins. Try > m P / a ) a aL) Lhe Postcavax—The posteava of the 8 mm. embryos of Didelphys PRECARDINAL PRECARDINAL DUCT OF CUVIER DUCT OF CUVIER AZYGOS AZYGOS - POSTCARDINAL POSTCARDINAL POSTCAVA. - LEFT UMBILICAL HEPATIC VEIN VEIN OMPHALOMESENT ERIC RIGHT HEPATIC VEIN VEINS LEFT SUB AL HEPATICO-SUBCARDIN ANT. REVEHENT JUNCTION MEIN SUBCARDINAL POSTCAVA PARS SUBCARDINALIS OMPHALOMESENTERIC ARTERY CROSS ANASTOMOSIS RIGHT POST. REVEHENT MESONEPHRIC ARTERY MEIN POST. REVEHENT ARDINA VEIN CARDINAL COLLATERAL SUBCARDINAL VEINS POSTCARDINAL POSTCARDINAL UMBILICAL, ARTERY P——EXT. ILIAC VEIN INT. ILIAC S RIN VENOUS G VEIN Fig. 10. Fic. 10. Reconstruction of the venous system of an 8 mm. embryo of Didel- phys. Ventral view. (Text Figs. 10 and 11), which represents only a portion of this vein as met with in the adult, is a vessel of relatively greater size than that found in the Dasyurus embryo. It extends as an unpaired vessel between the sinus venosus and a point slightly caudad of the origin of the ompha- lomesenteric artery where it anastomoses with the right and left post- cardinal veins which form its principal caudal continuation, and where it also receives the left anterior and the two posterior revehent veins. Charles F. W. McClure. args) Between the sinus venosus and the point where it receives the right an- terior revehent vein (hepatico-subcardinal junction, Text. Fig. 11) the postcava, at its cranial end, occupies a position ventral to the right lung (Fig. 31, Plate IL), and further caudad is embedded in the liver. Here it receives the following tributaries (Text Fig. 10): (a) One or two DUCT OF CUVIER URORSEIS THORACIC AZYGOS POSTCARDINAL POSTCARDINAL POSTCAVA RIGHT ANT. REVEHENT VEIN LECT SUBCARDINAL ANT. REVEHENT VEIN SUBCARDINAL HEPATICO-SUBCARDINAL JUNCTION POSTCAVA PARS SUBCARDINALIS MESONEPHRIC VEINS CROSS ANASTOMOSIS POST. REVEHENT AF VEIN LEFT ; IN KIDNEY SUBCARDINAL POSTCARDINAL POSTCARDINAL VENOUS RING URETER Iniges bile Fic. 11. Dorsal view of the venous system of an 8 mm. embryo of Didel- phys. Semi-diagrammatic. hepatic veins from the right side of the liver (V. hepatica revehens dextra) ; (b) a large hepatic vein from the left side of the liver (VY. hepatica revehens sinistra) which opens into the postcava in common with the hepatic continuation of the umbilical veins; (c) the continuation of the omphalomesenteric vein which, after tunnelling the liver, opens into the postcava independently of the umbilical veins and finally, (d) a number of small hepatic veins which open at irregular intervals. Be- 180 Venous System of Didelphys Marsupialis (1) tween the sinus venosus and the hepatico-subeardinal junction (Text Fig. 11) the posteava is without doubt formed, as in the rabbit, inde- pendently of the right subeardinal vein. The remaining portion of the unpaired postcava, that section of the vein which hes caudad of the hepatico-subcardinal junction, is formed from the right subeardinal vein with the exception of a portion near the hepatico-subcardinal junction which is partially embedded in the parenchyma of the liver and which is formed from the hepatic sinusoids in conjunction with the right sub- cardinal vein. ‘The term hepatico-subcardinal junction refers to the most cranial of the anastomoses that may exist between the right sub- cardinal and the hepatic circulation (Text Fig. 11) since in some cases the section of the posteava which is formed from the hepatic sinusoids and which hes partially embedded in the liver does not fuse along its en- tire extent, but only at intervals, with the right subeardinal vein. Fig. 34, Plate II, represents the section preceding and Fig. 35, Plate II, a section taken through the hepatico-subcardinal junction in which it is seen that ventrally the postcava is formed by hepatic sinusoids and dor- sally by the right subeardinal vein. Slightly caudad of the hepatico-sub- cardinal junction the posteava lies upon the dorsal surface of the liver (Fig. 36, Plate II), where, as well as caudad of the liver itself (Figs. 37 and 38, Plate III), it occupies the same relative position with respect to the mesonephros and suprarenal body and, with the exception of those from the liver, receives the same class of tributaries as the anterior reve- hent vein of the left side (left subeardinal). These tributaries are veins from the suprarenal body, the mesonephros, the genital anlage and from the tissue ventral to the aorta. Finally, the pars subcardinalis of the postcava does not, as in Dasyurus, anastomose at intervals along its course with the right postcardinal vein; the absence of such connections being probably correlated with the degeneration of the postcardinal vein. The Anterior Revehent Veins—The right anterior revehent vein (Text Fig. 11 and Fig. 34, Plate II) is derived from that portion of the right subeardinal which lies craniad of the hepatico-subcardinal junction. The left anterior vein (Figs. 10 and 11 and Figs. 34, 35 and 36, Plate IT, and Fig. 37, Plate III) consists of that portion of the left subcardinal which lies craniad of the anastomosis (Fig. 38, Plate III) between the two subeardinals. In the 8 mm. embryos of Didelphys this anastomosis be- tween the two subeardinals (cross anastomosis) is, as a rule, more exten- sive and complete than in the 6 mm. embryo of Dasyurus so that the left anterior revehent vein usually has the appearance of opening into the posteava rather than being directly continuous caudad, as in the Dasyu- rus embryo (Text Fig. 9), with the left posterior revehent vein. In one Charles F. W. McClure. 181 of the 8 mm. embryos, however, the fusion between the two subcardinals was not as complete as in some of the others so that the left anterior re- vehent vein could be traced directly craniad from the left posterior re- vehent vein (See Text Fig. 12). Both of the anterior revehent veins occupy the same relative position in the embryo with respect to the supra- renal bodies and the mesonephroi and, with the exception of the direct anastomoses with the postcardinals which are wanting, receive the same class of subeardinal tributaries as the corresponding veins in the 6 mm. embryo of Dasyurus. The Posterior Revehent Veins.—The right and left posterior revehent veins (subeardinals) which he caudad of the cross anastomosis can, in RIGHT ANT. REVEHENT VEIN SUBCARDINAL HEPATICO-SUBCARDINAY LEFT JUNCTION E m—— ANT. REVEHENT. VEIN POSTCARDINSL SUBCARDINAL POSTCAVA PARS SUBCARDINALIS: POSTCARDINAL CROSS ANASTOMOSIS POSTCARDINA POST. REVEHENT VEINS SUBCARDINAL Ge: Fic. 12. Reconstruction of the venous system of an 8 mm. embryo of Didel- phys in the region of the original cross anastomosis between the subcardinals. Ventral view. most of the 8 mm. embryos, be traced as continuous vessels between the cross anastomosis, into which they open cranially, and the hinder end of the body where they sometimes aid in the formation of the venous rings which encircle the umbilical arteries. Each posterior revehent vein lies ventral to the mesonephrie arteries on the medial side of the mesonephros and receives tributaries from the latter as well as from the genital anlage and tissue ventral to the aorta (Fig. 39, Plate III). Each vein also anastomoses at intervals along its course with the postcardinal vein of the same side as well as with a complicated system of vessels which, for the most part, lies dorsal or dorsolateral to it and which I shall describe under the name of the cardinal collateral system of veins (Vy. cardinales col- laterales). 182 Venous System of Didelphys Marsupialis (1) Correlated with the atrophy of the mesonephroi, the cardinal collateral veins, or veins which are derived from them, assume the function of the posteardinals in returning the blood from the hind limbs and pelvic re- gion to the root of the postcava (pars subcardinalis) ; and, after fusing ventral to the aorta, constitute the greater portion of the stem of the posteava which is developed caudad of the original cross anastomosis be- tween the subcardinals. From a physiological standpoint the cardinal collateral veins of Didelphys may be said to correspond to that portion of the postcardinal in the cat and rabbit which is formed on the medial side of the permanent kidney and ureter, respectively. The Cardinal Collateral Veins——The cardinal collateral veins, as rep- resented in the reconstructions (Text Figs. 10 and 13) and in section (Figs. 40 and 41, Plate IIT) constitute an extremely complicated system of vessels which, in the 8 mm. embryo, are so irregular in character that it is difficult, at this stage,’to assign to them any definite ground-plan arrangement which may be regarded as characteristic of these veins in general. In some of the 8 mm. embryos examined the cardinal collateral veins appear to be present, for the most part on one side (Text Fig. 10), while in others they approach a bilateral arrangement as represented by Text Fig. 13. They may anastomose in front with the postcardinals (Text Fig. 10, left side) or, as is usually the case, with the root of the posteava as in Text Fig. 18. They may also extend caudad, on each side, parallel to the postcardinals either as single vessels or as a network of vessels which spread out in the space ventral to the aorta as in Text Fig. 13. The cardinal collateral veins often anastomose with each other in the median line ventral to the aorta (Text Fig. 10); they may also form frequent anastomoses with the postcardinal and posterior revehent (sub- cardinal) veins and, on being traced caudad, appear, in some cases to be directly continuous with that portion of the circumarterial venous ring which encircles the umbilical artery ventrally (Text Fig. 13, left side). In a few cases the cardinal collateral veins could be traced for a short distance caudad of the circumarterial venous rings where they appeared to terminate in capillary vessels (Text Fig. 13). The question as to origin of the cardinal collateral veins is difficult of solution and with the material at hand impossible to determine definitely. They do not, however, appear to be formed through a longitudinal anas- tomosis between the dorsal somatic branches of the posteardinals, but rather through a longitudinal anastomosis between the cross connections which exist between the post and subcardinal veins. Having considered the postcardinal, cardinal collateral and posterior Charles F. W. McClure 183 revehent (subeardinal) veins of the 8 mm. embryo of Didelphys, we are now in a position to consider the circumarterial venous rings or loops which encirele the umbilical arteries. The Circumarterial Venous Rings.—It has been stated above, as well as in a preceding paper (McClure, 02), that in the 8 mm. embryos of Didelphys the umbilical arteries, instead of lying ventral to the post- cardinal veins, as in most mammals, or dorsal to the same, as in Echidna POSTCAVA LEFT ’ PARS SUBCARDINALIS ANT, REVEHENT SUBCARDINAL RIGHT POSTCARDINAL POSTCARDINAL ROSS ANASTOMOSIS POST. REVEHENT POST. REVEHENT SUBCARDINAL SUBCARDINAL CARDINAL COLLATERAL CARDINAL COLLATERAL POSTCARDINAL POSTCARDINAL VENOUS RING UMBILICAL UMBILICAL ARTERY ARTERY INT, ILIAC Fig. 13. Fic. 13. Partial reconstruction of the venous system of an 8 mm. embryo of Didelphys showing the cardinal collateral and posterior revehent veins and the venous rings which encircle the umbilical arteries. Ventral view. * (Hochstetter) and Dasyurus (Text Fig. 9), are encircled near their origin by complete circumarterial venous rings. These venous rings are situated slightly craniad of the point of junction of the external and internal iliac veins, and, so far as their general make-up is concerned, are ex- tremely variable in character, not only in the different embryos, but even upon opposite sides of the same individual. Two main types of venous rings may be distinguished :—One in which the portion of the ring which 184 Venous System of Didelphys ,Marsupialis (L) encircles the umbilical artery ventrally possesses a caliber either subequal with or greater than that which encircles it dorsally, as in Text Fig. 10 and Fig. 42, Plate III; the other, in which the portion of the venous ring which encircles the umbilical artery ventrally possesses a smaller caliber than that which encircles it dorsally as in Text Fig. 13 and Fig. 41, Plate III. The latter type of ring is by far the more com- mon of the two since, with one exception, it was characteristic of all the S mm. embryos examined. As regards the veins which enter into the formation of these venous rings there is also considerable variation and, in some cases, it is quite impossible to determine definitely how these rings are formed. In all of the rings the portion which encircles the umbilical artery dorsally is formed by the posteardinal vein. The portion of the ring which encircles the umbilical artery ventrally, however, may be formed exclusively by the cardinal collateral vein as in Text Fig. 13 (left side), or by a vein which appears to be formed as the result of a fusion between the cardinal collateral and posterior revehent (subcardinal) veins. In addition to the above, in one embryo (Text Fig. 10) the circumarterial venous rings appear to be formed exclusively by the postcardinal veins, although it is impossible to determine in this case to what extent the cardinal collateral veins may have also entered into their formation. The variable character of these circumarterial venous rings fore- shadows the unusual variations recently described by the writer in Part I of this paper as regularly occurring in the adult, and the relationship which exists between the two will be considered in connection with an- other topic. The presence of circumarterial venous rings about the origin of the umbilical artery is not so uncommon as is generally supposed to be the case. The writer has recently observed these rings in the embryos of a lizard (Sceloporus undulatus). Hochstetter, 88, and Miller, 03, have ob- served them in the embryos of the chick and the English sparrow (Passer domesticus), respectively, and Lewis, (02, Figs. 7 and 8, Plate 2) has recently figured them as occurring in a rabbit embryo of 14.5 mm. in length. In Sceloporus the portion of the ring which encircles the um- bilical artery dorsally disappears before the adult condition is reached, while in birds, as well as in the rabbit, it is the ventral portion of the ring that atrophies. In Sceloporus and birds the portion of the ring which is not formed from the posteardinal vein appears to be formed through a longitudinal anastomosis of the somatic branches of the post- cardinals, while in the rabbit it appears from Lewis’ figures as if it might be formed from the subeardinal vein. Whatever the case may be, I am Charles F. W. McClure 185 inclined to believe that some of the abnormalities which are met with in adult mammals, in which the internal iliac artery passes through a fora- men in the common iliac vein, as described by Treadwell, 96, McClure, oo, (1) and Weysse, 03, may be accounted for on the ground that they represent instances in which these embryonic circumarterial venous rings have persisted in the adult. Up to this point we have considered more or less in detail the general plan of the venous system as met with in the 8 mm. embryo of Didelphys and, since the latter represents the youngest stage of Didelphys possessed by the writer, its venous system may be taken as the starting point from which may be traced the subsequent transformations that lead up to the adult condition. From now on, therefore, and beginning with the 8 mm. embryo of Didelphys, we will trace in a connected manner through the different stages of embryos and pouch young possessed by the writer the transformations which the different portions of the venous system un- dergo before arriving at the adult stage. THr AzycGcos VEINS. In the adult of Didelphys there is, as a rule, but one azygos vein pres- ent and that is situated on the left side (Fig. 28, Plate I). At its cranial end it opens into the left precava about opposite the head of the third rib, while at its caudal end it invariably joins the postcava caudad of the renal veins and about opposite the second lumbar vertebra. Between its point of union with the postcava and about the middle of the tenth tho- racic vertebra, the left azygos vein hes dorsal to the segmental branches of the aorta; between the tenth thoracic vertebra and its connection with the precava, however, it lies ventral to these branches (see McClure, 03, pp- 381-2 and Fig. 28, Plate I, at the end of this paper). The right azygos vein, when present in the adult, opens into the pre- cava about opposite the head of the second rib. It is always a small and insignificant vessel, and its tributaries are confined to the first five inter- costal spaces of the right side. In the 8 mm. embryo of Didelphys, as stated above, each postcardinal receives a tributary slightly caudad of its junction with the duct of Cu- vier (Text Figs. 10 and 11). Each tributary, which can be traced caudad for only a short distance, lies lateral or dorsolateral to the aorta (Fig. 31, Plate Il) and ventral to the latter’s segmental branches. ‘These two tributaries, as stated above, which appear to be formed through a longi- tudinal anastomosis between the somatic branches of the postcardinals, together with the proximal ends of the two postcardinals, undoubtedly constitute the anlages of the right and left azygos veins. 13 186 Venous System of Didelphys Marsupialis (L) It is a curious fact that the azygos veins are more advanced in develop- ment in the 11.5-12 mm. embryos than in the youngest of the pouch young studied by the writer (10.5 mm.). This circumstance clearly proves that the opossums are not born, in all cases, at a corresponding period of development, but that some are born at a more advanced stage than others. In order, therefore, to give a connected account of the development of the azygos system it will be necessary to describe the conditions as met with in the 11.5-12 mm. embryos after those of the youngest pouch young have been considered. In the 10.5 mm. pouch young two azygos veins are present in the tho- racic region which, as in the 8 mm. embryo, open dorsally into the ducts of Cuvier, the opening of the right vein being somewhat craniad of that of the left. These two veins, as stated above, are formed from the cranial ends of the two postcardinals as well as from veins which have united with the latter and which have probably been formed through a longi- tudinal anastomosis between the somatic branches of the postcardinals. The right azygos can be traced caudad from its connection with the duct of Cuvier for about 89 sections where it appears to termi- nate as a small capillary vessel which hes on the ventral surface of the vertebral column. The left azygos is, however, of much greater extent and can be traced caudad as a continuous vessel for about 156 sections where it then appears to terminate in the region slightly caudad of the point where the omphalomesenteric vein enters the liver. Each azygos vein, along its entire extent, hes dorsolateral to the aorta and ventral to the segmental arteries and, at intervals along its course, receives tribu- taries from the body walls contiguous to the vertebral column (Fig. 43, Plate III). Somewhat caudad of the apparent termination of the left azygos vein (37 sections) small capillary vessels are met with which lie in the tissue dorsal and dorsolateral to the aorta and dorsal to the seg- mental arteries, which become more prominent near the origin of the omphalomesenteric artery and especially so, further caudad, in the neigh- borhood of the permanent kidneys (Fig. 46, Plate IV). These vessels can be traced without difficulty caudad of the anastomosis between the pars subcardinalis and the postcardinal veins where they form frequent anastomoses with vessels which le in the tissue ventral to the aorta (Figs. 47 and 48, Plate IV). These latter or ventral vessels with which they anastomose (Figs. 47 and 48, Plate IV) are, in my estimation, rep- resentatives of the cardinal collateral veins which have been described above in connection with the 8 mm. embryos. They can be traced caudad almost as far as the origin of the umbilical arteries, but whether they join the posteardinal veins at their caudal ends I am unable to determine definitely. Charles F. W. McClure - 187 The separation of the azygos system into two subdivisions (thoracic and lumbar) is a marked feature at this stage of its development. The separation may, however, be apparent rather than actual since a capillary anastomosis may exist between the two which cannot be determined in section. In later stages the two subdivisions do become connected so that the blood from the lumbar azygos tributaries is returned to the heart, for the most part, by the left thoracic azygos vein. In the 10.5 mm. pouch young, however, the large size of the azygos veins in the lumbar region precludes the possibility of any such route for all of the blood collected by them; and I am, therefore, inclined to believe that it is returned, for the most part, through capillaries directly to the postcava, which is the course pursued at a subsequent stage of development in which large and frequent anastomoses are formed between this vessel and the lumbar azygos veins. In the 8 mm. embryo the azygos veins of the lumbar region have not as yet been formed and this region is drained by the dorsal somatic trib- utaries of the postcardinal veins. This circumstance leads one to infer that the lumbar azygos veins as met with in the 10.5 mm. pouch young may also be formed from branches of the postcardinals and in the same manner as a portion of the azygos veins in the thoracic region, although, on account of the lack of intermediate stages, it is impossible to deter- mine this question. The azygos veins in the 11.5 mm. pouch young appear to present the same arrangement as in the preceding stage, although on account of the circumstance that the specimen was cut along the frontal plane it is dif- ficult to determine the exact extent of the thoracic azygos veins, as well as whether a direct anastomosis exists between them and the azygos veins of the lumbar region. There can be little doubt, however, if such an an- astomosis exists that it is still of minor importance as compared with that at a later stage, and that the thoracic and the lumbar azygos veins are, as in the 10.5 mm. pouch young, practically independent of each other. At the caudal end of the body the sections are cut almost at right angles to the long axis of the body so that in this region the lumbar azygos veins are not difficult to follow. In the region of the permanent kidneys and craniad of the point where the left anterior revehent vein joins the posteava (Fig. 49, Plate IV) the lumbar azygos veins are extremely prominent and lie, for the most part, dorsal to the segmental branches of the aorta. Between its junc- tion with the left anterior revehent vein and that with the two post- cardinals, the posteava gradually approaches the aorta and in the region 188 Venous System of Didelphys Marsupialis (L) dorsal to this section of the postcava the lumbar azygos veins send tribu- taries into the tissue ventral to the aorta. These tributaries, if they do not already anastomose by means of capillaries with the postcava are at least preparing to do so, since direct anastomoses between these two veins are of constant occurrence in this region in more advanced stages. Slightly caudad of the junction of the two postcardinals with the post- cava the lumbar azygos system anastomoses with the left postcardinal vein( Fig. 50, Plate IV) and further caudad becomes continuous with small vessels (cardinal collaterals, Fig. 51, Plate IV) which lie, one on each side, ventrolateral to the aorta between the aorta and the ureter, and which frequently anastomose with each other ventral to the aorta (Fig. 52, Plate IV). As in the case of the 10.5 mm. pouch young, I have been unable to establish a connection between the caudal ends of these vessels and the postcardinal veins. In the 11.5-12 mm. embryos the permanent kidneys have not migrated as far forward as in the 11.5 mm. pouch young. The postcardinal veins present the same arrangement as in the 10.5 and 11.5 mm. pouch young and still form the principal route by means of which the blood reaches the root of the postcava from the mesonephroi, the hind limbs and pelvie region. The azygos system, however, appears to be more highly developed in these embryos than in either the 10.5 or 11.5 mm. pouch young, a circumstance which has already been mentioned. The right and left azygos veins in the thoracic region open, as in the preceding cases, into the ducts of Cuvier. Instead, however, of termi- nating blindly at their caudal ends, as in the 10.5 mm. pouch young, they, or at least the vein of the left side, are now directly continuous with the lumbar azygos veins so that a continuous chain of veins can be traced from the ducts of Cuvier to the hinder end of the body. The junction of the left anterior revehent vein with the postcava still forms a promi- nent landmark at this stage of development, and the section of the un- paired postcava which lies caudad of this junction has become somewhat elongated and anastomoses freely with the lumbar azygos veins (Fig. 54, Plate V). Also, shghtly caudad of the root of the postcava, the lumbar azygos veins, by means of ventral prolongations, anastomose with the posteardinals (Fig. 55, Plate V), and then become directly continuous with the cardinal collateral veins which lie ventrolateral and ventral (Fig. 56, Plate V) to the aorta between the two postcardinals. The azygos veins of the thoracic region still occupy a somewhat dif- ferent position from that occupied by the azygos veins of the lumbar re- gion. In the thoracic region they lie ventral to the segmental branches of the aorta, while in the lumbar region they lie, for the most part, dorsal to these branches. Charles F. W. MecClure.- 189 The cardinal collateral veins in the 11.5-12, as in the 8 mm. embryos, constitute an extremely complicated system of vessels which lie in the tissue ventral and ventrolateral to the aorta between the postcardinal veins (Fig. 56, Plate V). Here they form frequent anastomoses with the postcardinals and with veins which occupy the position of the pos- terior reyehent veins (subcardinals). They, also, at their caudal ends, join the posteardinals and appear, as in the 8 mm. embryos, to form the ventral portions of circumarterial venous rings which encircle the origins of the umbilical arteries. In the 14 and 15 mm. pouch young of Didelphys the azygos veins show a marked advance in their development over that met with in the preceding stages; an advance which is undoubtedly correlated with the degeneration of the mesonephroi and the mesonephric divisions of the postcardinal veins. A right and a left azygos vein are present in the thoracic region. The vein of the right side is smal! in ealiber and, on being traced caudad, appears to terminate in the thoracic region. The vein of the left side possesses a large caliber at its cranial end, but gradually dimin- ishes in size from before backward where, as a rule, it becomes directly continuous with a single azygos vein of the lumbar region. AlI- though a direct anastomosis is established between the azygos veins of the lumbar and thoracic regions the character of the connection is such that the two systems, even at this stage of development, are, as in the preceding stages, practically independent of each other. The right thoracic azygos along its entire extent hes ventral to the segmental branches of the aorta. The left thoracic azygos, for a portion of its course, occupies the same relative position, but, at the caudal end of the thoracic cavity, where it becomes continuous with the lumbar azygos vein, it les dorsal instead of ventral to these arteries. The lumbar azygos system is represented by a single vein which les dorsal to the segmental branches of the aorta. It increases in size from before backward and in places frequently possesses a caliber as large as that of the postcava (Fig. 57, Plate V). The renal veins have both been formed; the vein of the left side taps the left anterior revehent vein near its point of junction with the postcava, as will be described further on. Caudad of the renal veins and between the latter and the junction of the posteava with the two posteardinals, the lumbar azygos vein anas- tomoses in a number of places directly with the postcava, so that the blood collected by its tributaries is now returned to the heart by the posteava. The anastomoses which are formed between these two veins are extremely variable in their character, since they may be formed on 190 Venous System of Didelphys Marsupialis (L) the right, the left, or on both sides of the aorta (Fig. 58, Plate V) ; a cir- cumstance which, we will see later, accounts for the variations in con- nection with the lumbar veins, as well as the variable manner in which the caudal end of the azygos may join the postcava in the adult (McClure, 03, p. 382). One of these anastomoses invariably occurs slightly caudad of the renal veins and another at the junction of the postcava and the two posteardinal veins and between these two some other anastomoses are met with which are apparently more or less variable in character. Remarkable changes, as will be more fully described later on, have also taken place in connection with the cardinal collateral veins. These veins, at their cranial ends, anastomose with the root of the postcava (pars subeardinalis) and at their caudal ends with the postcardinals ; and, in correlation with the atrophy of the mesonephric divisions of the postcardinals (Urnierennabschnitt) have so increased in size that in most of these pouch young they now return to the postcava practically all of the blood collected by the tributaries of the external and internal iliac veins. The original mesonephric divisions of the postcardinals now function chiefiy as mesonephrie veins (Urnierenvenen) which return blood from the mesonephroi to the pars subcardinalis of the postcava. In the 17 mm. pouch young the arrangement of the venous system is essentially the same as in the adult, so far as the completion of the post- cava and the formation of the azygos system are concerned. The cardinal collateral veins now receive all of the blood collected by the tributaries of the external and internal iliac veins and constitute that portion of the unpaired postcava which les in the adult caudad of the spermatic veins. The mesonephroi, although more atrophied than in the 14 and 15 mm. pouch young, are still functional and are connected with the body walls by means of extremely narrow mesenteries. ‘The meso- nephric divisions of the postcardinals have entirely ceased to be continu- ous vessels and are now represented by small veins which return the blood from the mesonephroi to the postcava. The changes, about to be described, that have taken place in connection with the azygos veins are without doubt correlated with the atrophy of the mesonephrie divisions of the postcardinal veins and the consequent completion of the postcava. In the 17 mm. pouch young the lumbar azygos vein now forms with the thoracic azygos of the left side a single, continuous vessel of consid- erable size which extends between the left precava and a point slightly caudad of the renal veins where, in the pouch young at hand, it joins the posteava on the right side of the aorta. Caudad of this point of junction with the posteava the lumbar azygos now ceases to be a continu- Charles F. W. McClure 191 ous vessel, and the blood from this section of the lumbar region is re- turned, as in the adult, directly to the posteava, by means of lumbar veins. These lumbar veins are undoubtedly formed through the per- sistence of the anastomoses that were formed at an earlier stage between the continuous lumbar azygos vein and the postcava. As these anas- tomoses may occur on either side or on both sides of the aorta, we find in them an explanation of the variations which were described in Part I of this paper in connection with the lumbar veins of the adult (p. 387), as well as those concerning the manner in which the caudal end of the azygos may join the posteava (p. 382).° The left azygos vein of the 17 mm. pouch young occupies exactly the same relative position with respect to the segmental branches of the aorta as in the adult (see Plate I, Fig. 28), in which along its cranial half it lies ventral and along its caudal half it lies dorsal to the segmental ar- teries of the left side. The transition from the ventral to the dorsal po- sition takes place at the caudal end of the thoracic cavity (about oppo- site the 10th thoracic vertebra in the adult) at a level which probably marks the embryonic point of union of the two originally separate com- ponents of the left azygos channel. It is, therefore, evident that the original positions occupied in the pouch young by the azygos veins of the thoracic and lumbar regions are retained in the adult. A tight azygos vein which opens into the right precava is also present in the 17 mm. pouch young. It is a small and insignificant vessel which lies ventral to the segmental branches of the aorta and which is confined to the anterior portion of the thoracic cavity. It is an interesting fact that the right azygos vein is apparently a con- ‘In four of the five adult specimens of Petrogale penicillata recently examined by the writer two essentially independent subdivisions of the azygos system were met with similar to those described above for the pouch young of Didelphys. The thoracic region was drained chiefly by a right thoracic azygos vein, while the lumbar region was drained, for the most part, by a single continuous vein which extended forward, dorsal to the aorta, and which opened into the postcava near the opening into the latter of the renal veins. The lumbar azygos vein, by means of slight connections, anastomosed with the postcava at intervals along its course and also received the lumbar veins. *The lumbar veins of the adult may open into the postcava either in pairs or, on either side of the aorta, by means of a common trunk. The caudal end of the azygos vein of the adult may join the postcava either to the left, which is the usual method, or to the right of the aorta; or it may bifurcate into two branches on the ventral circumference of the aorta which join the post- cava on the right and left side of the aorta, respectively. In this case the aorta is encircled by a venous ring formed by the azygos and the postcava. 192 Venous System of Didelphys Marsupials (L) stant character up to a late period of development, while in the adult its presence is an exception. Its constancy during the developmental period may account, however, for the fairly large percentage (30 per cent) of cases observed by the writer in which the vein was present in the adult, but in which it was extremely variable in character and confined to the first few intercostal spaces (McClure, 03, p. 383). A connection between the caudal end of the azygos vein and the post- cava is apparently not of constant occurrence among all adult marsupials. In Phalangista, Beddard, 95, found such a connection in only one of several individuals examined, and in this case, on account of its large size, it practically took the place of the posteava. The writer’s interpretation of the azygos and cardinal collateral veins seems the one best fitted to the conditions met with in the pouch young at hand, although it is possible that it might be shghtly modified if some of the material studied were in a better state of preservation. The cardinal collateral veins of Didelphys may possibly be regarded by some as corresponding to the derivative of the postcardinal veins which is formed in the embryos of some of the higher mammals on the dorsomedial side of the ureters (rabbit) and permanent kidneys (cat). I cannot accept this view, however, for the reasons that the cardinal collaterals occupy an entirely different position with respect to the aorta (Fig. 56, Plate V), and also appear to have a different mode of origin than the derivative of the postcardinal veins in question. THE COMPLETION OF THE POSTCAVA. Up to and including the stages of development represented by the 11.5-12 mm. embryos and the 11.5 mm. pouch young the unpaired post- cava as met with in the adult is as yet incomplete, since the portion which forms the caudal continuation of the pars subcardinalis has not been fully established. In the 8 and 11.55-12 mm. embryos, as well as in the 10.5 and 11.5 mm. pouch young, the postecava consists of an unpaired vessel which extends between the sinus venosus and a point in the lumbar region where it anastomoses with the two postcardinal veins which still form its principal caudal continuation. This unpaired portion of the postcava consists embryologically of two independent divisions: One formed between the sinus venosus and the hepatico-subeardinal junction, in a manner yet to be determined; the other between the hepatico-sub- cardinal junction and the junction between the posteava and the post- cardinals which is formed in part by the hepatic sinusoids, but chiefly by the right subeardinal vein. The unpaired postcava, as thus formed, re- ceives most of the blood collected by the tributaries of the external and Charles F. W. McClure 193 internal iliac veins, as in the 8 mm. embryo, through the mesonephric divisions of the postcardinal veins. From a functional standpoint the mesonephroi may be said to be at the height of their development as long as the mesonephric divisions of the postcardinals retain the function of returning most of the blood to the pars subeardinalis which is collected by the tributaries of the external and internal iliac veins. In the 14 and 15 mm. pouch young there is a noticeable degeneration of the mesonephroi, and correlated with this also a degeneration of the r 3 POSTCAVA RIGHT UROGENITAL ARTERY SPERMATIC UROGENITAL ARTERY SPERMATIC RIGHT : x CARDINAL = Fs AORTA POSTCARDINAL COLLATERAL AORTA CARDINAL COLLATERAL an: “TUR COLLATERAL COMMON ARTERY a rs, POSTCARDINAL ILIAC a ; ARTERY -* x EXT. ILIAC EXT. ILIAC EXT. ILIAC PUDENDO- PUDENDO UREN BE: VESICALIS VESICALIS VESICALIS PUDENDO INT. ILIAG VESICALIS INT. ILIAC pone INT. ILIAC VENOUS RING Fic. 14. Fig. 15. Fic. 14. Reconstruction (slightly schematic) of the venous system of a 14 mm. pouch young of Didelphys in which a postcava of Type II is already established. Ventral view. Fic. 15. Reconstruction (slightly schematic) of the venous system of a 14 mm. pouch young of Didelphys in which a postcava of Type III, A is al- ready established. Ventral view. mesonephric divisions of the postcardinals. As a result of this degenera- tion the blood from the hind limbs and the pelvic region is directed toward the pars subcardinalis of the postcava through the cardinal col- lateral veins; while the mesonephric divisions of the postcardinals (Ur- nierenabschnitt) retain the function of returning the blood from the mesonephroi and constitute the mesonephric veins (Urnierenvenen). The correlation which exists between the atrophy of the mesonephric 194 Venous System of Didelphys Marsupialis (1L) divisions of the postcardinal veins and the establishment of this new sec- tion of the postecava (cardinal collateral) is clearly illustrated by the following transverse sections (Figs. 59, 60 and 61, Plate V) and recon- structions of the venous system (Text Figs. 14, 15, 16, 17 and 18) of the 14 and 15 mm. pouch young. In the case represented by Text Fig. 14, the mesonephric divisions of the postcardinals are still, as in the 11.5 mm. pouch young, the chief channels through which the blood reaches the pars subcardinahs from the hind limbs and hinder end of the body. This condition is unusual for this period of development and represents the only instance met with among the 14 and 15 mm. pouch young, in which both of the postcard- inal veins function in such a manner. An advance in development over that in the preceding stages is evident, however, since the cardinal col- lateral of the right side has made a connection at its caudal end with the postcardinal vein and the posteardinals have anastomosed with each other ventral to the caudal artery. In all probability the cardinal collateral of the left side also joins its corresponding posteardinal, although I am un- able to establish definitely such a connection, on account of the vessel not being filled with blood at its caudal end. Text Figs. 15, 16 and 17 represent examples of unilateral atrophy in which, in one case the left (Text Figs. 16 and 17), and in the other the right (Text Fig. 15) mesonephric division of the postcardinal has atrophied, and in which there is an hypertrophy of the corresponding cardinal collateral vein. In each case the atrophied postcardinal now functions as a vein which returns blood to the pars subcardinalis solely from the mesonephros (Urnierenvenen) and not, as hitherto, from the hind limb and hinder end of the body. Finally, Text Fig. 18 represents a case in which the postcardinals have atrophied on both sides, with the result that both of the cardinal collateral veins collect all of the blood from the tributaries of the external and internal iliac veins and constitute the caudal end of the postcava, while both of the postcardinals now function solely as veins of the mesonephroi (Urnierenvenen). It has been stated in Part I of this paper (p. 398) that in 42 of the 101 adult opossums examined by the writer the postcava was either bi- fureated as far craniad as the level of the internal spermatic veins, or otherwise presented some indication of an incomplete fusion between the two vessels (cardinal collateral) which form the postcava caudal to the level of the internal spermatic veins; also, that in some of the adults, either one or both of the posterior internal spermatic arteries were found to pass between the two divisions of the postcava or through a foramen Charles F. W. McClure 195 in the same (McClure, 03, Plates I, II and IV). The presence of a bifurcated postcava in the adult is easily explained on embryological grounds as the result of a non-fusion of the two veins (cardinal col- lateral) which normally form the postcava caudal to the spermatic veins. Text Figs. 14, 15, 16, 17 and 18 clearly show how variable the character RENAL OMPHALO MESENTERIC ARTERY LEFT RENAL ~ARTERY RENAL RENAL VEIN AORTA POSTCAVA ANT. SPERMATIC ARTERY OF ADULT 2 UROGENITAL ARTERY SPERMATIC CARDINAL COLLATERAL PEP CARDINAL URETER COLLATERAL POST CARDINAL COMMON ILIAC ARTERY EXT. ILIAC oY COMMON INT. ILIAC PUDENDO VESICALIS: INT. ILIAC CAUDAL Fie. 16. Ere. 16. OMPHALO RENAL MESENTERIC ARTERY ARTERY RENAL ARTERY RENAL AZYGOS POSTCAVA LEFT URETER UROGENITAL ARTERY POSTCARDINAL COMMON ILIAC RTERY EXT. ILIAC PUDENDO- PUDENDO EDEN Vesicnitic VESICALIS MEDIAL RING LATERAL RING CAUDAL ARTERY TATE. ALT = Reconstruction (slightly schematic) of the venous system of a 15 mm. pouch young of Didelphys in which a postcava of Type II is already established. Hires 27. Ventral view. Reconstruction (slightly schematic) of the venous system of a 15 mm. pouch young of Didelphys in which a postcava of Type lie Bwiseal: ready established. Ventral view. This figure also shows the ventral portions of the lateral rings into which the Vv. pudendovesicales open. of the fusion may be between the two cardinal collateral veins even before the adult stage is reached, as well as the formation of the for- amina, through which the posterior internal spermatic arteries pass. In the 17 mm. pouch young the cardinal collateral division of the 196 Venous System of Didelphys Marsupialis (L) posteava is fully established and the posteardinals now function as veins which return blood to,the postcava from the still functional mesonephroi and the anlages of the genital glands. THrE MIGRATION OF THE PERMANENT KIDNEYS AND THE DEVELOPMENT OF THE RENAL VEINS. After the permanent kidneys have completed their forward migration in the embryos of the rabbit and cat, renal veins are developed which open into the posteava, approximately, at the level at which the latter joins the two posteardinal veins (cross anastomosis, Text Fig. 7). When UROGENITAL LEFT ARTERY SPERMATIC Gol eae CARDINAL Pp. COLLATERAL OST CARDINAL COMMON ILIAC ARTERY PUDENDO- VESICALIS COMMON INT. ILIAC TGs ass INT. ILIAC Fig. 18. Reconstruction (slightly schematic) of the venous system of a 15 mm. pouch young of Didelphys in which a postcava of Type III, B is already established. Ventral view. a double or bifurcated posteava is met with in an adult rabbit or cat the bifurcation reaches, approximately, as far forward as the level at which the renal yeins open into the postcava. In Didelphys, on the other hand, after the permanent kidneys have completed their forward migration, renal veins are developed which open into the postcava some distance craniad of the latter’s junction with the two posteardinal veins (Text Fig. 17). This circumstance now explains why the postcava of the adult opossum was never found by the writer (Part I, page 398) to be bifurcated as far forward as the level at which the renal veins opened into the posteava. The position of the renal veins in Didelphys with respect to the junction of the postcardinal veins and the posteava, does not appear to indicate that the permanent kidneys in Didelphys have undergone, relatively, a more extensive Charles F. W. McClure 197 migration than in the rabbit and cat, since the renal veins in Didelphys, as in the embryos of the rabbit and cat, open into the postcava only shghtly caudad of the origin of the omphalomesenteric artery and con- tiguous to the junction of the postcava and the left anterior reyehent vein (subcardinal). The opening of the latter vein into the postcava, however, lies relatively much further craniad of the junction of the post- cava and postcardinal veins in the pouch young, than is the case in the 8 mm. embryos of Didelphys and the embryos of the rabbit and cat. This circumstance I can only account for on the basis that the junction of the postcardinal veins with the postcava remains, more or less, as a fixed point, in front of which the vessels elongate more rapidly than those that lie behind. This growth in length, so far as the postcava is concerned, principally affects that portion of the vein which lies be- tween its junction with the two postcardinals and that with the left an- terior revehent vein. Strictly speaking, this portion of the posteava cor- responds to the original cross anastomosis between the two subcardinals ° (pars subcardinalis of postcava and left anterior revehent vein; see Text Figs. 10 and 12). A comparison of Text Figs. 11 and 17 gives a clear idea of the relative positions occupied by the permanent kidneys during their migration and after it is completed. The permanent kidneys are not represented in Fig. 7, but the renal veins sufficiently indicate their position. In the 11.5 mm. pouch young a renal vein was met with for the first time. Here a left renal vein was present, which opened into the post- cava in common with the left anterior revehent vein (Fig. 49, Plate IV). Both renal veins were present in the 14 and 15 mm. pouch young. In the adult opossum the left suprarenal body lies in close contact with the left renal vein (Fig. 28, Plate I) so close, in fact, that it is im- possible to speak of the existence of a left suprarenal vein. On account of the intimate relation, therefore, which exists betwen the left renal vein and suprarenal body, it appears probable that the slight venous con- nections between the two have been derived, as in the rabbit, from the left anterior revehent vein. ®Hochstetter (1893, Taf. XXIII, Fig. 25) suggests a somewhat similar explanation for the development of that portion of the unpaired postcava in Dasypus novemcinctus which lies, ventral to the aorta, between the renal veins and the origin of the posterior mesenteric artery. Referring to this portion of the postcava, he says (page 621): ‘ das der zwischen Miindiing der Nierenvenen und der Theilung in die beiden hinteren Hohlvenen gelegene Abschnitt der V. cava posterior einem starkeren Wachsthum der Lendenwirbelséule seine Entstehung verdanke.” 198 Venous System of Didelphys Marsupialis (L) During the migration of the kidneys the ureters also undergo certain changes in position. In the 8 mm. embryo they lie dorsal to the cardinal collateral and subeardinal veins along their entire extent and are not, at this period, so far as the writer can observe, encircled by venous loops. In the 14 and 15 mm. pouch young, on the other hand, at least in those cases in which the mesonephric divisions of the postcardinals have not yet atrophied, each ureter passes through a venous loop (Text Figs. 16 and 17) which is formed laterally by the postcardinal and medially by the cardinal collateral vein. The relation of the ureters to the veins at this period of development thus resembles the conditions met with in some placental mammals (cat and rabbit) with the exception that among the latter the medial side of the loop lies dorsolateral instead of ventro- lateral to the aorta, as is the case in the opossum. The manner in which the ureters migrate from a position dorsal to the cardinal collateral ves to the position which they occupy in the 14 and 15 mm. pouch young, ventral to these veins, is not clearly shown in the stages studied. J am inclined to believe, however, that the appar- ent discontinuity, mentioned above, which exists caudally between the posteardinal and cardinal collateral veins in the 10.5 and 11.5 mm. pouch young has been brought about by a ventral migration of the ureters. THE SPERMATIC VEINS. In the 8 mm. embryos of Didelphys, the blood from the anlages of the genital glands is collected by a number of tributaries (genital veins, Figs. 38 and 39, Plate III), which open into the derivatives of the sub- cardinal veins (pars subcardinalis of the postcava, the left anterior and posterior revehent veins). At a subsequent stage of development (14 and 15 mm. pouch young), with the retraction of the mesonephroi from the body walls, the genital veins return their blood to the posteava (pars subcardinalis) by means of a right and left mesonephric vein which opens into the postcava, caudad of the renal veins, at a point which corresponds to the junction of the postcava and the postcardinal veins (Figs. 59, Plate V). Since this junction corresponds to the level at which the spermatic veins open into the postcava in the adult, I am, therefore, convinced that these two mesonephric veins, together with their genital connections, are retained in the adult as the spermatic veins, although I have not been able to es- tablish definitely that such is the case. The spermatic veins in all of the adult opossums examined by the writer (101) were connected with the posteava caudad of a point mid- Charles F. W. McClure 199 way between the left renal and common iliac veins (Fig. 28, Plate I) ; and, when the posteava was bifurcated, the connection was invariably found at the level of the bifurcation (see Part I, Fig. 8, Plate IT). In none of the adults examined did the spermatics open into the renals, al- though an anastomosis between the latter and the spermatics was in- variably present, on each side, in the form of a small vein which fol- lowed the ureter (see Fig. 28, Plate I). In a number of adult Australian marsupials, however, the spermatics do not open into the postcava, as in Didelphys, but open into it at the base of the renal veins, as in Phascolomys Mitchelli (McClure, 03, p. 388), or into the renal veins themselves, as in Notoryctes typhlops (Sweet, 04). Considering the position at which the spermatic veins are developed in Didelphys, the question arises, how can these differences be explained? At the present time but two possibilities suggest them- selves to the writer: (1) Either the lumbar portion of the postcava may not elongate to such an extent in these two forms as in Didelphys, so that the renal veins are developed, as in the rabbit and cat, at the level of the root of the posteava (anastomosis between postcava and _ post- cardinals, Text. Fig. 7); or, (2) if an elongation does take place, as in Didelphys, the connection of the spermatics with the renal veins in Notoryctes may be accounted for on the ground that the spermatics have given up their original connection with the root of the postcava in favor of the channel, mentioned above, which follows the ureter and which opens into the renal veins. THE VARIATIONS PRESENTED BY THE POSTCAVA IN THE ADULT DIDELPHYS. In all mammals, hitherto examined, the posteava is formed in the adult through a union of its iliac tributaries which takes place in a defi- nite and uniform manner so that when variations occur they are re- garded as exceptions to the general rule. Such, however, is not the case in Didelphys marsupialis. Here, instead of occurring as exceptions, va- riations appear to be the rule, so that it is actually impossible in this mammal to assign any one mode of origin for the postcava that may be regarded as typical of the species. This opinion is based upon the ex- amination of 101 individuals; and a full description of these variations, as well as figures of the same, have already been published in Part I of this paper, to which the reader is referred (page 390). In all but two of the 101 adult opossums examined the variations of the posteava can be easily classed under three main types. In two in- 200 Venous System of Didelphys Marsupialis (L) dividuals, however, neither in its position with respect to the aorta nor in its mode of formation through a union of the iliac veins does the postcava conform to the usual marsupial type, but rather to the type of postcava which is characteristic of most placental mammals and, for this reason, these two exceptions are regarded by the writer as the only cases of postcaval abnormalities met with among the 101 opossums examined @Pare EL p..595): The three types under which the postcaval variations are classified are as follows: Type I. Those cases in which the internal iliac veins unite with the external iliacs ventral to the common iliac arteries or ventral to the aorta to form the postcava. This type of postcava is the one commonly met with among the Aus- tralian marsupials, and may be spoken of as the marsupial type (see Text Fig. VI, Part I). The writer at present knows of but three cases among the Australian marsupials, thus far examined, in which the post- cava is formed in any other manner; two in which i¢ is formed as in placentals and in a manner similar to that in the cat (Petaurus tagua- noides” and Phalanger ursinus”) and one, Trichosurus vulpecula,” in which it is formed as in Didelphys (Type IL) and as figured on Plate ie wie: 6, Parte): Type II. Those cases in which the internal iliac veins unite with the external iliacs dorsal to the external iliac arteries, or dorsal to the aorta to form the postcava. Type III. Those cases in which the internal iliac veins unite with the external iliacs both dorsal and ventral to the common iliac arteries or both dorsal and ventral to the aorta to form the postcava. So many variations of this last type were met with that a further sub- division of Type III was found necessary, as follows: é Type III, A. Includes those cases in which the principal union be- tween the internal and external iliac veins takes place ventral to the arteries In question. Type III, B. Includes those cases in which the principal union be- tween the internal and external iliac veins takes place dorsal to the arteries in question. Type III, C. Includes those cases in which the above-mentioned dorsal and ventral unions are about subequally developed. * Hochstetter, 93. 1 Morphological Museum, Columbia University, No. 199. @ Morphological Museum, Columbia University, No. 234. Charles F. W. McClure 201 The following table shows the distribution of the above-mentioned types among 99 individuals; the postcava of the two remaining adult opossums, as mentioned above, not finding a place in the classification. TYPE 3 io) TOTAL TV DE RRs. cas arate ciskousl tt arSteis Sieisieesns aa ove 11 18 29 AUS ViPV Gs Mee tarsy ches eye lio ierehigpslavieue of @gelomereneitey one 9 18 27 Type III OD cs Bret ois OR ROME RCT oR NCO POE 3 5 8 Fo ake ote de re one ese ee 9 15 oan CFR en rel cary cet eit oes 2 2 9 11 IDX FT Beale Geen ee ee ae aE ee RE Ie EOE 34 65 99 THE DEVELOPMENT OF THE THREE TYPES OF POSTCAVAL VARIATIONS Wuicuo NorRMALLY Occur IN DIDELPHYS MARSUPIALIS. Considering the uniform manner in which the three types of post- caval variations occur in the adult there can be little doubt that their development in the embryo is also a normal procedure, and that they are not abnormalities in the strict sense of the word. Also, the circum- stance that so many as 99 variations can be classed under so few as three types is certainly suggestive that there may be some common ground- type to which they can all be referred not only in the adult, but in the embryo as well. In the 8 mm. embryo of Didelphys, as stated above, the umbilical artery of each side, near its origin from the aorta, is encircled by a com- plete circumarterial venous ring. These venous rings (see Text Figs. 10 and 13), as stated on a preceding page, are situated near the conflu- ence of the external and internal iliac veins and are extremely variable in their character, not only in different embryos but even upon opposite sides of the same individual. For example, the portion of the venous ring which encircles the umbilical artery ventrally may possess a caliber subequal with or greater in size than that which encircles it dorsally (Text Fig. 10 and Fig. 42, Plate III); or, the portion of the ring which encircles the artery ventrally may possess a smaller caliber than that which encircles it dorsally (Text Fig. 13 and Fig. 41, Plate IIT). This variation in caliber of the venous rings, as well as the relations the venous rings hold to the umbilical arteries in the 8 mm. embryos, is certainly suggestive of the conditions which characterize the three types of postcayal variations in the adult, in which a. correspond- ing variation in caliber is met with as regards the veitis which lie dorsal 14 202 Venous System of Didelphys Marsupialis (L) and ventral to the common iliac arteries. On purely theoretical grounds, therefore, it is not difficult to explain the origin of all the adult varia- tions on the basis that the formation of a particular type of postcava, depends upon the manner, as well as upon the extent, to which the circum- arterial venous rings of the 8 mm. embryo might be affected by atrophy during the subsequent stages of development. On this basis the forma- tion of Type III, in which the postcava is formed through a union of the external and internal iliac veins which takes place both dorsal and ventral to the common iliac arteries, might be explained on the grounds that portions of the venous rings which le dorsal, as well as those which lie ventral to the umbilical arteries in the embryo, have been retained in the adult. See Text Figs. 19 and 20. Type III, as represented by these figures, in which both embryonic venous rings retain their integrity and individuality might then be re- garded as a ground-type” arrangement of the venous system, of which all of the postcaval variations which fall under Type III (Plates III, IV and V, Part I), are modifications, as well as are those variations which fall under Types I and II (Plates I and II, Part I). Thus Type III, A (see Plate III, Part I), in which the principal union between the internal and external iliac veins lies ventral to the common iliac arteries, might be formed as the result of the partial atrophy of the dorsal, and Type III, B (Plate IV, Part I), in which the principal union between the iliac veins lies dorsal to the arteries, might be formed as the result of the partial atrophy of the ventral portions of the circumarterial venous rings. Type III, C, in which there is practically no difference in the ealiber of the vessels which lie dorsal and ventral to the common iliac arteries( see Plate V, Part I), might represent a case in which atrophy had affected the dorsal and ventral portions of the circumarterial venous rings in a like manner. Type I (see Plate I, Part I), in which the internal iliac veins unite with the external iliacs ventral to the arteries to form the postcava, and Type II (see Plate II, Part I), in which the reverse is the case, might be formed as the result of the complete atrophy of the dorsal (Type I) and ventral (Type II) portions, respectively, of the circumarterial venous rings in the manner illustrated by Text Figs. 21 and 22. 18 Among the 101 adult opossums examined by the writer one was met with in which the postcava was formed as in text Fig. 20, in which the common iliac vein unites with the external iliac of each side by means of two vessels which lie dorsal and ventral, respectively, to the common iliac artery. See Figs. 13 and 14 on Plate III, Part I, which are dorsal and ventral views, respectively, of the same preparation. Charles F. W. McChire 203 POSTCAVA POSTCAVA AORTA RIGHT CARDINAL COLLATERAL AORTA RIGHT _ POSTCARDINAL VENOUS RING COMMON VENOUS RING nities EXT. ILIAC UMBILICAL aS COMMON ARTERY INT. ILIAC EXT. ILIAC) INT. ILIAC CAUDAL INT. ILIAC iereay Hig. 19: Fie. 20. Fic. 19. Diagram of the venous system of an 8 mm. embryo of Didelphys showing the circumarterial venous rings. Ventral view. Fic. 20. Diagram of the venous system of Didelphys in which the internal iliac veins have fused ventral to the caudal artery and in which a postcava of Type III has been established as the result of the persistence of the dorsal and ventral portions of both embryonic circumarterial venous rings. Ventral view. POSTCAVA POSTCAVA SPERMATIC SPERMATIC ' AORTA—+- AORTA ’ ° ‘ . LEFT ’ ae . CARDINAL RIGHT ¢ Sa SHC ARDINAL . A . («COLLATERAL CARDINAL i ’ ‘ z POSTCARDINAL = ate COLLATERAL * ' . 4 COMMON VENOUS RING COMMON VENOUS RING ILIAC A ARTERY 2 (Eke EXT, ILIAC EX L ARTERY COMMON COMMON INT, ILIAC INT. ILIAC INT, ILIAC CAUDAL ' CAUDAL ARTERY EXT. ILIAC ARTERY Wie. 21. MTG. 225 Fic. 21. Diagram of the venous system of Didelphys in which a postcava of Type I has been established as the result of the complete atrophy of the dorsal portions of the circumarterial venous rings. Ventral view. Fic. 22. Diagram of the venous system of Didelphys in which a postcava of Type II has been established as the result of the complete atrophy of the ventral portions of the circumarterial venous rings. Ventral view. 204 Venous System of Didelphys Marsupialis (L) The general principles, stated above, concerning the origin of the three main types of postcaval variations are, without doubt, fundamentally eorrect. The reconstructions of the pouch young clearly show that the formation of a particular type of postcava depends upon the manner as well as upon the extent to which certain veins that lie dorsal and ventral to the umbilical arteries (common iliacs in pouch young) are affected by atrophy. This general principle is well illustrated by the reconstruc- tion of the venous system of a 14 mm. pouch young (Text Fig. 15) in which a posteava of Type III, A, in which the principal union between the internal and external iliac vein les ventral to the common iliac arteries, is already established. In this particular case the internal iliac vein of the right side unites with the external iliac of the same side by means of two veins which lie dorsal and ventral, respectively, to the common iliac artery; while on the left side the union between these two veins takes place exclusively on the ventral aspect of the common iliac artery. Furthermore, it is evident, as the result of a complete atrophy of the ventral portion of the venous ring which encircles the right com- mon iliac artery, that a postcava of Type III, C could be established. In the latter case, the internal iliacs would then unite with the external iliacs by means of two vessels, subequal in caliber, which lie dorsal and ventral, respectively, to the common iliac arteries. The important ques- tion to be determined in this case, as well as in connection with other reconstructions of the pouch young, is the extent to which the vessels that le dorsal and ventral to the umbilical arteries in the 8 mm. embryos are involved in the formation of the vessels in the pouch young and adults which occupy corresponding positions with respect to the common iliac arteries. The only doubt that can exist as to their correspondence is the circumstance that the venous rings of the pouch young (Text Fig. 15) as well as those which occasionally persist in the adult (Fig. 17, right side, Plate IV, Part I) occupy a slightly different position with respect to the external and internal iliac veins than is the case in the 8 mm. embryos (Text Fig. 13). In the 8 mm. embryos (Text Fig. 13) the umbilical arteries, as well as the dorsal and ventral portions of the venous rings, lie somewhat craniad of the point of confluence of the internal and ex- ternal iliac veins; while in the pouch young (Text Fig. 15) and adult (Fig. 17, right side, Plate IV, Part I) these structures occupy a more caudal position, so that the dorsal portion of the ring is now formed by the section of the postcardinal which constitutes the internal iliac vein, and the ventral portion of the ring by a vein which joins, at its caudal end, the internal iliac vein. Although a difference exists regarding the position of the rings and arteries with respect to the internal and ex- Charles F. W. McClure 205 ternal iliac veins it is seen, on comparing the figures, that the relations of the dorsal and ventral portions of the venous rings to the arteries which they encircle are the same in all cases in that the ventral portion of the venous ring lies nearer the median line than the dorsal portion. In view of this last-mentioned relation to the arteries, as well as the cir- cumstance that the posteardinal vein (int. iliac) still forms the dorsal portion of the venous rings, I am convinced that the two cases cited above for the pouch young (Text Fig. 15) and the adult (Fig. 17, Plate IV, Part I), respectively, represent instances in which the ventral portion of the circumarterial venous rings of the 8 mm. embryo has been re- tained, and that the change in the position of the rings has been brought about secondarily as the result of a growth of the embryo. It has already been stated that the Jeft internal iliac vein of the 14 mm. pouch young in question (Text Fig. 15) joins the external iliac of the same side, exclusively on the ventral aspect of the left common iliac artery. It is plain from what we have learned from the reconstructions of the 8 mm. embryos that this ventral connection cannot have been formed by the posteardinal vein since the latter les dorsal to the um- bilical arteries of the embryo. This ventral union, therefore, can be ac- counted for only on the grounds that it has either been formed through the persistence of the same class of vessels as those that le ventral to the umbilical arteries in the embryo ; or, as will be described later on, through the persistence of a vein which has been secondarily developed in connec- tion with the V. pudendovesicalis. Whatever the case may be, the large size of the ventral anastomosis between the internal and external iliac veins of the left side is undoubtedly correlated with the complete atrophy of the vessel which, in the embryo, formed a union between these two veins dorsal to the artery. Text Fig. 17, which is a reconstruction of the venous system of a 15 mm. pouch young, presents a somewhat different arrangement ol the veins which unite to form the posteava, from that just described for the 14 mm. pouch young (Text Fig. 15). In this case (Text Fig. 17) the internal iliac veins unite with the external iliacs to form the posteava by means of five vessels, three of which lie ventral and two dorsal to the common iliac arteries. It is further seen that these dorsal and ventral connections between the iliac veins form, on each side, two complete cir- cumarterial venous rings, both of which encircle the common iliac artery. The ventral portion of the more medially situated rings is formed by a common vessel which is situated in the mid-ventral line and which is continuous caudad with the caudal veins; while the dorsal portion of the medial rings is formed by the postcardinal veins which also form 206 Venous System of Didelphys Marsupialis (L) the dorsal portion of the more laterally situated rings (lateral rings). The ventral portion of the more laterally situated ring presents a marked difference in caliber on opposite sides and receives a vein which the writer regards as the V. pudendovesicalis (McClure, 00, 2, p. 457). There can be no doubt as to the postcardinal origin of the dorsal por- tion of both sets of rings. There is some doubt, however, regarding the origin of the median ventral vein which forms the ventral portion of the two medial rings, as well as that of the ventral portion of the two lateral rings into which the V. pudendovesicalis opens. The median ventral vein presents the same relative position with re- spect to the dorsal portion of each of the two medial rings, as is the case with the ventral portion of the circumarteria! venous rings of the 8 mm. embryo (Text Fig. 13), the 14 mm. pouch young (Text Fig. 15), and the case of the adult (Fig. 17, right side, Plate IV, Part I), and, for this reason, has been most likely derived from the same class of vessels as those which form the ventral portions of the venous rings in the 8 mm. embryos. Whether, however, it corresponds to the ventral portion of one ring or has been formed as the result of a fusion between the ventral por- tion of two rings, as represented in the diagram, Fig. 20, it is impossible to state. Whatever its mode of origin may be, its presence in the pouch young undoubtedly accounts for the presence of a similarly situated ves- sel which is frequently met with among the adult variations (see Fig. 19, Plate IV, Part. 1): The ventral portion of each of the lateral rings, on the other hand, occupies an entirely different position with respect to the dorsal portion of the ring from what is the case with the ventral portion of the medial rings, since it lies lateral instead of medial to the dorsal portion of the ring. I am, therefore, inclined to conclude, for this reason as well as others given below, that the ventral portions of the lateral rings are secondary formations which are first met with in the pouch young and which are developed here in connection with the V. pudendovesicalis. In addition to the reason already mentioned, my reasons for so thinking are as follows: (1) On account of the presence of these veins in the 15 mm. pouch young (Text Fig. 17) in addition to the median ventral vein; as well as the occasional persistence in the adult of the ventral por- tion of a right lateral ring in addition to a vein whose origin cannot be accounted for unless it has been derived from the ventral portion of an embryonic circumarterial venous ring of the same side (see Fig. 4, right side, Plate I, Part I, and compare with Fig. 10, right side, on Plate II, Part I) and, (2) because the presence of these veins in the pouch young explains, for the most part, the variable character of the V. pudendovesi- calis in the adult. Charles F. W. McClure 207 The writer has already described in a previous paper (McClure, 00, 2, p. 457) the variable manner in which the Vy. pudendovesicales of the adult may open into the iliac veins. They may open in the adult into the angle of union of two veins which join the external and internal iliac veins, respectively, ventral to the iliac arteries; or, they may open into the angle of union of three veins, two of which lie ventral to the arteries and join the iliac veins as above, while the third les dorsal to the arteries and joins the external iliac vein (see McClure, 00, 2, Figs. 20 and 21). Also, they may open as single vessels on each side either into the external or internal iliac veins (Fig. 16, Plate IV, Part 1); or, into the external iliac vein on one side and into the internal iliac on the other (Fig. 9, Pilate: id, ‘Part.1). Cases in the adult in which the V. pudendovesicalis opens into the angle of union of two veins which join the external and internal iliacs, respectively, ventral to the arteries (as in Fig. 4, right side, Plate I, Part I, and in Fig. 10, right side, Plate II, Part I) can be explained on the ground of the persistence of the ventral portion of the lateral cir- cumarterial venous ring. Cases in the adult in which the V. pudendo- vesicalis opens as a single vessel into either the external or internal iliac vein (Figs. 8 and 9, Plate II, Part I) can also be explained on the ground that the ventral portion of the lateral venous ring gives up its connection with one or the other of the iliac veins so that the V. pudendovesicalis will necessarily open only into the iliac vein with which the connection has been retained. Although those cases in which the V. pudendovesicalis opens into the external and internal iliac veins, ventral to the arteries, appear to find an explanation, it is not so clear how this vein, as is frequently the case in the adult, makes connections with the iliae veins dorsal to the iliac arteries. It is possible that a considerable number of reconstructions of the pouch young would show that the V. pudendovesicalis does not al- ways open into the iliac veins as represented in Text Fig. 17, but that it may also, in some instances, open into the angle of union of two veins which, as in the case of an adult, join the external iliac vein dorsal and ventral, respectively, to the external iliac artery (see Fig. 4, left side, Plate I, Part I). It is evident, if this case of the adult represents the persistence of a condition which sometimes prevails in the pouch young we then have an explanation of those peculiar cases in which the V. pu- dendovesicalis opens into the iliac veins dorsal to the iliac arteries. Finally, I think it may be stated without fear of refutation, that the variable character of the V. pudendovesicalis in the adult is correlated with the variable manner in which the iliac veins unite to form the post- 208 Venous System of Didelphys Marsupialis (L) cava, although, at the present writing, it is quite impossible to establish a relationship between a particular type of postcava and the manner in which the Vv. pudendovesicales join the iliac veins. From what has already been stated above concerning the evanescent character of the ventral portion of the lateral venous rings it is clear that the type of postcava which at present characterizes the 15 mm. pouch young (Text Fig. 17) and which would most likely prevail in the adult, is Type III, B, and possibly of the variety represented by Fig. 19 on Plate IV of Part I. It is also possible that the ventral median vessel in Text Fig. 17 (ventral portion of medial rings) might become com- pletely atrophied before the adult state was reached so that a postcava of Type II would result, possibly of the variety represented by Fig. 7 on Plate II of Part I, in which the connections between the internal and iliac veins present a marked difference in caliber. In case of either of the two possibilities the ventral portions of the lateral rings could persist in the adult as in Fig. 10, right side (Plate IJ, Part I); or, they could give up their connections with the external iliacs so that each V. pudendo- vesicalis would open into an internal iliac vein as in Fig. 7 (Plate II, Part I). It is also evident that the condition represented in Fig. 9 (Plate II, Part I) might result, in which the V. pudendovesicalis opens on one side into the external and on the other into the internal iliac vein. We are now in a position to further consider the character of the an- astomosis, ventral to the common iliac artery, which exists between the left external and internal iliac veins in the 14 mm. pouch young (Text Fig. 15). ‘It has already been stated that this anastomosis, ventral to the artery, has probably been brought about either as the result of the persistence of a vein whieh corresponds to the ventral portion of an em- bryonic cireumarterial venous ring, or as the result of the persistence of a vein which has been developed secondarily in the pouch young in connection with the V. pudendovesicalis. It is not improbable that the ventral portion of one of the lateral rings might, in some cases, become so enormously hypertrophied, that it would function in the adult as the sole channel through which the blood reached the postcava from the pel- vic region. It is impossible, however, to state definitely what is actually the case in the 14 mm. pouch young, although I am inclined to believe that in this particular case (Text Fig. 15, left side) it is the ventral por- tion of a lateral ring which has persisted. My reason for holding this view is based on the relations of the V. pudendovesicalis to the ventral anastomosis in question. Text Fig. 18 represents another reconstruction of the venous system Charles F. W. McClure 209 of a 15 mm. pouch young in which a posicava of Type III, B, has al- ready been established ; that is, the type in which the principal union be- tween the internal and external iliac veins lies dorsal to the common iliac arteries. In this case, however, the connection between the internal and external iliac veins which lies ventral to the arteries does not consist of a single median vessel as in Text Fig. 17, but has the appearance of being formed as the result of a fusion between two medianly situated vessels, one of which, the right, follows a somewhat curved course. These median ventral vessels in Text Fig. 18 undoubtedly have the same origin as that of the single median ventral vessel in Text Fig. 17, al- though it is a difficult matter to determine in either case whether the ventral portions of one or of both of the embryonic circumarterial venous rings are involved in their make-up. The anastomosis between the ven- trally situated veins and the right internal iliac in Text Fig. 18 is most interesting, however, since it appears to explain the presence in the adult variations of a similarly situated vessel which lies ventral to the arteries and extends between the internal iliac vein and the external iliac of the opposite side. See Figs. 15, 16 and 18 on Plate IV, Part I, for examples of this type of variation. ‘There is one marked difference to be noted in comparing the venous systems of these two 15 mm. pouch young as rep- resented by Text Figs. 17 and 18. In Fig. 17 the ventral portions of the lateral rings anastomose with the external iliac veins, while in Fig. 18 this anastomosis is wanting. Whether this latter condition indicates that the ventral portions of the lateral rings are undergoing atrophy or that they are merely in the process of formation, it is impossible to state, although I believe the former view to be correct, on account of the large size and prominence of the vessels which unite the iliacs dorsal to the arteries. These dorsal vessels in Text Fig. 18, as well as the similarly situated vessels in all of the other pouch young, are de- rived from the postcardinal veins. Text Fig. 16 represents still another reconstruction of the venous system of a 15 mm. pouch young in which a postcava of Type II is al- ready established. In this case the connections between the internal and external iliac veins lie exclusively dorsal to the common iliac arteries ; there being no indication of any vessels which unite these veins ventral to the arteries, except the ventral portions of the lateral rings which, as in Text Fig. 18, are either in the process of formation, or, as 1s more likely, are undergoing atrophy. Finally, Text Fig. 14 represents the reconstruction of a 14 mm. pouch young in which a postcava of Type IT is also already established. In this case there is no anastomosis formed ventral to the common iliac 210 Venous System of Didelphys Marsupialis (1) arteries between the external and internal iliac veins, either in the form of vessels which lie in the median line, or of those which are more lat- erally situated and which have been described above as the ventral por- tions of the lateral rings. Numerous examples were met with by the writer in which the postcava was formed in the adult in exactly the same manner as that represented by Fig. 14 (see Figs. 6, 7 and 8, Plate II, Part I) ; while the two variations represented by Figs. 9 and 10 on the same plate, are easily explained on the ground that the internal iliac veins have given up one of their connections with the external iliacs. From what has already been said regarding the pouch young there can be no doubt that the establishment of a particular type of postcava in the adult depends upon the manner as well as the extent to which certain vessels which he dorsal and ventral to the iliac arteries are affected by atrophy. There can also be no doubt but that, in all cases, the vessels which lie dorsal to these arteries are derived from the postcardinal veins. There is, however, some doubt in the case of certain vessels which extend between the iliac veins, ventral to the arteries. A doubt may exist whether all of these ventrally situated vessels have been derived from the ventral portions of embryonic circumarterial venous rings; or, whether they may not, in some cases, be new formations which have been developed in the pouch young, independently of these rings. It is probable that in such a variable venous system as that of Didel- phys any venous channel which might be established in the embryo or pouch young between the internal and external iliac veins could, in cer- tain circumstances, be retained in the adult as a functional channel. I am, therefore, inclined to believe that in addition to the embryonie cir- cumarterial venous rings, other venous elements may occasionally enter into the formation of the vessels which form an anastomosis between the iliac veins ventral to the common iliac arteries. In all probability, the median ventral vessel in certain cases under Type I, as in Figs. 1 and 2 (Plate I, Part I) is formed as the result of the persistence of a single median vessel similar to that met with in the 15 mm. embryo (Text Fig. 17). It is a difficult matter to determine, however, whether both of the anastomoses between the iliac veins as in Fig. 3 (Plate I, Part I) have been derived from the ventral portions of the lateral rings, or, whether such is the case only with the anastomosis on the left side. It is also a question, on account of their connection with the Vy. pudendovesicales, whether the two veins which unite the iliac veins ventral to the arteries in Fig. 14 (Plate III, Part I) are not de- rived from the ventral portions of the lateral rings rather than from the ventral portions of the embryonic circumarterial venous rings. This and Charles F. W. McClure - Paha similar questions cannot be definitely decided without examining a large number of embryos and pouch young; and, furthermore, without, at the same time being fortunate enough to meet with a similar type of varia- tion. Whatever the case may be regarding the origin of these ventrally situated vessels, the venous channels which can be retained in the adult are all well defined in the embryos and pouch young. And, although certain difficulties are apparent in determining, in all cases, which of these embryonic venous channels have actually been retained in the adult, it is not impossible to interpret the adult variations (three types of posteaval veins) on the basis that they represent the possible combina- tions which could ensue as the result of the persistence or atrophy of certain of these embryonic vessels. EXPLANATION OF THE Two ABNORMALITIES OF THE PostcaAvaA WHICH CANNOT BE CLASSED UNDER TyPss I, II anp III (sEE Text Figs. VII ann VIII, Part [). As stated on page 395, Part I of this paper, the main features which characterize these two abnormalities and distinguish them from the variations described under the three types are twofold: (1) All of the posterior tributaries of the postcava, including the external or com- mon iliac veins, as the case may be, unite dorsal to the arteries to form the postcava, as is usually the case in placental mammals; (2) the post- cava lies to the left of, instead of upon the ventral surface of, the aorta, and resembles in this respect the conditions met with in placentals when the left instead of the right postcardinal vein persists as the caudal end of the postcava. Both of these variations are figured on page 396, Part I of this paper (Figs. VII and VIII) to which the reader is referred. It appears to the writer that these two abnormalities in question may be explained on the ground that the caudal portion of the unpaired post- cava has been formed, in each case, from one (the left) instead of from both of the cardinal collateral veins, as is usually the case in Didelphys. The persistence of the left vein explains the position of the postcava on the left side of the aorta; while the persistence of a single vein instead of two to form the caudal section of the postcava possibly duplicates the same physiological conditions that prevail in most placental mammals, and necessitates a union between the postcava and the iliac tributaries of the opposite side dorsal to the arteries. ‘The position of the ureters was normal in both cases since they were situated lateral to the postcava along their entire extent. For this reason 212 Venous System of Didelphys Marsupialis (L) it is evident that the cardinal collateral vein must have entered into the formation of the postcava rather than the postcardinal, otherwise the left ureter would occupy the same relative position that it does in Text Fig. 17, and pass caudad between the postcava and the aorta. Text Fig. 23 is a diagram illustrating the probable modifications which the venous system has undergone in establishing the abnormality represented by Text Fig. VII in Part I of this paper. The shaded por- tions indicate the veins which have atrophied and the crosses (++) the new formation by means of which the postcava anastomoses with the ilae tributary of the right side, dorsal to the aorta. AORTA POSTCAVA LEFT SPERMATIC VEIN POSTCARDINAL LEFT * CARDINAL RIGHT COLLATERAL CARDINAL COLLATERAL URETER VEIN NOUS RING Vase EXT. ILIAC VEIN INT. ILIAC VEIN Fic. 23. Diagram illustrating the probable modifications which the venous system has undergone in establishing the abnormality represented by text Fig. VII in Part I of this paper. Ventral view. THE UMBILICAL, ABDOMINAL AND OMPHALOMESENTERIC VEINS. The Umbilical Veins.—In the youngest embryos of Didelphys (8 mm.) studied by the writer, the right and left umbilical veins, usually after fusing at the umbilicus to form an umbilical sinus, can be traced for- ward as independent vessels (Figs. 38, 37, Plate III, and Figs. 36, 34, 33, Plate II) to the ventral surface of the liver. Here they again fuse to form a sinus (Fig. 32, Plate IL) from which they are continued dorsad through the parenchyma of the liver in a channel common to both which opens into the postcava in common with the left hepatic vein (Text Figs. 10 and 24). The hepatic continuation of the umbilical veins opens into the post- eava slightly craniad of that of the omphalomesenteric vein (Text Fig. 10) and, so far as the writer can determine, the umbilical and omphalo- Charles F. W. McClure - 213 mesenteric veins do not anastomose with each other at any point within (except by sinusoids) or without the liver. Near their entrance at the umbilicus considerable variation was met with in the 8 mm. embryos as regards the size of the umbilical veins. In some cases the right (Fig. 38, Plate III) and in others the left umbilical vein was the larger of the two, so it can be said that at this stage of development the umbilical vein of a particular side does not invariably predominate as the principal chan- nel between the allantois and the liver. Although a marked difference in size may characterize the umbilical veins in the region of the umbilicus, the smaller of the two veins invariably increases in size as the liver is ap- LEFT HEPATIC OMPHALO=— MESENTERIC POSTCAVA LEFT UMBILICAL UMBILICAL POSTCARDINAL /ASTBISIINAL ABDOMINAL EXT, ILIAC Wig. 24. Fic. 24. Diagram of the venous system of an 8 mm. embryo of Didelphys showing the umbilical and abdominal veins. Ventral view. proached, so it can be said that both umbilical veins are highly developed up to a relatively late stage of development; a circumstance which, as shown by Broom, 98, for Trichosurus, appears to be characteristic of the marsupials as thus far examined. 7 In the 11.5-12 mm. embryos of Didelphys one large umbilical vein now forms the principal channel between the allantois and the liver; a vein which | regard as the left umbilical vein. This large vein (Fig. 53, Plate V) lies in the ventral body-wall shghtly to the left of the mid-ven- tral line, and to its right is situated a much smaller vessel which is diffi- cult to follow in consecutive sections, but which is probably the remains of the right umbilical vein. The two umbilical veins appear to anastomose in places with each other, so that one might almost regard the larger of 214 Venous System of Didelphys Marsupialis (L) the two veins as being formed, in places, through a fusion of the two umbilical veins. On reaching the ventra! surface of the liver, the large umbilical vein enters the latter through which it continues as a single channel which at first turns caudad, and then dorsad before opening into the postcava as in the 8 mm. embryo, in common with the left hepatic revehent vein (Text Fig. 25). In the 10.5 mm. pouch young both umbilical veins can be followed for only a short distance in front of the umbilicus which is now closed. Further forward, however, only one large umbilical vein can be clearly distinguished, which now returns blood solely from the body-walls, but 0. A J ) 11. 5-12 MM. EMBRYO UO SUSI HEM a! Vieuiine POSTCAVA POSTCAVA ) PORTAL LIVER— OMPHALO = MESENTERIC LIVER * * UMBILICAL FIG. 44 UMBILICAL FIG. 45 Pie. 25. Iie, PAey ADULT POSTCAVA LIVER HEPATIC REVEHENT ( UMBILICAL 2) eae PORTAL, Figs. 25, 26 and 27. Diagrams illustrating the transformations which the umbilical and omphalomesenteric veins undergo in the embryos and pouch young. Lateral views. which is still continued through the liver where it opens into the post- cava, as in the preceding stages, without anastomosing directly with the omphalomesenteric vein (Fig. 44, Plate III, and Fig. 45, Plate IV, and Text Fig. 26). In the older pouch young the abdominal portion of the left umbilical vein ceases to be of prominence, and, so far as the writer can determine, entirely disappears before the pouch young have attained a length of about 17 mm. Its presence was noted, however, in the 14 and 15 mm. pouch young, although its connection with the hepatic circulation could not be determined. The hepatic continuation of the left umbilical vein, after it has given Charles F. W. McClure 21: i f up its connection with the abdominal portion, continues to function in the pouch young as a revehent vein of the liver, and I am inclined to believe that it is also retained in the adult (‘Text Hig. 27) as the hepatic vein (revehent) which opens into the postcava in common with or in close proximity to the large left hepatic vein (see Text Fig. V, Part I, which represents a corrosion of the hepatic veins of the adult). The arrangement of the umbilical veins in the 6 mm. embryo of Dasy- urus is essentially the same as that described above for the 8 mm. em- bryos of Didelphys; the only exceptions being that the two in Dasyurus are of about the same size and that their continuation within the liver opens into the postcava independently of the*left hepatic vein (Text Fig. 9, and Figs. 29 and 30, Plate IT). So far as known to the writer, Broom, 98, is the only investigator who has hitherto described the umbilical veins of the marsupials and, al- though his description is somewhat fragmentary, it conclusively shows, when compared with the above observations of the writer, that the plan of the umbilical circulation in marsupials not only differs from that in the higher mammals, but that there is also a difference even among the marsupials themselves. Broom states that in an 8.5 mm. embryo of Trichosurus a single mod- erate-sized vein brings back the blood from the allantois and on reaching the umbilicus opens into a rather large sinus which lies round the margin of the umbilicus. From the umbilical sinus two large umbilical veins pass up to the liver on either side of the large umbilicus. The vein of the left side opens into the liver at a point which corresponds to that at which the left umbilical opens in the higher mammals; the right um- bilical vein opens into the liver on the right side of the quadrate lobe and differs from the left in receiving a number of tributaries from the abdominal walls. Regarding the course of the umbilical veins within the liver, Broom states as follows: “ Each vein, on entering the liver through a small opening in its wall, falls into a comparatively large venous space. The tracing of the veins in the liver at this stage is a matter of considerable difficulty; but there is little doubt that each intra-hepatic venous sac gives off a small branch inwards and slightly downwards to the portal vein, and divides above into a large number of branches, which spread over the periphery of the upper part of the liver, and then pass inwards to fall into the inferior vena cava.” Broom further states that “In a 10.5 mm. Trichosurus embryo the umbilical sinus, though very much reduced, can still be detected. The development of the sides of the abdominal wall has brought both the 216 Venous System of Didelphys Marsupialis (1) right and left veins much nearer to the middle line, and a further inter- esting change has taken place in that the right vein has become much reduced and no longer opens into the liver. It is now merely a small vein which brings some blood from the anterior abdominal wall into the umbilical sinus. The left vein which now carries all of the allantoic blood to the liver, runs only a little to the left of the middle, though the recti muscles are still widely apart.” “A little later all trace of the right vein disappears, and the left vein, though comparatively small, follows a course very similar to that of the umbilical vein in the higher mammals. At birth, of course, the circula- tion through the umbilical vein ceases. It will be observed that this doubling of the umbilical vein is very dissimilar to the condition found in the higher mammal, and very similar to that found in the early lacer- tilian embryo.” The Abdominal Veins——The abdominal veins are most prominently developed in the 8 mm. embryo of Didelphys and consist of two small vessels which he in the ventral body wall caudad of the umbilicus (Figs. 40 and 41, Plate III). These two veins resemble in all their relations the posterior division of the abdominal veins in the embryos of reptiles, since thev receive tributaries from the body walls, open cranially into the umbilical veins and connect caudally with external iliac veins (Text Fig. 24). Veins occupying the same relative positions as the abdominal veins were also met with in the 11.5-12 mm. embryos of Didelphys, al- though they were much less prominent here than in the 8 mm. embryos. The abdominal veins are undoubtedly transitory in character and con- fined to the embryo during its uterine existence since no traces of them were met with in any of the pouch young examined. | The Omphalomesentertc Veins.—In the 8 mm. embryo of Didelphys the omphalomesenteric veins (Figs. 34, 35, 36, Plate II, and Figs. 37 and 38, Plate III) are represented by a single large vein whose earlier transformations I have been unable to follow. There can be little doubt, however, that a venous ring is formed about the intestine at a previous stage, as in the rabbit, since such a ring is actually present in the 6 mm. embryo of Dasyurus (Fig. 29, Plate II). In the 8 mm. embryo the large omphalomesenteric vein enters at the umbilicus on the left side of the intestine and then curves dorsad until it lies dorsal to the same. In this position it enters the liver through which it passes, without at any time anastomosing directly with the umbilical veins, and opens into the post- cava slightly caudad of the opening of the umbilical veins (Text Fig. 10 and Fig. 33, Plate II). In the 11.5-12 mm. embryos of Didelphys the omphalomesenteric vein, except for minor changes due to the elongation Charles F. W. McClure 21 ~2 of the embryos, maintains essentially the same relations as in the preced- ing stage and, after tunnelling the liver, also opens into the posteava inde- pendently of the umbilical veins. In the 10.5 mm., as well as in all of the older pouch young, the hepatic continuation of the omphalomesen- teric vein, instead of forming a continuous channel through the liver to the postcava, is broken up by the hepatic sinusoids so that the omphalo- mesenteric vein now functions as an advehent vein of the liver, or, in other words, has become transformed into the portal vein (Text Fig. 26). From the above description of the hepatic circulation in Didelphys it is evident that it differs widely from that met with in monotremes or in any of the higher mammals thus far described. Although in mono- tremes the ductus venosus Aranzii differs from that of the higher mam- mals in that it does not form the direct continuation of the left umbilical vein, it is nevertheless formed through a union of the portal and umbili- cal veins (Hochstetter, 96). In none of the embryos of Didelphys studied by the writer was a ductus venosus Aranzii formed as in monotremes or placental mammals, since in every instance noted both the umbilical and omphalomesenteric veins passed through the liver without at any time, except by sinusoids, anastomosing with each other. It, therefore, ap- pears questionable to the writer whether one can rightly speak of a ductus venosus in Didelphys that would correspond to that in monotremes and placental mammals, and for this reason this term has been omitted in the preceding description of the hepatic circulation. The nearest approach to the conditions deseribed above for the om- phalomesenteric and umbilical veins of Didelphys appear to be present in birds as described by Hochstetter (03, Fig. 156, page 136). Here the omphalomesenteric and left umbilical veins open into the proximal end of the postcava without previously anastomosing with each other within the liver, except by sinusoids. tESUME AND GENERAL CONSIDERATIONS. For convenience of description, the posteava of the adult Didelphys was described in Part I (page 386) as consisting of the following sub- clivisions : A prehepatic division which includes that portion of the vein which extends between the right auricle and the most cranial of the hepatic veins; an hepatic division which is embedded in the liver and which in- cludes that portion of the posteava into which the hepatic veins open; a renal division which includes that portion of the posteava which lies between the most caudal of the hepatic veins and a point just behind the most caudal of the two renal veins, and a postrenal division which con- 15 218 Venous System of Didelphys Marsupialis (L) sits of that portion of the postcava which les caudal to the renal veins. The following table shows the approximate relations which exist be- tween the veins in the embryo and the above-mentioned sub-divisions of the postcava in the adult: ADULT RABBIT EMBRYO DIDELPHYS EMBRYO BrehnepatiG irene ceet se V. hepatica communis... a FIeNaAtiC: tse eee ce Hepatic sinusoids ..... Hepatic sinusoids and a small portion of the right sub- cardinal vein. IRM Gooagoocoscuocaqamedn, Soloeerobimel 552 Right subcardinal. PoOstrenaillare sf aanide Right postcardinal ....Cross anastomosis, (formed by both subcardinals), and right and left cardinal col- lateral veins. 1. After the permanent kidneys have completed their migration in the embryos of the rabbit and cat, renal veins are developed which open into the postcava, approximately, at the level at which the latter joins the two postcardinal veins. In Didelphys, on the other hand, after the permanent kidneys have completed their forward migration, renal veins are developed which open into the postcava some distance craniad of the latter’s junction with the two postcardinals; a circumstance which now explains why the post- cava of the adult opossum was never found by the writer to be bifurcated as far forward as the level at which the renal veins opened into the post- cava. The position of the renal veins in Didelphys, with respect to the june- tion of the postcardinal veins and the postcava, does not appear to indi- cate that the permanent kidneys in Didelphys have undergone, relatively, a more extensive migration than in the rabbit and eat, since the renal veins, as in the embryos of the rabbit and cat, open into the postcava only slightly caudad of the origin of the omphalomesenteric artery, and con- tiguous to the junction of the postcava and the left anterior revehent vein. The opening of the latter vein into the posteava, however, lies relatively, much further craniad of the junction of the postcava and post- cardinal veins in the pouch young than is the case in the 8 mm. embryos of Didelphys and the embryos of the rabbit and cat. This circum- stance I can only account for on the basis that in Didelphys the junction of the posteava and the postecardinal veins remains, more or less, as a fixed point, in front of which the vessels elongate more rapidly than those that lie behind. This growth in length, so far as the postcava “ After Lewis (02, page 242). Charles F. W. McClure 219 is concerned, principally affects that portion of the vein (cross anasto- mosis) which lies between its junction with the two postcardinals and that with the left anterior revehent vein. The left renal vein of Didelphys is developed in connection with the left anterior revehent vein at the point where the latter opens into the postcava. The right renal vein is developed, as a rule, slightly craniad of the left and, possibly, from one of the urogenital tributaries of the pars subeardinalis of the posteava. Both renal veins were met with for the first time in the 14 mm. pouch young. 2. In the rabbit, the portion of the right subcardinal which, in part, forms the stem of the postcava terminates, approximately, at the level at which the renal veins will be developed; while the stem of the post- cava caudad of the renal veins is developed from the right postcardinal, together with a derivative of the latter which is formed on the medial side of the ureter. In Didelphys, however, the portion of the subeardinal which, in part, forms the stem of the postcava does not terminate at the renal level, but at the level at which the internal spermatic veins subse- quently open into the postcava; while caudad of the spermatic level the posteava is formed by two veins which usually fuse in the median line ventral to the aorta. This last feature, so far as I know, is distinctively a marsupial character. These two veins have been described in the pre- ceding pages under the name of the cardinal collateral veins. In both the embryos and pouch young the cardinal collateral veins occupy a po- sition ventrolateral or ventral to the aorta and, in this respect, differ from that of the posteardinal derivative which is developed on the medial side of the ureter, lateral to the aorta, and which forms, in part, the stem of the postcava in the rabbit. They are also to be distinguished from the posterior reyehent veins (subeardinals) with which, however, they form frequent anastomoses. In correlation with the degeneration of the post- cardinal veins the cardinal collaterals increase in size and subsequently function in place of the postcardinals in returning the blood to the root of the postcava from the hind limbs and pelvic region. 3. In the adult rabbit the postrenal division of the postcava lies to the right of the aorta and is usually formed through a union of its iliac tributaries which takes place dorsal to the arteries. In the adult Didel- phys, on the other hand, the postrenal division of the posteava lies ventral to the aorta and its iliac tributaries normally unite in such a variable manner to form the postcava that it is actually impossible to assign any one mode of union for the iliae veins that may be regarded as typical of the species. In consequence of this variability, the writer has classified the different modes of union which characterize the external and internal bs 220 Venous System of Didelphys Marsupialis (LL) iliac veins of the adult under three types. Type I, in which the internal iliac veins unite with the external iliacs ventral to the arteries to form the posteava (marsupial type); Type II, in which the internal iliac veins unite with the external iliacs dorsal to the arteries to form the post- cava; Type III, in which the internal iliac veins unite with the external iliacs, both dorsal and ventral to the arteries, to form the postcava. From an embryological standpoint it is not a difficult matter to deter- mine that the establishment of a particular type of postcava in the adult Didelphys depends upon the manner, as well as upon the extent to which certain well defined vessels in the embryos and pouch young, which le dorsal and ventral to the umbilical or common iliac arteries, are affected by atrophy during the subsequent stages of development. These dorsally and ventrally situated veins are usually met with in the embrvos and pouch young in the form of circumarterial venous rings which encircle the origin of the arteries in question. In establishing the three types of posteaval veins this embryonic ground-plan undergoes the following modifications : Type I is established as the result of the complete atrophy of the ves- sels which he dorsal, and Type II as the result of the complete atrophy of the vessels which he ventral to umbilical or common ilhac arteries. Type III, which is a combination of Types I and II, is established as the result of the persistence of vessels which lie both dorsal and ventral to the arteries in question. So far as known to the writer, no adult vertebrate has hitherto been described which presents such a series of normally occurring variations of the venous system as those described by the writer for Didelphys. Also, as far as I am aware, a fixity of type normally characterizes the main stem of the venous system of all other adult vertebrates so that va- riations, when they occur, are exceptions rather than the rule. It is an intereseting fact that an essentially similar ground-plan of the venous system as that described above for Didelphys, in which a cireum- arterial venous ring encircles the origin of the umbilical arteries, is also characteristic of the embryos of a number of other vertebrates. These vertebrates, however, differ from Didelphys in that the modifications which the embryonic ground-plan undergoes take place in a definite direction, so that a characteristic or fixed type of venous system normally results in the adult. For example: A circumarterial venous ring occa- sionally encircles the origin of the umbilical arteries in reptilian em- bryos (Sceloporus), although only the ventral or postcardinal portion of the ring normally persists in the adult. Circumarterial venous rings which encircle the origin of the umbilical Charles F. W. McClure 221 arteries are invariably present in the embryos of birds, as thus far exam- ined (Hochstetter and Miller), although in the adult only the dorsal portion of the embryonic ring persists normally as a functional vessel. In the embryos of Echidna (Hochstetter) the internal iliac veins (posteardinals) at first le ventral to the iliac arteries, but subsequently anastomose with the external iliacs by means of two vessels, one on each side, which he dorsal to these arteries so. that the postcava is at one time formed through a union between its iliae tributaries which takes place both dorsal and ventral to the iliac arteries. The adult condition is reached as the result of the complete atrophy of the anastomosis between the iliac veins which lies ventral to the iliac arteries (see Text Figs. X and XI, Part I). In this, as in the preceding cases, however, a fixity of type normally prevails in the adult regardless of the conditions which prevail in the embryo. Among the Australian marsupials it is not as yet known whether cir- cumarterial venous rings encircle the umbilical arteries as in the em- bryos of Didelphys. There is no question, however, as to the constancy with which, in most of these animals, certain ventrally situated vessels aid in forming the stem of the postcava in the neighborhood of the iliac arteries. Cireumarterial venous rings have recently been figured by Lewis (02, Plate 2, Figs. 7 and 8) as encircling the origin of the umbilical arteries of a 14.5 mm. rabbit embryo. In this case the ventral portions of the rings normally atrophy, while only the dorsal or posteardinal element of the rings persists in the adult as the functional channel. The persistence of the ventral as well as the dorsal portion of such a venous ring may possibly account for those interesting abnormalities in the adult mammal in which the common iliac artery passes through a foramen in the com- mon iliae vein. In establishing the adult conditions in Didelphys this embryonic eround-plan, as stated above, is not modified in any one definite direc- tion, but in such a manner that the resulting condition may be repre- sented by any one of the possible combinations which such a ground- plan is capable of producing. These possible combinations constitute the three types of postcaval variations which have been described in the preceding pages under Types I, II and III. The production of these va- riations is in every sense a normal procedure, and it is an interesting fact that the variations described under Type I (Fig. 1, Plate I, Part I) re- semble the usual condition of the adult postcava in the Australian mar- supials, while those under Types III, B (Fig. 18, Plate IV) and Type IT (Figs. 6 and 7, Plate II, Part I) are identical, respectively, with the em- 222 Venous System of Didelphys Marsupials (LL) bryonic and adult condition of the postcava in Echidna (see Text Figs. x and 2 Part: L). Furthermore, two cases were met with among the 101 adults exam- ined in which the postcava occupied the same relative position with re- spect to the aorta and was formed through a union of its iliac tributaries in exactly the same manner as in placental mammals when the left in- stead of the right postcardinal vein forms the caudal end of the stem of the postcava. These two cases are regarded by the writer as the only actual cases of abnormalities met with among the 101 adults examined. They are figured and described in Part I (page 395) and further con- sidered from the standpoint of their development in Part II (p. 211). It is impossible to state what the causes may be which are responsible for such a series of normally occurring variations as those which charac- terize the postcava of the adult Didelphys. Whatever they may be, they are apparently inherent in the individual itself since there is as much variation among the individuals of the same litter as among the in- dividual members which constitute the species in general. ‘ It appears to the writer that the causes which account for this constant variation in Didelphys may be analogous to those which only sporadically act in other vertebrates, but which are responsible for the well-known series of venous abnormalities which one occasionally meets with in the adult. Why they should constantly act in Didelphys and only ocecasion- ally act in other vertebrates, however, is difficult of explanation unless it is indicative of an extreme plasticity which may be regarded as charac- teristic of the species in general. This view certainly coincides with the investigations of Allen, or, upon the variable character of the skeleton of Didelphys, as well as with those of Oldfield Thomas, 88, who in re- ferring to Didelphys marsupialis, var. typica, savs (p. 327) : “ This wide- spread species, owing to its remarkable variability in color, has been made the basis of a very considerable number of nominal species, of which the most commonly recognized are the North American D. virginiana, the Brazilian D. cancrivora, and the striped-faced D. azare. I find, how- ever, such a considerable amount of variability in the specimens from every locality and such an entire absence of constancy in any character or set of characters, that I am constrained to unite the whole of this group of opossums into a single species, to which the Linnean name D. marsu- pialis is of course applicable.” It is generally conceded that variations of the venous system oceur with greater frequency among domesticated animals than among those living in the wild state: an idea, however, which is most certainly erro- neous, as proved by the conditions met with in Didelphys. x Charles F. W. McClure 223 +. In the rabbit embryo the portal vein (omphalomesenteric) on reaching the liver anastomoses directly with the left umbilical vein to form the ductus venosus Arantii, so that the latter, at a certain period of development, returns to the heart most of the blood that reaches the liver through the portal and left umbilical veins. In Didelphys, how- ever, no such direct anastomosis takes place between these two veins, but each vein is continued through the parenchyma of the liver in a separate channel which opens into the proximal end of the posteava independently of the other; a condition which, in some respects, resembles that met with in birds. So far as known to the writer, Broom is the only investigator who has hitherto described the umbilical and omphalomesenteric veins in the embryos of marsupials (Trichosurus) and, although his account is some- what fragmentary it conclusiyely shows, when compared with the above observations of the writer, that the plan of the embryonic hepatic circu- lation in marsupials not only differs from that of the higher mammals, but that there is also a difference even among the marsupials themselves. 5. Abdominal veins are present in the 8 mm. embryos of Didelphys which resemble in all respects the abdominal veins of reptiles. They he in the mid-ventral body-walls, connect cranially with the umbilical veins at the umbilicus and caudally with the external iliaes. In conclusion, I may state that in 1902 I received a letter from Dr. J. P. Hill, of the University of Sydney, in which he was kind enough to send me a few rough sketches illustrating the development of the veins in Perameles. He specifically stated that the schemes were not drawn to scale and, as they represented only a series of preliminary observa- tions, he did not care to vouch for their accuracy in detail. The general conclusions which he drew from his observations are most interesting, and I quote them in full. “ From these rude schemes there can be no doubt as to the origin of the posteaval vein from an unpaired anterior portion and paired posterior portions which probably fuse as shown in the 17 mm. stage. The most interesting find to me was that of a defi- nite renal portal circulation in connection with the mesonephros.” These observations coincide with mine on Didelphys so far as the de- velopment of the caudal portion of the stem of the postcava is concerned. The presence of a definite renal portal system was not observed by the writer either in the Dasyurus embryo nor in any of the embryos of Di- delphys examined, but its presence in Perameles, however, further illus- trates the unexpected as well as unusual characters which one occasionally meets with in the embryo, as well as in the adult of the marsupials in general. Of these characters, so far as the venous system is concerned, 224 Venous System of Didelphys Marsupialis (L) the following may be mentioned: ‘The presence of veins in the adult of Didelphys which undoubtedly correspond to the posterior vertebral veins of the sauropsida (Part I, pp. 380-1, these veins have not yet been observed in the Australian marsupials) ; the course pursued in the adult by the V. cordis magna which is similar to that in birds (Part I, p. 375) ; the presence of a type of postcava in the adult of Petaurus taguanoides and Phalanger ursinus which is similar to that met with in placentals in which the posteava lies to the right of the aorta and is formed through a union of its ilae tributaries which takes place dorsal to the aorta; the presence of posterior abdominal veins in the embryo of Didelphys; the absence of an anastomosis in Didelphys, between the left umbilical and omphalomesenteric veins, to form a ductus venosus Arantii, as in pla- cental mammals. LITERATURE CITED. ALLEN, J. A., or1.—A preliminary Study of the North American Opossums of the Genus Didelphis. Bull. of the American Museum of Natural History, Vol. XIV. Bepparp, F. E., g5.—On the Visceral Anatomy and the Brain of Dendrolagus Bennettii. Proc. Zool. Soc. of London for 1895. Broom, R., 98.—On the Arterial Arches and Great Veins in the Foetal Marsupial Jour. of Anat. and Physiology, Vol. XXXII. HocHSTETTER, F., 88.—Beitrage zur Entwickelungsgeschichte des Venen- systems der Amnioten. I. Vogel. Morph. Jahrb., B. XIII. ——— g2.—Beitrage zur Entwickelungsgeschichte des Venensystems der Amnioten. II. Reptilien (Tropidonotus und Lacerta). Morph. Jahrb., Bd. XIX. ——— 93.—Beitrage zur Entwickelungsgeschichte des Amnioten III. Sauger. Morph. Jahrb., Bd. XX. ——— 96.—‘Monotremen und Marsupialier” in Semon’s Zoologische For- schungsreisen in Australien, Bd. II, Lief. ITT. ——— 03.—Die Entwickelung des Blutgefasssystems in Handbuch der ver- eleichenden und experimentellen Entwickelungslehre der Wirbeltiere, Lief. 14 und 15. 3 Lewis, F. T., 02.—The Development of the Vena Cava Inferior. Amer. Jour. of Anatomy, Vol. I, No. 3. o4.—The Question of Sinusoids. Anat. Anz., B. XXV. Miter, A M., 03.—The Development of the Postcaval Vein in Birds. Amer. Jour. of Anatomy, Vol. II, No. 3. McCuiurg, C. F. W., 00, (1).—On the frequency of Abnormalities in connection with the Postcaval Vein and its Tributaries in the Domestic Cat (Fe- lis domestica). Amer. Naturalist, Vol. XXXIV, No. 399. ——— oo, (2).—The variations of the Venous System in Didelphys virginiana. (Preliminary Account). Anat. Anz., Bd. XVIII. Charles F. W. McClure 225 McCriure, C. F. W., or.—The Spermatic and Mesenteric Arteries of Didelphys virginiana (Kerr, Linn.). The Princeton University Bulletin, Vol. XII, No. 3. o2.—The Anatomy and Development of the Posterior Vena Cava in Di- delphys virginiana. Biological Bulletin, Vol. II, No. 6. 03.—A Contribution to the Anatomy and Development of the Venous System of Didelphys marsupialis (L), Part I, Anatomy. American Journal of Anatomy, Vol. II, No. 3. SELENKA, E., 86-7.—Studien tber Entwickelungsgeschichte der Thiere. -Das Opossum, Heft 4, 1 und 2. ——— o1.—Studien tker Entwickelungsgeschichte der Thiere. Heft 5, 1. SEMON, R., 94.—Monotremen und Marsupialier. Zoologische Forschungsreisen in Australien und dem Malayischen Archipel, Bd. II, Lief. 1. STROMSTEN, F. A., 05.—A Contribution to the Anatomy and Development of the Venous System of Chelonia. Amer. Journ. of Anatomy, Vol. IV, No. 4. Sweet, G., o4.—Contributions to our Knowledge of the Anatomy of Notoryctes typhlops, Stirling. Proc. Royal Soc. Victoria, Vol. XVII (New Series), Paria: THOMAS, OLDFIELD, 88.—Catalogue of the Marsupialia and Monotremata in the Collection of the British Museum (Natural History). TREADWELL, A. L., 96.—An Abnormal Iliac Vein in a Cat. Anat. Anz., Bd. XI. Weysse, A. W., 03.—The Perforation of a Vein by an Artery in the Cat (Felis domestica). Amer. Naturalist, Vol. XXXVII, No. 439. EXPLANATION OF FIGURES ON PLATE I. Fie. 28. Arteries and veins of an adult female Opossum (Didelphys marsu- pialis, L. or, as more commonly called, D. virginiana, Kerr, L.). Ventral view. Heart reflected to the right and liver, for the most part, cut away. The post- cava is formed as in Type II, in which the internal iliac veins unite with the external iliacs dorsal to the common iliac arteries. In addition to the Type of postcava mentioned above the following features should be noticed: The peculiar course pursued by the V. cordis magna; the position occupied by the azygos vein with respect to the segmental arteries; the absence of the anterior and posterior mesenteric arteries; the anastomosis between the renal and spermatic veins which lies on the medial side of the ureter, and the two pairs of internal spermatic arteries. EXPLANATION OF FIGURES 29 to 61 ON PLATES II-V. PATE Lil Figures 29-36. Fics. 29 (section 164) and 30 (section 171). Transverse sections of a 6 mm. embryo of Dasyurus, Series I. Fics. 31 (section 187), 32 (section 208), 33 (section 211), 34 (section 225), 35 (section 226) and 36 (section 238). Transverse sections of an 8 mm. embryo of Didelphys, Series VIII. 226 Venous System of Didelphys Marsupialis (1) Prate TT. Figures 37-44. Figs. 37 (section 244) and 388 (section 253). Transverse sections of an 8 mm. embryo of Didelphys, Series VIII. Fie. 39. Transverse section of an 8 mm. embryo of Didelphys, Series X, incomplete. Fics. 40 (section 384) and 41 (section 389). Transverse sections of an 8 mm. embryo of Didelphys, Series IX. Fic. 42. Transverse section of an 8 mm. embryo of Didelphys, Series III, incomplete. Fics. 43 (section 293) and 44 (section 350). Harvard Embryological Col- lection, Series No. 614. Transverse sections of a 10.5 mm. pouch young of Didelphys. PLATE IV. Figures 45-52. Figs. 45 (section 368), 46 (section 505), 47 (section 520) and 48 (section 521). Harvard Embryological Collection, Series No. 614. Transverse sections of a 10.5 mm. pouch young of Didelphys. Fics. 49 (section 244), 50 (section 214), 51 (section 199) and 52 (section 197). Harvard Embryological Collection, Series No. 617. Frontal sections of a 11.5 mm. pouch young of Didelphys. PLATE V. Figures 53-61. Fies. 53 (section 635), 54 (section 750), 55 (section 772) and 56 (section 789). Transverse sections of 11.5-12 mm. embryo of Didelphys, Series II. Fic. 57. Transverse section of a 14 mm. pouch young of Didelphys, Series IV. Fic. 58. Transverse section of a 15 mm. pouch young of Didelphys, Series XII. ; Fic. 59 (section 442). Transverse section of a 15 mm. pouch young of Didelphys. Series VII. Fic. 60. Transverse section of a 15 mm. pouch young of Didelphys, Series IX. Fic. 61 (section 448). Transverse section of a 15 mm. pouch young of Didelphys. Series VII. THE VENOUS SYSTEM OF DIDELPHYS MARSUPIALIS PLATE | Cc. F. W. McCLURE ARCH OF AORTA LEFT PRECAVA A. PULMONALIS LEFT AURICLE Vv. CORDIS MAGNA LEFT VENTRICLE Vv. AZYGOS POSTCAVA AORTA DIAPHRAGM Ris LIVER RIGHT SUPRA-RENAL BODY LEFT SUPRA-RENAL BODY Vv. RENALIS DEXTRA A. COELIACOMESENTERICA Vv. RENALIS SINISTRA JUNCTION OF AZYGOS AND POSTCAVA Oiaiteutets LYMPH BODY ANASTOMOSIS BETWEEN RENAL AND SPERMATIC VEINS A. SPERMATICA ANT. A. SPERMATICA ANT, ANASTOMOSIS BETWEEN RENAL AND SPERMATIC VEINS A. SPERMATICA POST. A. SPERMATICA POST. Vv. SASL LIES TES Vv. SPERMATICA SINISTRA TENDON OF PSOAS PARVUS URETER RIGHT OVARY TENDON OF PSOAS PARVUS Fi J : “00, UTERUS BLADDER AMERICAN JOURNAL OF ANATOMY-—Voxk. V. VENOUS SYSTEM OF DIDELPHYS MARSUPIALIS (L) F, W. McCLURE C. ish tig NIBA NIBA TWONISWN LHOIY AONISWA 1337 Y3AI1 NIZA SIlLWd3H 41431 WO1309 VYAVOLSOd NIBA OWS LNASSAWO1VHdWO NIZA TWONIsnn AYSLYV OIMSLNSESIW =OWHdWO SNYNIGYVOSNS Suvd VAVOLSOd TNIGYYOLSOd TNIGYVOLSOu VLYOV eh SL, VAVYOLSOd SNN1 LHOIY \WNIGYVYOLSOd NIZA SODAZV SOIOVYOHL 1437 NIBA WONISWN NIZA qWoneawn TYNIGYVOSENS NIBA SNVYNIQYVOSNS 1IN3H3A3¥Y “LNYV Suvd 1337 VWAVOLSOd SOYHdSNOSSW TWNIGUYD1LSOd AMERICAN JOURNAL OF ANATOMY--VOL. 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V IV PLATE SOYHdSNOS3W 83134n IYNIGHVYO1SOd 41431 WO1309 41337 qWw¥31v1109 TYNIGHVvO Of Ola yYL¥OV SSVINY WW LINSS SSVINV IWLINSS SOYHdSNOSIW NIGUYVO1LSOd WV WO1309 TWNIGYVOLSOd SOYHd3NOS3W 12 OL] S9VINY TWLINSS SOYHd3NOS3W SOYHd3SNOS3W IWNIGHYOLSOd TWNIGHYVOLSOd 4497 NISA go Wwualvno09 ViNOv WY3LYI090 TWNIGHYO TWNIGHYD 6% DLL VAVOLSOd TVYNIGYVYOsNS BOVINV ae LN3H3A34 “LNY WLIN39 ia AWNIGYVOLSOd STL Ti ts We SOYHd3SNOS3IWN gw nS t SOSAZV ASNOIM yvYaWnt 1431 VENOUS SYSTEM OF DIDELPHYS MARSUPIALIS (L) Cc. F. W. McCLURE 99 OL AY3.LN3AS3W AVNIGYVYOLSOd SOYHdSNOS3W TVWNIGHVOLSOd \ 41437 WH31LV1109 TWNIGHYS 49 OL BDV INV qv LINSS ee VYLYOV SODAZY vNIGHYvO.1LSOd yVvSNN1 lb oie AYSLNSS3IW ANIGHVOLSOd fies TWNIGHVOLSOd Z so} SOYHdSINOS3AW eeu aNOS a “*" .3NaIy SNISA SODAZV YVEWN SO OLS NIZA. TvONMIawn NIZA TVONISWn HOI i431 AMERICAN JOURNAL OF ANATOMY--VOL. v PLATE WV: yalayn SOYHdSNOS3IN 1331 IVNIGYVOLSOd WO1309 NIZA Wwu3LV71109 TWNIGHVO 4Y3134ynN TVNIGUYO.LSOd 41337 SOYHdSNOS3W —= WO1309 ASNQGIx SOYHdSNOS3W 4437 19 OL ANTLNASSW AVWNIG8VOLSOd . NIBA WwualLv1109 qWNIGYVS 43.135YN NIQUYDLSOd NOTS09 ASNOIM SOYHd SNOSAWN 09 OL Wy3Lv1109 YNIGHVOLSOd TyYNiauvolsog ff AvNIaYvo a = VAVO1SOd SOYHdSNOS3W Y¥3134n Y¥3135y4nN 1437 WO1309 t Eb) VLUOV WOAYLN 8S ILL 39v0NY TWLINSS SSVINV TIWLINSS Y¥3135yN ¢ ASNGIW ale sii] SOYHdSNOSSW SOYHdSNOS3aWN wo1309 A STUDY OF THE STRUCTURAL UNIT OF THE LIVER. BY FRANKLIN P. MALL. From the Anatomical Laboratory of the Johns Hopkins University. WitH 74 FIGURES AND 7 TABLES. In studying the structural development of an organ it is necessary to consider the systems within it as a whole and to determine their relations to one another. Analytical methods, which must precede synthetical methods, have shown that organs are built up of like parts, or structural units, which are analagous to the leaves of a tree. However, in the growth of an organ the units are not thrown off annually, but are gradually shifted and transformed into new units. It follows that in a study of the kind proposed it is always necessary to consider the unit in relation to the organ as a whole throughout its development, and to do this we must constantly resort to reconstruction. Of course this cannot be done with much success, in the ordinary sense of the term, but for the present purpose, the tables may be considered as reconstruction. Geologists, geog- raphers, archwologists and anatomists each have their own methods of reconstruction, and I have utilized them all, more or less, in the present study. I undertook the study of the structural development of the liver on account of its well-known and sharply-defined lobule. It was thought at the beginning that this lobule was the simplest of all the structural units and therefore the most suitable for a study of this kind. It soon became evident that the lobule was not the structural unit, and that both lobules and units were extremely difficult to follow in their development, for they are constantly blended with adjacent lobules, or units as the case may be. Furthermore, lobules or units once formed do not remain, but sprout, fracture and rearrange themselves, thus making the various pictures ob- tained complex and difficult to interpret. The work has been carried on during a number of years, after being laid aside in order to take up the same question in other organs. These secondary studies,—usually made by others connected with me,— have aided my work for the liver materially, which I now venture to present in a more or less connected form. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 18 228 A Study of the Structural Unit of the Liver HistroricaL NOTE. In 1664 Wepfer described lobules in the liver of the pig, and two years later they were again described by Malpighi who gave them their name. Malpighi states that the livers of all vertebrates are conglomerate glands, being composed of lobules which in turn contain acini. For a long time after this the capital problem in the anatomy of the liver was the study of the structure of the lobules and their relation to one another. In 1733 Ferrein described these lobules as being composed of two sub- stances, brown and yellow (substantia fusca and substantia flava) which formed respectively its medullary and cortical portions. In general this description was accepted by anatomists, sometimes, however, with a re- versal of the arrangement of the colors in the medullary and cortical por- tions of the lobule.’ | In 1832 E. H. Weber showed that the two colors of the lobule are due to an unequal distribution of blood in it, and a year later Kiernan, in his classic paper, denied altogether that the lobule was composed of two substances as described by Ferrein. We owe to Kiernan our present conception of the lobules; he described their shape and relation to one another, the amount and character of tissue between them, and what is more, their relation to the vascular system ; he also introduced our present nomenclature. The defining line around a lobule was broken up into spaces and fissures, spatia interlobularia when three lobules came to- gether, and fissure interlobulares between each two adjoining lobules. The spaces and fissures, which were not always easy to demonstrate, were no doubt included by Ferrein in the cortical portion of the lobule. It is seen that Kiernan’s interlobular spaces and fissures form a network between the lobules, and for this reason Theile calls them the substantia reticularis, and the lobule proper the substantia granosa. It was also shown that the order of the reticular and granular substances are reversed in hepatic congestion; in it the brown reticulum encircles yellow gran- ules, pseudogranules, as Theile calls them. The yellow “ pseudolobules ” are tough and more consistent than the true brown lobules. Before the time of Kiernan the usual confusion of terms naturally arose. For instance, Autenrieth accepted Ferrein’s cortical and medullary por- tions of the lobule, only he reversed the order of their colors. Evidently he was describing “ pseudolobules.” Merkel, who also no doubt studied hyperemic livers, did the same. Krause took the “ happy mean ” course 1See Kiernan, Phil. Trans., 1833; Theile, Handworterbuch der Physiologie, II, 1844; and Oppel, Lehrbuch der Vergleichenden Mikroskopichen Anatomie der Wirbelthiere, III, 1900. Franklin P. Mall 229 and described pseudolobules, 7. e., the yellow interlobular connective tissue, with hepatic veins in their center. Cruveilhier made the same blunder. Numerous other terms were used in a variety of ways, as, for instance, acinus which meant anything from a cell to an entire lobule, according to different authors. The lobule, as described by Kiernan, received its strongest support in its having on its periphery the terminal twigs of the portal vein, hepatic artery, bile duct, and an increased quantity of connective tissue, which an the pig forms a distinct capsule. Had it not been for an occasional animal with a lobule so well outlined and a great authority like J. Miiller, it is probable there would still be much confusion in spite of the “happy means ” and the innumerable terms. The study of the structure of the liver illustrates beautifully the value of great minds in the study of any subject. We see during a period of two centuries that the gen- eralizations of Malpighi, Ferrein, and J. Miiller are consistent and prac- tically correct in spite of the great amount of confusion and opposition brought from many quarters. Taking all of the facts into consideration, analysis by means of injection experiments, finally gave us a structural unit of the liver which has withstood all opposition. Lobules of the liver are certainly not well marked in most animals and it is seen by the foregoing that the lobules were as often found en- circling the portal twig as around the hepatic twig. A glance at Fig. 1 will show why either arrangement is correct. With the facts before him, it is fot remarkable that E. H. Weber denied the anatomical existence of the lobule, 2. e., a lobule that can always be seen and is always the same. However, J. Miiller, with the livers of the pig and of the polar bear as examples set the question at rest for a time. The “ psuedo lobule” of Theile, with the strong connective tissue of the portal space as a center, is tougher than the true lobule which has only a delicate reticulum to hold it together. Theile has shown that it is easy to isolate the “pseudo lobule” of the dog’s or the rabbit’s liver, while it is impossible to isolate the true lobule. In fact, if livers of these animals are crushed and washed in a stream of water, the whole system of lobules is isolated, clustered around the branches of the portal vein, forming a specimen which may be likened to a bunch of grapes. Sabourin has described the liver as being composed of biliary lobules with the terminal bile ducts as their centers.’ He has accepted the pseudo ?Sabourin, Le Progrés Méd., VI, 1883; Recherches l’anat. normale et pathol. de Ja glande biliaire de homme, 1888; Rev. Méd., X XI. ©o 30 A Study of the Structural Unit of the Liver lobule of Theile as the true unit of the liver, which in Phoca * is outlined by a capsule as the hepatic lobule is in the pig. The biliary or portal lobule has been used as a basis by Berdal* in his histology and has been Fic. 1. Diagram of a transverse section of a group of lobules with lines indicating the course of the capillaries. The lobules as usually understood are marked with circles. P, a portal unit; n, nodal point; p’ a portal unit outlined as in partial congestion. a. advocated by myself for a long time.’ Recently it has been discussed as the secreting lobule by J. B. MacCallum °, and has been defended from an embryological standpoint by F. T. Lewis.’ ’ Brissaund et Sabourin, Compt. rend., Soc. de biol., XL, 1888. * Berdal, Eléments d’histologie normale, Paris, 1894. 5 Mall, Zeit. f. Morph. u. Anthropol., II, 1900. ® MacCallum, J. B., English translation of Scymonowicz’s Histology. 7 Lewis, F. T., Anat. Anz., XXV, 1904. Franklin P. Mall 231 In all other glands we make the duct the center of the structural unit. From this center often the artery and the framework radiate. In the liver everything radiates from the so-called interlobular space,—arterial and portal blood yessels, bile duct, lymphatics, nerves and connective tissue ; the liver develops from this point; physiologically everything cen- ters there. So, viewed from any standpoint, it is the center of the struc- tural unit. Throughout my description I shall use the term portal structural unit, portal unit, structural unit, or unit, for the clump of tissue which sur- rounds each terminal branch of the portal vein. In order to avoid con- fusion I shall use the term lobule in its old sense,—as the hepatic lobule,— for after much discussion carried on during two centuries, it has become well established. The old idea, the idea of Wepfer, Malpighi, Ferrein, Kiernan, and J. Miiller should be marked with the word lobule; the new idea, associated with the unity of structure, should be called the unit. VASCULAR PROPORTION. Roux has stated in one of the theses in his Habilitationsschrift* that the lobular subdivisions of the liver are due, in their arrangement and form, to the vascular system. This same idea is again brought forth several years later in the Introduction to his Archiv.’ In this he says, on page 17, “ Die Gliederung der gewohnlichen, baumartig veristelten Driisen in Liappchen erscheint durch die gestaltenden Wirkungen der Epithelien, also der specifischen Teile, bedingt und ist, so weit dies richtig ist, Selbstdifferenzierung der Driisensubstanz. Bei der Leber dagegen, einer Netzdriise, erscheint die normale Grosse und Gestalt der Lappchen und auch die lobulire Gliederung selber durch die Blutgefasse bedingt, und zwar einmal durch die geeignete Kapillarlange wie zweitens durch die Eigenschaft der letzten Veristelungen der Vena porte, beim Wachsthum des Kapillarnetzes dichotomische Verzweigungen in letz- terem auszubilden. Die acindse Gliederung des Leberparenchyms stellt somit eine von dem Blutgefisssystem. abhingige Differenzierung der Driisensubstanz dar.” A much more extended discussion of the growth and proportion of the vascular system is given by Thoma in his numerous papers, but that ’ Roux, Ueber die Leistungsfahigkeit der Principien der Descendenzlehre zur Erklarung der Zweckmassigkeiten des thierischen Organismus, Breslau, 1880, and Gesammelte Abhandlungen, I, 1895, p. 134. ®° Roux, Einleitung zum Archiy fiir Entwickelungsmechanic der Organismen. Leipzig, 1894, p. 17. 232 A Study of the Structural Unit of the Liver which relates to the capillaries in particular is to be found in his brilliant It is not 10 study of the blood-vessels of the area vasculosa of the chick. possible to discuss in detail the many observations and arguments in this model research without extending this paper far beyond the space of this Journal. However, an excellent summary of Thoma’s work is given in his Pathology, from which I will quote several pages from the English translation.” Thoma’s work is summed up in three laws or histomechan- ical principles (page 265), as follows: (1) “The increase in the size of the lumen of the vessel, or what ts the same thing, the increase in the surface of the vessel wall, depends upon the rate of the blood-current. The surface of a vessel wall ceases to grow when the blood-current acquires a definite rate. The vessel in- creases in size when this rate is exceeded, becomes smaller when the blood-stream is slowed, and disappears when it is finally arrested. “This law which brings the growth of the surface of the vessel wall into dependence upon the rate of the flow of the blood is, I consider, the first and most important histo-mechanical principle which determines the state of the lumen of the vessel under physiological and pathological conditions. It will be further proved, however, in many places in the general, as well as in the special parts of this book. “A second histo-mechanical principle may be added to this, viz., the growth in thickness of the vessel wall is dependent wpon its tension. Further the tension of the wall is dependent upon the diameter of the lumen of the vessel and upon the blood-pressure. “The proof of this law is to be sought, in the first place, in the varying strength of the wall of the larger and smaller arteries, veins, and capil- laries. In certain diseases of the vessels (arteriosclerosis, aneurism) there are apparent exceptions which will be discussed in their proper place. “The third histo-mechanical principle has not hitherto been so com- pletely demonstrated as the first two. It will, therefore, be put forward merely as an hypothesis, which runs as follows: increase of blood-pres- sure in the capillary areas leads to new formation of capillaries. “The three histo-mechanical principles were, in the first place, em- ployed to explain the developmental processes in the area vasculosa of the chick. In this flat extended area a capillary network is found at an ” Thoma, Untersuchungen ueber die Histogenese und Histomechanik des Gefasssystems. Stuttgart, 1893. 4 Thoma, Text-book of General Pathology and Pathological Anatomy. Trans- lated by Bruce. London, 1896. Franklin P. Mall. 233 early date in which no arterial and venous channels can be differentiated (Fig. 2). A few channels are, however, selected by the blood-stream in consequence of the general direction which is given to it by the position of the ends of the primitive aorta on the one side, and of the venous ostia of the heart on the other. These channels (Fig. 2, a, 6, c) contain the more rapidly flowing streams. They, therefore, dilate and become con- verted into arteries and veins. (Fig. 3). * Other channels, in which the rate of the flow of the blood has a cer- Fie. 2. Capillary channels of the area visculosa after forty-eight hours’ incubation. S, peripheral end of the primitive aorta; a, b, c, selected blood- channel, X 30. After Thoma. tain medium force, remain as capillaries, and lastly, some channels which offer great resistance to the stream, and are thus very slowly traversed, atrophy, or disappear altogether. The rapid growth of the selected chan- nels diminishes the resistance to the blood-stream, so long as the capillary area remains unaltered. The blood-pressure in the capillary area accord- ingly rises and leads to new formation of capillaries. New communica- tions are thus formed between the terminal ramifications of the arteries and veins; the capillary_area is thus relieved, and its blood-pressure falls. Arteries and veins have now become wider and longer, and the capillary 9 234 A Study of the Structural Unit of the Liver area has increased in extent. A larger quantity of blood will flow into it, therefore, and this will involve a corresponding increase in the total resistance to the stream within the enlarged capillary areas. The chain of processes described may therefore be repeated until any one link in the chain becomes incapable of further increase. ie) ean =e SS GS ZC po Y BESS Qo oe OOS ROLBD Ni 0 Ox S 60) Ew Dn SLO, Fic. 3. Blood-vessels from the area vasculosa after fifty-seven hours’ in- cubation. The same part as in Fig. 2. S, peripheral end of the primitive aorta; a, b, c, the selected channels of entrance to capillary network; V, V, V, venous exit of latter; d, d, d, the beginning of the second capillary network. x 25. After Thoma. “Tf we consider that this chain of processes is constantly repeated within short spaces of time, and that at each time only a slight alteration of the previously existing relations is produced, we may form a fairly accurate conception of the mode of growth of the vascular system. The details of this will not be considered here. If, however, we apply the above principles to any organ whatever which has a longer existence Franklin P. Mall. 235 than the area vasculosa, we must admit that the histo-mechanical princi- ples justify us in assuming that, after the organ has ceased to grow, the rate and presence of the blood in all its capillaries are approximately equal. G, A SPE De Ag, NK LAL S << Ae gy Tie ue y a, os WY Sng SWRA SNS Seas FSIS , SEI E Kain "Bo ATT EK SEVP ES FESR Ge PAE DELO @ Fic. 4. Part of the area vesicular of a chick incubated seventy-four hours. The dorsal aspect is presented. V, V, veins. The arteries are dark ae2is After Thoma. “In this organ, according to the first histo-mechanical principle, all blood channels in which the rate of fiow exceeds a certain maximum, must increase in lumen and become converted into arteries and veins. Vice 236 A Study of the Structural Unit of the Liver versa, all vascular channels will disappear in which the rate of the blood- stream falls below a certain maximum. If, however, the lumen of the vessel bears a fixed relation to the rate of the blood-current, the interval between the maximum and minimum cannot be great. From this it ap- pears that, after growth is completed, the rate of flow must be fairly uni- form in all the capillaries of an organ. “The conversion of capillaries into arteries diminishes the resistance of the blood-stream, and leads to an increase of pressure in the capil- laries. If, then, according to the third histo-mechanical principle, new capillaries are formed at all places in the capillary area in which the pressure of the blood exceeds a certain limit, these capillaries, again, re- duce the pressure by forming new connections between the arteries and veins. The third histo-mechanical principle, therefore, implies that, during the growth of the organ, new capillaries are being formed every- where, and that, after complete growth, the blood-pressure in all capillary areas of the same organ is fairly uniform. “The width of the lumen of the capillary channel at the close of the period of growth must be almost the same in all areas of the same organ, since it depends on the rate of flow, and this rate is uniform in all capil- laries of the same organ. “These conclusions are in perfect harmony with the actual state of matters. It appears, however, that in the different organs there are great differences in the width of the lumen and in the number of their capil- laries, in the rate of flow, and in the quantity of the blood flowing through a given area of the vessel in a given time. “ Tf these facts be compared with the results which were obtained above, according to which the first vascular spaces, the rudimentary capillaries, were formed by the secretory activity of the cells forming their wall, we are compelled to assume that the metabolic processes and other special characteristics of the various organs also exercise a determining influence on the peculiarities which distinguish their capillaries. It must be imagined that the individual characters of the organ, and its size in rela- tion to other organs, decide firstly the number of capillaries in the whole organ and in a single part of the organ; further, the special relations existing between the rate of flow and the lumen of the capillary channel ; and lastly, the height of the blood-pressure which will lead to the forma- tion of new capillaries. If, for example, the growth of the capillaries is arrested in one organ at a rate of flow a, corresponding to a lumen }, in a second organ the growth of the capillary Iumen might perhaps be arrested at a rate of flow A corresponding to a lumen B.° Thus, in the Franklin P. Mall - 237 one organ, capillary new formation would occur when the pressure of the capillary blood exceeds the limit c, while, in the other organs, this limit might be higher at the blood-pressure C. “The number of capillaries, their lumen, and the rate of flow of the blood-stream passing through them, determine, as has been observed, the total quantity of the blood which flows through the entire organ. We thus arrive at the remarkable result that it ts the organ iself which de- termines the quantity, the rate of flow, and the pressure of the blood flowing through it; and that this is effected by means of fixed relations which are expressed generally in the three histo-mechanical principles. The conditions which produce the uniformity of pressure and rate of the blood-current in all capillary areas of the same organ are included in these principles. “ According to the generally accepted view of the problem of the cir- culation, which was formerly quite sufficient to serve as a basis for the account of its general disturbances, the pressure, the rate, and the amount of the blood-flow appeared to be directly dependent upon the action of the heart. According to the view given here, on the other hand, it is the metabolic processes in the organs, which determine first for the in- dividual organs, then for the whole of the organs—that is, for the circu- lation as a whole—the amount of blood propelled within a given time, its pressure and its rate of flow. In this case, the working-power of the heart appears as the equivalent of the sum of the histo-mechanical de- mands made by the organs.” It will be seen that Thoma concludes, and I think properly, that capil- laries of like component parts of an organ are of equal size and length, and that the rapidity of the circulation through them is also equal. This idea I have also tried to develop in various papers upon the structural unit of organs. It appears that each organ is broken up into units which are of equal value from anatomical and physiological standpoints. What takes place in one unit takes place in all of the rest. A good ex- ample is to be found in the intestine where the structural unit is a villus surrounded at its base with a circle of intestinal glands (crypts). In the center of the group is the main artery which passes directly to the apex of the villus and ending there divides abruptly into an umbrella of capil- laries which lie at the periphery of the villus. These capillaries are about of one diameter and length, and no matter what course is taken by the blood the distance and resistance in passing from the artery to the vein is always the same.” Ludwig pointed out that the capillaries of an organ ™MVall, Abhandl. d. K. S. Gesell. d. Wiss:, XIV, 1887. 238 A Study of the Structural Unit of the Liver were always equally favored by the circulation, and that many descrip- tions and illustrations of the blood-vessel, as, for example, of the villus and the glomerules, could not possibly be correct. If in reality the blood- vessels of these structures were arranged as is frequently pictured, the blood would have to take the capillaries in the course of the least re- sistance, while in those of the greatest resistance it would stagnate or come to a standstill. 'Thoma’s first law explains how an equal distribu- tion which favors no part of an organ is brought about. In development the vessels in which the blood stagnates degenerate, and in those in which the rapidity is too great the lumen is enlarged. There seems to be a tendency to maintain a “normal” fiow of blood through the capillary. After capillaries are well dilated they become arteries and veins, and the thickness of their walls is now dependent upon their tension, according to Thoma’s second law. These two laws are constantly at work, and regu- late accurately the diameter and thickness of the walls of the arteries and veins. . Before considering Thoma’s third histo-mechanical principle, it is necessary to discuss his numerous measurements as well as to give data which I have accumulated. The whole question hinges upon the cause of the new formation of capillaries for which Thoma has not found a law, but has merely put forward an hypothesis. Thoma made many measurements of arteries and their branches and tabulated Bencke’s measurements of the aorta with its branches. These measurements show that the area of all of the branches of the aorta equals about the area of the ascending aorta, being a little less before the thirti- eth year of age and a little greater thereafter. Thoma gives a few measurements of small arteries in which the area of the immediate branches equals about that of the main stem. 'These measurements, how- ever, are not constant in live animals, for if the observations are con- tinued, the caliber of the branches increases out of proportion, and ulti- mately their area exceeds that of the main stem.” This change Thoma ascribes to a change in the vascular tone. In other parts of the same work,” as well as elsewhere, he appears to be somewhat uncertain regard- ing the equality of the area of a vessel and the area of all of its branches. Also in a later publication the arguments seem to accumulate against this view.” Thoma states, however, that the exceptional cases are found Thoma, Histogenese u. Histomechanik, 66. 4 Thoma, Ibid., p. 86; Pathology, 275 and 276. 1 Thoma, Ueber den Verzweigungsmodus der Arterien. Arch. f. Entwick. d. Organismen, XII, 1901. Franklin P. Mall | 239 in growing arteries, the umbilical, for instance, which is to be expected, for the peripheral bed is enlarging. After the vessels cease to grow the area of the vascular bed is about the same from the ascending aorta to the smallest arteries; the bed enlarges in the capillaries. Under such conditions (homonomous ramification) the average rate of the current is equal in all of the arteries. Whether the ramification is homonomous or heteronomous appears to me to be of little consequence, and I have pointed out the uncertainty of Thoma’s statements for my own measurement, which are quite nu- merous, and decidedly in favor of a heteronomous ramification. 'Thoma’s assumption of homonomous ramification is based largely upon the meas- urements upon the aorta and its branches. From now on, however, the vascular bed enlarges, at first slowly, and more rapidly as the capillaries are approached. The bed has doubled itself in the arteries one millimeter in diameter and has increased about fivefold in arteries .05 mm. in diameter. A change so slight as this could barely be detected when the _ measurements are made in adjoining internodes. In order to obtain re- liable figures the measurements must be made farther apart. For in- stance, it is easy to lay the intestine of the dog into a series of anatomical units to correspond with the arteries—mesenteric arches, arches to the submucosa and arteries to the vilh. If the area of the superior mesen- teric artery is 7 sq. mm. and that of the ends of the main branches but 12 sq. mm., it will be seen that when a trunk divides into two branches the change in area will be but slight. But when we compute the number of villi, and this is easily done, we determine at the same time the num- ber of terminal arteries to the villi, all of which are about of the same size. At this point, as Table I shows, the artery is .0225 in diameter and the bed is nearly 60 times the area of the superior mesenteric artery. If the ramification were homonomous down to the arteries of the villi there should be but 17,000 villi, the number which can be counted upon 10 sq. em. of mucous membrane. No matter how the following tables are compared, it is seen that there is a gradual widening of the vascular bed from the branches of the aorta to the capillaries. 240 A Study of the Structural Unit of the Liver TABLE I. Giving the vascular bed of the dog’s small intestine. (Mall, Abhandl. d. K. S. Ges. d. Wiss., XXIV, 1887.) Area Vessels Number Diameter of Section mm. sq. mm. (US UMerIOGEMIeESENMLELIC ac vererroreneretelenerst cite il 3.0 7.07 2A INET AN CHES os sieve oirela a otetoraes si onelots teucveyte 155 1.0 11.78 MenmMina la pranches tre sernsetec everest tens 45 6 12.72 Short intestinal’ arteries = sacra. ser 1,440 .08 7.24 on snintestinal arteries. cecaeccis ec 459 192 13.29 Long and short intestinal arteries..... meee hee 20.53 Terminal branches of short intestinal ATTETICSEs crs te So cin trtete eer rae 8,640 .05 16.96 Terminal branches of long intestinal ATEETIES bi 13.5 etecheeedene arate vecalev a eucus\eusi eres 18,000 .053 39.71 [oie Rotaleterminal branches. erie etic 26,640 aie 56.67 From the submucosa to the crypts..... 4,000,000 .008 201.06 From the submucosa to the villi...... 328,500 301 247.94 AT FErICSHOL, the: avallllit-eva a vacteutete ee ieee 1,051,000 0225 “417-97 : Q Upper one-bhinds eae 31,536,000 008 1,585.17 Capillaries! yrer Gaethind 46h aeeeee 15,768,000 005 309.6 [4] Total capillaries of crypts and villi.... 51,304,000 arene ROO BESS Weins of ther Villit 23 Reena 2,102,400 .0265 1,159.57 Veins penetrating the muscularis mu- GOSH ah sia alive od Ree a Oe LA taeteetioe 131,400 .075 580.51 Terminal branches in the submucosa. . 18,000 .128 231.62 Anastomoses in the submucosa........ 2,500,000 .032 2,010.62 Terminal branches of the long and shortuintestinal veins) 2. 422s el cr 28,800 .064 92.65 one aNcCEStINal Velie. ciate acierie et 459 44 69.79 SHoreanbtestimialeviei sr acre miei rier 1,440 112 14.19 Last branches of superior mesenteric VC LIMP Ee tawens ck vet at's So. siaraaus creuthaterenethonas 45 15 79.52 Branches of the mesenteric vein....... 15 2.4 67.56 IMESENTECICG Vieille). ste iciscoscce ei vie @ ee lene che a 6.0 28.27 MUSCLE COATS. [sls DirectwmiuUsclemartenlesays. o's wie < ite erste 1,800 .03 1.27 [3] Recurrent muscle arteries.-.....-..... 3,600 .04 2.54 Capillariesworethencinreulanisi: .. 1... 27,000,000 .003 190.85 Capillaries of the longitudinalis....... 9,000,000 .003 63.62 [4 eMotalzcapillawiesmererrc cick emis. clelaesn. 36,000,000 Bate 254.47 iSite [omecmivc ddcd cca qs occ ano Td aomomor 3,600 112 35.46 Franklin P. Mall . 241 TABLE II. Giving the vascular bed of-this dog’s stomach. (Mall, Johns Hopkins Hos- pital Reports, I, 1889.) Area Vessels Number Diameter of Section mm. sq. mm, /\CO) ee la Fb OG DIO od eb SOLO ORE CEES ieee 1 6.0 28.27 WAC ARIS arercise oi ok Si eee u 2.75 5.92 PG ASURTG ieee) scpecreareieaeneen teres, chortle ate aes if eT 2.27 SS LOTTE py cncntcce eta cle, caertad Sue tous te. atthe ove eee eee i 2.5 4.91 ID REVOEN BC On ais Shred ch gel el cM Ce ee alee a es 1 aie 5.92 From the gastric..... 1 isi 2.27 Z 1 1.92 2.89 To the stomach- From the splenic..... { 4 486 74 From the hepatic .... alt AB 196 [2] Otay pvrgre exes Bt toa: 6.096 From the branches of the first order (HO) WOKS) Girone Cnoucdoobouueoasec 108 .415 14.58 SECON mOnd Ianto hs clonic cos oie Dan ater 740 2 23.26 Sie Ond ens tek. heh ase atcwise ook he ealeeee 5,920 .075 26.17 TOM EMMI COSA ities 2 ieivern ene a oactent 76,960 .025 37.79 Slellate arteries: tater lsceaeed avers ose averetensyars 615,680 017 139.59 FEN MCapillariege aus ccs fsa eveersrorn eee ose wre ee 22,800,000 .006 645.24 Subepithelial venous plexus........... 1,643,600 02 493.08 imienrclandular plexuses oe eee cc 431,649 .037 445.89 Subpeiandular plexus) sss ocdemiece 333,090 .049 577.25 Branches piercing the submucosa...... 12,768 .O867 75.33 Large branches in submucosa......... 1,480 2 44.4 IMEI SeLrOMEStOMachiens: sty vcracielcieeletote ele 108 aD 21.6 EVA ONG Chat ars depen eee ee ohecadoren suave oy ape teres 1 2.0 3.14 Gastro-epiploicaadextranssse scence i 2.5 4.91 Gastro-epiploicas simistray 4.-2..sss Roux, Ges. Abhandl., I, p. 19. Franklin P. ‘Mall - 251 animals.” It seems to me that there must be other agencies that would prevent such a catastrophe. In fact, we have an abundance of examples of a reduction of enlarged capillaries whenever they occur. Thoma has given a satisfactory explanation of the closure of the ductus arteriosus and of the ductus venosus, but that is not quite to the point in this case. How- ever, in the beginning of the capillary system of the liver, around the omphalo-mesenteric vein, we have an excellent case. This question will be taken up at greater length subsequently, so at present I shall be very brief. The liver grows around and into the omphalo-mesenteric vein, and while so doing we have a double circulation, a more direct one through the constricted vein and a more circuitous one through the capillaries of the liver. But, in spite of this, the vein is gradually eliminated, leaving only a capillary plexus. The aortic arches of amphibia are eliminated in a similar way. From them loops of capillaries grow into the external gills which gradually take the place of the artery. There are numerous other examples. Minot,” who has recognized the fundamental importatice of the destruction of a main channel and its conversion into a system of capillaries, calls such vessels sinusoids, and the circulation through them a sinusoidal circulation. Not only are blood-vessels which are too large reduced, but it appears in the development of the blood-vessels in the tad- pole’s tail as if the new blood-vessels were always growing in the direction of the greatest resistance, for the nearest complete arch is already the shortest course from the artery to the vein; yet another and more distant one is to be formed. The first and guiding blood-vessel is the capillary which grows in all directions, forming a plexus. Secondary changes make arteries and veins of them and their laws of growth have been discovered and clearly stated by Thoma. The normal shape of the capillary is tubular with 4 lumen about .008 mm. in diameter. They arrange themselves into a plexus with a tendency to come in contact with every surrounding cell. However, the tissues vary considerably in this respect, the first capillaries growing to them or past them in tufts. In general, the capillary ar- rangement is influenced by the tissue or organ into which it grows, but its conversion into main trunks and branches is controlled by the circu- 2° See Oppel, Lehrbuch, III, p. 984. Brissaund and Sabourin are undoubtedly in error regarding this statement. I have made and examined hundreds of injections made with granules which would pass through small arteries but not through the capillaries, and have never seen such an anastomosis. Further, celloidin corrosions, which often include part of the capillaries of the lobule, never show such connections. * Minot, Proc. Bost. Soc. Nat. Hist., X XIX, 1900. 252 A Study of the Structural Unit of the Liver lation. Ultimately the arrangement is such that all capillaries of an organ are equally favored by the circulation. This means that the capillaries have about the same diameter and length with about the same amount of blood passing through them during a given period of time. If too little blood passes through them, in a lobule of the liver for instance, some of the capillaries disappear; if the circulation comes to a standstill all of the capillaries are obliterated. So their very life is dependent upon a proper or normal circulation. If a capillary is too long, the resistance within it is increased, and the circulation is slowed with a subsequent reduction of length. So in order that a capillary may remain, it must have a definite lumen, a definite length and a definite amount of blood passing through it in a given time. The diameter varies from .005 to .01 mm., according to the organ in which it is located. The average is .0O8 mm., the diameter of the mammalian red blood corpuscles. In some of my tables the diameter is given as .003 mm., but these measurements are from hardened and mounted tissues. The length of the capillary is less than half of a millimeter, through which the blood flows in less than a second. So, morphologically, a capillary is a blood-vessel .008 mm. in diameter, .5 mm. long with a renewal of blood every half-second. If this renewal of blood is permanently diminished enough of the capillaries are obliterated to reestablish the normal circulation in those that remain. If the quantity is permanently increased, according to Thoma’s first law, some of them are converted into arteries and some into veins. If the increased circulation is continued without a corresponding increase in the number of capillaries, the artery will extend into the vein just as is the case in the liver when the ductus venosus is formed. The anlage, then, of the vascular system is the capillary; artery and vein are secondary and are differentiated out of them by the flow of blood set in motion by the beat of the heart. As the capillary bed increases the flow through the arteries increase, and the heart hypertrophies and the vascular proportion is maintained. In round numbers, in the dog, the arteries continue to grow until the rapidity of flow is 30 mm. a second in an artery .05 mm. in diameter, 150 mm. in an artery, 1 mm. and 300 mm. in the aorta. Thoma fixes the rapidity of the circulation in the aorta of man at 228 mm. a second, and over 34 mm. a second in an artery .04 mm. in diameter. The unequal growth of different portions of an organ accounts for the unequal size of the arteries which supply them. The whole thing works from the periphery to the center. In this way a succession of organ units is formed all the way from the first divisions of the artery which supply the lobes, to its final twigs, which supply the lobules. Franklin P. Mall . 253 It is seen from what has been said above that it is undoubtedly the growth of the tissue of the organ which leads the way. Into this new- formed tissue the capillaries grow and they have an inherent power which makes them grow into an anastomosing tubular system. The density of the capillary plexus is influenced by the tissues into which they grow, but their length and arrangement is determined by the circulation through them. A vascular proportion is constantly maintained for each organ down to the minutest vascular twig. Capillaries through which the rate of circulation is below the normal shrink or disappear, and when it is above the normal they enlarge into either veins or arteries. A cap- illary too long will eventually cut itself off on account of the increased resistance to the circulation in its own walls. An increased flow of blood rarely causes an artery to empty directly into a vein, because the deter- mining factor is nearly always to be found in the capillaries themselves. The growth of the capillaries causes some of them to change into arteries and veins, and the equilibrium is thus easily maintained. In rare in- stances, however, the amount of blood thrown into an organ may be in- creased greatly, as is the case when all of the blood from the umbilical vein is suddenly forced through the liver. It follows that the circulation through a chain of capillaries from the portal to the hepatic vein is much above the normal capillary circulation, and, as a result, the ductus venosus is formed. EARLY DEVELOPMENT OF THE LIVER. The early development of the liver has been worked out by His and others, and therefore it need not be discussed to any great extent. The liver bud, as shown in Fig. 6, is well marked in an embryo at the end of the second week (2.1 mm.). It grows rapidly and then encircles the left omphalo-mesenteric vein, in the chick and in man, and both the right and the left in the dog. At the same time that the liver tissue en- circles the vein it also invades it, carrying the endothelial lining ahead of the sprouts and thus forms a series of sinuses, or the sinusoids of Minot. While this process is taking place the umbilical veins are gaining much in importance and a large share of the blood which formerly re- turned to the heart through the omphalo-mesenteric now returns through the umbilical veins. Figures 7 and 8, from an embryo 4.5 mm. long, and Figs. 9 and 10, from an embryo 4.5 mm. long, illustrate this point. In the embryo 4.3 mm. long large sprouts of liver tissue have invaded the common omphalo-mesenteric veins which have also extended, forming a large ring of Minot’s sinusoids encircling the intestine as described by fas) | _— A Study of the Structural Unit of the Liver His. At this time the umbilical veins are broken in their course, having already passed the first stage of their growth, and from now on are des- tined to pass through the liver rather than past it (Fig. 8). It is inter- esting to note that the primary sinusoidal liver—that portion which arises with the omphalo-mesenteric vein—is formed while the umbilical vein empties directly into the ductus Cuvieri. The process is at its height in an embryo of about the same age (No. 76), as shown in Figs. 9 and 10. The growth of the liver around and through the omphalo-mesenteric veins is accompanied by the growth of capillaries from this vein into the new anlage. Hand in hand with this process the circulation through the Fic. 6. Section through the third occipital myotome of a human embryo 2.1 mm. long (No. 12 of my collection). X50. O, third occipital myotome; coe, coelom; v, vein; st, septum transversum; /7, liver; ph, pharynx; wv, um- bilical vesicle. omphalo-mesenteric veins is further reduced by the growth and enlarge- ment of the umbilical veins. A double force is at work: blood is diverted by the umbilical vein which is gradually assuming greater importance and by the capillaries which supply the embryonic liver. According to Thoma’s first law, the diminished rapidity of the circulation is followed by a reduction of the lumen and in order to accomplish this reduction in the present case, the liver sprouts first grow into the vein instead of around it. The operation of Thoma’s law in this case is so extensive that it reduces a main trunk to capillaries which forms a condition recognized by Minot as a sinusoidal circulation. At the time the liver circulation is entirely sinusoidal, 7. e., about the Franklin P. Mall - 255 end of the third week, it is composed of a single lobule with the vein en- tering it on one side and the collecting vein leaving it on the opposite side. The turning point between the first and second stages of develop- ment is shown in Fig. 11. In the embryo represented by this figure the omphalo-mesenteric veins are broken completely into capillaries in the liver, and one umbilical vein has been transferred from the ductus Cuvieri to the lower part of the liver. The single liver lobule here is perfect; it is composed of a complete capillary network without an anas- iS ULV. HIG. 7% Fic. 7. Section through a human embryo 4.3 mm. long (No. 148). X 25. T,, T;,, T;, third, fourth and fifth thoracic myotomes; i, intestine; 7, liver; v, ventricle; ba, bulb of the aorta; am, amnion; wv, umbilical vein. Fic. 8. Semidiagrammatic reconstruction of the veins of the liver of a human embryo 4.3 mm. long (No. 148). JL, liver; wv, umbilical vein; vom, omphalo-mesenteric vein; i, intestine. tomosing vein through it. A rough estimation of the vascular proportion shows that the area of the capillaries is fully 100 times that of the enter- ing veins. In the next two embryos, Figs. 12, 13 and 14, all of the blood from the left umbilical vein passes through the liver—the right vein having been obliterated. Within the liver it is seen that the right om- phalo-mesenteric vein is open, while the main branches of the hepatic and portal veins have made their appearance. With the growth of the liver the capillary bed has increased which is naturally followed by a more rapid circulation in the distributing and collecting capillaries, and con- 256 A Study of the Structural Unit of the Liver sequently they are converted into veins. All of the blood from the um- bilical veins now passing through the liver increases the circulation through the small liver so much that a venous channel (right omphalo- mesenteric vein) remains open, or in case it be closed it is opened up again. The two new branches within the liver care for the circulation through its left lobes, and may have been formed directly from the left omphalo-mesenteric vein. At any rate, we see in them two permanent main trunks of the liver,—the vena hepatica sinistra and the ramus angularis arising from the recessus umbilicalis.~ In the next stage which Fic. 9. Section through a human embryo 4.5 mm. long (No. 76). X 25. VC, cardinal vein; a, aorta; vom, omphalo-mesenteric vein; vu, umbilical vein; h, heart. Fic. 10. Semidiagrammatic reconstruction of the veins of the liver of a human embryo 4.5 mm. long (No. 76). JL, liver; wv, umbilical vein; vom, omphalo-mesenteric vein; 7, intestine. is found during the fifth week the right omphalo-mesenteric vein is ob- literated and the ductus venosus is formed as a new and more direct chan- nel. In place of the obliterated omphalo-mesenteric vein there are two new permanent veins, the ramus dextra of the hepatic vein and the ramus arcuatus et descendens of the portal system. We now have a liver of two ** An excellent description of the vascular system of the mammalian liver is given by Rex (Morph. Jahrb., XIV, 1888). As much as possible I have used his nomenclature. Franklin P. Mall - PEN lobules, representing the right and left lobes, with a vascular system in each identical in arrangement with that of a liver of one lobule. (Fig. 11.) When the umbilical vein first shifts from its entrance into the ductus Cuvieri to the hver it has taken the course in its new position, of the least resistance, as a glance at Fig. 15 shows. There is a mass, if not an excess, of capillaries in the liver at this time and this vein with its loose wall makes the change suddenly as is shown in Fig. 11. This brings to the liver an excess of blood which is followed by keeping open, or opening in case it has closed, the right omphalo-mesenteric vein. The continued growth of the liver and its capillaries increases the circulation Vv.o.m. jae, all Gaels Fic. 11. Semidiagrammatic reconstruction of the veins of the liver of a human embryo 4 mm. long (No. 186). JL, liver; wv, umbilical vein; vom, omphalo-mesenteric vein; i, intestine. Fic. 12. Semidiagrammatic reconstruction of the veins of the liver of a human embryo 6.5 mm. long (No. 116). L, liver; vom, right omphalo-mesen- teric vein; uv, umbilical vein; m, mesenteric vein; rhs, ramus hepatica sin- istra; ra, ramus angularis; i, intestine. in the distributing and collecting branches which is followed by their con- version into permanent venous trunks: first those on the left side and then those on the right side. The excess of blood is still continued and on account of the shifting of the right omphalo-mesenteric vein with the growth of the right lobe of the liver the route becomes circuitous, and a new and more direct channel, the ductus venous, is formed. This has 258 A Study of the Structural Unit of the Liver already taken place in the specimens shown in Figs. 17 and 20; in a later stage, Fig. 25, the omphalo-mesenteric still remains open after the ductus venous is formed. During all this time the vascular proportion remains normal, that is, the area of the capillaries is about 50 times that of the main portal trunk. The distributing branches are on one side of the lobule, and the collecting branches on the other. With an increase of the number of lobules, how- ever, they are no longer set parallel, but at various angles with one an- other. Were they continued parallel they would have to spread as a Ties 18 Fic. 14. Fic. 13. Section through the liver of a human embryo 5 mm. long (No. 80). X25. C sixth cervical myotome; a, aorta; cv, cardinal vein; s, stomach; w, umbilical vein; l/pc, lesser peritoneal cavity. Fig. 14. Semidiagrammatic reconstruction of the veins of the liver of a e human embryo 5 mm. long (No. 80). JL, liver; vu, umbilical vein; 7. vom, right omphalo-mesenteric vein; rhs, ramus hepatic sinistra; rw, recessus um- bilicalis; ra, ramus angularis; m, mesenteric vein; i, intestine. sheet with a thickness of a millimeter, the maximum normal length of a capillary. In an embryo at the end of the fifth week, Fig. 25, two new lobules have made their appearance and the two primary lobules have begun to divide. The hepatic and portal veins are telescoping; they are beginning to dovetail with each other. The new branches of the portal have gone into the field of the hepatic and the new hepatic veins have entered into the portal field. By this process, and by this process only, can a spherical vascular organ be built up maintaining a normal vascular Franklin P. Mall . 259 proportion. All through the organ the terminal twigs of the distributing and of the collecting veins must not be over a millimeter apart, and this naturally keeps the units small and determines the ratio between the terminal twigs and the capillary bed. In the embryo of the end of the fifth week, Fig. 25, the right and left portal twigs have begun to divide, and from the recessus umbilicalis a Fig. 15. Lateral reconstruction of a human embryo 7 mm. long (No. 2). L, liver; ph, phrenic vein; 1, 2, 3, 4, branchial pouches; Roman numerals, cranial nerves; Arabic characters, spinal nerves. new group of veins have formed and radiate into the middle and left lobes of the liver. On the hepatic side the left branch has divided into two trunks and two new branches have appeared: the vena cava inferior and the vena hepatica media which has its terminal right and left branches. 20 of the Liver Fie. 16. Section through the embryo 7 mm. long (No. 2). X 25. T,, first thoracic myotome; cv, cardinal vein; wb, Wolffian body; s, stomach; IUpe, lesser peritoneal cavity; J, liver; h, heart; st, septum transversum. Fic. 17. Semidiagrammatic reconstruction of the veins of the liver of the embryo 7 mm. long (No. 2). Viewed from in front. L, liver; wv, umbilical vein; m, mesenteric vein; ru, recessus umbilicilis; dv, ductue venosus; ra, ramus angularis; ra’, ramus arcuatus; rhd, ramus hepatic dextra; rhs, ramus hepatica sinistra. Fic. 18. Lateral view of a model of the liver in position of a human em- bryo 9 mm. long (No. 163). X12%. O,, eighth cervical myotome; li, liver; 1, lung; s, stomach; wf, Wolffian body; ph, phrenic nerve; pc, pleuro-peri- cardial membrane; pp, pleuro-peritoneal membrane; dc, ductus Cuvieri. Franklin P. Mall - 261 The right omphalo-mesenteric vein is still present and the ductus venous is well marked. In this case the liver is formed of four main lobules, and with the subdivision of the middle and left hepatic veins into two branches each, six primary lobules are seen to correspond with the six primary lobes of the mammalian liver. In this case the vena hepatica dextra superior et inferior is represented by the open omphalo-mesenteric vein and the anlage of the vena cava inferior. In the next stage, Figs. 26 and 28, the normal arrangement of these veins is found for the vena cava inferior really belongs to the middle lobe. Fig. 20. Fig. 19. Section through the embryo 9 mm. long (No. 163). x 12%. C,, eighth cervical myotome; pp, pleuro-peritoneal membrane. Fic. 20. Ventral view of the veins of the liver of the embryo 9 mm. long (No. 163). JL, liver; i, intestine; wv, umbilical vein; vp, vena portae; g, gas- tric vein; m, mesenteric vein; ra, ramus angularis; ra,, ramus arcuatus; rs, ramus sinistra; rd, ramus dextra; dv, ductus venosus. With the completion of six lobules we recognize fully the adult form of the liver. Each lobule now represents one of the six lobes of the mam- malian liver; each of the primary lobules is to expand into a whole lobe. The primary lobules radiate from a center and have between them the 262 A Study of the Structural Unit of the Liver main trunks of the portal veins; each interlobular vein at this stage is to form a main trunk in the adult. At this time we have terminal vessels to follow from stage to stage, which is impossible to do in adult speci- mens. The process of sprouting and interlacing continues at a rapid pace from now on, and for the present I shall give illustrations from the livers of two embryos of the eighth week. The first (No. 22), Fig. 26, is from a wax plate reconstruction carried as far as I could conveniently, and Fig. 27 is from a photograph. The second (No. 6) Fig. 28, is from a graphie reconstruction which could be carried out pretty well, and Figs. — Fic. 21. Lateral view of a model of the liver in position of a human em- bryo 11 mm. long (No. 109). X 8%. Li, liver; 1, lung; r, first rib; ph, phrenic nerve; s, stomach; wf, Wolffian body; pp, pleuro-peritoneal mem- brane. 29-31 are three views of a wax model of the exterior of the liver. These illustrations together show the form of the liver and the main vessels with their lobular branches. There are about 700 branches of the third order in the adult liver, and rough estimations made from Figs. 27, 29-31 give. about this number. The lobules in these specimens are about 0.4 mm. in diameter, considerably smaller than in the adult. In general branches of the hepatic and portal veins of the same order are as far apart as possible with a tendency to run at right angles to each other. The branches of the first order or main trunks have been present from the time of the earliest differentiation of the liver, while those of the second BraniiinPs Mall +: 263 ‘ae Gh, PAPA Fic. 23. | Bre, 24. Fic. 22. Section through the body of the embryo, 11 mm. long (No. 109). %10. The liver is attached to the septum transversum, st; 3, first rib; 1, third rib. Fic. 23. Section through the embryo, deeper than in Fig. 22. Just in front of the septum transversum in the liver is seen a section of the ramus hepatica sinistra and coming forward the ramus hepatica media. Fic. 24. Section through the same embryo showing the umbilical vein, recessus umbilicalis and the ramus arcuatus. Behind in the liver is the vena cava, to its left the open right omphalo-mesenteric vein (see Fig. 25); in front is the gall bladder and between it and the omphalo-mesenteric vein in the ramus arcuatus. 264 A Study of the Structural Unit of the Liver and third order date from the beginning of the dovetailing process. A word more about the vena cava inferior. In its beginning it belongs en- tirely to the liver and is completely surrounded with liver tissues. In the adult liver two small branches empty into it in addition to the main branches mentioned above. The first is closely associated with the vena hepatica media accessoria. The other arises from the omental lobe and Fic. 25. Ventral view of a reconstruction of the vasicular system of the embryo 11 mm. long (No. 109). X 25. Uv, umbilical vein; pv, portal vein; rad, ramus angularis; ru, recessus umbilicalis; rd, ramus descendus; ra, ramus arcuatus (possibly ramus ascendus); rc, right arborization of the recessus umbilicalis; r/7, left arborization of the recessus umbilicalis; dv, ductus veno- sus; vc, vena cava; vom, omphalo-mesenteric vein; 7m, ramus media; rs, ramus sinistra. usually goes directly to the vena cava, but occasionally communicates with the vena hepatica sinistra. It is seen that the vena cava collects blood directly from the quadrate and Spigelian lobes. Franklin P. Mall . 265 er ale Dy my! wis so) ) Fic. 26. Main trunk of the liver from an embryo 20 mm. long (No. 22). From a reconstruction in wax. X12. Uv, umbilical vein; vp, portal vein; ra, ramus arcuatus; ra, ramus angularis; ru, recessus umbilicalis; dv, ductus venosus; vs, vena cava; rd, ramus dextra; rm, ramus media; rs, ramus sin- istra; rl, left arborization of the recessus umbilicalis. Fig. 27. Photograph of a section of the human embryo, 20 mm. long (No. 22). % 15. Ru, recessus umbilicalis; dv, ductus venosus; rm, ramus media. Between the two branches of the ramus media may be seen a branch of the ramus acendus cut transversely. These branches are of the second order and the terminal branches the beginning of those of the third order. In this case the lobules are .5 mm. in diameter. 266 A Study of the Structural Unit of the Liver THE Hepatic LOBULE AND THE PorTAL UNIT. It is seen from what has been said above that the final branches of the portal and hepatic veins are always as far from one another as possible throughout all stages of their development as well as in the adult liver. At all times this distance is half the diameter of a lobule and since this is in the neighborhood of one millimeter the distance is about half a mil- Fic. 28. Reconstruction of the vasicular system of tne liver of a human embryo 24 mm. long (No. 6). X 20. All of the important vessels are fully formed. The stage is the same as that shown in section, Fig. 27. Uv, umbili- cal vein; vp, vena portae; ru, recessus umbilicalis; ra, ramus arcuatus; rd, ramus descendens; ra, ramus angularis; 7, r, right arborization of ru; re, left arborization of the recessus umbilicalis; vh, vena hepetica; dv, ductus venosus; ds, vena dextra superior; di, vena dextra inferior; md, vena media dextra; ms, vena media sinistra; ss, vena sinistra superior; si, vena sinistra inferior; vc, vena cava. limeter, the normal length of a capillary blood-vessel. It is also appar- ent, as indicated by Fig. 1, that the liver breaks up into two sets of units arranged respectively around the terminal twigs of the two sets of veins. Franklin P. Mall 267 That the unit arranged around the hepatic vein was finally accepted as the lobule is largely due to excessive amount of connective tissue along Fic. 29. Ventral view of a wax model of the embryo, 24 mm. long (No. 6) x 10. Uv, umbilical vein; @b, gall bladder. Fic. 30. Superior view of the same liver. the portal twigs in the pig’s liver, a condition almost peculiar to this animal. Had the liver of Phoca been studied in the place of that of the 268 A Study of the Structural Unit of the Liver pig the portal unit would have been accepted, for in general either set of lobules is only occasionally well outlined and thus marked in some mam- mals. In the human liver, as in the dog’s, there are more terminal portal twigs than hepatic and this together with other structures which accom- pany the portal vein, makes it easy for practical purposes to call the he- patic unit the lobule. However, it is just as easy, if not easier, to con- sider the portal unit the lobule if one is so inclined. From the standpoint of pathology, it is easy to construct a description of the liver based upon a portal lobule. Especially marked are these lobules in venous hyperemia, in pigmentation and in cirrhosis in which Fic. 31. Dorsal view of the same. Gd, gall bladder; wv, umbilical vein; S, Spigelian lobe; vc, vena cava inferior. there is a marked regeneration arising from the bile ducts. Sabourin” has used these arguments successfully in favor of the portal lobule as the histological unit of the liver. However, his results are also not new, as may be seen by glancing over the historical note accompanying this paper. But his point is sound and shows that the liver histology may be con- structed around the terminal portal veins as well, if not better, than around the terminal hepatic veins. His extensive monograph is illus- trated with several hundred diagrams, many of which are fanciful, for they are defective in one respect. If a series of circles are crowded to- gether to form hexagons and each of the angles is then used as a center * Sabourin, Recherches, etc., de la Glande Biliaire. Paris, 1888. Franklin P. Mall - 269 of a series of superposed hexagons of the same size, the new series of circles will not form an equal layer, but will overlap each other. Thus, in his Fig. 227, there are six hepatic veins surrounding one portal, while in the next figure the opposite is the case. He should have had them of equal number, having an alternating space common to both systems, the nodal point, as I call it. However, the work of Sabourin is excellent and deserves much more attention than it has received outside of France. ¢ Be ES . mk Pe 3 t = “ = = Ss = Pen NNT Fic. 32. From a corrosion in celloidin of the terminal branches of the portal and hepatic veins. xX 20. The hepatic vein is larger and marked by many constrictions forming a ‘sspiral valve.’ J, interlobular veins; c, central vein; s, sublobular vein. The typical liver lobule, as described by Kiernan,” is based upon the study of the pig’s liver, and is composed of either a single lobule, or of clusters of them. It is not clear which he considers the real unit, for there are all gradations between single lobules and compound lobules composed of at least 25 single ones. As the veins grow larger capillaries cease to arise from them, and the opened yein shows at the point of tran- sition the bases of adjoining lobules shining through its wall; at this » Kiernan, Phil. Trans., 1833. 270 A Study of the Structural Unit of the Liver point, according to Kiernan, the intralobular veins change into sublobu- lar. This distinction is rather arbitrary and of little value, but has clung as a parasite to the text-books. In general hepatic veins with capillaries arising from them are called central or intralobular veins and larger veins are called sublobular; sublobular veins are hepatic veins from one to two millimeters in diameter. Fig. 33. Photograph of a celloidin corrosion of the liver lobule and the portal unit. X 2. The dark clumps are the portal and the light anastomosing bodies are the lobules. Fie. 34. HIGs oD: Fic. 34. Plastic diagram of a group of anastomosing lobules with the terminal branches of the portal vein, marking the centers of the portal units, added. Enlarged about 10 diameters. Fic. 35. Diagrammatic outline of the group of lobules, shown in Fig. 34, with the hepatic vein added. I have studied carefully the hepatic lobule in the dog’s liver and found that in general I can confirm practically everything that Kiernan has said of it. Numerous injections have been made of the hepatic vein, either singly or in combination with injections of other vessels. Figure Franklin P. Mall. 271 32 is made from a celloidin corrosion specimen of both the portal and hepatic systems. The “spiral valve ” of the hepatic vein, which is always present in the dog and the cat, is well shown in such specimens. From the study of granular injections of the hepatic vein with cinnabar, ultra- marine blue, chrome yellow and baryta, it is found that the capillaries arise from veins which are about .17 mm. in diameter. This arbitrary point, Fig. 32, S, marks the beginning of the sublobular vein, although numerous capillaries still arise from it. After its walls become markedly thickened capillaries no longer arise from the sublobular vein, but in their place smal] veins arise which supply portions of a lobule and there- Fig. 36. Photograph of a corrosion preparation of the portal and hepatic trees. X 2. At the X two of the terminal hepatic veins anastomose. The “special valve’ may also be seen. fore cannot be considered central veins. In my study I have called the hepatic veins in the neighborhood of .09 mm. in diameter intralobular veins, and those .17 mm. or a little larger sublobular veins. In Table VI they have been classed respectively under the sixth and fifth orders. The form of the hepatic lobule can be well outlined by washing vessels of the liver first with saline solution, then with alcohol, after which cin- nabar and lamp-black celloidin are injected respectively into the portal and hepatic veins. With considerable pressure the capillaries are injected more or less with red or with black. Figure 33 is from a specimen of this kind with red in the hepatic vein and black in the portal vein. In this specimen the lobule was but partly injected with red celloidin and in the corrosion but the center of the lobule is shown. ‘To the extent in which ras) ~2 2 A Study of the Structural Unit of the Liver capillaries arise from the hepatic vein it is encircled by the red mass. It is seen that the celloidin entered the lobule only at the tips of the veins, that is from the intralobular veins. The sublobular veins are clear and have arising from them intralobular veins which again have clusters of lobules attached to them. The lobules are in clusters to correspond with the branching of the interlobular veins. The outline of one in perspective is given in Fig. 34, which is reduced to a diagram in Fig. 35. While the hepatic lobules are irregular, anastomosing, and of unequal size, the portal units are regular, more spherical and of equal size. The Fic. 36a. Portal and hepatic veins from a corrosion preparation of the liver of the dog. X10. The two sets of vessels were injected with black and red celloidin mixture respectively, after which the liver was hardened in alcohol. A block of tissue was cut into very thick serial sections which were digested for a number of days in a solution of pancreatin at 37° C. After the cells were all dissolved, leaving only the connective-tisue frame- work and the injected celloidin the section were preserved in glycerine. The minutest twigs of celloidin are held in place by the delicate reticulum Loprils. branches of the portal vein are much more delicate and regular than those of the hepatic. A comparison between the two is shown in Figs. 32 and 36, while the single portal branch is shown in Fig. 37. In general the portal branches are more regular than the hepatic, as far from them as possible with a tendency to run at right angles to them. The portal veins never come to the surface of the liver and never anastomose; the Franklin P. Mall - 273 terminal hepatic branches are very irregular, often come to the surface of the liver and sometimes anastomose. There is much difference of opinion regarding the statements given in the above sentence, but anyone who will take the trouble to make a few good celloidin corrosions will find them correct. Branches of the fifth order of the portal vein are .15 mm. in diameter ; those of the sixth order .05 mm. The interlobular veins are about half the diameter of the intralobular and twice as numerous. Even these Fic. 37. Photograph of the terminal branch of the portal tree. X 2. often branch before they give rise to capillaries. While the hepatic vein receives capillaries down to veins marked S in Fig. 32, the portal twigs of the same figure give off capillaries only at their extreme tips. Unless the extreme tips of the hepatic vein, Fig. 32, C, are taken as centers of the lobule and clusters of the tips of the portal vein, J, as centers of the portal units will these two correspond in number. The relative number is shown in Fig. 38, which is from a free-hand model in clay from a celloidin corrosion. The protruding points, C, mark the position of the tips of the central veins. The tracing, Fig. 35, shows the same. Not only are the centers of the portal unit marked by the tips of the 274 A Study of the Structural Unit of the Liver portal vein, but also by the tips of the hepatic artery, as well as those of the bile duct. Furthermore, it is probable that the lymphatics arise from the same point and that the nerves and connective tissue spread from it. From time to time I have found large groups of karyokinetic figures there, which, together with the pathological evidence, make this the re- generative or growing point of the liver. The portal unit is the true structural unit of the liver. Fig. 38. Lateral view of a model of a group of lobules of the dog’s liver. The outside vessels are terminal portal branches. H, sublobular vein; c, ele- vations in the lobule over the tip of the central veins within; n, nodal points; p, portal vein. GROWTH OF THE HEPATIC LOBULE AND OF THE PorTAL UNIT. When I began the study of the development of the lobule of the liver twenty years ago, I thought that I had selected the simplest and most definite lobule for investigation. It seemed then easy to follow the lobule from stage to stage and thereby gain a comprehensive picture of the histogenesis of the liver. It has turned out, however, that most of the work—the hundreds of injections, experiments and sets of serial sec- tions—has been in vain, and but the faintest sketch remains from which to picture. The great difficulty is to recognize the same things from step to step, and this is obtained with certainty only in very young livers, Franklin P. Mall - 275 where all of the veins are of one order; the six central veins of the embryo become permanent main trunks in the adult. In development, the liver structure shifts distalwards, successively tearing off its capillary connec- tions with the main veins, gradually rearranging the architecture of the lobules, often fracturing them and scattering them. Portions of each of the six primary lobules go to thousands of new lobules. None of the main trunks of a large liver, like that pictured in Fig. 27, give off capil- laries at birth. So we must conclude that in a child the liver structure is entirely rearranged each year which calls for a destruction and regen- eration of at least a billion capillaries and towards puberty ten times this number. In the estimation of the number of blood-vessels of the liver it has been found convenient to classify the branches of the vascular tree under six orders, designating the main trunks as the first order and those di- rectly related to the lobule as the sixth order. It is seen by studying Fig. 27, which is from an embryo of the eighth week, that but the first three orders are present with capillaries arising from all of them. By the time the liver is fully formed each of the third order, which are 700 in number, must give rise to an equal number of those of the sixth order, while the liver increases 7000 times in volume. It follows that the lobule must increase in volume as the liver grows, and, in fact, this is the case. When the lobules are well formed, as at the end of the second month, they are .5 mm. in diameter; at birth 1 mm., and in the adult 1.5 mm. Actual measurement also shows that the weight of the liver at the end of two months is .2 gms.; at birth, 75 gms. and in the adult 1500 gms. As the lobules are shifting more distalwards, it is found that the cap- illaries have a greater and greater tendency to arise from a single order, so that when the liver is fully formed capillaries arise only from the sixth order of the branches of the portal vein, and from the fifth and sixth orders of the hepatic vein. It is evident then that the stretching of the liver is in all directions and that there are additions to the tip of all of the blood-vessels, both within the liver and on the periphery. Not only is the liver tissue shifted more distalward, but the vessels already laid down are stretched, and from their trunks new vessels arise to supply new Jobules which have arisen from fractured portions of adjoining lobules. Toldt and Zuckerkandl“ have advanced ideas similar to the ones I have formulated above. They state that the younger the liver the simpler is its vascular system, and that in the youngest stage the whole liver may be 31 Toldt and Zuckerkandl, Sitzungsber. d. K. Akad. d. Wiss., Bd. 72. Wien, 1876. 21 276 A Study of the Structural Unit of the Liver likened to a single lobule of the adult. In embryos four weeks old there is a distributing and collecting end to each of the lobules present and not until the eighth week is the adult form to be recognized in the struc- ture of the liver. Furthermore, they state that in their growth the lobules split and give rise to numerous new lobules. The process of expansion and rearrangement is expressed in the dia- gram, Figs. 39 and 40, which may be viewed to represent either a portal NIG 39: Fia. 40. Fics. 39 and 40. Diagrammatic illustration of two stages of a growing hepatic vein. D, main vein; c, its branch; 7, 2, 8, 4, 5, the same vessels in both diagrams; a, a, new branches from the stem c; b, a new branch on the main stem, d in which the successive stages of the central vein are marked éwe, andue”. or an hepatic twig. As the vessels represented in Fig. 39 grow, the liver tissue increases in quantity, but the liver lobules do not increase in size indefinitely, because Thoma’s first law is constantly at work and will soon break up the larger lobules into a number of smaller ones. In all cases the length of the capillaries remains constant, and when they appear to be too long and too numerous it is always found that some of them have already turned into small veins and thus mark the beginning of new iobules, or of new portal units. A more advanced step is represented in Fig. 40. The lobules or units of the two stages are marked with corre- sponding numbers. But each of them is splitting at its end and new vessels, a, have also arisen from the main trunk. As there were no lobules Franklin P. Mall oo ~ ~2 at the points marked a before, the new ones must have been differentiated from adjoining lobules. The process by which this has taken place may be expressed by the twig 6. At a much earlier stage all this tissue was arranged in.a single lobule around the vessel d. Then it spread over the branch ec, and finally as the vessel d elongated a new lobule, b, arose. Its central vein was marked successively by the vessels, e, e’ and e”. It may be considered that the Figs. 39 and 40 represent the process of growth of the liver in one dimension of space, which becomes much more complex when viewed in two dimensions, as is shown in Figs. 41, 42 and 43. The single branch, a, Fig. 41, becomes the main branch, a, Fig. 43. Hire: 424i. 1G. - 42. Fig. 43. Fics. 41, 42 and 43. Diagrams of three successive stages of the portal and hepatic veins in a growing liver. A, hepatic side; d, portal side; b, and c. successive stage of the hepatic vein; e and f, successive stages of the portal vein. The successive orders of new branches, 6 and c, explain themselves. Finally the lobule ¢* is adjoined by two different kinds of lobules, ¢° younger than itself, and b older. The portal vein has spread into this region, corresponding with the hepatic, and we see the branches reaching out in all directions, keeping equidistant from one another. This diagram is practically correct for most regions of the liver where there are a suc- cession of portal and hepatic veins alternating, so that in the region, L, there is another vessel like a, and in the region F another like d. But when these vessels, a and d, are the only ones that run out to the edge of the liver, the vessel e must cross a into the field R, and the vessel b must 278 A Study of the Structural Unit of the Liver cross d into the field Z. In fact, there is quite a regular crossing of portal and hepatic veins in many portions of the liver, and it indicates that at one time the main stems were the only vessels in that portion of the organ. I shall not venture to describe the growth of the vascular system of the liver in three dimensions of space, but refer the reader who desires it to a good double (portal and hepatic) corrosion with the diagrams given in Figs. 39 to 43. If he takes the pains to apply them to double corro- sions of the livers of very young and of old animals, I think he will find them of some aid. I wish, however, to add two points. First, if the vessel, b, Fig. 40, is imagined cut transversely, as represented in Fig. 1, it will be seen that the lobule represented by it must have arisen from three adjoining lobules. Secondly, if the tip of the lobules 7, 2, etc., are considered in three dimensions of space it will be found that the growing part of the lobule is always at a certain point, which is as far as possible from both portal and hepatic tips, and is marked n in Figs. 1 and 38. In the diagrammatic section, Fig. 1, it is seen that there is a special ar- rangement of the capillaries passing towards this point, and since it is so constant, can be located in any lobule and is of such great morphological significance I shall term it the nodal point of the lobule. The nodal points are always located in Kiernan’s interlobular fissures, but the fis- sures are not always nodal points. In Fig. 38 a line drawn through the letters ¢, n, e, n, c, n, ec marks the middle of a Kiernan fissure, but only the points marked n are nodal points. MEANING OF THE NopAL Pornts. In general, it is stated that the capillaries of the lobules of the liver radiate from the central vein and in so doing branch until the periphery of the lobule is reached where they communicate with the plexus of inter- lobular veins, as described by Kiernan. It was shown, however, by Krukenberg and others that the terminal portal twigs do not anastomose and this in itself indicates that the usual description of the capillaries of. the lobule is incorrect, for there must be some kind of collecting system for that portion of the periphery of the lobule devoid of veins. Correct illustrations of the vascular arrangement of the lobule in cross section are given by Stohr and Bohm and von Davidoff without any description of them in the text. A careful study of the vascular arrangement of the lobules will show that the capillaries themselves are the collecting vessels due to their own anastomosing system. A diagrammatic representation of this system in Franklin P. Mall | 279 a cross section of a group of lobules is shown in Fig. 1. It is here shown that the shortest course between the terminal portal and hepatic veins is taken by perfectly straight capillaries, and as the region away from the straight course is approached the general direction of the capillaries be- comes more and more bent. It is thus seen that the deflected capillaries from several adjoining lobules come together, forming points which can easily be seen in the sections of any liver. In general the picture is sharper in the rabbit’s liver than in that in any other animal I have examined, especially when it is taken immediately under and parallel with y ss eS AS - Pace Sy Dory LA On laa — oC \p SE Gy Yolo a MN CA SOC ~~ Os Tere ioe) ~ WA CQ Gres NS 7 YOR! a5 ane (4 re — A'S Gacy Ree) eee SEY Sea Ry = OC VA NF OK oe) AACE SH eK Ss SC = eh | eae 7 eee 53 CHES gH’ ory RS [Se ay oe a € = Fic. 45. Fic. 44. Terminal distribution of a portal twig entering three portal units. x 85. The capillaries all arise from the tips of the vein. Hic. 45. Terminal hepatic vein with the capillaries arising from it. Xx 85. the surface of the liver in order to strike the lobules at right angles. Thus we have in the liver lobule two sets of capillaries, long ones and short ones, while according to 'Thoma’s first law they should all be of the same length. This stumbling block caused me a great deal of trouble, for at first I saw no way to overcome the difficulty. An elaborate model of the vascular system of the lobule seemed to show that as much fluid, 280 A Study of the Structural Unit of the Liver or more, passed through the longer and less direct capillaries than through the shorter and direct ones. The capillaries passing through the nodal puints, therefore, seem to be as well favored as those taking the shorter course. In the diagram it is seen that the nodal point is fed from three sources, and on account of the great number of capillaries in it the resistance to the circulation is probably diminished. It would follow that some of the main feeding capillaries should be converted into veins, and in growing livers this is the case, but every time a new vein is formed, we have a new vascular unit, or a new lobule with two new Hic. 46. Arrangement of the capillaries at the nodal point of a lobule. x< 85. P, portal vein; h, hepatic vein. but smaller nodal points to complicate the situation again. This process might be continued until the portal branches communicated with the hepatic, were there not some self-regulating force to check it. It appears that this force is due to the normal length of the capillary which is about 4 mm. in the direct course. In the indirect course, 7. e., through the nodal points, this distance is about .8 mm., but each nodal point is fed from three sides instead of from one, and this arrangement may account for this increase in distance without the formation of new veins. If the hepatic and portal veins are injected with thick granular masses—cinnabar, lamp-black or ultra-marine blue suspended in gelatin— Franklin P. Mall 281 it will be found that in successful cases these terminal veins with the capillaries arising from them are filled. Figures 44 and 45 show this distribution from the tips of the portal and hepatic veins, marking the centers of the portal unit and the hepatic lobules. Both are drawn to the same scale and show the relative arrangement of their capillaries. The portal twigs give rise to capillaries only at their ends, while in the i) < Fic. 47. Tracing of the vessels around a lobule showing the relative number of terminal and hepatic and portal branches. X 40. Portal vein slightly injected. hepatic the origin of the capillaries extends much farther down the vein than is shown in the drawing. The portal vein lies of course in an interlobular space and its three main branches extend into the adjoining fissures. Together they mark the center of a portal unit. Figure 46 shows the arrangement of the capillaries throughout a nodal point. The oo 8 2 eo A Study of the Structural Unit of the Liver course of the capillaries is in a more direct line from the portal to the hepatic, from the portal to the portal and from the hepatic to the hepatic than in other directions. Fic. 48. Tracing of the terminal hepatic and portal veins with the nodal points marked n. X 40. Hepatic veins slightly injected. Figures 47 and 48 show the first spreading of granular injections and their relation to the lobule. It is seen in both cases that the most favored vessels point toward the nodal points, 7. e., these capillaries are a little larger than the rest of the capillaries of the lobule; they have Franklin P. Mall . 283 grown sufficiently to favor the capillaries of the nodal point. Figure 49 is from a more extensive injection of the hepatic vein with lamp-black gelatin. It is seen that the injected area, which is sharp, is angular in shape, with projections directed towards the nodal points. We have . here again the well-known picture of the beginning of passive con- gestion, which incidentally marks the portal units beautifully. Enough has been said to indicate that the growth of the lobule takes place at the nodal point. That does not mean that the cells multiply at this point, but simply that the new vessels, alternately portal and hepatic SS O — = ee SSS aoe CS © O f é ( ‘\s Fic. 49. Tracing to show the extent of a granular injection of the hepatic vein. »% 40. The portal vein was first injected with blue gelatin and the thick granular lamp black gelatin was forced into the hepatic vein. The portal units are outlined as in chronic passive congestion. grow toward this point and break it into fragments to form new nodal points. In order to test this question a dozen sets of sections were made of the livers of growing rabbits and fcetal pigs with more or less satis- factory results. The rabbit which is a favorable object for this kind of study has a lobule of constant size (.6 mm.) from birth, until it is fully grown. In the pig the lobule measures .8 mm. in embryos 4 cm. long until a number of months after birth; in the adult they are 1.4 mm. in diameter. 284 A Study of the Structural Unit of the Liver Tn the set of rabbits’ livers, hardened in a variety of ways, at was found that whenever the distance between two adjoining portal veins is consid- erably greater than the average diameter of a lobule, a small portal vein grows into the nodal point which separates them. The same is true re- garding the hepatic veins as shown in Fig. 50. From all appearances, the hepatic branch, 4, is a recent one, growing into the large nodal point which had pushed apart the hepatic veins 7 and 5. No doubt earher in its development, the whole field of this figure formed one nodal point, and Fic. 50. Section of the liver of a rabbit one day old. x 85. Hardened in Flemming’s solution. P, portal branch; h, hepatic branch; n, nodal point; 1, 2, 3, 4, order of growth of the vessels; the next vessel will appear at 5, and then it will grow towards the nodal point 6. then the hepatic vein, 7, grew into it. This was followed by portal veins, 2, then 3, then by hepatic vein 4. Ata later stage the portal vein, 2, will send a branch into nodal point 6, and so on. In a measure, we can corner a bit of liver tissue at the junction of two main stems, as shown in Figs. ‘51 and 52. It is fair to assume that the tissue at this angle grows with the rest of the liver, for a time at least, and that the small vessel arising from the portal in Fig. 51 and that from the hepatic in Fig. 52 are new Franklin P. Mall . vessels growing into the nodal point, n. 285 But the growth of the liver lobules can never be proved by the study of any section or specimen, for = S SS 55) is y- Waar (A GEEp ee ay. a ay Vi =H J ZN 14) WAT) uss = A a Sivas asec BSED yr es ea a ma ae NR Ree! Sea e5 fF a i KX ATTN Tice, Gul Section of a rabbit’s liver eleven weeks old to show the of a new branch from a portal trunk growing towards a nodal point. y i a; BUT ANEARS TUT aaeatay {\ . Y ty Rie. 52. x 40. The same as Fig. 51 to show the origin of a hepatic branch at all times there is an equilibrium; the cells do not multiply to be fol- lowed by the growth of veins, but they go forward side by side. All ‘grades of veins can be scen in any sections of livers, young or old, and origin . x 40. © 86 A Study of the Structural Unit of the Liver the imagination of the investigator can patch them together, correctly or not as the case may be. But the final evidence is obtained by studying serial sections of early livers, where the same vessel can be followed from stage to stage. The very first vessels that grow into the nodal points in the human em- bryo are shown in Fig. 25 from a specimen of the end of the fifth week. The vena cava and the vena hepatic media on the hepatic side and the ramus arcuatus, the ramus descendens and the ramus angularis from the portal side are new vessels. All of the branches of the main trunks with the branches of the second order are shown in the reconstruction, Fig. 28, and in the section, Fig. 27. Here the new branches of the hepatic alternate with those of the portal, each newly-formed field, as it is formed, receiving its proper branch in the next stage. The best ex- ample is the vena hepatica media in an early stage and the rest of the main trunks and their branches as they arise in order. There are as many nodal points as there are portal units, and more than there are lobules, unless the complex lobule is cut into blocks. The arrangement is shown in Fig. 38, which shows one lobule with six ter- minal portal veins encircling it. If it is considered that these veins are related to adjoining lobules, an estimation of two terminal portal veins to one hepatic, as I have it in my table, is not far from being the correct number. The reconstruction shows that terminal portal twigs run paral- lel, recur again, and run at right angles with the intralobular vein. If the portal units are imagined around the interlobular veins of Fig. 38, it is seen that both apex and base of the same lobule may represent the distal ends of different units. Adjacent intralobular veins and nodal points mark the outline of the portal units. RELATION OF THE HEPATIC ARTERY TO THE PorRTAL UNITS. There always has been and still is much confusion regarding the dis- tribution of the hepatic artery and the reason for this is very evident when it is considered that it communicates at its end directly, and pos- sibly indirectly also, with the capillaries of the lobule. To test this ques- tion thoroughly, I have made numerous single, double and triple injec- tions with granular and fluid substances in order to determine the courses the arterial blood may take during life. Long ago Ferrein stated that there were two kinds of branches of the portal vein within the liver, one which conveyed blood to the lobule and Franklin P. Mall . 287 the other which collected blood from the capillaries of the hepatic artery. That the collecting veins of the gall bladder and surrounding connective tissue empty into the vena portal is easily proved by a simple injection of a granular mass into this vessel. But the conclusion that all, or even a great portion, of the blood from the hepatic artery is collected by similar, put smaller, veins which enter the branches of the vena porte within the substance of the liver is a doubtful one, in my opinion. Theile, who made a careful study of these vessels, called them the rami vasculares (a ferm generally ascribed to Kolliker) and brought forth very meagre evidence that they are present in great number. In fact, his best proof is the ob- servation occasionally of a vein which arises in the hilus of the liver and enters the quadrate lobe before it communicates with a branch of the portal vein.” Theile believes that the rami vasculares venosi enter very small portal branches because he was never able to see them opening into the larger branches after they had been cut open. The presence of these branches, he claims, explains why an injection into the hepatic artery enters the portal vein and why an injection into the portal vein enters the artery as well as the hepatic vein. My own injections speak decidedly against internal roots to the portal vein, except those that arise from the gall bladder and that neighborhood, and can be recognized with the naked eye. After the arterial branches once enter the substance of the liver all of their twigs, including those of the capsule, communicate directly into the capillaries of the lobule, and from there are collected into the hepatic vein. It is usually stated that the portal branches are distributed under the capsule and collect the blood of that region, but this is incorrect. If a liver is injected with two granular masses of different colors, one into the hepatic vein and the other into the portal, it will be found that in all cases it is always the branches of the hepatic vein which come to the surface of the liver and spread out between the meshes of the arterial plexus. From our present knowledge of the vascular system of the lobules we can easily understand how these three sets of vessels communicate freely at this point. In order to test this question in another way, I injected whipped blood into the artery of a fresh liver and found that three-fourths of it came out of the portal vein and one-fourth out of the hepatic vein. In another experiment the arterial pressure was kept constantly at 100 mm. Hg. with the same result as above. Then upright glass tubes were “® Theile, Handworterbuch d. Physiologie, II, 1844, p. 342. 288 A Study of the Structural Unit of the Liver inserted into the cannule connected with the veins, with the following result : Blood rose in the tube in the Time Portal vein Hepatic vein 1 minute. 5 cent. .0 cent. 2 z ee (BH) 3 ss Li eae SeDn ie 4 ss ae w(O)5) 5 oi IPR 5) Waly Further experiments show that at a given pressure it takes about as long for a liter of whipped blood to flow from the portal vein to the hepatic vein as in the opposite direction. Together these tests show that the artery communicates more freely with the portal vein than with the hepatic, apparently speaking in favor of Ferrein’s venous rootlets to the portal vein. If it is considered that under normal conditions there is a high blood-pressure in the portal vein, higher than in any other vein, it is not remarkable that an injection into the artery should flow more freely from the portal vein than from the hepatic vein. There seems to be no definite way to settle this question, except by making sections of injected specimens. If a cannula is tied into the hepatic vein and a single spurt of an aqueous solution of Prussian blue is made into it, it is found that numerous minute blue spots appear below the peritoneal surface of the liver. Sections of such specimens show that all of the fluid has entered the substance of the liver at the centers of portal units. If the injection is pushed a little farther—until the lobules are outlined—a large portion of the blue enters the terminal portal veins from the common capillary plexus of the lobule. As soon as this has taken place the fiuid backs into the larger veins, forms secondary injec- tions of other units and the picture becomes confused. In order to obviate this, I injected the artery with Prussian blue gelatin in which were sus- pended a large number of granules of cinnabar. The blue again flowed over into the portal and the hepatic veins, but the granules all lodged in the capillaries in the periphery of the lobule. Very few granules were found in any of the terminal portal twigs. This experiment shows at least that the bulk of the granules reach the capillaries of the lobule without passing through the portal vein. But an insignificant number of red granules are found lodged in the capillaries within the capsule of Glisson, and these encircle the bile ducts. The first experiment, with but a spurt of Prussian blue into the artery, shows that the long delicate arteries give rise to capillaries which form a plexus around the bile ducts and then enter the center of the portal Franklin P. Mall 289 units together with a terminal portal twig. Now these arterial capillaries communicate with the capillaries of the lobule, as do all of those that encircle the bile ducts. At no point does any of the injected mass enter the portal branches within the liver unless it is as a backward injection, in a direction the blood does not circulate normally. To test this question thoroughly the whole portal tree was first plugged with a thick granular injection mass made by mixing lamp-black or baryta with gela- tin. The venous tree thus plugged did not cut off the capillaries, but pre- vented a second injection into the artery from spreading in the vein. In Fic. 58. Picture to show the termination of the hepatic artery. X 40. P, portal vein; h, hepatic artery. The portal vein was first plugged with a granular mass and then an aqueous solution of Prussian blue was injected into the artery. The extent of the capillary injection with the blue is shown. general it was found that baryta gelatin for the portal vein and aqueous Prussian blue for the artery gave the most satisfactory result. All the vessels and capillaries injected with either fluid are always sharply de- fined. In such an experiment it is possible to force the blue fiuid through all of the capillaries arising from the artery and in case they collect within the capsule of Glisson which empty into the portal vein, their beginnings should be marked. But at no place were such veins found; the blue had only percolated through the white mass in the interlobular veins. The capillary plexus around the bile ducts communicated directly with the 290 A Study of the Structural Unit of the Liver eapillary plexus of the lobule. This condition seemed to be true down to the largest bile duct. At no time did I find a collecting vein within the substance of the liver, and I must, therefore, declare the rami vasculares venosi as mythical. It is evident by studying good injections of the artery after the portal vein has been plugged that the artery communicates with the lobule throughout the extent of the vessels of the sixth order and possibly in part with those of the fifth order (Fig. 53). All the capillaries in the cap- sule of Glisson in this region communicate only with those of the lobule and they do not communicate at all with the portal vein. In those regions of the liver immediately around portal veins of the fourth order it is always found that in their immediate neighborhood there are both ar- teries and veins of the sixth order which ramify again, as stated above. So down to and including vessels of the fourth order all of the capillaries of the artery communicate directly with the capillaries of the lobule. By consulting the table giving the number of vessels of the various orders it is seen that this observation excludes the possibility of any veins of Ferrein arising from oyer a million terminal arteries and leaves them to arise from the walls of the main trunks of the first three orders; probably there are no more veins of Ferrein that empty into the vena porte than can be seen with the naked eye. The hepatic artery then supplies the gall bladder and the hilum of the liver, and the veins from this region communicate with the portal vein. The branches of the artery then enter the lobes of the liver with the branches of the portal vein and the bile ducts. Here the artery gives off a few branches to the bile duets which form a capillary plexus around them, after which it communicates with the capillary plexus of the lobule. By far the greater number of arteries enter the centers of the portal units and communicate at once with the capillaries; they supply the periphery of the lobules. There are about a million of these very small terminal arteries, one for each portal unit which then spread out toward the nodal points and the hepatic veins. The branches that spread over the capsule of the liver supply the subcapsular portal units and then communicate with the hepatic veins. Some of the hepatic veins per- forate the subperitoneal lobules as described by Kiernan; none of the portal twigs reach the surface. The great bulk of the arterial blood is equally distributed from the centers of the portal units and is fully mixed with portal blood before it reaches the nodal points or the hepatic veins. Franklin P. Mall 291 RELATION OF THE CONNECTIVE TISSUE TO THE STRUCTURAL UNIT. From the very earliest appearance of the liver, from the time the sprouts of epithelial cells invade the omphalo-mesenteric vein and break it into sinusoids, it is extremely difficult to demonstrate connective tissue cells within the liver substance. In all cases the endothelial cells lining the capillaries of the lobule come in apposition with the liver cells, and there are no nuclei between them. The cells which have been described as connective tissue cells have been abundantly proved to be von Kupffer’s stellate cells, and these are, according to von Kupffer’s last paper, the en- dothelial cells of the capillaries.” It is impossible to demonstrate sharp outlines to the lining cells of the capillaries of the liver lobule with nitrate of silver. Successful injec- tions show the markings in the portal vein until it reaches the lobule and there they stop. From now on the endothelial cells form an exten- sive syncytium with large openings through which the blood plasma comes in direct contact with the liver cells. However, there is a framework of fibers which has been described from time to time during the last fifty years as delicate, naked fibers which encircle the capillaries as they pass through the lobule.” This adventitia capillaris of His can be demon- strated by brushing fresh sections, but clear pictures were not obtained until special methods were invented for this purpose by Oppel” and by myself.” Oppel isolated the net-work by his special precipitation method which showed the thickness of the fibrils and their relation to the sur- rounding tissue. By my method all the cells were destroyed by digesting fresh sections in pancreatin, leaving only the fibrils which for special reasons were classed with the reticulum fibrils of the lymph node as well as those of other organs.” It is now generally admitted that the (it- terfasern and my reticulum are identical and that they form the frame- work of the lobule.“ That they are the same is shown by digesting a section upon the glass slide by the method of Spalteholz when pictures of reticulum identical in form and arrangement with the Gitterfasern are obtained. Upon the network of fibrils of reticulum which encircle the *% The extensive literature upon this subject may be found collected with a critical discussion in Oppel’s Lehrbuch, III, 1900. % Kupffer, Arch. f. Mik. Anat., LIV, 1899. 33 Oppel, Anat. Anz., V, 1890; VI, 1891. 3° Mall, Abhandl. d. K. S. Gescell. d. Wiss., XVII, 1891; and Johns Hopkins Hospital Reports, I. 37 See also Mall, On the development of the connective tissues from the con- - nective-tissue syncytium. Amer. Jour. Anat., I, 1902. % Hoehl, Arch. f. Anat., 1897; and Oppel, Lehrbuch, III, p. 1009, 1900. 22 292 A Study of the Structural Unit of the Liver capillaries the syncytium of endothelium les. We have, therefore, but three elements within the liver lobule, liver cells, a syncytium of endo- thelial cells, and a network of reticulum between them. I have been unable to find any of the fibrils of the reticulum of the liver in embryo pigs less than 2 em. long. If frozen sections are made of fresh livers at this stage it will be found that they are very delicate and can be crushed under the coverglass very easily. When such prepara- tions are stained by allowing a solution of magenta to run under the coyerglass, it is seen that a network of stained fibrils lies between clumps of liver cells. In any such sections it is easy to determine that all of the fibrils of the young reticulum surround the capillaries and are in intimate connection with Kupffer’s endothelial cells. The fibrils, or rather the syncytium is delicate, and can be broken easily by slight pressure upon the coverglass. Frozen sections are easily broken into granules by shak- ing them slightly in water, showing that the reticulum is not strong. When digested for a short time, at room temperature the liver cells dis- integrate, leaving only the delicate syncytium to which many small gran- ules adhere. Pressure upon the cover glass shows that the reticulum is very elastic. Acetic acid does not cause it to swell and become trans- parent. It is not difficult to obtain fresh specimens with all of the capillaries surrounded with this delicate reticulum with the endothelial nuclei im- bedded in it. The continuity of the endothelial cells with the embry- onic reticulum is complete, and thus forces us to the conclusion that the fibrils are developed from the endothelial cells in the same manner as I have shown that they are developed from the connective-tissue syncytium elsewhere. This observation, however, is entirely out of harmony with the develop- ment of connective tissues in general, for they arise from mesenchyme, while the reticulum of the liver arises from the angioblast. However, the reticulum fibrils are in no way connected with the liver cells and there is no third group of cells in this neighborhood. It is possible that these fibrils reach into the lobule from distant interlobular spaces where connective tissue cells may be found. If the liver of a dog is carefully crushed with the fingers in a stream of water all of the lobules are gradually destroyed and the portal and hepatic trees may be separated. At the end of the tips of the portal tree there are small enlargements which correspond with the portal units; no corresponding lobules are found to adhere to the tips of the hepatic veins. The stronger tissue—the capsule of Glsson—is thus isolated, while the Franklin P. Mall . 293 framework of the lobule is destroyed. Sections of the tips of the two systems of vessels show that more connective tissue extends to the periph- ery of the lobule along the portal vein than along the hepatic vein. How- ever, in nearly all animals it is not the entire lobule which is surrounded by an increased amount of connective tissue, but only that which marks the center of the portal unit. From the study of the connective tissue of the liver by various meth- ods, it is found that it is impossible to draw a line of separation between the interlobular and the intralobular tissues. One appears to be con- tinued into the other. However, there are stronger bundles which take a direct course toward the hepatic vein, not always following the capil- laries. These are the so-called radial fibers. More delicate fibrils com- municate with them and form a dense network around the capillaries. In general the fibrils radiate from the centers of the portal unit towards the nodal points as well as towards the terminal hepatic veins. They are of course arranged as are the capillary blood-vessels, which were discussed above. While the liver is growing it is evident that with the destruction and transformation of the lobules and portal units the reticulum must be con- stantly tearing and shifting. This is possible with such a delicate embry- onic tissue, and it may be that the connective tissue around the portal vein in a given stage lay within a lobule in an earlier stage. Veins of the third order are terminal in embryos about 2 em. long, 1. e., they are interlobular and intralobular, while later on these same veins become main trunks. In the pig’s liver there is no indication of any connective tissue capsule of the lobule before birth, and it probably does not appear until the liver is fully formed. Sections of the liver of pigs two months old show the lobule outlined by marked bands of cell radiating from the centers of the portal units to the centers of the nodal points. Possibly at this time the reticulum between the lobules is a little denser than that within the lobule. However this may be, the capsule of Glisson is but slightly marked, having within it but few nuclei of connective tissue cells. It is evident that the connective tissue of the liver must be studied anew from the standpoint of an ever-changing lobule during development. THE LYMPHATIC Ducts. Hand in hand with the development of the capsule of Glisson, the lymphatic ducts grow into the liver. According to Professor Sabin, they arise from the receptaculum in embryo pigs and grow along the trunks of the artery and portal vein. How rapidly they grow and function has 294: A Study of the Structural Unit of the Liver not yet been determined, but it is certain that in the cat and the dog they do not extend beyond the center of the portal unit. I have been able to trace them in numerous specimens beyond portal vessels .06 mm. in diameter, and this naturally puts them into the center of the unit. One great obstacle in the way of studying the finer lymphatics is that the amount of connective tissue and the size of the portal vein seem ‘to vary in inverse ratio, and when the veins of the sixth order are distended to their maximum the surrounding connective tissue is compressed, and conse- quently the lymph ducts are completely obliterated. It is not easy, there- fore, to obtain clear pictures of the lymphatics from their very beginning down to the main trunks. The origin of the lymphatics of the liver was first definitely determined by MacGillavry,” who studied this subject under the direction of Lud- wig. Long before the work of MacGillavry it had been observed that ligature of the bile duct was followed by passage of bile over into the lymphatics, and the artificial fillmg of the lymphatics naturally followed, by injecting a colored fluid into the bile duct. Sections of liver, in which the lymphatics had been filled with Prussian blue, or with asphalt, showed that the fluid injected into the bile ducts leaves them at the periphery of the lobule to enter spaces surrounding the blood capillaries, the so-called perivascular lymph spaces. These spaces communicate at the periphery of the lobule, that is, in the center of the portal unit, directly with the interlobular lymph channels. Frequently there is an extravasation of the injection mass into the blood capillaries of the lobule. These observations were subsequently confirmed by numerous compe- tent investigators, using the method employed by MacGillavry as well as that of direct injection of Prussian blue into the walls of the portal and hepatic veins. In successful injections made in this way it is found that the Prussian blue injected enters the center of the portal unit and from there radiates and encircles its blood capillaries.” Such injections, how- ever, are always accompanied with numerous extravasations of the 1m- jected material into the surrounding tissues, and often there is a secondary injection into the blood capillaries. This fact has raised an objection to the direct injection of the lymphatics from the bile capillaries. It ap- pears more probable, the opponents say, that the extravasation of bile, or the injected material into the center of the portal unit enters the lym- phatic radicals of the capsule of Glisson, and from them the larger lymph channels and the perivascular spaces of the capillaries are filled. Fur- 3° MacGillavry, Wiener Sitzungsber., 1864. * Budge, Ludwig’s Arbeiten, 1875. Franklin P. Mall _. 295 thermore the injected mass may pass from the pericapillary spaces di- rectly into the capillaries, thus accounting for their frequent injection. According to Fleischl,” all the bile is taken up by the lymphatics after ligature of the bile duct, and in case the thoracic duct is also ligated no bile or only a trace of bile ever reaches the blood. The observation of Fleisch] has been confirmed by Kunkel,” Kufferath “ and Harley.” It is extremely difficult to understand why the bile does not enter the blood capillaries in case it passes from the bile capillaries over into the peri- vascular spaces before it reaches the interlobular spaces after ligature of the bile duct. A further objection to the idea that the perivascular spaces first take up the bile, after ligature of the duct, is the fact that fluids injected into the bile duct pass with ease over into the lymphatics but only with difficulty into the bile capillaries. In all cases it appears as if the main origin of the lymphatics is at the center of the portal unit and that the radicals communicate freely with the perivascular lymph spaces. Furthermore, it appears that the course the bile takes after liga- ture of the bile duct, or of a fluid injected into the bile duct in passing to the lymphatics, is well within the center of the portal unit and not within the lobule. This idea is greatly strengthened since we know that the walls of the capillaries of the lobule are extremely porous, being com- posed of a dense basketlike layer of reticulum fibrils “ upon which lie the endothelial or Kupffer’s syncytial cells. This layer of reticulum fibrils encircling each capillary has been isolated by Oppel “ and by myself “ and is sufficiently described above. The capillary walls then are very pervious, blood plasma passing easily from them out into the perivascular spaces to bathe the liver cells. It is well known that a large quantity of lymph is constantly passing from the liver, much more than from any other organ. That this lymph comes directly from the blood is indicated by its high per cent of pro- teid matter, nearly equal to that of the blood, and from two to three times that of the lymph from other parts of the body. The course the lymph takes from the blood capillaries to the lymph radicals, 7. e., its natural course, can easily be marked by injecting colored 1 Fleischl, Ludwig’s Arbeiten, 1874. “Kunkel, Ludwig’s Arbeiten, 1875. “ Kufferath, Arch. fiir Physiol., 1880. “Harley, Archiv ftir Physiol., 1893. *® Kupffer, Arch. f. Mik. Anat., 54. Oppel, Arch. Anz., 1890. 47 Mall, Abhandl. d. K. S. Ges. d. Wiss., XVII, 1891. See also Johns Hopkins Hospital Bulletin, XII, 1901. 296 A Study of the Structural Unit of the Liver gelatin into any of the blood-vessels of the liver. I have usually found it most convenient to inject the gelatin into the portal vein, but it is just as easy to fill the lymphatics by injecting either the hepatic artery or hepatic vein. In all cases the colored fluid reaches the main lymph chan- nels in the same way. The colored gelatin flows with great ease from the capillaries at the center of the portal units as well as from those around the smaller hepatic veins into the lymphatics. After the lymphatics have all been filled it is well to inject a small quantity of fluid of different color into the blood-vessels. A much better method of making double injections is to mix red granules with a glue gelatin or blue granules with ase Fig. 54. Section through the center of a portal unit of a cat. X 500. Stained by Van Gieson’s method. The hepatic artery was injected with cinnabar gelatin, and the portal vein with Prussian-blue gelatin. L, lobule of liver; c, capillaries; a, artery; 1, lymph vessel; plv, persivacular lymph Jue space; pll, perilobular lymph space; w, bundles of white fibrous tissue be/ tween which are loose connective tissue fibrils and cells. a red gelatin, the fenestrated lining membrane of the capillary acting as a sieve which allows the fluid to pass but holds back the granules, as is the case with the blood corpuscles and plasma in life. When the portal vein is injected with Prussian-blue gelatin at a low pressure, it is found that in a few minutes the lymphatics are all filled with the blue mass. Livers injected in this way are best hardened in formalin and then cut by the freezing method, for alcohol causes the Ce Franklin P. Mall - 297 gelatin to shrink. Such sections show that the blue fluid has entered the lymphatics at the center of the portal unit. The specimens are more in- structive when the injection is stopped just as the first lymphatics are filling with the colored gelatin. By following the larger portal veins and lymphatics back into the liver substance it is found that the interlobular connective tissue is entirely filled with blue where the lymphatics are in- jected, but only partly colored blue when they are not. In other words, the blue extravasates from the capillaries at the center of the portal unit and invades the connective tissue to reach the beginning of the lym- phatics, when of course it is carried rapidly from the liver. The nearest course from the capillaries to the lymphatics is at the center of the portal unit where the amount of connective tissue is small, for as colored fluid begins to enter lymph channels only the tips of the capsule of Glisson are entirely tinged, while the larger portal spaces are encircled by a zone of color. Furthermore, it is found that in certain instances, where the injection was too brief, that the blue did not enter the lymphatics at all. In such specimens all of the interlobular spaces are surrounded by a zone of colored gelatin which does not enter the main lymph channels. A successful injection of the lymphatics is illustrated in Fig. 54. The granular blue enters the capillaries of the lobule, c, with ease, and from them the liquid blue is filtered through the capillary walls to enter the perivascular lymph space, pul. This space communicates at the center of the portal unit directly with a large lymph space between the liver cells and the capsule of Glisson, which may be called the perilobular lymph space. These spaces, pl/, in turn communicate with the lymph radicals. It is further shown by injecting the liver with aqueous Prussian blue that there are no capillaries between the periphery of the lobule and the interlobular connective tissue. The liver cells come in contact with the capsule of Glisson. An injection of brief duration with blue gelatin soon fills the perilobular lymph spaces, so that it appears as if all groups of liver cells at the periphery of the lobule were separated from the inter- lobular connective tissue with capillaries. In case cinnabar granules are mixed with the blue a few of these granules are found in the peri- vascular and perilobular lymph spaces, the openings in the walls of the capillaries being large enough to allow a few of the smaller granules to escape. As the injection is extended the blue invades the connective tissue spaces from the lymphatic radicals more and more until a lymph channel is reached, when of course it rapidly fills all of the larger ducts. Were there a direct channel from the perilobular lymph spaces the blue 298 A Study of the Structural Unit of the Liver would flow through it at once without further filtration through the interlobular connective tissue spaces. The course the cinnabar granules take also speaks against a direct channel between the perilobular lymph spaces and the interlobular lymph channels. A few of the granules enter the perilobular lymph spaces, but none of them reach the main lymph channels. All of my specimens without exception force me to the conclu- sion that there are no direct channels connecting the perivascular and perilobular lymph spaces with the lymphatics proper other than the ordi- nary spaces between the connective-tissue fibrils of the capsule of Glisson. These spaces, however, are relatively large, permitting of a rapid trans- fusion through them. Injections with a hypodermic syringe into the walls of the smaller portal veins naturally fill the surrounding lymphatic vessels, and when no valves are in the way the injected fluid passes to the origin of the ves- sels, or lacunze, which are located in the center of the portal units. From here the fluid passes through the main connective-tissue spaces into the perilobular and perivascular lymph spaces, and frequently from them into the blood capillaries. When the injection of the lymphatics is made through the bile ducts I have always found that there is an extravasation at the center of the portal unit, although the bile capillaries are often injected to the nodal points. The extravasation does not take place from the bile capillaries, but only from the duct as it communicates with the capillaries as well as from the larger bile ducts. Such extravasations naturally are then taken up by the lymphatics and carried from the liver. If after ligature of the bile duct the bile enters the perivascular lymph space within the lobule it may still be carried to the lymphatics, as the direction of the current of lymph is constantly from the blood capillaries to the lymphatics. That the blood capillaries of the hyer communicate more freely with the lymphatics than do the bile ducts is proved by injecting the bile duct and the portal vein with fluids of different color under the same pressure at the same time. In all the experiments I made the fiuid injected into the vein appeared in the lymphatics first. In many instances beautiful injections of the lymphatics were obtained from the vein while the fluid injected into the bile duct did not extravasate at all, showing at least that the veins communicate with the lymphatics much more freely than do the bile ducts. It is seen from the above description that the lymphatics of the liver do not drain all portions of the liver lobule, but only those portions that are formed by the centers of the portal units. There are no lymphatics at Franklin P. Mall - 299 the center of the lobules nor at the nodal points. At the center of the portal units there is a very free communication between the blood capil- laries and the lymph radicals in the tips of the capsule of Glisson. So the lymph circulation is marked at this point, 7. ¢., the center of the portal structural unit, while in the rest of the unit it is insignificant or wanting altogether. ’ RELATION OF THE BILE Ducts TO THE STRUCTURAL UNITS. All of our knowledge of the growth of the liver lobule indicates that the multiplication of the cells is in those portions of its periphery which mark the centers of the portal units. However, this statement is eXx- tremely difficult to prove. It is probable that the bile ducts communicate with the capillaries of the lobule throughout the whole length of the ducts of the sixth order, much as is the relation of the hepatic artery with the blood capillaries of the lobule, and unlike that of the portal vein, which gives rise to capillaries only at its tip. Much has been done to gain a clear understanding of the development, growth and regeneration of the liver cells, but the results are very meager, for only in rare instances are karyokinetic figures found in them. Fre- quently, however, cells with two nuclei are found and these appear to be scattered quite evenly throughout the lobule. I have studied many sets of serial sections of livers in all stages of development and have nearly always failed to find karyokinetic figures. In the few specimens in which cell divisions were present they were in groups of several hundred around the terminal bile ducts. MacCallum “ has also found a specimen in which there were numerous karyokinetic figures at the periphery of the lobule together with indications that the cells are being destroyed around the central vein. Ponfick* has shown that such figures are very numerous in the early stages of regeneration after removal of a large portion of the liver. In his specimens the dividing cells were found distributed evenly throughout the lobule which, on account of its erowth, has become much enlarged with a disarrangement of the radiating strands of cells. Recently Schaper” has discussed the question from a broad scientific standpoint and concludes that when the regeneration of the liver tissue forms typical lobules; the growth has taken place entirely within the minuter bile ducts. This conclusion is admitted by MacCallum ™ for only those cases in which 4 MacCallum, W. G., Jour. Amer. Med. Assoc., 1904. © Ponfick, Vir. Arch., CXXVIII, Supplement, Heft., 1895. * Schaper, Arch. f. Entwicklungsmechanik, XIX, 1905. 5 MacCallum, Johns Hopkins Hospital Reports, ».& 300 A Study of the Structural Unit of the Liver the liver cells have all been destroyed ; then the epithelial cells of the gall ducts take upon themselves the more complicated process of regeneration of liver tissue. At any rate, it is now well known that liver cells often contain more than one nucleus and that in a variety of pathological dis- turbances as well as in normal development the bile ducts have a tremen- dous power of growth. The aberrant bile ducts have been known since the time of Ferrein, and probably represent liver tissue which was present and active at some earlier stage of development.” It has been proved quite conclusively by Toldt and Zuckerkand1 in their excellent study on the growth of the liver that degeneration takes place in one part of the organ while it is growing large in another portion. The vasa aberrantia mark those portions which have degenerated as along the left lateral ligament and the region of the vena cava and the gall bladder. For example, the gall bladder in its growth encroaches upon the substance of the liver and causes its atrophy. The liver lobule in degenerating is often reduced to small islands which have the portal vein on one side of them and the hepatic on the other, returning to its early embryonic state. It is probable that a similar but diffuse degen- eration is taking place in many portions of the growing liver, for vessels which are of equal size in a given step are often found very unequal sub- sequently. It is also known that pressure by foreign bodies, by exostoses and by the ribs in excessive lacing may produce atrophy of the liver which is always marked by aberrant bile ducts, with hypertrophy elsewhere in the organ. The striking experiments of Ponfick first showed us to what extent the liver may regenerate. His valuable communication also illustrates most beautifully that liver lobules do not hypertrophy, but sprout and give rise to new lobules, a conclusion which he thinks he disproves. Pon- fick finds that after a portion of the liver has been removed the lobules in the remaining portion coalesce, and are not sharply defined as they should be in their hypertrophy (p. 86). He repeatedly states that it is difficult to find enlarged lobules, but in their stead he finds heart-shaped or clover-leaf-shaped lobules (pp. 104, 107), exactly what is to be ex- pected in a growing liver. However, he does state that when the liver hypertrophies evenly in all directions the circumferences of the lobules are increased, two, three, or even four, times. This statement he illus- trates with a figure of a lobule (Fig. 2) which is compound and on ac- count of the large veins in it must be from its base, a condition which may be found in any liver which is not growing. His figure 7 which is 2 Toldt and Zuckerkandl, Sitzungsber. d. Wiener Akademie, LXXII, 1876. Franklin P. Mall . 301 enlarged to the same scale as Figs. 1 and 2, and Fig. 3, which is on a larger scale, are not given to show that the lobules hypertrophy when the liver regenerates and are therefore found to be about of normal size. It is proved by Ponfick’s experiments, it seems to me, that in regeneration of Fic. 55. Fig. 56. Fig. 57. o i. Fiaes. 55, 56 and 5 Three views of a model of the liver of a human em- bryo, 17% mm. long (No. 9). X16. Gb, gall bladder; wv. umbilical veins. the liver, the lobules do not enlarge, but sprout and give rise to new lobules, as is the case in the growing liver. By comparing the livers of three embryos (Figs. 29-31 and 55-60) it is seen that only their upper surfaces are regular in form from stage to 302 A Study of the Structural Unit of the Liver stage; the processes extending into the abdominal cavity are irregular, to fit into the spaces that there are for them to grow into. Thus, in its MIGe was: Mie. 59. Fic. 60. Fies. 58, 59 and 60. Three views of a model of the liver of a human em- bryo, 24 mm. long (No. 10). X 8. growth the liver may atrophy at one portion and expand in another, the aberrant bile ducts marking those portions of the liver which have been Franklin P. Mall 303 shifted ; they are present in those portions of the liver which had to make way for encroaching organs. Not only must large masses of the liver disappear entirely, but also smaller areas throughout the liver, especially along the trunks of the main vessels, as the liver is growing from its cen- ter towards its periphery. Hand in hand with this change, the plexus of bile ducts which surrounds the main trunks of the portal vein shifts towards the periphery, leaving only a single vessel in its place, which, of necessity, becomes very variable, as has been pointed out by Rex. : In a liver which has been well formed, as in the rabbit’s liver shortly after birth, the cells radiate from the terminal bile ducts towards the nodal points and the central veins, as indicated by the lines in Fig. 1. The point of juncture between the bile ducts and liver cells is not sharp and the younger the liver the more difficult it is to determine it. In fact, in young embryos it is extremely difficult to follow the bile ducts into the structural units, t. e., to the lobules. Injections show that the younger the specimen the more extensive is the plexus of bile ducts around the terminal veins, which indicates that an intermediate tissue, neither true lobule tissue nor true bile ducts encircle the terminal portal veins in growing livers, as is shown beautifully in a pig two months after birth. When the liver is finished, this tissue is reduced to a minimum. When the liver begins to regenerate, it becomes conspicuous again as “ newly- formed bile ducts.” With a plexus of bile ducts encircling a portal vein of the sixth order throughout its whole extent we have the most intimate connection between the bile ducts and the center of the portal unit, from which additions can be added to the unit. As the cells are added they seem to pile up in the nodal points, for the distance between the terminal portal and hepatic veins does not increase but remains constant. Hand in hand with the growth of the nodal points the capillaries follow, and on account of their increased number the resistance to the circulation through them is diminished, and, according to Thoma’s first law, veins from both sides are extended into them; these alternate, as the obserya- tions above described have demonstrated. . é To obtain an additional key by which we may unravel the growth and architecture of the liver units numerous tests have been made in the Anatomical Laboratory of the Johns Hopkins University, by Hendrick- son, Sudler, Johnson, Sabin, Hill, and myself, with more or less satis- factory results. At present we are able to follow in a connected way the formation of the bile ducts and capillaries in embryos from 5 em. long upward. Possibly at some later date they may be followed back to their earliest appearance. Furthermore, it is probable that some simple meth- ods will soon be found, by which the history of the blood-vessels can be 304 A Study of the Structural Unit of the Liver determined much better than it is given now, and since it appears that the development of the artery and bile ducts are parallel the study of the one will help to clear up the other. Fig. 62. Fie. 63. Fics. 61, 62 and 63. Golgi specimens of the livers of human fcetuses, 5 cm. and 10 cm. long, and at term. X 53. After Hendrickson. Bile capillaries and ducts can be outlined beautifully by Golgi’s method in human embryos 5 em. long, or longer, as Figs. 61 to 63 show. Franklin P. Mall 305 But it is difficult to imterpret these specimens, for it is not easy to deter- mine which vessel is a portal vein, unless reconstructions are made, which is often out of the question. In the earliest stage, Fig. 61, the capil- laries encircle both hepatic and portal veins, the vessel to the left being an hepatic vein. The same is probably true in an older embryo, Fig. 62, while in a feetus at birth the bile duct pictured lies at the junction of two portal veins. When the terminal ducts are arranged in order, as shown in Figs. 64-67, it is seen that the first bile ducts are formed around the portal veins from bile capillaries. Longitudinal sections, Figs. 68-72, indicate the same. ‘This interpretation of the specimens, which was Fic. 66. Fig. 67. Fics. 64, 65, 66 and 67. Golgi specimens of the livers of fcetal pigs, 5, 6, 7 and 8 cm. long. X53. The portal twigs are shown in transverse section. After Hendrickson. first given by Hendrickson™ is rational, and subsequent observations, which I have been able to make from some of Mr. Eben Haill’s skillful injections of the bile ducts in the embryo, corroborate Hendrick- son’s view. The untimely death of Dr. Hendrickson made his prelimi- nary report his final publication upon this subject, and it is now a pleas- ure to me to carry out in part one of his desires. The obstacle at the time of his publication was a lack of knowledge of the vascular tree and complete pictures of the bile ducts, especially in young embryos. Mr. Hill has supplied the latter by filling the bile ducts of a pig’s embryo 10 cm. long. In the early stages diluted Higgin’s India ink was injected di- * Hendrickson, Johns Hopkins Hospital Bulletin, 1898. 306 A Study of the Structural Unit of the Liver rectly into the stomach from which it flowed over into the intestine and backed up into the bile duct. Within the liver it filled the main trunks which correspond with those of the portal vein and then filled a capillary network around portal branches of the first order. An illustration of this specimen is given in Fig. 73. This figure shows that the vessels Gao: Hires vale. Mies 2% Figs. 68, 69, 70, 71 and. 72. Golgi specimens showing the terminal portal twigs with their surrounding bile ducts and capillaries in longitudinal sec- tion in fetal pigs 8, 16, 19, 21 cm. long, and in the adult pig. Xx 53. After Hendrickson. pictured in Figs. 65-67 are probably of the:second order, while that in Fig. 64 is of the first order and, therefore, represents a main trunk. The bile duct-system can be injected with greater ease in older em- bryos, for in embryos over 15 em. long the injection may be made di- rectly through the gall bladder. It is unnecessary to give all intermedi- ate stages, for Fig. 74, which is from an embryo 20 em. long, helps to tell the whole story. With it may be compared Figs. 68-71, for one gives the main trunks and the terminal plexus and the other gives the terminal plexus and the bile capillaries. Franklin P. Mall 307 In the adult liver the artery communicates with the lobule throughout the extent of the vessels of the sixth order; the connection between bile ducts and bile capillaries is probably even more extensive. No bile capil- laries arise from bile ducts of the fourth order, the liver tissues in their immediate neighborhood being drained by the plexus of the fifth and 7 x at Fie. 73. Bile ducts of a pig, 10 cm. long, injected with India ink. x 60; II, portal branches of the second order; III, portal branches of the third order. From a specimen made by Mr. Eben Hill. sixth orders. So in the center of the portal unit the branch of the portal vein ramifies, while along a portion of its axis the artery and duct spread ° out. The unit is bounded on its periphery by a number of intralobular veins and nodal points, as shown in Fig. 1. In the development of the liver the shifting of the peripheral plexus 23 ; 308 A Study of the Structural Unit of the Liver of bile ducts is of great importance and helps to clinch much that has been said above about the development of the liver. In an embryo 10 em. long this plexus encircles portal branches of the second order (Fig. 73). In an embryo twice as long the plexus has passed the veins of the third order and now encircle completely those of the fourth or fifth orders. So as the liver tissue is shifting towards the periphery is) Qs Das, - EOE Re as at ee ni . 23 ~ Fic. 74. Injected bile ducts of the liver of a pig, 20 cm. long. x 50. B, bile duct; p, portal vein; h, hepatic vein; II, III, IV, respective order of the branches. From one of Mr. Hill’s specimens. PNG Se branches which were once central in every respect, are reduced entirely to main trunks, and throughout this process of growth the structural units remain practically of one size. Thus from one vein encircled by one structural unit a million are formed in the dog. Throughout this growth the vascular proportion is constant. Within the center of the unit the duct expands into a plexus from which regeneration takes place. The periphery of the unit is marked by nodal points which in one sense are embryonic units. THE DEVELOPMENT OF CHROMATOPHORES IN NECTURUS. BY ALBERT C. EYCLESHYMER. From the Anatomical Laboratory of St. Lowis University. WITH 7 FIGURES. The questions regarding the origin of pigment in the epidermis of vertebrates is one of deep interest not only to the histologist, but also to the pathologist. The literature shows that two different conclusions have been reached. One group of workers (Aeby, Keelliker, Ehrmann, Ribbert and others) have regarded the epidermal chromatophores as modified mesenchymal cells, which have wandered into the epidermis. Another group (Kodis, Jarish, Kromayer, L. Loeb, Strong and others) have considered the epi- dermal chromatophores as modified epithelial cells which have differen- tiated in situ. In the course of my studies of the larve of Necturus, I have been re- peatedly attracted not only by the peculiar movements of the chroma- tophores in the normal embryo, but also by the striking changes in their character brought about through decapitation. These casual observations led to a new method of studying the origin and movements of chromatophores. The method was briefly the follow- ing: The larve were placed in a bed of cotton in the fibers of which they soon became entangled, and were thus held in a given position for an in- definite period. The water in the receptacle containing the cotton was of course frequently changed. The larve were then observed under the higher magnification of the binocular dissecting microscope, and the movements of the living chromatophores followed. This study was then supplemented by a study of serial sections of larve of corresponding stages. Larve 11-12 mm.—The first appearance of pigment is found in the larvee of this length. When observed under the binocular microscope, this pigment appears as minute black dots lying deep down in the trans- parent connective tissues. If these minute structures be persistently watched for a few hours, or even examined at short intervals, it is easily seen that they gradually increase in size and slowly approach the sur- face. When first observed, the pigment seems to be confined to the body AMERICAN JOURNAL OF ANATOMY.—VOL. V. 310 The Development of Chromatophores in Necturus of the cell, but it soon extends to the protoplasmic processes.. It is then possible to follow the constantly changing positions of the processes. re Oh GS Op Ee es ~ SS en ee _— —-~=> Sor GPa SS _ ee ea Ses See Fig.2 af: BE eae TS Sonus, deb This amceboid movement becomes more clearly defined as the chromato- phores approach the surface. Serial sections of larve of this stage show that the chromatophores are Albert C. Eycleshymer 311 not restricted to any particular locality. In the vicinity of the myotomes they are found for the most part in the intermuscular mesenchyme. An- terior to the myotomes they are irregularly scattered and although a few are found in the outer portion of the dermis, they are for the most part located in the deeper mesenchyme. A study of the formation of pigment in the mesenchymal cells shows that it first appears in the immediate vicinity of the nucleus, and from this locality extends into the cytoplasmic processes. The pigment gran- ules are at first separate and distinct, but as the cells become more deeply pigmented, the granules become less distinct. It is thus possible in a general way to differentiate between the younger and the older chroma- tophores. Fig. 1 is taken from a section through the head of a larve of the above length, and shows two stages in the growth of the chromato- phore. The deeper cell (a) represents one of the first stages in the formation of the pigment. The pigment is here largely confined to the region of the nucleus, having extended but slightly into protoplasmic processes. The cell nearer the surface (b) represents a later stage in which the pigment has extended farther into the protoplasmic processes. Other sections show various stages in the formation of pigment from its first appearance in the region of the nucleus to its extension into all the protoplasmic processes of the cell. The epidermis at this time is made up of different kinds of cells. The first and most numerous are the ordinary polyhedral cells, which contain fine yolk granules. The second and less numerous are the large oval or spherical cells which contain very large yolk granules, and prob- ably form the unicellular glands. The third and least numerous are certain cells which possess more or less extended cytoplasmic processes and which, from their granular contents, staining capacity, and general form, closely resemble mesenchymal cells. Such a cell is shown in Fig. 2, c. lying among the epidermal cells. Whether these cells are modified epithelial cells or are mesenchymal cells, which have wandered into the epidermis at some earlier stage, cannot be definitely determined. As will be seen later cells of this type give rise to one group of epidermal chro- matophores. Larve 15-16 mm.—In the preceding stage but few of the chromat- ophores were at the surface of the dermis, but in the present stage large numbers of them have reached its outermost surface and through their widely branching processes form an open meshwork. These superficial chromatophores are most numerous over the dorso-lateral surfaces of the head, but they are also scattered along the body, being confined for the most part to an irregular dorso-lateral band which extends from the re- gion of the gills to the posterior limb buds. 312 The Development of Chromatophores in Necturus In sections of this stage one frequently finds conditions such as that represented in Fig. 3, in which the protoplasmic processes of the dermal chromatophores extend among the ceils of the epidermis. Other sections show widely branched chromatophores lying wholly within the epidermis, as shown in Fig. 4. From the study of sections alone, one would readily infer that these epidermal chromatophores are simply the dermal chromat- ophores which have wandered into the epidermis. I have ex- amined many sections with the hope of finding a chromatophore in which the cell body lay partly in the dermis and partly in the epidermis, but such a cell has not been found. All doubt, however, is dispelled by using the binocular microscope under which one can readily see the dermal chromatophores pass outward into the epidermis. In the epidermis one frequently observes the peculiar type of cells de- scribed under the preceding stage. These cells may be as yet unpig- mented or they may show varying degrees of pigmentation, often the pigment is confined to the region of the nucleus as shown in Fig. 5, d, again the pigment has extended to one or more of the cytoplasmic pro- cesses, as represented in Fig. 6, e. Larve 17-18 mm.—The chromatophores show a marked increase in number over the preceding stage. In a number of larve, they have ex- tended well down over the upper surface of the yolk. In the head re- gion there is a median dorsal line which is almost free from chromato- phores. On either side of this line chromatophores have extended down- ward to the upper margin of the nose and eye. The upper margin of the retina is now deeply pigmented,and not infrequently numbers of chromat- ophores are observed directly over the lens. They have extended to the base of the gills, although but few are seen in the gill bars. A few are present in the dorsal surfaces of both the anterior and posterior limbs. The dorso-lateral veins are present along the dorso-lateral surface of the yolk. Even at this early stage, the chromatophores are becoming more densely aggregated along the lines of these veins. Now as in the pre- ceding stages, one can see in the region sparsely pigmented a continual mi- gration of the dermal chromatophores from a deeper to a more superficial position. In those regions which are densely pigmented, one can readily see an increasing number of the dermal chromatophores passing into the epidermis. . Serial sections of this stage show a continued formation of the dermal chromatophores in the deep mesenchyme, and especially in the intermus- cular spaces. As they pass toward the surface the pigment extends into the cytoplasmic processes and they become more and more branched. The greater number of these chromatophores pass to the outer layer of Albert C. Eycleshymer. 315 the dermis and there remain, but a considerable number can be followed directly, as they pass into the epidermis. The epidermis in addition to the increased number of chromatophores of this type also shows a considerable increase in the chromatophores of the second type which are as yet found in all stages of formation from the earliest condition to the condition shown in Fig. 7, which represents the complete formed chromatophore. CONCLUSION. The chromatophores found in the epidermis are of two kinds. One is but shghtly branched, taking on in general a pyramidal form. The other is highly branched, taking on a mossy appearance. The former becomes pigmented in sitw within the epidermis. They may be mesenchymal cells which have wandered into the epidermis before becoming pigmented, or they may be modified epithelial cells. The second type is derived from the mesenchymal cells which wander into the epidermis after becoming pigmented. ON THE NATURE OF THE GRANULE CELLS OF PANETH IN THE INTESTINAL GLANDS OF MAMMALS. BY SIDNEY KLBIN, S. M., M. D. From the Hull Laboratory of Anatomy, University of Chicago. WITH 5 FIGURES. The recent activity in the investigation of the chemical and physio- logical properties of the succus entericus, and the discoveries of new enzymes which are produced by the intestinal mucous membrane, create a renewed interest in the structure and relationship of the elements com- posing the intestinal epithelium and glands, which are the sources of this secretion. It becomes a fundamental problem of intestinal histology to determine as far as possible the cytological and microchemical characters of these elements and to compare them in these respects with similar elements of known function from other sources. Of special interest in this connection are the peculiar, coarsely granular cells which occupy the deeper ends of the glands of Lieberkiihn, and which were first observed in 1872 by Schwalbe, 72, in fresh material from the intestine of the rat. For some reason Schwalbe’s description attracted little attention, and it was not until 1888 when Paneth, 88, rediscovered them and described at some length their microscopic and chemical characters, that these cells became generally recognized as constant constituents of the intes- tinal glands of certain mammals. For this reason they are generally known as the granule cells of Paneth. Paneth regarded these granular cells as a specific kind of gland cell wholly different from the globlet cell. Concerning their origin he was somewhat in doubt, although he favored the view that they were derived from indifferent mitotic cells farther up the gland, because of the fact that the granules became fewer towards the middle of the gland where the mitoses occurred. Paneth described the granules, as observed in fresh preparations of the mucous membrane, as moderately refractive structures, although not so refractive as fat. Distilled water and solutions of caustic potash had no effect on them, although they shrank somewhat in the latter and became AMERICAN JOURNAL OF ANATOMY.—VOL. V. 316 Granule Cells of Paneth in Intestinal Glands of Mammals more refractive. Ether and alcohol on the other hand dissolved the granules slowly and in diluted acids they disappeared instantly. By means of osmic acid and of picric acid he succeeded in fixing the gran- ules and the cells which contained them. Flemming’s fluid gave unsat- isfactory results. He regarded the cells in question as a special kind of glandular cell different from the goblet cell. Concerning the fate of these cells Paneth did not express himself definitely although he inclined to the view that they are completely used up in secretion and are replaced by mitotic cells farther up the gland. His attempts to show that this was the case by observing the effect of physiological stimulation, however, did not lead to the desired result, inasmuch as the cells were as numer- ous in the animals which had been fed as in those which were examined in a state of hunger. Nicolas, g1, also studied the granule cells and described at considerable length the different varieties of cells to be found in the bottom of the gland of Lieberkiihn. Some of these he regarded as secretory phases in the history of the cell of Paneth. Of these he recognized several, of which the following may be mentioned: (a) indifferent cells with clear protoplasm; (b) fine granulations appear in the protoplasm-primary granules; (c) the granules contain a safraninophilous body in the form of a crescent or semicircle, the rest of the granule staining in Flemming’s fluid; (d) the secretory activity has attained its maximum and the cell is completely filled with granules containing a safraninophilous body; (e) the cells expel the granules; (f) the cell contracting after expelling its contents assumes the aspect of the small narrow cell with deeply stained protoplasm; (g) the cell recovers itself and assumes the appear- ance of stage a. Nicolas also observed that in the later stages of secre- tion the nucleus became smaller, often irregular in shape, and stained diffusely, whence he concluded that the nucleus participated in the secre- tory activity of the cell. Bizzozero, 93, did not acept the conclusion of Paneth and Nicolas that the granule cells were specific glandular elements, but attempted rather to bring the facts with regard to them into accord with his theory that the glands of Lieberkihn were not in reality true glands, but merely foci for the regeneration of the surface epithelium, and to convert the appar- ently adverse fact of the occurrence of peculiarly organized elements in the bottom of the glands into an additional proof of the validity of his theory. He claimed to have found, in material from the intestine of the mouse stained in safranin and hematoxylin after fixation in Hermanns’ fluid, what he considered to be transitional forms between Paneth cells and goblet cells. In these preparations the mucin in the goblet cells Sidney Klein 317 was stained a violet color while the Paneth granules became red. The cells which were regarded by Bizzozero as transitional cells contained both small red granules and large blue mucin granules. As these cells were observed in an intermediate position in the gland between the Paneth cells below and the goblet cells above it seemed probable to Bizzozero that the mucin in them had been produced by the transformation of Paneth eranules. He assumed, therefore, that the Paneth cells were young goblet cells. : Subsequent investigators, however, among whom may be mentioned Moller, 99, Zimmermann, 98, Zipkin, 04, and Schmidt, 05, have failed to find the transitional elements described by Bizzozero, and have accepted the conclusion of Paneth and Nicolas that the granule-cells are specific elements engaged in a special kind of secretion. Schaffer, g1, described and figured these structures in the glands of Lieberkiihn of the duodenum and jejunum of man although he did not succeed in staining the granules. Zimmerman found that the granules stained strongly in iron hematoxylin in sections of human small intes- tine fixed in sublimate. He regarded the cells of Paneth as serous cells. Moller, 99, studied the structure of the glands of Lieberkiihn of a large number of mammals, chiefly in material fixed in a formaldehyde bichromate mixture, and stained in the Ehrlich-Biondi mixture, although he also used other fixing fluids for purposes of control, and applied the iron-hematoxylin method with good results. Moéller found that the cells of Paneth occurred in the intestinal glands of the mouse, guinea-pig, rabbit, ox, sheep, and horse. His results were negative as regards the cells of Paneth in the pig, cat, and dog, although he regarded the failure to find them in the first-named animal as due to a failure to fix the granules. Moller also found that the granules in different cells often exhibited different affinities for the stains employed, so that, for example, in sections stained in the Biondi-Ehrlich mixture some granules stained red, others yellow, greenish-yellow, or dark olive green. This difference he thought to be due to different functional conditions of the cells, the changes which the granule underwent from the time of its first formation in the cell to the time when it reached its mature form being indicated by its staining properties. In some cells he found indications of the fusion of the separate granules to a common mass which in part occupied the meshes of the cell framework, in part the wide lumen of the gland. These facts he regarded as undoubted indications of a real secretory activity on the part of these cells. He found no transitions between Paneth cells and goblet cells. 318 Granule Cells of Paneth in Intestinal Glands of Mammals Zipkin, 04, describes the Paneth cells of Inuus rhesus as present with- out exception in the bottom of every crypt, often lying beside one another in considerable numbers. The protoplasm of these cells always stain more deeply than that of the surrounding cells. Oppel, 97, described, in the glands of Lieberkiihn of Echidna, cells, at the bottom of the gland, the inner segment of which was finely granu- lar. The granules diminished in number as the mouth of the gland was approached and in the upper portion of it were wholly lacking. Schmidt, 05, studied the distribution of the cells of Paneth in the human intestine and confirmed the observations of Bloch, 03, who found them in practically every gland of the ileum and jejunum, as well as of the duodenum. In addition, Schmidt found Paneth cells frequently present in the glands of the vermiform appendix, although he was not able to find them in other portions of the large intestine except in three cases of pathological conditions. Concerning the occurrence of Paneth cells in the large intestine of the infant where Bloch claims to have observed them, Schmidt records a negative result in five newborn children. For the differentiation of goblet cells from Paneth cells Schmidt used mucicarmine by means of which he obtained a sharp distinction even in the foetal intestine. As far as the function of the Paneth cells is concerned he regards the fact of their absence from the intestines of even young carnivora as opposed to the conclusion which might be drawn from Bloch’s observation of their occurrence in large numbers in the large intestine of suckling infants, that they have something to do with the secretion of a substance which is active in the digestion of milk. He is rather inclined to the view that inasmuch as they are constantly present in the glands of herbivorous animals they affect some constituent of the vegetable food. As far as the occurrence of Paneth granule cells in lower classes of Vertebrata is concerned comparatively few references can be found in the lterature. Nicolas, 91, in the article already referred to mentions their occurrence in the lizard without stating the species examined, and KK. Bizzozero, 04, has described, in the depressions between the folds of the intestine in Teleostomes, cells which contain numerous granules stainable in haematoxylin but differing in their characters from the young goblet cells which occur in the same location. The last decade has been particularly fruitful in researches dealing with the morphology and microchemistry of glandular cells. As a result of these, new methods have been devised and new criteria established for distinguishing between zymogenic cells and mucous cells. In particular Sidney Klein : 319 may be mentioned in this connection the basal filaments of Solger, 94, which have been shown by the researches of Bensley, 96, Garnier, 00, Cade, 00, Zimmermann, 98, and others to be a structure common to many sero-zymogenic cells. Bensley, 96, 98, has also shown that the basal filaments correspond to the chromatin of the nucleus in their staining reactions and like the latter contain iron in the form of an organic compound and thus represent morphologically the substance presumably of nuclear origin which Macallum, 95, long ago discovered in gland cells of various sorts by means of staining reactions, and sub- sequently confirmed by means of the microchemical reaction for iron. As far as mucin is concerned no microchemical reaction has been, as yet, discovered, which is effective in recognizing this substance in isolated cells in sections. The work of P. Mayer, 97, has, however, provided us with a number of new staining solutions which, while they do not permit us to say whether a given cell does or does not secrete mucin, yet furnishes evidence which may be of much value when taken in connection with that from other sources. Up to the present no special attention has been directed to the ques- tion of the presence of Macallum’s prozymogen in the cells of Paneth, either in the form of basal filaments or as a diffused compound in the base of the cell, although several observers, notably Zipkin, 04, and Nicolas, have called attention to the deeper staining of the protoplasm of these cells as compared with neighboring cells. The results, more- over, of attempts to discover experimentally, differences in the aspect of these cells corresponding with phases of physiological activity have not been decisive. Accordingly, at the suggestion of Professor Bensley I undertook the reinvestigation of these structures in the hope that the application of new staining and microchemical methods would reveal new facts which would be of assistance in forming an opinion as to their nature and their relationship to other intestinal epithelial elements. At a very early stage in the investigation the discovery was made that in the opossum, Didelphys virginiana, the cells of Paneth occurred not only in the glands of Lieberkiihn but also mingled with other epithelial elements on the sides of the intestinal villi even at their very tips. This remarkable fact, which possesses no parallel in any other mammal, so far as is known, possesses so much significance in the interpretation of the Paneth cells that a somewhat extended description is called for. The small intestine of the opossum is characterized by extremely long villi and a very thin tunica mucosa. Corresponding to the latter the glands of Lieberkiihn are very short and contain a scarcely recognizable 20 Granule Cells of Paneth in Intestinal Glands of Mammals Se) Fig. 2. Fig. 1. Fic. 1. Villus and subjacent glands of Lieberktihn of the opossum. From a preparation stained in iron-alum hematoxylin and mucicarmine. Fic. 2. A portion of the epithelium of the villus shown in Fig. 1 as seen under Leitz Homog. Imm. 1/12, Oc. 4. Sidney Klein 321 lumen. Fig. 1 illustrates fairly well the nature and distribution of the three kinds of epithelial cells in the glands and in the villi. The prepara- tion is from material fixed in Bensley’s bichromate-sublimate-alcohol fluid and stained with iron haematoxylin followed by mucicarmine. By this means the granules are stained blue-black in the cells of Paneth, red in the goblet cells. Thus a sharp differentiation is obtained between these cells even in the glands of Lieberkiihn where the young cells contain comparatively little of the secretion-antecedent. The Paneth cells on the side of the villus are large and resemble very closely typical goblet cells (fig. 2). The theca is filled with large discrete granules which do not react with mucicarmine but on the contrary stain intensely in iron haematoxylin. These granules also stain strongly in the neutral gentian mixture recommended by Bensley, 02, for staining zymogen granules, the mucous goblet cells remaining colorless. The granules in the Paneth cells occupy the meshes of a network which is formed by the cytoplasm separating the granules. At the proximal end these cells are narrower and contain a nucleus which is somewhat elongated in the direction of the long axis of the cell and often slightly cupped on the side next the theca. The basal protoplasm is small in amount and uniformly more deeply stained than that of neighboring cells, with the exception of the narrow cells which are obviously undergoing degeneration. Tested with Macallum’s reagents for the detection of organic iron a positive result is obtained but not enough to be convincing evidence of the presence of prozymogen in the cell. The search for basal filaments also proved without result although the positive outcome of these observations in the guinea-pig, to be described presently, gave ground for the belief that had a more abundant material been available, and had it been possible to examine it in different physiological states, a positive result might have been obtained. The glands of Lieberkiihn in the opossum are remarkable for their low grade of development, and, although the three main types of cells are present, the amount of secretion which the Paneth cells and goblet cells contain indicates that they are to be regarded rather as young elements than as cells already functioning as secreting organs. Indeed, in some respects, these glands present but little advance over the epi- thelial buds to be found in the intestinal epithelium of Batrachia, and to this extent realize Bizzozero’s idea of a gland of Lieberkiihn which serves merely as a place for the production of new cells which ultimately migrate to the free surface and there reach their full functional develop- ment. Many mitoses are always present in the glands, some in mucin- 322 Granule Cells of Paneth in Intestinal Glands of Mammals holding cells, others in the cylindrical cells. I have not been able to assure myself definitely of the occurrence of mitoses in the cells of Paneth. The small size of these cells and their more irregular shape and arrangement make the exact determination of the nature of the mitotic cells somewhat difficult. The distribution of the cells of Paneth in the intestinal epithelium of the opossum, the occurrence of the fully loaded cells in the surface epithelium and of immature cells in the gland cannot be reconciled in any way with Bizzozero’s view that they are young cells which only achieve their full development as mucus-secreting goblet cells, nor, indeed, with any view except that they are specific elements engaged in the production of a special secretion. The material from the guinea pig proved the most fruitful in results as regards the cytological characters of the cells of Paneth and in this animal results were obtained which bring the cells of Paneth into lne with other sero-zymogenic cells such as the cells of the parotid gland, the chief ‘cells of the fundus glands and the pancreatic cell. At first, considerable difficulty was experienced in obtaining accurate fixation of the granules. Aqueous sublimate, Bensley’s alcohol-bi- chromate-bichloride mixture, and Kopsch’s formaline bichromate mix- ture, were tried with only partial success. A few of the cells at the very edge of the section, in these imperfect fixations, would be found to have retained the granules while from the majority of the cells they had either been removed entirely or only retained in an imperfect and dis- torted form. Very frequent in these cases were the crescent-shaped granules described by Nicolas in the Paneth cells as one of the stages in the secretory history of the cells. A great deal of the work was done on material fixed in 10 per cent formaldehyde which penetrated somewhat better than the other fluids mentioned above, although in this fixing fluid the crescentic-shaped granule was common. When the work was nearly completed we succeeded in obtaining complete fixation of the granules by means of a combination of equal parts of alcoholic sublimate and Kopsch’s fluid. In preparations fixed in this mixture the granules retained their round form and were perfectly fixed in all the cells of the material. For staining, Bensley’s neutral gentian was employed with good success to differentiate Paneth cells, the granules of which stained intensely violet, from goblet cells which remain colorless or faintly violet. Another method which has rendered great service is staining in iron haematoxylin followed by mucicarmine. By this method the granules of the Paneth cells are stained deep blue-black, those of the goblet cells carmine red. Sidney Klein ; 323 To demonstrate prozymogen as basal filaments or as a diffuse chromo- phile substance in the base of the cell toluidene blue was employed in saturated aqueous solution. Better results, however, were obtained by a method devised by Bensley of staining in toluidene blue, orange G, and acid rubin. This method is as follows: the sections cut as thin as possible in paraffin and fastened to the slide by the water method are passed through benzole, absolute alcohol, and graded alcohols, to water. They are then stained for a period of one minute with a mixture containing equal parts of the saturated aqueous solutions of Orange G, and acid rubin. Then wash in water and stain for one minute in saturated aqueous solu- tion of toluidene blue. Wash in water; transfer to absolute alcohol; clear in benzole, and mount in balsam. The result as far as the distri- bution of the toluidene blue is concerned is much the same as that ob- tained by staining with this dye alone. The intensity of the blue stain, however, is much increased, and in addition the method offers the ad- vantage of the contrast stain produced by the rubin and orange. By this method chromatin and prozymogen (or basal filaments) are stained intensely blue, protoplasm faint bluish, zymogen granules red, and the contents of goblet cells remain unstained. Confirmatory evidence of the presence of prozymogen in the Paneth cells was sought by means of the microchemical reaction for organic iron introduced by Macallum. In the guinea pig Paneth cells are very abundant in the glands of Lieberkiihn of the small intestine. They occupy chiefly the deep ends of the gland where they often form a continuous layer which is inter- rupted by comparatively few goblet cells. A few also occur on the sides of the gland but the upper ends of the glands are wholly free from them. The structure of these cells depends on the stage of physological activity. In the animals which are kept constantly supplied with food of which they are allowed to partake at will, the cells are cylindrical in shape, the outer end being somewhat broader than that which is directed towards the lumen. In each cell two zones of about equal width are easily recognized. The distal zone directed towards the lumen of the gland is occupied by fine granules which are so closely crowded that it is often difficult to recognize the thin laminae of cell-protoplasm which separate them from one another. In material fixed in aqueous sublimate, however, many cells may be found from which the granules have been removed and here we find the distal zone occupied by a fine meshwork which corresponds in the size of its spaces to that of the granules, indi- cating that each granule occupies a small space in the protoplasm, a thin 24 324 Granule Cells of Paneth in Intestinal Glands of Mammals lamina of which separates it more or less completely from its neighbors. The granules stain intensely in iron hematoxylin and in neutral gentian but remain quite unaffected by muchaematein or mucicarmine. The proximal or basal zone of the cell contains an oval nucleus which is surrounded by a small quantity of protoplasm which takes a slightly deeper stain than that of neighboring cylindrical cells. Some of the cells contain a larger quantity of this basal protoplasm and in a few of the cells this exhibits a distinct radial striation, in which case the deeper stain is largely confined to the striae. The presence of these basal stria- Fic. 3. Bottom of gland of Lieberktihn of the guinea-pig after twenty-four- hour fast. From a preparation stained by orange-rubin-toluidene blue method. Leitz 1/12, Oc. 4. tions was, however, more easily demonstrated in those animals which were protected from an excess of physiological stimulation by controlling the amount of food taken and supplying it at regular intervals. Fig. 3 represents the lower end of the gland from the small intestine of a guinea pig which had fasted for twenty-four hours after receiving a mixed meal of carrots and oats. The aspect of the cells in this case is very different from that seen in the animal feeding irregularly. In the first place the granules are more than twice as large, and there appears to be a larger number, although, for obvious reasons, it is difficult to be sure of this. In sections of the intestine stained with toluidene blue alone, or with Sidney Klein 325 toluidene blue and orange-rubin, the basal cytoplasm of practically every cell exhibits a radial striation which is exactly similar to that described in various sero-zymogenic gland cells by Bensley, Solger, Garnier and others. This character is well illustrated in fig. 3 which is from a speci- men stained in the toluidene blue-orange-rubin method. The basal filaments stain intensely in toluidene blue, less intensely in iron haema- toxylin, but may be observed without difficulty in sections stained with alum-haematein. The most effective method of demonstrating the basal 4 § Fie. 4. Gland of Lieberktihn of guinea-pig. From preparation treated by Macallum’s method for the detection of masked iron; Leitz 1/12, Oc. 4. C A yo. 7 icine oa ES AE NILDER, filaments is by means of the microchemical reaction for organic iron of Macallum, because the result is not confused by the faint protoplasmic stain which is obtained generally in staining with toluidene blue. This method consists in liberating the iron from its organic combinations by treatment of sections from material hardened in alcohol with a solution of sulphuric acid in alcohol for several hours at 37.5 C. and then demonstrating the iron at the point of its liberation by means of haema- toxylin (see Macallum, 95). ‘The result, as far as the Paneth cells are concerned, is a strong reaction in the substance of the basal filaments and in the nuclear chromatin (fig. 4). In some of the Paneth-cells a more 2 oo or) Granule Cells of Paneth in Intestinal Glands of Mammals diffuse reaction is obtained indicating that the specific substance on which the staining reaction of the basal filaments depends is present although not definitely organized in the form of filaments. The absence of the basal filaments from the majority of the cells of the animal which has been kept constantly supplied with food is doubtless due to the fact that in this case the cells are subjected to a physiological stimulus which is practically continuous, which results in a constant drain on the reserve substances of the secretion, both the granular zymo- gen and its antecedent prozymogen. Fic. 5. End of gland of Lieberkiihn of guinea-pig six hours after food. Preparation stained in iron-alum hematoxylin and mucicarmine; Leitz 1/12, Oc. 4. In order to determine the effect of physiological stimulation on the Paneth cells I have examined them in sections taken at gradually in- creasing intervals after feeding, from animals which have previously fasted for twenty-four hours in order to bring the cells to the condition of maximum loading. The results of these experiments show beyond a a doubt that the cells of Paneth respond to the stimulus of food, although considerable differences were found in the rate of disappearance of the granules in different sets of experiments. The condition of the cell in animals which have fasted for twenty-four hours has been already de- Sidney Klein ; 327 scribed and figured (Fig. 3). As early as four hours after feeding, a change in the number and size of the granules may be noticed. They are obviously reduced in number and are somewhat smaller. At six hours the condition represented in Fig. 5 is presented. The cells are longer and narrower and the granules are small, few in number, and occupy the distal segment of the cells only. Indeed, at this stage the cells have assumed very much the same appearance as they present in the animal which is feeding irregularly, although the amount of prozymogen is greater in the six hour stage. At no stage of secretion have I found the fusion of granules into large masses described by Nicolas, if a fixative was employed which was effective in fixing the granules in all parts of the tissue. With some of the fixatives mentioned at the beginning of this paper great differences were found in granules in different cells both in staining power and in form. Very common in these imperfect fixa- tions were the granules composed of a faintly stained central mass with a deeply staining crescent at one border corresponding to the safranino- philous body of Nicolas. I have no doubt that these appearances are entirely due to imperfect fixation, and that the crescent-shaped granules have no existence in the living cell. On the other hand, the different be- havior of granules towards the same fixative even in the same cell indi- cates clearly that some of the granules differ from others either chemi- eally or physically, and it is probable that this difference is due, as Nicolas supposed, to a change in the granule preparatory to its solution and extrusion from the cell as a part of the secretion. As regards the prozymogen the experiments did not result in a great change in its amount. It is probable that an equilibrium is established between the rate of production and use of this substance which results in the amount in the cell being kept fairly constant. SUMMARY OF RESULTs. The results recorded show clearly that the cells of Paneth correspond in their structure and microchemical reactions to the enzyme-producing cells of other granular organs, such, for example, as the cells of the paro- tid gland, the chief of the fundus glands of the stomach, and the cells of the pancreas. In common with these cells the cells of Paneth contain granules which do not stain in the specific stains for mucin, such as mucicarmine and muchamatein, and which react like zymogen granules to such stains as iron hematoxylin, neutral gentian and acid rubin. In addition they contain in their basal segment a substance which is distinguished by its 328 Granule Cells of Paneth in Intestinal Glands of Mammals affinity for basic dyes, such as toluidene blue, sometimes as a diffused substance in the base of the cell, generally in the form of basal filaments. The failure of previous observers to find this substance is probably to be explained by the fact that the study of these cells has generally been undertaken in herbivorous animals which like the guinea pig show the effects of an almost continuous secretory activity. Furthermore, this basal substance, whether diffused in the basal cytoplasm or in the form of the so-called basal filaments, gives when treated by Macallum’s method a decided reaction for iron. For these reasons it seems certain that we have to do here with a substance exactly comparable to the prozymogen of other zymogenic cells. In the opossum the cells of Paneth are found not only in the glands of Lieberkiihn, but also on the surface of the mucous membrane. In- deed, when the small size of the cells in the glands, their large size on the villi, and the generally rudimentary character of the glands in this animal are taken into consideration, it seems probable that the cells are formed in the glands, but only reach physiological maturity after mi- grating to the surface in the way described by Bizzozero. ‘This is of course only true, as far as we know at present, of the opossum, although it is possible that the examination of other polyprotodont marsupials might reveal similar conditions in them. In placentals the cells of Paneth appear to be confined to the bottoms of the glands of Lieberkiihn, which thus function as true glands as maintained by Oppel. Whether the condition found in the opossum is the primitive condi- tion for mammals or not it is impossible to say, although this view pre- sents many interesting possibilities. Nicolas’ observation that they oc- cur as a part of the general intestinal epithelium in a lizard points in this direction. The observations bearing on the occurrence of Paneth cells in lower vertebrates are, however, as yet, too few to enable any opinion to be offered as to their phylogenetic source. The distribution of the cells of Paneth in the opossum absolutely ex- cludes the possibility of the cells of Paneth being young mucous cells, and equally opposed to this view are the facts brought out by Nicolas, Moller, and the writer, as to the indications of active secretion in the structure of the cells and as to their response to physiological stimulation. The cells of Paneth of the guinea pig respond to physiological stimulus of food by secretion as indicated by changes in the form of the cell and reduction in the number and size of the granules. The crescent-shaped granules of Nicolas and others are due to im-— perfect fixation and have no previous existence in the cell. Sidney Klein 329 It seems clear from these facts that the cells of Paneth are specific elements engaged in the secretion of a special substance, probably an enzyme which is of use in digestion. It is not, however, possible to con- nect the Paneth cells with the formation of the new substances, secretin, erepsin, and enterokinase, because these substances are also found in the small intestine of carnivora in which Paneth cells do not occur. Nor is it possible to connect them definitely with any particular class of food, as Moller suggests, because they have been found not only in herbivorous and granivorous animals, but also in insectivora. In conclusion, I wish to express my indebtedness to Professor Bensley, at whose suggestion and under whose direction the work was undertaken, for friendly guidance and advice during the progress of the investigation. REFERENCES. BENSLEY, R. R., 96.—The Histology and Physiology of the Gastric Glands. Proc. Canad. Inst., Toronto, 1896. I, pp. 11-16. 98.—The Structure of the Mammalian Gastric Glands. Quart. J. Micr. Sc., Lond., 1898, N. S. XLI, pp. 361-389. 03.—The Structure of the Glands of Brunner. The Decennial Publi- cations of the University of Chicago, 1903. First Series, X, pp. 279-326. Bizzozero, E., o4.—Sur la régénération de l’épithélium intestinal chez les poissons. Arch. ital. de biol., Turin, 1904, XLI., pp. 233-245. BIzzozERO, G., g2.—Ueber die schlauchformigen Driisen des Magen- darmkanals und die Beziehungen ihres Epithels zu dem Oberflachen- epithel der Schleimhaut. Arch. f. mikr. Anat., Bonn, 1892, XL., pp. 325-374. GARNIER, C., 00,—Contribution a ]’étude de la structure et du fonctionnement des cellules glandulaires séreuses. J. de l’anat et physiol., etc., Par., 1900, Année XXXVI, pp. 22-98. MAcaLtLum, A. B., g1.—Contributions to the Morphology and Physiology of the Cell. Tr. Canad. Inst., Toronto, 1891, I., pp. 247-78. g5.—On the Distribution of Assimilated Compounds of Iron other than Hemoglobin and Henatins in Animal and Vegetable Cells. Quart. J. Micr. Sc., Lond., 1895, XXXVIII., pp. 175-274. MAYER, P., g7.—Ueber Schleimfarbung. Mitth. a. d. zool. Station zu Neapel. Leipz., 1897, XII., pp. 303-30. MOLLER, W., 99.—Anatomische Beitrage zur Frage von der Sekretion und Absorption in der Darmschleimhaut. Ztschr. f. wissensch. Zool., Leipz., 1899, LXVI., pp. 69-135. NicoLas, A., g1.—Recherches sur l’épithélium de Vintestin gréle. Internat. - Monatschr. f. Anat. u. Physiol., Leipz., 1891, VIII, pp. 1-62. OpPEL, A., g7.—Lehrbuch der vergleichenden mikroskopischen Anatomie, Jena, 1897, Teil II, Schlund und Darm. 330 Granule Cells of Paneth in Intestinal Glands of Mammals PANETH, J., 88——Ueber die secernierenden Zellen des Diinndarm-epithels. Arch. f. mikr. Anat.; Bonn, 1888, XX XI, pp. 1138-191. ScHAFFER, J., g1.—Beitrage zur Histologie menschlicher Organe. Sitzungsb. d. k. Akad. d. Wissench., Math. -naturw. Cl., Wien, 1891, Vol. C, Abth. III, pp. 440-481. Scumipt, J. E., 05.—Beitrage zur normalen und pathologischen Histologie einiger Zellarten der Schleimhaut des menschlichen Darmkanales. Arch. f. mikr. Anat., Bonn, 1905, LXVI, pp. 12-40. ScHWALBE, G., 72.—Beitrage zur Kenntniss der Drtisen in den Darwandungen insbesondere der Brunner ’schen Drwtsen. Arch. f. mikr. Anat., Bonn, 1872, VIII, pp. 92-140. Sotger, B., 94.—Zur Kenntniss der secernierenden Zellen der Glandula sub- maxillaris des Menschen. Anat. Anz., Jena, 1894, IX, pp. 415-419. ZIPKIN, R., 04.—Beitrage zur Kenntniss der groberen und feineren Struk- turverhdltnisse des Diinndarms- von Inuus rhesus. Anat. Hefte, Wiesb., 1904, XXIII, pp. 113-186. SOME PHASES OF THE GASTRULATION OF THE HORNED TOAD, PHRYNOSOMA CORNUTUM HARLAN. BY CHARLES L. EDWARDS AND CLARENCE W. HAHN. From the Biological Laboratory, Trinity College, Hartford, Connecticut. WitH 15 Trext FIGURES. The following account of the gastrulation of this very interesting iguanid is the outcome of investigations carried on at the University of Cincinnati in 1899 and 1900 and at Trinity College in 1900 and 1901. The embryos were collected at Austin, Texas, in 1892-1894. Except for the cleavage and the beginning of gastrulation the collection embraces the complete embryology of Phrynosoma conutum, but in this paper we present only the general phenomena of the gastrulation as interpreted from the stages in our possession. The breeding and nest building habits of the horned toad have been described by Edwards, 96. Breeding takes place in the months of June, July and August. Contrary to all pre- vious accounts in which species of the genus Phrynosoma are given as Viviparous* it was observed that at least in the case of P. cornutum at Austin, Texas, the eggs, numbering in some instances as many as twenty- five, are deposited in nests formed in a chamber at the end of a tunnel in the ground which the female burrows, and then, after laying the eggs, carefully refills with the loose pellets of earth. At the time the eggs are laid the embryo has attained the stage in ontogeny equivalent to that represented by Peter, 04, Taf. II, Fig. 17, as N. T. Nr. 68 for Lacerta agilis. The Phrynosoma embryo when it leaves the oviduct is 2 mm. in its greatest length. The head bend forms a wide acute angle at the pro- jecting mid-brain, while the neck bend forms an obtuse angle. The body is slightly curved, the caudal end being twisted around to the right. In the open space of half the length of the body between the tip of the fore- brain and the tail lie the well marked, distended allantois and the strongly curved, prominent heart. In order to obtain the earlier stages, it is necessary to take the eggs 1This error, repeated by Gadow, o1, Dp. 533, was corrected by Edwards, 03, p. 826. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 332 Some Phases of the Gastrulation of the Horned Toad from the oviduct of a gravid female immediately after she has been chloroformed. The oblong eggs are cream-colored and when laid the soft, moist, semi-transparent membraneous shell allows the embryonic area to show through, forming a dark pinkish oval area on the upper side of the egg. The egg shell becomes tough on drying, but not brittle or stiff. To fix the embryos free from yolk and separated from the egg shell, a disk somewhat larger than the embryonic area was cut out. In removing this a considerable portion of the yolk immediately beneath was carried with it to sustain the embryo until it could be supported on all sides by physiological salt solution. By the careful use of a current from a pipette, the yolk was removed and then the shell membrane and the vitelline membrane. Sometimes, in very early stages, it was found de- sirable to allow the shell membrane to remain on the blastoderm for its support. Usually a drawing was made of the unstained embryo with the aid of about sixty diameters magnification, in order to facilitate the in- terpretation of sections In general, Fleming’s mixture of chromic-aceto- osmic acid was employed for fixing followed by successive alcohols. A modification of Mayer’s hemalum was found superior to hematoxylin and other hematin stains, both for sections and specimens in toto. For the latter Mayer’s hemalum diluted with twenty parts of ammonia alum was employed. The specimen was decolorized in 1-10 of 1% hydro- chloric acid made up in 70% alcohol. Alcoholic cochineal also gave good results in toto. Benzopurpurin was advantageous in older stages. Orange G was used as a plasma stain in sections. Clearing was accomplished by the use of anilin, or clove oil, removed subsequently by xylol Owing to the radially symmetrical appearance of the embryonic area in the earliest stages, they were extremely difficult to orient. They were embedded in celloidin and then the celloidin was pared down until the embryos could be observed under the low power of a microscope when triangular blocks were cut with definite relation to the anterior and pos- terior end of the blastoderm. These were reémbedded when sectioned. The celloidin also protected the delicate embryos which had become brittle after several years in alcohol. The youngest embryo in this collection has passed through cleavage and the first phase of gastrulation being in the second phase of gastru- lation as first worked out for the lizard by Wenckebach, 91, p. 75. This stage is represented in surface view in Fig 1. Superficially it re- sembles a like stage of Lacerta viridis, according to the drawings of Will, 95, b, Fig. 6, Pl. 1; also of the turtle embryo as represented by Mit- sukuri, 94, Fig. 1, Pl. 6, and of Tuatara (Hatteria) as figured by Dendy, 99, Fig. 1. The embryonic area is pushed up above the surrounding Charles L. Edwards and Clarence W. Hahn 333 blastoderm in the form of a cap with vertical margins leveled toward the center of the crown and having a deep recess in the posterior edge where the blastopore is located. The length of the area is about 4 mm. The width is slightly less. At the anterior margin the cap tapers to a round point which indicates more rapid growth in this plane. The recess at the posterior edge indicates either an ingrowth of the upper layer cells at this point or a backward movement of parts on either side of it. Sec- tions prove that the former is true. , This stage is represented as seen in longitudinal section in Figs. 2 and 3. ‘These sections are slightly diagonal. Fig. 2 passes through the blasto- a aa.pel----- 4 bl’po! b. Fic. 1. Dorsal view of a very early stage in which probably the mesoblast sac has not broken through into the subgerminal space. a., anterior; aa. em., area embryonic; aa. pel., area pellucida; bl.’po., blastopore; p., posterior; x 74 diameters. pore, but runs to the left of the median plane in the anterior region of the embryonic area. The extent of this rotation may be judged from the fact that Figs. 2 and 3 are the 2d and 3d sections which pass through the embryonic area, there being 9 sections included in this area. All the structures of interest are to be found in these two sections. The elevation of the cap above the surrounding blastoderm is appar- ently due to the rapid increase in thickness and extent of the epiblast over this area. The accumulation of the mesoblast may take part in this elevation, but the absence of mesoblast in the greater part of the anterior Some Phases of the Gastrulation of the Horned Toad 334 CPE ED aes TSAR) ie SAS eS RR) ROO has ack, “a6 Ss ae a) NS a ey COS” aa ~ Day, ersee ore Ne) SPP Yar Oe £9) Hips SES IN cere” ORS Bao; 2 iS EE A cB eo Cycertel) meNagogpe 7 C07 339 Charles L. Edwards and Clarence W. Hahn ‘gsepqodAq “710, “Y pur “ud “p) pur ‘q ‘Dp ‘e-Sta UL a10doysR[q 94} Youno1gy UBIPOTL ST ZOLA “S19 9UIBIP (0G Sqselqida *)q, 9 ‘ grodoysetq “0d, “14 “4 °BIq JO FUSTA yz OF WOTPOOS 4xou tssoooad peog * ‘snooy daap 98 ATWO IB "99 ‘oad $4SB[qOsour ‘ i i ae 3 aCe gy LON: F ee oe 5) ee [> er SD Oe Be fe ie Testers oe eS ene Ss Dex, SY CF mS nq, ‘sue: seqetd oatytmtad “1d “p) Seyerd [eanou “U “D) add¥e qoryM Sousst} paqussaidad o4B *9 “7 ‘p °e “aTq UL 1 04} SI g ‘STA = “FUOAZ UT OUT g[pplur oy} JO FJoT OY} OF SUNT ING ‘[ ‘Sig UL MOTA ooBJANS UL W99S WAIpO RIG OY JO SUOTIOIS jeurpnysuoy “¢ ANV @ ‘SHIA ‘2 “phd 5) xh ie Ss Sie S a feyAe) Boar : oe oS q = Se jiSesea 336 Some Phases of the Gastrulation of the Horned Toad embryonic area proves that some other agent maintains the elevated po- sition of the thickened epiblast. As in other reptiles the upper and lower layer are connected by a mass of mesoblast at the posterior edge of the embryonic area. Here by the invagination of the primitive plate of Will is formed the mesoblast sac (Mesodermsackchen of O. Hertwig, 03, p. 828). That all of the meso- blast in Figs. 2 and 3 was derived from the proliferation and invagination of the region of the primitive plate and blastopore, can not be positively affirmed, yet it seems highly probable. The mesoblast at the anterior margin in Fig. 3 is in direct connection with the mesoblast under the primitive plate. The mesoblast cell masses are continuous with the epiblast of the pos- terior and lateral lips of the blastopore which leaves little doubt as to their origin. From these two sources there is a lateral and a forward extension of the mesoblast cell masses. From the floor of the mesoblast sac one mass extends forward in the middle region (Fig. 2, ms’bl.) It is continuous laterally with the lateral extensions, the floor of the mesoblast sac contributing to the lower portion of these also. The in- turned epiblast, or lateral roof of the mesoblast sac is con- tinued laterally and forward by a mass of mesoblast (Fig. 3, ms’bl.™) having a high position. Laterally this mesoblast bends down and back (Fig. 2, ms’bl.“") to unite with the mesoblast from the fioor of the meso- blast sac (Fig. 2, ms’bl.#). It thus forms a pouch on either side which is continuous posteriorly with the mesoblast sac in the median line. The floor of the mesoblast sac is continued anteriorly for a short distance under the chorda anlage into a sheet of mesoblast. In a middle position it spreads laterally over the Jateral pouch above mentioned, while farther back, as the floor of the mesoblast sac, it is continuous with the ventral wall of the lateral pouches. Under the region designated primitive plate (Fig. 2, la. pr.) the meso- blast is in the form of a network, and, while it seems to be spreading from these centers of origin, it is not being encroached upon by new additions, or proliferation, inter se. Mesoblast of this nature can be traced from the hollow pouches extending laterally on either side of the primitive streak, to the anterior margin of the embryonic area where it fills in the space between the epiblast and hypoblast (Fig. 3 ms’bl.i), According to Will a similar forward growth of mesoblast on each side of the chorda takes place in Lacerta agilis, L. muralis and a like condi- tion exists in the turtle (Mitsukuri, 94), snake (Will, 98) and in Spheno- don (Dendy, 99). The mesoblast sac becomes a canal reaching far into the mass of meso- Charles L. Edwards and Clarence W. Hahn 337 blast, almost to the middle of the embryonic area. At the mouth it is funnel-shaped, being wider perhaps laterally than vertically. Its dorsal wall is the thick infolded epiblast destined to become the chorda. The epiblast of the depressed ventral wall of the blastopore becomes meso- blast deeper in the canal, for this mesoblast is produced by the forward growth of epiblast cells. Since the dorsal and ventral walls of the meso- blast canal contribute to the lateral mesoblast by infolding and lateral growth, the mesoblast sac may be regarded as having no lateral limita- tions, but extending between the above named mesoblast anlagen. How- ever, the scctions of this stage only indicate this for a short distance in front of the blastopore. The head process is four or five cells thick where it is continuous with the epiblast at the blastopore. It is continuous laterally at this point with the ectodermic folds that give rise on either side to the dorsal limbs of the mesoblastic pouches. Anteriorly it be- comes a wide belt of cells, three or four deep, and thin at the edges (Fig. 3, pre. ce.) extending quite to the anterior limit of the neural plate. As in Fig. 3, anterior sections do not have mesoderm adjacent to the chorda laterally. A part of the tissue under the chorda in Fig. 3 is mesoblast (Fig. 3, ms’bl.“) of primary origin, but under the greater part of it is mesoblast (Fig. 3, ms’bl.!) which is derived from the primary mesoblast. In the adjacent sections the hypoblast is easily traceable to the limits of the embryonic area and there is no mesoblast lateral to the chorda in the forward end. In Figs. 2 and 3 the epiblast represented is not all in the same plane (e’bl#? and e’bl.#) ; e’bl.4 is cut in a diagonal plane and e’bl.# is cut vertically. In Fig. 2 (a, 6 and la. pr.) and Fig. 3 (a, b, c) aré repre- sented tissues which appear only at deep focus. The epiblast over the whole top of the embryonic-cap is four or five cells thick, but it thins out rapidly toward the base of the uprising wall, becoming a thin one-celled layer in the extra-embryonic area (Figs. 2 and 3, e’bl.‘). The hypoblast is uniformly one cell thick over the whole embryonic area, except under the chorda where it appears to be two or more cells thick, but this con- dition is of limited extent. Extra-embryonic mesoblast separates these two germ layers but a short distance from the embryonic area (Fig. 2 ms’bl.i Fig. 3, ms’bl.###). From these observations we may conclude that at a time when the epiblast is in the form of a much thickened cap the mesoblast sac forms a canal stretching forward into the mass of tissues that are then accumulating at the posterior part of the embryonic cap and perhaps opening into the sub-germinal cavity in front of this mass of tissues. The mesoblast which is being produced around the blastopore, stretches antero-laterally from it in the forms of two hollow sacs of Some Phases of the Gastrulation of the Horned Toad oN) eS) (o/s) closely packed cells, one on each side, which act as feeders to surrounding parts, there being an extension of it along each lateral margin to a posi- tion well in front of the embryonic cap. The cavities of these sacs are in communication with the blastopore. The epiblast turns in at the blastopore and gives rise to the chorda and mesoblast. The latter also receives accessions below from the primitive plate region, in fact from epiblast cells of the floor of the mesoblast sac as we shall endeavor to prove later. Fic. 4. Longitudinal section of an embryo in which the cap-like condition is less marked but in which the mesoblast sac has not yet fused with, or broken through, the hypoblast. bl.’po., blastopore; cd.d., chorda dorsalis; e.’bl., epiblast; h.’bl., hypoblast; la pr., primitive plate; ms.’bl., mesoblast; x 16674 diameters. The next oldest blastoderm in the collection was sectioned lengthwise. In the stage just described we have not been able to affirm positively that the mesoblast sac does not communicate with the subgerminal space, but in the second stage (Fig. 4) the hypoblast is unbroken. It differs from the younger stage in the absence of the cap-like elevation, in the more compact and mature condition of the primitive plate, and in the absence of the mescblastic pouches so characteristic of the early stage. They are already flattened and their cavity all but obliterated. The chorda is relatively shorter than in the embryo represented in Figs. 2 and 3, but it is actually of about the same length while the whole blastoderm is about Charles L. Edwards and Clarence W. Hahn 339 two and one-half to three times as long as the blastoderm of Figs. 2 and 3. It is very nearly identical to Will’s Fig. 36, Taf. 6, which is a section of the embryo represented by him in Fig. 6, Taf. 1, above referred to as equivalent to Phrynosoma, Fig. 1. The second stage has three separate solid masses of mesoblast proliferation and ingrowth. ‘Two are from either side of the primitive plate and may be traced forward on either side. The cells become scattered at the edges of the growth. Some of these scattered cells may be seen between the thin epiblast and hypoblast at the anterior margin of the embryonic area, but not in the middle Tine. . ee Bee ™murg nas a la.pr bl.’ bo. marg. bl’ bo. Fie. 5. Dorsal view of a blastoderm older than Fig. 1. The elevation of the embryonic area has given place to a flat plate and the blastopore has changed shape. ad.em., area embryonic; bl.’po., blastopore; glb. vt., yolk spheres; ld. pr., primitive plate; marg. bl.’po., margin of blastopore; mur. g., germinal wall; * 74 diameters. Here the epiblast and hypoblast are closely adherent both in and outside of the embryonic area. The third mass of mesoblast growth is from the ventral wall of the notochord. The primitive plate sends forward a mass of cells (Fig. 4, ms’bl.%4) detached from the hypoblast and extend- ing almost as far as does the chorda. It is comparable to ms’bl.% of Fig. 2. We do not regard it as a permanent source of anterior mesoblast, rather as evidence of a mesoblast sac. After very careful search it has 25 340 Some Phases of the Gastrulation of the Horned Toad been impossible to discover unmistakable mesoblast cells outside the im- mediate vicinity of that from the embryonic area. On all sides are crowded hypoblast cells derived from the germinal wall, to which the thin epiblast is closely apphed. In several instances mesoblast cells have been seen some distance from the embryonic mesoblast yet so similar in position to isolated mesoblast cells that are undoubtedly migrants from the embryonic area, that it seems safe to assume that they, too, have wandered. All cases of this character have been in the vicinity of iso- lated masses of wandering mesoblast. There is no evidence that up to the age of these two embryos, mesoblast arises elsewhere than around the blastopore. In subsequent stages all mesoblast found in the extra em- bryonic area must be suspected of having its origin in the detached cells which we have already called attention to some distance from the cell mass to which they originally belonged. The caplike elevation of the blastoderm of Phrynosoma gives place to a flat embryonic area. Fig. 5 is a dorsal view of this stage. In this blastoderm the embryonic area was .95 mm. long and .89 mm. wide. A few large yolk spherules can be seen through the blastoderm in front of the blastopore, whence they extend forward over an ever widening area and may be seen around the rim of the embryonic area, except on the posterior side. They may possibly owe their size and form to the action of reagents, but their pecular distribution is, without doubt, due to some structural condition before fixation. It is a very common thing to find in sections, large yolk laden cells engrossed by the hypoblast adjacent to the germinal wall, and beneath this hypoblast, large yolk masses. Hence it seems natural to regard the yolk masses in Fig. 5 as evidence of the rapid addition of yolk-laden formative. cells to the hypoblast from the adjacent yolk mass. From the surface view there is evidence of greater thickness of the blastoderm back of the blastopore than is the case in the youngest stage. This is due rather to the spread of mesoblast than to thickening of the epiblast. The blastopore is less V-shaped than earlier ana more lke a half-moon. The depression between the primi- tive plate cells within the blastopore and the epiblast wall which rises in front of it represents the posterior end of the mesoblast sac. It is V-shaped in section (Fig. 10) opening postero-medianly. The inturned edges of the epiblast along the entire length of the blastopore imply a process of ectodermic invagination along the whole margin. The surface view scarcely suggests the part the primitive plate is taking in this process. This same embryo was subsequently sectioned in a longitudinal plane. Charles L. Edwards and Clarence W. Hahn 341 Fig. 6 is a semi-diagrammatic drawing of a sagittal section, and Fig. 7 of the next section to one side. In the latter the continuity of the epi- blast and primitive plate mesoblast with the anterior mesoblast confirms what has been seen in the surface view with regard to the infolding epi- blast and establishes the lateral growth of the primitive plate mesoblast as well. Hence, both the posterior and anterior lips of the blastopore are undergoing a process of invagination. The yolk masses can be seen adhering to the hypoblast and anteriorly it is receiving additions of large yolk-laden cells from the germinal wall. At this stage the mesoblast bre.ce. can.nent. Fig. 7. ld Fics. 6 anp 7. Longitudinal sections of the embryo represented in Fig. 5. Fig. 6 is sagittal and Fig. 7 is the third section to the right of Fig. 6. can. n/ent., canalis neurentericus; e.’bl., epiblast; glb. vt., yolk spheres; h.’bl., hypoblast; la. pr., primitive plate; ms.’bl., mesoblast; prc. ce., head process; X 109 diameters. canal is an open passage into the subgerminal cavity, the canalis neuren- tericus, (cf. Hertwig, 03, pp. 832-4). The head process has become the lower layer along the middle line. This is due, no doubt, to the fact that its elongation has kept pace with the increase in length of the epi- blast, hence after fusing with the hypoblast in a position near the middle of the embryonic area at the time, this point is carried forward relatively by the rapid elongation of the head process. The hypoblast has not yet grown together under the head process as it does later. While our ob- Some Phases of the Gastrulation of the Tlorned Toad 342 ‘SIOJOUIVIP 0NZ X “6 “STW !SiojouIRIp 006 X °8 “SIA “HTOA “9 °2 $ AOTIOYS0d “a : [TBM [eUTOL.es “A -unw : ayRi[d aATputad “udp Sasetqoday -7qQ, -y -4seR[qide “7q,*a !st~esaop Bpaoyo “p pa ‘adtodoyseq “od, 1q :1OLI0jUB “DD “Bpazogo Soul0d0q 41 e194M JO 9dpa AIBA OYI YB JSBTqosour wItOf 07 UL SUTTAINY YsR[qIde oY} SMOYS 4] ‘JUST OY} OF UOTZOES YxOU 949 ST BSI *peyBagjo A]QQSIYS T[YS St Borw oruOAAQqud SOUL “UBIPOU SI g°oIq “Gg “BIW UY Jepjo [TMs 96R4S BJO SUOTJOOS [RUIPNJISUOT "6 ANY g “SDIY ‘6 “DIT SO RO! Roan A RONG Ks Oanan es Charles L. Edwards and Clarence W. Hahn 343 servations do not confirm the hypothesis, it seems probable that along with the process just described, the space from the median hypoblast in front of the primitive plate to the point where the chorda is in contact with the hypoblast anteriorly is due at first to the degeneration of the hypoblast and lower layer of the chorda invagination which Will, 93, found in the Gecko and represents in Figs. 57 and 58, Pl. 9. Then the rapid forward growth of the chorda carries its anterior contact still farther from the primitive plate hypoblast. In Fig. 7 one may see the anterior reach of the lateral mesoblast which has established the five or six mesoblast cells that are to be seen in the middle line in front of the embryonic area in Fig. 6. Longitudinal sections of a stage which is a little younger than this are represented in Figs. 8 and 9. The cap-like form still persists. Other conditions are essentially the same as in the embryo just described. The head process is fused with the hypoblast and extends to the germinal wall, but the histological differentiation has not taken place in the an- terior third of its length. In Fig. 9 the continuity of the epiblast and primitive streak mesoblast is not different from conditions described in the older embryo of this stage. The extension of the primitive plate cells under the chorda verifies the assertion previously made that the primitive plate mesoblast proliferates or grows laterally and forward as the ventral wall of the mesoblast sac. By so doing it is the counterpart of the epi- blast on the dorsal wall in a single invagination. In this stage the net- work of mesoblast cells to be seen under the primitive plate in Fig. 2, has been replaced by the solid tissue. The condition persists, however, posterior to this region. Three or four sections from the median line this embryo has the same appearance as in the older specimen represented in Fig. 7. Cross sections of this stage are reproduced in Figs. 10-15 Fig. 10 passes through the blastopore where the V-shaped depressions mentioned in connection with Fig. 5 are prominent. Here the epiblast may be seen turning into these depressions and fusing in this section with the epiblast of the floor of the depression in the formation of a lateral growth of mesoblast along the mesoblast sac. The appearance of the nuclei of the epiblast and of the floor of the mesoblast sac is identical, and in mesoblast cells, which are continuous laterally with each of these tissues, there are here and there small dark nuclei, similar to the epi- blast nuclei. These nuclei in mesoblast cells are not met with except in the immediate vicinity of the epiblast and the floor of the mesoblast sac. Under the blastoporic epiblast is a layer of mesoblast of limited lateral extent, which is sharply marked off from the overlying epiblast. This condition prevails in sections back of this point, but three sections an- 344 Some Phases of the Gastrulation of the Horned Toad marg. bl, po. can.nent. itz poe SORC RUSH eee Fig. 15. Caniaient. qigbls @hbt Figs. 10-15. Cross-sections of an embryo of about the same age as Fig. 5, probably a little older. Dl. ’po., blastopore; can. n’ent., canalis neurentericus; cd. d., chorda dorsalis; e.’bl., epiblast; h. 'bl., hypoblast; marg. bl.’po., mar- gin of blastopore; ms. 'Dl., mesoblast; < 200 diameters. Charles L. Edwards and Clarence W. Hahn 345 terior to Fig. 10 the separation cannot be made out (Fig. 12). In the third and fourth section forward (Figs. 12 and 13) several epiblast nuclei are distinguishable in the upper region of this mesoblast layer, otherwise its epiblast character has given place to that of mesoblast. The straggling nuclei indicate that the mesoblast underlying the mesoblast sac is mesoblast derived from the epiblast. Near the anterior end of the neurenteric canal this layer lies on each side of it, Fig. 14. While pos- teriorly the ventral mesoblast is separate from the epiblast of the floor of the mesoblast sac, it is continuous farther forward with lateral meso- blast which is plainly derived from the epiblast, as shown by the isolated epiblast nuclei above referred to. Hence, we are led to conclude that the lateral is derived mesoblast from two ectodermal sources in the sense just as explained. In Fig. 13 the tissue derived from the upper wall of the mesoblast sac in the middle line is the chorda, that from the upper wall on either side of the middle line is the upper layer of mesoblast (ms’bl.'), that from the lower wall of the mesoblast sac is the lower layer of meso- blast (ms’bl.”). In Fig. 14 where the mesoblast sac approaches the hypoblast, it divides the mesoblast from the lower wall of the mesoblast sac so that from here forward there is a lateral layer of lower mesoblast (ms’bl.#) on each side. This condition can be traced forward for sev- eral sections. Ectoderm nuclei may be found here and there in the lateral mesoblast also, Figs. 10, 11, 12. In Fig. 11 is seen the line of juncture of chorda and epiblast just in front of the anterior hp of the blastopore. The chorda is well differentiated from the lateral mesoblast immediately in front of its place of origin (Fig. 12), but it becomes less sharply separated from it as one passes forward (Figs. 13, 14), and but a short distance forward it is quite indistinguishable from the lateral mesoblast. No doubt the differentiation of cells proceeds as a process from behind forward. There is no evidence that the chorda becomes separated from the lateral mesoblast by the fusion of the upper meso- blastic layer with the lower mesoblastic layer as in the Chelonia, Mit- sukuri, 92, (Figs. 14, 15, 16). The significance of these two layers of mesoblast can be no other than that they are the upper and lower wall of a much compressed hollow pouch such as that described in the young- est embryo here figured (Figs. 1, 2 and 3). One must conclude that from the V-shaped depression seen at the entrance to the mesoblast sac in surface view (Fig. 5), and in section Fig. 10, a pouch highly com- pressed laterally has grown forward and laterally in a diagonal direction, that the upper wall of this pouch is derived from the epiblast at the sides and in front of the mesoblast sac and that the lower wall is formed by the spreading of a small knot of epiblast tissue in the floor of the meso- 346 Some Phases of the Gastrulation of the Horned Toad blast sae laterally and forward, that the cavity of the pouch is obliterated to a mere crevice except in the median plane where it remains as the mesoblast sac, in its last condition, the canalis neurentericus, open ven- trally where mesoblast and hypoblast come together. DISCUSSION OF LITERATURE. While the general process of gastrulation in Phrynosoma is similar to that in other reptiles, there are some striking differences. In Hatteria (Dendy, 99) there is a stage when the embryonic area very much re- sembles the cap-like elevation of the Phrynosoma embryo represented in Figs. 1-3. The ectoderm is similarly elevated and thickened, beneath is a cellular mass of hypoblast and on the posterior margin of the area is the blastopore, a depression of considerable breadth. From the vicinity of the blastopore, the mesoblast spreads laterally and the head. process grows forward. * This early growth of mesoblast, when the mesoblast sac is very shallow, exists in Phrynosoma. In Hatteria, however, the head fold either appears much earlier than in any of the lizards, or Dendy’s figure is of a stage in which the blastopore has become closed with age. The lack of information as to further details of the development of the blastopore in Hatteria renders the above comparison of little value. Be- cause of the work of Mitsukuri our knowledge of the embryology of the Chelonia is much more complete. In appearance, the blastoderm of Clemmys Japonica (Mitsukuri 94, Fig. 1, Pl. VI) as seen in surface view, is much the same as the older stages of Phrynosoma after the blasto- derm has flattened on the yolk. None of Mitsukuri’s figures suggest any elevation of the blastoderm. From his figures (Mitsukuri, 94, Figs. 9, 13, 15, Pl. VIII), it is very apparent that in Clemmys there is less cellu- lar differentiation than in Phrynosoma at this early stage. The accumu- lation of yolk in and about the region of the primitive streak obscures the lateral spread of mesoblast. There are certainly no median or lat- eral cellular pockets at this or later stages. Mitsukuri describes a lateral growth of mesoblast from the primitive streak, but does not call attention to any evidence that it is a hollow evagination of the mesoblast sac. Similarly the growth of the head process anteriorly is en masse and gives no evidence of a ventral wall (Mitsukuri, 94, Figs. 15 and 16, Pl. VIII). Only in stages subsequent to the breaking through of the mesoblastic canal and the cellular differentiation of all three germ layers does Mit- sukuri find evidence that the lateral mesoblast is an evaginated growth from between the hypoblast and chorda. There is a somatic and splanch- nic mesoblast, the former continuous with the chorda, the latter con- Charles L. Edwards and Clarence W. Hahn 347 tinuous with the hypoblast which does not pass under the chorda. As we shall point out at another place, the condition here referred to may, and perhaps should, have a slightly different interpretation than that which Mitsukuri has put forward. The spread of mesoblast laterally from the primitive plate begins later in Clemmys than in Phrynosoma if we may assume that the blastopore appears at the same time in each case. The early development of the Squamata differs but slightly in the two suborders. The Ophidia are like the Chelonia in having the cellular dif- ferentiation less marked than the Lacertilia. The shape of the embryonic area in the Ophidia is not clear from Hertwig’s two figures of the earliest stages (Hertwig, 03, Fig. 415, A and B). The blastopore is more or less posterior to the embryonic area. It is a broad, posteriorly arched de- pression with no sharp angles. In slightly iater stages (Hertwig, 03, Fig. 424, A and B) the embryonic area becomes narrow posteriorly, a condition not encountered in Phrynosoma at any time (Figs. 1 and 5). It is but shghtly elevated in the Ophidia and consequently not sharply marked off from the extra embryonic area by a bench (Phrynosoma, Fig. 1). The blastopore of both moves, relatively speaking, into the em- bryonic area as ontogeny progresses. ‘The mesoblast sac in the snake is clearly shown by Hertwig’s figures (03, Figs. 427 and 428). It differs from Phrynosoma in having the epiblast and chorda anlage less thick and less compact and in having no specially marked lateral pockets from the blastopore. Cell islands in the subgerminal region are characteristic of the snake. At the time the mesoblast sac comes into communication with the subgerminal space, isolated groups of cells remain where the lower wall of the mesoblast sac and the hypoblast broke away, thus estab-. ishing the neurenteric canal: (Hertwig, 03, Figs. 430, 431). While this condition probably exists in Phrynosoma, nothing of the kind has been observed in the stages thus far examined. Hertwig’s figures of cross sections (Hertwig, 03, Figs. 443-447) represent a solid outgrowth of mesoblast from the lateral angles of the blastopore and at no place do they reveal a lamination of the mesoblast suggesting a separate origin for somatic and splanchnic layers. The gastrulation of lizards as worked out by Wenckebach, g1, has nothing of striking contrast to the particular genus we are now studying. In Lacerta (Will, 95, Wenckebach, 91) and in Platydactylus (Will, 92, Taf. 6), there is not such a marked elevation of the embryonic area. Both have the mesoblast sac developed in a characteristic way, but con- ditions in the Gecko seem a little more closely allied to those of Phryno- soma. In a very early stage there is a much larger space between the , 348 Some Phases of the Gastrulation of the Horned Toad epiblast and hypoblast of the horned toad than in either of the forms just mentioned. This may account for the greater development of the lateral mesoblastic pouches of the horned toad. No figures of cross sections are given by either Wenckebach, or Will, that represent such a lateral exten- sion of the mesoblast sac, yet it seems probable that they may exist. There is in the blastoderm of the Gecko a condition which corroborates the interpretation we have given above of the gastrulation in Phryno- soma, namely that there are two paired, and one median, hollow pouches derived from the sides and front of the mesoblast sac respectively. In Will’s stage III (Fig. 48 Pl. 7) the nresoblast sae is very shallow, the head process is in evidence and presumably some lateral spreading of mesoblast. In stage IV (Fig 55, Pl. 9) the head process, through the extension of the mesoblast sac has become a long hollow blind sac, flat- tened considerably between epiblast and hypoblast. By the disintegra- tion of the lower wall of the sac and of the underlying hypoblast (Fig. 57, Pl. 9) the mesoblast sac is placed in communication with the seg- mentation cavity. It is obvious that this median sac of the Gecko gas- trula is homologous with the median sae of the Phrynosoma gastrula and that the condition shown in Figs. 2 and 3 is derived in the same manner as that in Will’s Fig. 57, Pl. 9. But Will makes no mention of lateral pouches which are doubtless more conspicuous in Phrynosoma because as we have already pointed out, in the latter, there is no dorso- ventral compression. Will’s explanation of the continuity of the chorda with the hypoblast in the anterior median region of the blastoderm is in full accord with conditions found in late gastrula stages of Phrynosoma. Will describes a similar median pouch in Lacerta viridis (Will, 95b, Fig. 36. RataGi)ie In the early development of some lizards one does find a slight eleva- tion of the posterior margin of the blastoderm (Will, g5a, Fig 36, Taf. 6, L. viridis; Will, 93), but in no sense comparable to the conditions in Phrynosoma. In other cases there is no suggestion of it (Weldon, 83, Wenckebach, g1, Strahl, 82). Conditions in the formation of the em- bryonic area and mesoblastic pouch in Lacerta are substantially the same as in the Gecko (Wenckebach, 91). There are some minor differences in the development of the chorda. The unpaired median invagination even at the very beginning forms a compressed triangular shaped cavity in the lizards, while it is much less compressed at first in Phrynosoma, becom- ing more and more compressed later. As in the Gecko, the genus Lacerta does not develop mesoblast by prominent hollow lateral pouches from the antero-lateral sides of the mesoblast sac. In fact, there is some con- fusion as to the exact origin of the mesoblast. Some authors (Will, 95b) Charles L. Edwards and Clarence W. Hahn 349 state that it arises, in part, from hypoblast budding before invagination and in part grows forward as a solid mass from the anterior region of the mesoblast sac in the middle of which the chorda becomes differen- tiated (Weldon, 83, Balfour, 79, Will, 95). Other investigators derive all the mesoblast from the sides of the chorda and from a lateral growth of the primitive plate after invagination has begun (Wenckebach, 91, Strahl, 83). There is a very close resemblance of the cross sections of Phrynosoma embryos in late gastrula stages, to cross sections of Lacerta and the Gecko figured by Will (95b, Figs. 43°, 44°, Taf. 7; 93, Figs. 59b, Taf. 10-Taf. 36 and of Clemmys figured by Mitsukuri, 92). Mitsukur1 interpreted this condition as showing that the lateral mesoblast has been derived by a process of cell budding and an outgrowth from the edges of the chorda and the median margin of the hypoblast. Assuming that the absence of true hollow lateral sacs in Lacerta does not forbid one from regarding the lateral solid growth of mesoblast as having its origin in the primitive streak together with epiblast infolded on either side of the chorda anlage, one must regard the two layered mesoblast as having arisen in part from a posterior source and having migrated forward and also from the sides of the mesoblast sac as far forward as it may have extended. This agrees perfectly with the decrease in mesoblast as one passes forward as found by Mitsukuri in Chelonia (Mitsukuri, 92, Figs. 14,15 and 16). But from this point of view, one cannot say that the mesoblast is derived from the hypoblast, nor is there any evidence in Phrynosoma that such is the case. The close connection of the hypo- blast and splanchnic layer ef the lateral mesoblast is a necessary conse- quence of the breaking away of the hypoblast and lower wall of the me- dian invagination, or mesoblast sac, placing the chorda in contact with the hypoblast anteriorly and leaving the broken edges of splanchnic mesoblast and hypoblast on either side to grow together later as Mit- sukuri describes when he says the point* moves to the pointy (92, Fig. 16). According to the interpretation here given the somatic mesoblast will probably receive additions farther anterior than the splanchnic, the latter having a posterior source as its feeder and the former both a pos- terior source and possibly anteriorly from the chorda anlage. By compar- ing Fig. 13 with Fig. 15 we find the splanchnic mesoblast decreasing in lateral extent. In fact, there is practically no evidence in Phrynosoma that either the chorda or hypoblast contributes anything toward the ori- gin of the mesoblast. Will, in his descriptions of the Gecko, has already presented the view here set forth, but Mitsukuri, 92, states that in Che- lonia the hypoblast turns upward laterally to become the splanchnic layer of mesoblast and that the chorda contributes to the somatic mesoblast. 350 Some Phases of the Gastrulation of the Horned Toad The egg of Phrynosoma stands in closer relation to the lower vertebrates than any other amniote in that the protoplasmic pole of the egg seems less encumbered with yolk, the blastoderm at least is so elevated that processes going on in it are quite as independent as in the Amphibian egg. We may say that the development of this iguanid is a link in the chain of evidence which supports the Weldon, 83,-Will, 93, theory of yolk cleavage wherein the lower layer tends toward the cleavage of the whole mass of the yolk as in the Axolotl, and the molluse Bythinia tentaculata, figured by Weldon. LITERATURE CITED.’ Ba.rour, F. M., 79.—On the early development of the Lacertilia, together with some Observations on the Nature and Relations of the Primitive Streak. Stud. morphol. lab. Univ. Cambridge I, id., Quart. J. Micr. Sen ve 1942 pps a ple BaLLowiTz, E., o1.—Ein Kapitel aus der Entwicklungsgeschichte der Schlan- gen: Die Schicksale des Urmundes bei der Kreuzotter und der Ringelnatter. Verhandl. anat. Ges., pp. 80-88, 11 figs., Bonn. BaLLowI1z, E., 05.—Die Gastrulation bei der Blindschleiche (Anguis fragilis L.). 1: Die Gastrulationserscheinungen im Flachenbild. Ztschr. f. wissensch. Zool., v. 83, Nov. 10, pp. 707-741, pls. 28-37. DeENDy, ARTHUR, g9.—Outlines of the Development of the Tuatara Sphenodon (Hatteria) punctatum. Quart. J. Micr. Sc., v. 42, pp. 1-87, pls. 1-10. EDWARDS, CHARLES LINCOLN, 96.—Notes on the Biology of Phynosoma cornu- tum Harlan. Zool. Anz. (498), 1896. EDWARDS, CHARLES LINCOLN, 03.—A Note on Phrynosoma. Science, N. S., v. 17 (488), May 22, pp. 826-827. Gapow, H., 0r1—Amphibia and Reptiles. Lond., 1901, pp. xiii, 1, 668, 181 figs. GERHARDT, U., o1.—Die Keimblattbildung bei Tropidonotus natrix. Anat. Anz., v. 20, pp. 241-261, 17 figs. GERHARDT, U., o2—Nachtrag zu der Abhandlung “ Ueber die Keimblatter- bildung bei Tropidonotus natriz.” Anat. Anz., v. 20 (27), pp. 570- Sia. HerRTWIG, O., 03.—Die Lehre von den Keimblattern. Handb. d. vergl. u. Ex- periment. Entwicklungslehre, v. 1 (1), pp. 699-1018, figs. 246-670. MitsvuKkuRI, K., 92.—Contributions to the Embryology of Reptilia. 38: Further Studies on the Formation of the Germinal Layers in Chelonia. J. Coll. Se. Imp. Univ. Japan, v. 5 (1), 18 pp., 3 pls., Tokyo. MitsuKkvrI, K., 93——On the process of gastrulation in Chelonia. Contribu- tions to the Embryology of Reptilia (4). J. Coll. Se. Imp. Univ. Japan, v. 6, pp. 227-277, 3 pls., 4 figs., Tokyo. PETER, KARL, 04.—Normentafel zur Entwicklungsgeschichte der Zauneidesche (Lacerta agilis). Normentafeln zur Entwicklungsgeschichte der Wirbeltiere, by Keibel, F. (4), 165 pp., 4 pls., 14 txt. figs. 7A complete bibliography of the embryology of Reptiles is found in Peter, o4. Charles L. Edwards and Clarence W. Hahn 351 STRAHL, H., 82.—Beitrage zur Entwicklung von Lacerta agilis. Arch. f. Anat. u. Physiol., Anat. Abt. (Lacerta agilis), pp. 242-278, 2 pls. STRAHL, H., 83.—Ueber Canalis neurentericus und Allantois bei Lacerta viri- dis. Arch. f. Anat. u. Physiol., Anat. Abt., pp. 323-340, 1 pl. WELDON, W. Fr. R, 83.—Note on the early Development of Lacerta muralis. Quart. J. Micr. Sc., v. 23 (2), pp. 134-144, pls. 4-6. WENCKEBACH, K. F., g1.—Der Gastrulationsprozess bei Lacerta agilis. Anat. Anz., Vv. 6, pp. 57-61 and 72-77, 15 figs. Wit, L., 92.—Beitrage zur Entwicklungsgeschichte der Reptilien. 1: Die Anlage der Keimblatter beim Gecko. (Platydactylus facetanus.) Zool. Jahrb., Abt. f. Anat. u. Ontog., v. 6, pp. 1-160, 11 pls., 14 figs. Wut, L., 93.—Beitrage zur Entwicklungsgeschichte der Reptilien. 2: Die Anlage der Keimblatter bei der menorquinischen Sumpfschildrote (Cistudo lutaria Gesn.). Zool. Jahrb., Anat. Abt., v. 6, pp. 529-615, Re plse ela nese Witt, L., 952.—Ergebnisse einer Untersuchung des Gastrulationsprozesses der Eidechse. Sitzungsb. d. k. Preuss. Akad. d. Wissensch., pp. 335-342. WILL, L., 95>.—Beitrage zur Entwicklungsgeschichte der Reptilien. 3: Die Anlage der Keimblatter bei der Hidechse. Zool. Jahrb., Abt. f. Anat., v. 9, pp. 1-91,'°7 pls:, 17 figs. Wut, L., g5e.—Die neuesten Arbeiten tiber die Keimblattbildung der Amnio- ten. Zusammenfassende Uebersicht. Zool. Zentribl., v. 1 (4/5), pp. 129-139, 15 Figs.; (8), pp. 297-304; (9), pp. 337-340. Witt, L., 97.—Die oberflachliche Furchung des Reptilieneies. Arch. Freunde Naturgesch. Mecklenburg, v. 50, pp. 169-189, 2 pls., 5 figs. Wu, L., 98.—Ueber die Verhaltnisse des Urdarms und des Canalis neuren- tericus bei der Ringelnatter (Tropidonotus natriz). Sitzungsb. Akad. Wiss., Math.-phys. Klasse, pp. 609-618, Berlin. Wut, L., 99.—Ueber die Verhdltnisse des Urdarms und des Canalis neuren- tericus bei der Ringelnatter. Biol. Zentrlbl., v. 19, pp. 396-407, 6 figs. 26 = é eo a ae ay ~) SOME RACIAL PECULIARITIES OF THE NEGRO BRAIN. BY ROBERT BENNETT BEAN, Instructor in Anatomy, University of Michigan. From the Anatomical Laboratory of the Johns Hopkins University. WirH 16 Ficures, 12 CHARTS, AND 7 TABLES. From time to time in the past hundred years attempts have been made to determine the distinctive points of difference between the Caucasian and the Negro brain. While differences in skull capacity, in brain weight and size—especially of the frontal lobes—or in the gyri have been demonstrated by Gratiolet, Tiedemann, Broca, Manouvrier, Peacock, Marshall, Parker, and others,—more recently by Waldeyer in Germany and by Elliott Smith in Egypt,—yet no exact measurements of the brain, such as we have of the skull, are to be found.’ An effort will be made to show by measurement of outline drawings of brains in different positions, by composites of these outlines, and by actual drawings from individual brains that there is a difference in the size and shape of Caucasian and Negro brains, there being a depression of the anterior association center and a relative bulging of the posterior association center in the latter; that the genu of the corpus callosum is smaller in the Negro, both actually and in relation to the size of the splenium; and that the cross section area of the corpus callosum is greater in relation to brain weight in the Caucasian, while the brain weight of Negro brains is actually less. The amount of brain matter an- terior and posterior to the fissure of Rolando is roughly estimated, but other points of possible difference, as in the gyri, the insula, the opercula, the “ Affenspalte,” the proportions of white and gray matter, and the cerebro-cerebellar ratio are necessarily omitted in this study. In December, 1904, I reported to the Association of American Anato- mists the results of the measurements of fifty-four brains, thirty-seven from American Negroes, and seventeen from American Caucasians, Since 1The brains measured for this work are in the Wistar Institute under the same numbers given in Table I. AMERICAN JOURNAL OF ANATOMY.—VOL. V. 27 354 Some Racial Pecuharities of the Negro Brain that time I have examined about one hundred additional brains, making in all one hundred and fifty-two, of which one hundred and three are from American Negroes and forty-nine are from American Caucasians. The work was undertaken at the suggestion of Dr. Mall, as a result of information by Dr. Hrdlicka, of the U. S. National Museum, that racial differences exist in the Negro brain. Dr. Hrdlicka had observed par- ticularly that the brain of the full-blood Negro has relatively small volume and straighter lines anteriorly to the central fissure, the sides of the Caucasian brain over the same area showing, even in dolichocephals, more mass and arching. I wish here to express my hearty appreciation for the interest Dr. Hrdlicka has displayed in my work since its incep- tion and for his generosity in allowing me to make this study. Most of | the brains studied are from the collection at the Anatomical Laboratory of the Johns Hopkins University and were placed at my disposal by Dr. Mall who has also controlled the measurements taken. Some of the specimens were obtained through the courtesy of Dr. Page from the Baltimore City Alms House, and some from Dr. W. G. MacCallum, of the Pathological Department of the University In order to make more exact measurements and comparisons of the brain it is necessary to determine the more fixed points, from which to measure the more variable, and at the suggestion of Dr. Mall the follow- ing arbitrary line was passed through the brain as an axis, and its mid- point naturally becomes the brain center. The details regarding these will be discussed later on (p. 404). At this point I wish to state that the axis passes between the hemispheres through the brain stem, passing just above the anterior commissure and just below the splenium (Fig. 2a). The axis usually measures the greatest length of the brain. The position of the brain center is in the middle of the axis and varies but slightly in different specimens. It is seen that the surface of the brain can be measured in great part by extending radii from the center to the surface which may also be marked in degrees,— of latitude and longitude.” The outlines of the brain are generally given in sagittal section (0°), in transverse section (90°, right or left), and by rotating the brain on this axis to a point midway between these two (45°, right or left). “ Ante- rior” has not been separated from “ posterior,” but the numbers from 0° to 180° are used rather than an “equator ” with 0° to 90° for the anterior half of the brain and 90° to 0° for the posterior half. The first table (Table I) gives a list of the brains from which drawings and measurements were made. The brains are arranged in eight groups, owing to the different methods used in their preservation. Robert Bennett Bean _ 355 TABLE I. RECORD OF MATERIAL USED. Number of Cadaver. Group. ee ee ee ee ee ee eee ee ee ee eee ee ee : ; j D 42 ne oc: rr OS 3 = nae E BS a =| Z (3) “4 —Q Po q anes 8 = ot As! gs & o “4 san no 3 z See een rch a oc Be 3 2 iy AS, 5 ) 5 cS) oe > 3 Ho. 2 2 oO 2, 3 4 Sh ARS 4) Uy pean 3 3 id 3 i} ° q o i) oS es 4 z ~ a 2 p> » A a ~ ° og of : é ao aa Ors _S a ~o ad o) } bp 2 ap © = (o} Sp 5 — He q +. © 5) 4 aie ae Oi a i 3 23 = 0 3 4s Re Es Ha ® Rs ZS On ry < cs L Pee Sas at = o Ss Negro Male (1400) 13880 770 Side aiare Hanging Negro Male (1420) 1400 668 tele cous Hanging Caucasian Male Serie Sardis 805 fos O06 Asthenia Negro Male joan Rete 610 eters ROOD Asthenia Caucasian Male (1430) 1410 700 Sete Bos Asthenia Negro Male ates 1157 qo 188 Medium Tuberculosis Negro Female (1170) 1150 643 188 37.2 Asthenia Negro Male (1890) 1370 710 152 41.2 Pneumonia Negro Female (1820) 1300 640 152 52.5 Alcohol Negro Male (1245) 1225 492 163 46.7 Frozen Negro Male (1135) 1115 605 160 55.8 Tuberculosis i Caucasian Male (1358) 1330 653 168 47.2 Asthenia 1 Negro Male (1150) 1130 706 165 43.1 Pneumonia 2 Caucasian Male (1200) 1180 630 173 46.7 Nephritis 6 Caucasian Male (1840) 1320 735 173 47.6 Pneumonia 1 Negro Female (1080) 1060 602 147 89.0 Pneumonia 2 Caucasian Male (1555) 1535 730 188 86.2 Pneumonia 3 Mulatto Male (1440) 1420 722 183 70.3 Tuberculosis fe 1 Negro Male 5006 seas 642 apts Sooc Tuberculosis 34 1 Caucasian Male (1185) 1165 453 178 tial Asthenia ate 0 Negro Male (1100) 1080 522 157 61.2 Heart disease 0 Negro Male (1060) 1040 438 157 61.2 Tuberculosis 0 Negro Male (1135) 1115 525 165 72.6 Tuberculosis 1 Negro Male (1355) 1335 bes 168 81.6 Heart disease 2 Negro Male (1240) 1215 533 163 63.5 Nephritis 5 Negro Female (1145) 125 4 be lind: 47.6 Nephritis 2 Negro Male (1200) 1180 663 178 72.6 Tuberculosis 7 Negro Female (1130) 1110 603 154 Allg 0h Wontesh: crane 2 Negro Male (1875) 1355 730 176 86.0 ° Hemorrhage 2 Caucasian Female (1010) 990 463 163 44.2 Asthenia 0 Negro Male (1270) 1245 687 186 68.0 Shot 7 Negro Female (1025) 1005 368 188 72.6 Heart disease 1 Caucasian Male (1280) 1260 773 190 75.0 Pneumonia 1 Caucasian Male (1500) 1480 910 193 67.1 Heart disease 3 Negro Male (1185) 1165 458 127 27.9 Epilepsy 1 Negro Female (1035) 1015 525 157 86.0 Heart disease 5 Negro Male (1360) 1340 AO 168 77.1 Suffocation 20 Negro Male (1245) 1225 568 178 85.0 Heart disease 1 Caucasian Male (1390) 1370 742 178 85.5 Pneumonia 3 Negro Male (1270) 1245 645 163 48.0 Typhoid 4 Negro Female ( 910) 893 427 176 40.8 Asthenia il Negro Female (1060) 1040 620 154 46.3 Tuberculosis 2 Negro Female (1225) 1205 557 163 72.6 Pneumonia 1 Caucasian Male (1300) 1280 Ne 188 84.0 Pneumonia 6 Caucasian Female (1190) 1170 568 171 59.0 Tuberculosis 2 Negro Male (1130) 1110 614 157 75.8 Heart disease 2 Caucasian Male (1330) 1310 666 163 80.8 Tuberculosis 9 Caucasian Male (1480) 1460 722 160 64.0 Heart disease 0 Negro Female (1045) 1025 487 163 62.0 Pneumonia 0 Negro Male (1120) 1100 500 . 130 34.4 Pneumonia 3 356 Some Racial Peculiarities of the Negro Brain TABLE I.—ConrTINvUED. AQABA ARBAOn TMNT WAST NWN TWT HHH Bee ee Pepto ee Group AAAAMD ry 2 - s 4s ° oe H 2 2) E| ra m Oo a a ee 3 5 % 2 Z < fen} 1520 40 Caucasian 1521 32 Negro 1522 36 Caucasian 1523 40 Negro 1524 35 Mulatto 1526 11 Negro 1527 77 Caucasian 1528 37 Negro 1529 42 Caucasian 1530 70 Negro 1581 25 Mulatto 1532 65 Mulatto 1533 50 Negro 1538 67 Caucasian 1544 27 Negro 1553 42 Mulatto 1582 19 Negro 1583 80 Caucasian 1591 67 Caucasian 1593 43 Mulatto 1650 28 Mulatto 1653 29 Negro 1659 63 Negro 1660 82 Negro 1661 73 Negro 1662 45 Neero 1667 81 Negro 1678 42 Negro 1680 62 Nevro 1681 45 Negro 1682 85 Caucasian 1683 42 Caucasian 1684 50 Negro 1685 65 Negro 1686 35 Negro 1687 64 Negro 1690 40 Caucasian 1691 62 Negro 1692 24 Caucasian 1693 50 Caucasian ‘1695 66 Mulatto 1696 45 Caucasian 1697 74 Caucasian 1699 32 Negro 1700 28 Negro 1701 39 Negro 1702 45 Caucasian 1704 50 Negro 1706 73 Negro 1707 77 Caucasian o wal Male Female Female Male Male Male Female Male Male Male Female Male Male Male Female Female Male Female Male Female Male Female Female Male Male Female Male Female Male Male Male Male Female Female Female Female Male Male Female Male Female Male Female Male Female Male Male Male Male Male (fresh). Weight of brain in gm. (1540) (1230) (1065) (1145) (1180) (1140) (1410) (1475) (1010) (1100) (1420) (1170) (1310) (1160) (1140) (1275) (1235) (1000) 1050 1560 1040 1219 1080 1380 1320 1220 1230 1090 980 1450 1200 1250 1320 1140 1410 980 1200 1225 1400 1200 1340 1335 1275 Weight of brain in gm. (when measured). Ov bo o 1210 1045 1125 1160 1300 1120 1390 1455 990 1080 1400 1150 1290 1140 1120 1255 1235 1000 1050 1520 1000 1210 1020 1060 1290 1265 1170 1100 1040 925 1420 1160 1235 1250 1055 1340 955 1205 1185 1355 1132 1275 1255 1175 h Ba aH : ats a eg a | 1 ) ae AS S) mH ~& eS A ie leer = S Dn > . Fe Se Boo ee = = eae Brust heros 2 E 2. a Sat er eee S odd hee ° + Se ie Ss — eH as! ~ (2) °o a o S ° kg; ~ = rob) w mo oc 2 ga Bo = a 52 880 aa Og 2 5 a8 50g qn ee aes 2 2 Ce) Q . wd. Se 3 og of 3 = we O88 ee ye ek is A ae 6 Cie hae 2 S < as ao o <=) a o 1S ef 2 g = g ; Eco Yea=p Geechicimnn Se ey a eS) Aisio 5 bo 2 a oF OF ag oe 3 of S22 ame: xm D ee eas Bia a s) Sei 1708 60 Caucasian Male 1350 1295 610 183 Mileles © TV thasicrises 4 j 1709 26 Negro Male 1475 1410 825 165 Woke. MON A” Asa ctomerets 43 . 1711 80 Negro Male 1175 1090 620 173 CRED yeh cst 29 A 1712 70 Caucasian Male 1325 1210 710 185 LK Uae A PAD NS CE Aros ne 1713 49 Negro Male 1240 1175 680 175 49.4 Asthenia 29 1715 20 Negro Female 950 860 405 137 DUES bebe! ald ciate ctaveso¥ 53 De 1716 48 Caucasian Male 1265 1238 500 167 Bebe ole Ms eerie as Ms bis 1718 22 Negro Male 1200 1130 765 170 70.3 Tuberculosis 29 3 719 46 Caucasian Male 1445 1855 880 193 79.4 Nephritis ats 2 1720" 53 Caucasian Male 1430 1245 760 186 59.0 Pneumonia 1 1722 19 Negro Female 1050 1010 520 173 SOO ee sistent 46 4 1723 38 Caucasian Male 1275 1230 545 165 Ieee MP Sodeatend Ao 5 1727 55 Negro Male 1265 1227 710 157 Light Tuberculosis 22, 4 1728 50 Negro Male 1830 1270 675 162 56.7 Accident 50 0 1729 53 Negro Male 1410 1460 ia 182 Medium Heart disease 50 5 1730 22 Negro Female 1005 915 525 150 Light Tuberculosis 36 2 1731 70 Negro Male 1450 1415 820 179 67.0 Nephritis 35 4 1734 50 Caucasian Male 1360 130 yO 172 Heavy Nephritis Be 2 1736 82 Negro ' Male 1310 1245 570 162 53.0 Asthenia 28 ‘te 1788 22 Negro Male 1275 1240 635 168 49.9 Tuberculosis 27 5 1789 73 Negro Male 1120 1060 ee 168 Light Tuberculosis 29 5 1741 50 Negro Male 1220 1175 ale 163 Heavy Heart disease 46 3 1748 60 Caucasian Male 1520 1475 820 175 56.0 Tuberculosis 51 4 1749 74 Caucasian Male 1040 1030 750 160 57.6 Nephritis ae 2 2469 35 Negro Male Raves 1150 585 180 oom ~SCwaoroad ; 0 2521 23 Negro Male 1895 1290 490 172 Heavy Pneumonia 27 0 2522 38 Negro Male 1350 1270 640 170 Heavy Pneumonia 42, 0 2524 45 Negro Male 1350 1230 660 154 Heavy Heart disease 36 0 2535 24 Negro Male sisje 1065 615 170 Medium Tuberculosis 34 0 87 Negro Male : 1150 583 ste saoos, MO" i Micocubarc 56 0 163 48 Negro Female 1130 920 485 165 Heavy Cancer Brown 0 164 57 Caucasian Male sees 1145 575 Shere eretche Nephritis sf 0 169 87 Caucasian Male 1110 1060 430 Cancer 0 172 45 Negro Male ee 1020 625 date Ateees, Sane Wh aan ree 0 173 45 Negro Male 1245 690 163 Heavy Nephritis 0 177 15 Caucasian Male ahi 950 420 siete dose Tuberculosis 5 0 193 29 Negro Male ane 910 430 175 Light Tuberculosis Brown 0 1G. 58 Caucasian Male 1240 990 588 SB Semehe Cy | )wretestasiere HE 2G. 48 Caucasian Female 1106 900 BOB) cater helersts | ieisisvereinvnve 5 8G. 48 Caucasian Male 1250 1110 (CUM Ao able ae id SDS OoSe 4G. 53 Caucasian Male 1300 990 CU SS. moDOn neoceseS 5G. 16 Caucasian Female 915 840 IEE” Soper cape ~ Abeaease 6G. 25 Caucasian Male 1460 1080 GAN” batt. sooen. . “weooecuoome 105 1 Negro Male AGO 860 445 Hothe a baOe ) a, WOOO oe 107 2 Negro Male . 830 540 (il * “ood © 1» woodedare 39 108 Ihe? Negro Female 435 155 53 By we ee PES Gone 53 2 109 Phot Negro Male 700 245 58 ACN We | Usisiacycters 52 uf 110 1 Negro Male 525 190 55 3.4 Birth 53 aie 111 6* Negro Male 600? 255 ators SScOLA Ee eicopocsas are 112 6* Negro Male COOP ISO ee mB ccr Ate, MM at Mejerdiscctcle 113 7 Negro Male See te Birth 114 2 Negro Male SOO SOUR ates e. Feces Lh Ryeteroetorcte * Months. + Birth. 358 Some Racial Peculiarities of the Negro Brain TABLE I. RECORD OF MATERIAL TAKEN FROM RETZIUS AND SPITZKA,! | ; a a 5 ee ees = q o 5p ales &p S) oS — Oe ; si 5 3 o Cote ee A a co) © a ° 2 HD =} s 2 e a o re 2s [| § ee =| SoU Macey ee 5 z q $2 & 3: Sime =I A 0 iS) 3) 3 Fa as) S = >) ) Z 73) exhibit a characteristic adult female Negro brain and a small adult female Caucasian brain for comparison, the two being selected because they are so nearly alike, yet the racial differences are noticeable. The frontal lobes of the female Negro brain are long and slender, while the parietal region is full and bulging. The peculiaries noted in the other outlines may be seen in these also. Examination of about fifty Negro skulls, and hundreds of Negro heads has convinced me of a noticeable characteristic: the appearance to be 366 Some Racial Peculiarities of the Negro Brain obtained by a view from behind at an angle of about 30° above the hori- zontal looking directly forward. 'The outline of the head or skull seen in this way is pointed anteriorly and broad and flattened posteriorly. This may be seen in the Negro brains under the same conditions. Here we see the small frontal lobes, the large parietal region and the straight, flat sides over the anterior association centers. That this is not only ap- parent, but real, may be determined by measurements of the radii from the brain center to the outlines of the plane passing through the brain axis at an angle of 45° above the horizontal plane of each hemisphere. Such measurements are found in Table II, which gives the dimensions of this plane in each non-distorted brain. Radii are projected from the brain center for each 10° angle, and perpendiculars are dropped from the brain axis for each centimeter on the axis from either end of the brain, and these radii and perpendiculars are measured from their origin out to the surface of the brain. From Table II the following summary is given: TABLE II.a AVERAGES OF THE ASSOCIATION CENTERS. LEFT SIDE RIGHT SIDE Z eer 4 5 Se E Spas ene ae o: 8. & 2 & ses D QD S) Bog SR Tee ed ae bh cal =o oo Dp) uM 4 oO oo De eS pee ee es ee ee ees fee os) oso a a 8 8 a 25 Ar 3 & Be soe. eS Sh iS ao Se) eis IZ ncc) < a pa ra fee 4 aw = mm. mm. mm. mm. mm. mm Caucasianymalenas-acmec ot) GlGSe 0) rill 9 Se ers 4 eee Orne Omen opera ING@erosmale. Scarce. sroce 43 168 66 73 90 45 168 66 74 89+ Caucasian female ....... 8 161 GA mG (aneeeg.6 8 160) 46h = Ciao INesro femailley ce eisc ciacer 22 158 62 68 91 22 158 63 69 91 The numbers represent averages in each case for the number of brains given. The fifth column of numbers on each side represents the averages of indices of the association centers. The index of the association centers for each brain is obtained by dividing the length of the radius for each center by the length of one-half the brain axis, and dividing the result ob- tained for the anterior association center by the result obtained for the posterior association center. The quotient represents the proportion of the size of the anterior association center in terms of the posterior asso- ciation center, the latter being 100 in each case, the brain axis also en- Robert Bennett Bean 367 tering as an element. For each increase of 20 mm. in the length of the brain axis there is an increase of about one unit in the index. For ex- ample, the index for the left hemisphere of the male Caucasian brain is 98, the length of the radius to the anterior association center is 70 mm., that to the posterior association center is 71 mm. 70:71 ::98: 100 is correct, considering the brain axis element 84 mm. Increase the latter and the index rises, reduce it and the index falls. The index varies, directly with the size of the anterior association center, and inversely with the size of the posterior association center. Increase 70 and the in- dex is increased; diminish 70 and the index is diminished. Increase 71 and the index is diminished; diminish 71 and the index is increased. The index gives a simple numerical expression that may be used to ad- vantage in the comparison of brains, and in the comparison at present in hand it affords an excellent indication of existing differences. It is ob- served from the table that the index of the male Caucasian brain is the largest; the index of the female Caucasian comes next; with the female Negro third, and the male Negro the lowest. This indicates that the rela- tions of the brain axis and anterior association centers are similar to the index of the association centers, while the posterior association center is dissimilar in the two sexes and races. The index is shghtly larger on the left side, except in the female Caucasian. This may be due to the gyrus frontalis inferior, or to a larger motor area on the left side in the males. The relative differences of the association centers in the males of the two races on the right side are represented in Fig. 11, which is a com- posite of the 45° outline of the thirty-four male Caucasian and the forty- five male Negro brains The brain axis is practically the same length in each (167-8 mm.). A difference in the size and shape of the two out- lines is evident on the inferior surfaces of the frontal and occipital lobes below the axis, as well as above it, the Caucasian brain being further be- low the axis and more curved along the frontal lobe, while the Negro brain is further below the axis and more curved along the inferior surface of the occipital lobe, a difference which materially diminishes the size of the frontal lobe in the Negro and increases the size of the occipital. The flatness of the anterior association center is seen in the Negro outline, and the actual areas of the parts of these outlines are as follows: Area of the anterior lineal half of the composite Negro outline...48.4 sq. cm. Area of the anterior lineal half of the composite Caucasian EADS LAS peal a Res OOO MCRD CO.CC. CHOICE CORA DORER ARRON CROP eo lor t=O eGo 01k Area of the posterior lineal half of the composite Negro outline...48.2 sq. cm. Area of the posterior lineal half of the composite Caucasian OLE GIS RIED, OEIC EN ORT DICE O DIDIC ORO eRe ECR OG ORION 56.2 sq. cm. INDIVIDUAL BRAINS CAUCASIAN fe) NEGRO r MULATTO © ; CN =) 09 60 65 70 5 80 MM CHART I. Right Side.—Relation of the radii of the anterior association center (ordinates) to the radii of the posterior association center (abscissie); taken with the brain tilted 45°, the former at 60° from the anterior end, the latter 120°, as in Figure 3». The perpendicular line OWN gives the mean for the anterior association centers for both races; the horizontal lines C, N, for the posterior association centers of the Caucasian and Negro respectively ; and the diagona lines are the mean of both centers; for the Caucasian, C, for Negroes, N, and for both races combined, M@. This is true of the first four charts. Robert Bennett Bean_ 369 That these differences are manifested not only in mass, and by aver- ages, but individually, may be determined by examining Table I, and Charts I and II, taken from the numbers in Table II, and giving the relation of the anterior and posterior association centers in each brain. The anterior association center in all cases is represented by the numbers from the column under 60°, the posterior association center by the num- bers from the column under 120°. The charts are made up by the use of ordinates and abscisse, the former representing the length of the radii of the anterior association center, the latter the length of the radii of the posterior association center. An arbitrary line drawn on the charts from the 68-mm. ordinate on each side divides the symbols into racial groups, the Caucasian above the line and the Negro below, indicating a longer radius to the anterior association center in a larger number of brains among Caucasians. This line divides the two sides differently. On the left side a larger number of Caucasian symbols fall below the line and a larger number of Negro symbols fall above the line than on the right side. The symbols that are over the line represent the extremes of each race in relation to the other race. A greater number of Negro extremes have a larger left anterior association center, and conversely, a greater number of Caucasian extremes have a smaller left anterior as- sociation center. The extremes may be represented by a table taken from Charts I and II. TABLE IIb. EXTREMES OF THE ANTERIOR ASSOCIATION CENTER. Left Side. Right Side. a {A Sanbols Above the Below the Above the Below the y ° arbitrary line. arbitrary line. arbitrary line. arbitrary line. @WaMGASTAN) 2.5 ales oe stesis se 24 16 Dine 11 INGETO® ace are-eis ove teisans exes) s/o. 15 45 10 50 The numbers in this table are of value only in comparing the two sides of the body. On the left side there are 16 Caucasian extremes and 15 Negro extremes. On the right side there are 11 Caucasian extremes and 10 Negro extremes. The deduction from this is that there is greater dissimilarity of the brains of the two races on the right side than on the left side. The majority of the Negro symbols fall below the line, and the majority of the Caucasians fall above on each side, this being the most noticeable difference, that the anterior association is smaller in the Negro than in the Caucasian. The radius to the anterior association center of the left hemisphere invariably passes over the gyrus frontalis inferior, so that this may mean a greater development of the gyrus in the 28 : 370 Some Racial Peculiarities of the Negro Brain Negro extremes, and a less development in the Caucasian extremes. It is possible that the size of the motor area may account for this differ- ence on the two sides. INDIVIOUALBRAINS Jaq qn C CAUCASIAN + 0 NEGRO - 8 ve MULATTO - © | | | ee CP ee Cuart Il. Left Side—Relation of the radii of the anterior association center (ordinates) to those of the posterior association center (abscisse). See Chart I, Legend. A system of means is adopted for the charts. Extremes are avoided in this way, and a medium for comparison is obtained which is fairer Robert Bennett Bean ~ 371 and more readily visualized on the charts than would be the case with averages or curves. Horizontal lines are drawn on the charts to represent the means of the radii of the anterior association centers (ordinates), vertical lines are drawn to represent the means of the radii of the pos- terior association centers (abscisse), and lines are drawn at 45° from these to represent their combined means. In Chart I the Caucasian or- dinate mean is 69.5, the Negro ordinate mean is 65.5, 1. e., the Caucasian brains have a mean radius to the right anterior association center of 69.5 mm., while the mean radius to this center in the Negro brains is only 65 mm long. The Caucasian and Negro abscissa means are the same, 72.5 mm., therefore the mean radius to the right posterior association center is the same in the two races. A comparison of the means of the two sides taken from Charts IT and II is found in the following table: TABLE IIc. MEANS OF THE ASSOCIATION CENTERS. Left Side. Right Side. Ca 2 = —_ Bo 68 #2 68 2 Em Difference of the a8 Ha Difference of the oO Qs combined means. on ge combined means. ee oe i, iS <5 a << <5 <4 Caucasian ... 69 (als 71.25 — 70 =.1.25 69.5 TS 72.5 — 70 =2.5 ING2ZTOP cas sis es 65 zed 76.5 —70—6.50 65.5 UAE ih. ——10'==7,0 The ordinate means are slightly larger on the right side than on the left side in the two races, hence the mean anterior association center is larger on the right than on the left. It is demonstrated (Table II*) that the averages of the anterior association centers are slightly larger on the right side than on the left in the females of the two races, but the relative difference is in favor of the left side in both male and female. This is evi- dent from the index of the association centers (Table II *) and from the differences of the combined means (Table II¢). The differences of the two sides are slight and may be negligible in the means and the averages. On the other hand the extremes (Table IL”) present a marked racial dif- ference in relation to the two sides of the brain, the left anterior associa- tion center being large in the Negro extremes and small in the Caucasian extremes. The conclusion is that the extremes affect both the means and the averages, explaining the apparent contradiction in each. The abscissa means are the same for all, except on the left side of the Caucasian which is 1 mm. less than the others. This indicates a smaller posterior associa- tion center on the left side of the Caucasian. The differences of the com- ~> Oo Some Racial Peculiarities of the Negro Brain © bined means for the two races (45° lines) are obtained by subtracting the ordinate 70 mm. from the abscissa of the point at which the 45° line crosses this ordinate. The numbers obtained are purely arbitrary, but afford a basis of comparison for the two sides and the two races. The smaller the number the larger the anterior association center in relation to the posterior association center, and the larger the number the larger the posterior association center in relation to the anterior association center. On comparing this with the index of the association centers (Table II 2) it will be found that the deductions are the same from each, i. e., the anterior association center is larger relatively to the posterior association center in the Caucasian than in the Negro, and larger on the left side in each than on the right side, although the latter difference is slight. Or the converse of this proposition may be taken. The posterior association center is relatively larger in the Negro than in the Caucasian and larger on the right side than on the left. A line on the charts at 45° representing the mean of all brains separates the races in much the same way as the arbitrary line before described. A table presents this figuratively : TABLE IId. EXTREMES OF THE COMBINED MEANS OF THE ASSOCIATION CENTERS. Left Side. Right Side. Cs —_A~—— s Above Below Above Below Symbols. the line. the line. the line. the line. Caucasian a cccsotee. 32 10 33 3 INGET Open dcine rockon oe 18 45 14 48 In this table, as in others, a more marked racial difference is found on the right side than on the left; fewer brains being over the line on the right side. It is interesting to find all of the perfect adult male mu- lattoes in white territory on the charts, each one being near the line rep- resenting the mean of all brains. Examination of the charts will reveal the fact that all the symbols range along this line or in the direction of it from left to right, and from below upwards as the size of the brains are shown to be larger, the Negro symbols being below and to the right of the line, while the Caucasian symbols are above and to the left, except those represented in heavy type in the above table as the “ Extremes of the Combined Means of the Associatioi Centers.” To summarize: An attempt is made to demonstrate that the anterior association center is relatively smaller in the Negro brain than in the Caucasian; that the Yobert Bennett Bean : 373 jeft anterior association center of Negro brains resembling the Caucasian brain in shape is larger than the right, while the left anterior association center of Caucasian brains resembling the Negro brain in shape is smaller than the right, although this difference may be in the gyrus frontalis CAUCASIAN NEGRO MULATTO Cuarr Ill. Right Hemisphere.—Relation of the average length of radii at 60° in the sagittal plane (0°, Fig. 2a), in the horizontal plane (90°, Fig. la), and in the plane with the brain tilted at 45° (Fig. 3a); to the average of the radi at 120° in the same plane. The average is obtained by adding the length of the radii in these three positions and divid- ing by three. inferior or the motor area, instead of in the anterior association center ; and an attempt is also made to point out minor racial differences in in- dividual brains. To accomplish this, outline drawings of individual 374 Some Racial Pecuharities of the Negro Brain brains in various positions are presented; composites are constructed based upon actual measurements; a table of actual measurements is com- piled from which an index of the association centers is worked out; and charts and tables are produced to determine the averages, the means, the CuHaAart IV. Left Hemisphere.—See legends of Charts III and I. extremes, and the extremes of the combined means, of the association centers. Not only is the anterior association center smaller in the Negro than in the Caucasian, but the whole frontal lobe of the Negro is smaller, as Robert Bennett Bean 375 may be determined by examining Charts III and IV, constructed from the numbers in Table III, and also from the position of the fissure of Rolando, to be discussed further on, and the areas of the brain outlines anterior to this fissure. The numbers in Table III are obtained by meas- uring the radii at 60° and 120° of the three outlines of the horizontal, vertical and 45° planes intersecting the brain axis, the numbers repre- senting the average length of these three radii in each instance. Charts III and IV are constructed in a manner similar to that described for Charts I and II, and they are treated throughout in the same way. The arbitrary line is found to separate the races similarly, but it passes through the 64.5 mm. ordinate instead of through the 68 mm., which means that the average length of the 45° radii to the frontal lobes for the three planes is less than the average length of the radii to the anterior association center. The arbitrary line is an approximate compound ordi- nate mean in this table as well as in Table IIT», representing the ordinate mean for all brains on Charts I and IT, and III and IV respectively. A table showing the comparison of the frontal lobes in the two races is as follows: TABLE IITa. EXTREMES OF THE FRONTAL LOBES. Left Side. Right Side. = (zy —= oe ya ae} * Saas) Symbols. Above the Below the “Above the Below the arbitrary line. arbitrary line. arbitrary line. arbitrary line. WauGaSiam Ss ecisiec, stasiehee a 34 10 32 12 INGEST ON Sete csla onc attactoe eet 30 52 29 54 This presents the fact that there is a greater number of large frontal lobes among the Caucasian brains (66 large, 22 small), and a greater number of small frontal lobes among the Negro brains (106 small, 59 large) the relations being nearly proportional, and practically the same on the two sides of the brain in each race. The difference between the two sides found in Tables [1 and II” evidently lies about a point on the 45° plane where the 60° radius intersects the outline of this plane. This point lies over the anterior association center on the right side, and over the gyrus frontalis inferior on the left side. From Table II? it is deter- mined that the average for this side is relatively greater on the left side in each race. From Table II¢ it is determined that the mean for this point is relatively greater on the left side in each race. From Table [I> it is determined that the extreme for this point is greater in the Negro brain and less in the Caucasian. We may conclude that in general the gyrus frontalis inferior is well developed in the two races, causing the 376 Some Racial Peculiarities of the Negro Brain left side to be more prominent at this point, but extreme Negro brains that approach the Caucasian brain in type have a larger gyrus frontalis inferior and extreme Caucasian brains that approach the Negro brain in type have a smaller gyrus frontalis inferior. Of course this difference may be due to the anterior association center or to the motor area, in- crease in the size of either causing the gyrus frontalis inferior to bulge. It is interesting to note in this connection relatively to the arbitrary line in Charts III and IV, that all the adult male mulattoes (3) are above the line on each side, while all the female mulattoes (4) are below, ex- cept on the left side. Only three (of 26) female Negroes are above the line on the left side, and five on the right side, and all of these are close to the line. Only four (of 35) male Caucasians are below the line on the right side, and three on the left side, and these are all near the line. This indicates a divergence in the males of the two races and a conver- gence in the females. Evidence of the same relation is obtained from Table II? in the index of the association centers, the Caucasian male be- ing 98-97; the Negro male, .90-89; the Caucasian female, 96-97; and the Negro female, 91-91, for the left and right sides, respectively. This fulfills the biological law that the females are more homogeneous, the males more heterogeneous, the latter being more apt to vary from the type, or to be extreme. A slight difference from that found in the association centers is found in the frontal and parietal lobes of the brain in relation to the means. A table is given for comparison, which is derived from Charts III and IV in the same way that Table II¢ is derived from Charts I and II. TABLE IIIb, MEANS OF THE FRONTAL AND PARIETAL LOBES. Left Side. Right Side. as aN fs wos ae aoe ee a2 3s Sembol Ss £2 Differenceofthe #3 £2 Difference of the pyzahos: ae 2S combined means. ad Do combined means. Sais af: £E ao moO os 2) Aas Caucasian. seas Od 69 72—T0=2 66.5 69.5 72.5 — 70 =2.5 INGETOM ye tee cietavere 63.5 - 68:5 7o—7T0=5 63.5 68.5 (3 — (VS On comparing this table with Table II°, it is found that the differences are similar, but mot so great. The inferences are that the frontal lobes are smaller in the Negro than in the Caucasian, but practically the same size on the two sides in each race; that the parietal lobe is slightly larger in the Caucasian than in the Negro, but practically the same size on the -~2 ~2 Robert Bennett Bean 3 two sides in each race; and that the left frontal lobe is relatively larger than the right in each race, this difference being very slight. The extremes of the combined means of the two lobes may be repre- sented in a table prepared in the same way as Table II4, and with like re- sults, except that the differences are not so marked in this table as in Table IT?. TABLE IIIc. EXTREMES OF THE COMBINED MEANS OF THE FRONTAL AND PARIETAL LOBES. Left Side. Right Side. Se , i, , a > Symbols Above Below Above Below the line. the line. the line. the line. @AUCASIAM! Asc bie waite wee tee 35 9 36 9 INGOT ON a 5 oc a svaclersus oue!s, oie enone 26 55 25 56 A greater racial difference exists on the right side than on the left side, t. e., more Negro brains have a relatively large frontal lobe, and a relatively small parietal lobe on the left side than on the right side; and more Caucasian brains have a relatively small frontal lobe and a rela- tively large parietal lobe on the left side than on the right side, although this difference is manifested in two Negro brains and one Caucasian brain only. The racial separation of the races by the 45° line representing the mean for all brains is presented in this table by the fifty-five Negro symbols below the line and the thirty-five Caucasian symbols above the line, on the left side, and by the fifty-six Negro symbols below the line, and the thirty-six Caucasian symbols above the line, on the right side. It is evident that the frontal lobe of the Negro brain is smaller than the frontal lobe of the Caucasian brain, as demonstrated in Charts III and IV, and Tables III#, III and III*. This racial difference has been recognized by anatomists heretofore, but in only a few individual. in- stances has it been emphasized.’ Eyen Tiedemann” that eminent continental champion of the Negro, although recognizing few differences between the brains of the Negro and the European, does admit that the frontal lobes of the Negro brain are smaller than those of the European. This difference is not so great, how- ever, as the difference demonstrated between the anterior association cen- ters of the two races, as represented in outlines, tables, and charts. Flechsig, in his masterly work on the development of the fiber tracts and cortical areas as represented by myelinization, throws some light on the connections of the great association areas, and on their probable func- 1 Reference Nos. 1, 2, 3, 8, 10, 17, 20, 23, 24, 32, 33, 35, 36, 39, 52, 59, 62, 65, 66, 68, 79, 82. Fae, Loy 56. dis) -? CO Some Racial Peculiarities of the Negro Brain tion. ‘The cortex may be divided into three grand areas representing the sequence in development. First the primary sensory areas develop, repre- senting the area for smell in the lamina perforata anterior and extending through the septum pellucidum and the fornix to the uncus and cornu ammonis; the area for touch and muscle sense, and the motor area, in the gyrus centralis posterior and anterior, and the gyrus frontalis su- perior, the sequence for the types of fibers for this area being sensory, motor, callosal, horizontal and arcuate, and association bands; the area for sight around the fissura calcarina, the gyrus descendens and the oc- cipital pole; the area for taste possibly just posterior to the splenium and connected with the subiculum cornu ammonis; and the area for hearing in the gyrus temporalis superior. Next there develop several centers of unknown meaning in the cuneus, the anterior extremity of the temporal lobe, the posterior extremity of the gyrus frontalis inferior, the gyrus subangularis and suprangularis, their positions being near the primary sense areas but not touching them. All the areas so far mentioned develop before birth, except the gyrus superangularis, while the remaining areas develop after birth. They make up the third grand division composed of the three association cen- ters, anterior, posterior and temporal, and include the border zones to the areas already developed, these having short fibers, and the terminal or central zones of the association centers with long fibers. The central zones are the last to develop. The anterior association center is in close relation to the areas representing the body, and in slight relation to the olfactory area, while the others are in close relation to the areas of special sense. In his earlier works Flechsig * determined that lesions of the anterior association center caused alteration, or loss, of ideas regard- ing personality, the ego, the relations of self subjectively and objectively ; a diminution in capacity. for ethical and xsthetic judgment: a loss of self-control, of the powers of inhibition, of will power; and in fact all the symptoms which Bianchi observed on higher apes in which the fore brain on both sides had been extirpated. In simple lesions or in the early stages of the lesion, when the person is “ subjected to unaccustomed stimuli, especially to sexual excitement, anger, or vexation, he may lose al] control of his movements and acts, so that simple influence may lead him to try to satisfy his desires without any regard to custom or good taste. In later stages of the disease imbecility may appear, with entire loss of the mental pictures regarding his personality ” (Barker*). The individual may distort his own personality, and be unable to distinguish the imagined from the real; thus he may think himself of enormous dig- nity, of great importance, or that he is possessed of great wealth, or that Robert Bennett Bean 379 he is a genius. Lesions of the posterior association center do not present so clear a picture, and naturally so because of its more intimate connec- tion with the special senses. It is generally understood that the posterior association center is objective, while the anterior is subjective, the one representing the powers of conception in the concrete, the other, the powers of thought in the abstract. The relative differences found in the association centers of the two races is suggestive in relation to the known characteristics of the two, in view of Flechsig’s work. The Caucasian is subjective, the Negro objective. The Caucasian—more particularly the Anglo-Saxon, which was derived from the Primitives of Europe, is dom- inant and domineering, and possessed primarily with determination, will power, self-control, self-government, and all the attributes of the subjective self, with a high developmeat of the ethical and wsthetic faculties. The Negro is in direct contrast by reason of a certain lack of these powers, and a great development of the objective qualities. The Negro is primarily affectionate, immensely emotional, then sensual and under stimulation passionate. There is love of ostentation, of outward show, of approbation; there is love of music, and capacity for melodious articulation ; there is undeveloped artistic power and taste—Negroes make good artisans, handicraftsmen—and there is instability of character in- cident to lack of self-control, especially in connection with the sexual relation; and there is lack of ortentation, or recognition of position and condition of self and environment, evidenced by a peculiar bumptious- ness, so called, that is particularly noticeable. One would naturally ex- pect some such character for the Negro, because the whole posterior part of the brain is large, and the whole anterior portion small, this being especially true in regard to the anterior and posterior association centers. Flechsig’s work favors the conclusion that the gyrus rectus may have a definite relation to smell, and the gyrus frontalis su- perior to muscle, and as both of these gyri are well developed in the Negro, and the motor area and Broca’s convolution also being large, the presumption is that the anterior association center is exceedingly small in the Negro. The findings in regard to the relative size of the anterior and posterior portions of the Negro brain correspond to those of Broca* on the Negro cranium. His conclusions are as follows: 1. That the face of the Negro occupies the greater portion of the total length of the head. 2. That his anterior cranium is less developed than his posterior, rela- tively to that of the white. 3. That his occipital foramen is situated more backwards in relation to the total projection of the head, but more forward in relation to the 380 Some Racial Peculiarities of the Negro Brain cranium only. Topinard™ corroborates these statements, and concludes that the Negro has the cerebral cranium less developed than the white, but its posterior portion is more developed than the anterior. It falls within the occipital races of Gratiolet *~* and the Caucasian in his frontal races. Barnard Davis“ demonstrated practically the same in relation to the radii from the external auditory meatus to the three regions of the skull, frontal, parietal and occipital. The white and the black races are evidently opposites in cardinal points. The one is subjective, the other objective; the one frontal, the other occipital or parietal; the one a great reasoner, the other emotional; the one domineering, but having great self-control, the other meek and submissive, but violent and lacking self- control, especially when the passions are aroused, or any sudden danger appears; the one a greyhound, the other a bulldog. Spitzka “ emphasizes the differences of the two parts of the brain, an- terior and posterior, in comparing the brains of Prof. Joseph Leidy, Maj. J. W. Powell and Prof. Cope, by contrasting the characteristics of these eminent men, and in so doing corroborates Flechsig’s work and lends plausibility to the generalizations given above. Wagner ““™ gives some interesting figures in relation to the relative size of the various lobes in man and the ourang-outang which may be appropriately presented here. Man. Ourang. OT OMEADU LOWES e-cpsi cera ocereraceno onsen eevee Tense ere eae ac sence nec ah els 43.6 36.8 ipanrictaleands Occipital Mlohbesmeasces sae seem cere eeols 34.6 43.6 The Negro evidently stands in an intermediate position in this rela- tion, which becomes more evident when the areas anterior and posterior to the fissure of Rolando are considered. SuLcus CENTRALIS. FISSURE OF ROLANDO. The racial difference found in the lobes of the brain and in the associa- tion centers is also observable in the position of the sulcus centralis and the relation of the amount of brain matter anterior and posterior to it. The position of the fissure is practically the same in the two races in rela- tion to the brain axis and the brain center, but the amount of brain mat- ter anterior to the fissure is less in the Negro, while the amount posterior to it is more than is to be found in the Caucasian. The inferior end, cen- tral part, and superior end of the fissure of Rolando are located on the brain outlines of sixty-three brains, in degrees from the anterior end of the brain axis, as in other measurements, with the radii extending from the brain center. The superior terminal point of the fissure is also lo- Robert Bennett Bean 381 cated by direct measurement from the brain center on the horizontal planes. Table IV shows the individual measurements taken in this man- ner. ‘Table IV? presents the averages. TABLE IVa. AVERAGE POSITION OF THE FISSURE OF ROLANDO. Left Side. Right Side. > JN me Naor Inferior. Middle. Superior. Inferior. Middle. Superior. Caucasian male ......... De a73%e SSS s ROTO Mai ee S8o. | HOGS INGETO IMATE fj ses cele es 27 76 88 108 a 87 108 Caucasian females 2a..... 13 68 83 107 74 82 107 INIGHeoy AMEN. Coco ode oe aE all 80 90 111 81 86 112 A difference of 1° may be allowed for the personal equation in these measurements, and the female Caucasian measurements may be elimi- nated in the discussion, because only three brains of this kind were meas- ured. The male Caucasian and the male Negro fissure of Rolando have practically identical relative positions, while the female Negro fissure is located nearer the posterior end of the brain than is that of the male in either race. This would seem to indicate that more of the brain lies anterior to the fissure of Rolando in the female Negro than in the males, but by actual measurements of the parts there is less (Table V*). This apparent discrepancy is due to the fact that the frontal lobes of the female Negro are comparatively longer, but narrower transversely, and from above downward, than those of the males of the two races. The areas of individual brain outlines are found in Table V, and the averages for these are in the following table. TABLE Va. AVERAGES OF AREAS OF THE BRAIN OUTLINES 1N RELATION TO THE FISSURE OF RoLAnpo. AREAS IN SQUARE CENTIMETERS. Left Side. Right Side. EA Anterior. Posterior. Anterior. Posterior. Caucasian male ....... 22 146.2 140.5 148.3 1929 INGgro) Malerneatecss cee 22 146.6 145.0 146.7 145.7 Caucasian female ...... 3 118.1 116.6 119.1 ESE Negro female ......... 10 125.4 122.3 125.1 123.9 To compile these tables the three outlines, such as are taken for each hemisphere shown in Figures 14 to 3, the sulcus centralis was located on each of the three outlines, radii were projected on the horizontal plane to the inferior end of the fissure, on the vertical, or mesial plane, to the OS (9 2) ra) Some Racial Peculiarities of the Negro Brain superior end of the fissure, and on the 45° plane to the middle part of the fissure, and lines were drawn from the brain center to the inferior surface of the occipital and frontal lobes, striking them tangentially. These lines are taken as limits of the outlines, because no lines are shown in the drawings. The radius to the sulcus centralis is taken as the dividing line between the anterior and posterior parts of each outline. The temporal lobe is not included in the drawings. The area of each hemisphere, in three planes, both anterior and posterior to the sulcus centralis is determined by means of the planimeter. The results are found in Table V. These results are averaged, the averages for the an- terior part of each outline being added to one another, the same being done for the posterior part, and the sums placed together for comparison matable V2: The anterior part of the Negro brain outline is the same size as the an- terior part of the Caucasian brain on the left side; the anterior part of the Caucasian brain is larger than the anterior part of the Negro brain on the right side; while the posterior part of the Negro brain is larger than the posterior part of the Caucasian brain on each side. In the right hemisphere the racial distinction is considerable; in the left it is not so great. The similarity of the two races in the apparent size of the frontal lobes on the left side may be due to the greater size of the left motor area and of the left gyrus frontalis inferior in the male negro, as heretofore pointed out. The areas of the female Caucasian brain need not be con- sidered, because only three are given. The areas of the female Negro brains are less than the areas of the males in either race and the racial distinctions are relatively the same as in the male Negro. The distinc- tions throughout may be expressed in ratios of the anterior to the pos- terior parts of the brain representing the posterior part by 100 in each case (Table V°). TABLE Vb. RATIO OF THE ANTERIOR TO THE POSTERIOR PARTS OF THE BRAIN. Left Side. Right Side. Caucasianwmalemarceeeeeecoeeeeoee in. 104 : 100 106 : 100 INGerotmalers oi.stesiee ces lelsternce 2 ano. 101 : 100 . 100+ : 100 Caucasianstemalein renee ee eee oe 101 : 100 103 : 100 Neerojfemaler 5 x.yosevacerete cictsicie ders « 102 : 100 101 : 100 This table brings into clearer view the differences mentioned above. The frontal lobe of the male Caucasian is relatively larger than that of the Negro, and the right frontal lobe is both relatively and absolutely larger than the left. The right frontal lobe of the female Negro is rela- Robert Bennett Bean 383 tively smaller than the Caucasian, and the left is relatively and absolutely larger than the right. The female Caucasian is similar to the male Caucasian and the male Negro is similar to the female Negro, but in a less degree. It might have been supposed that the fissure of Rolando is further posterior in the Negro brain than in_ the Caucasian, and that the small size of the frontal lobe in the Negro is an apparent and not a real deficiency of brain matter, but the above meas- urements indicate that the frontal lobe and all the brain matter an- terior to the fissure of Rolando is less in the Negro than in the Caucasian. As the gyrus rectus is apparently larger in the Negro than in the Cau- casian, and the gyrus frontalis inferior is larger in the Negro than in the Caucasian, and as the frontal lobes in the Negro appear larger than they really are, owing to the projection downward of the convolution just mentioned, as well as to the projection upward of the superior erbital plates and the gyrus frontalis superior, if it be true that the motor area and the left gyrus frontalis inferior are larger in the Negro, then it must be true that the anterior association center is con- siderably smaller in his case than in the Caucasian, because even the apparent size of the whole frontal lobe is smaller in the Negro. 'That the anterior association center is smaller in the Negro seems plausible when the corpus callosum is examined, in which the racial distinction is more pronounced than in the brain outlines, the anterior end (genu) being distinctly smaller in the Negro. Corpus CALLOSUM. The cross section area of the corpus callosum is measured with the planimeter from outlines made directly on glass, and from other outlines made on paper by projection. These areas are given in Table I, with the brain weights taken at the time the outlines were drawn. Measure- ments made from Retzius” photographs and drawings of brains by others are given in Table I’, with brain weights, when possible, for comparison. Chart V is made up from these two tables, the brain weights (abscisse) being given in grams, and the areas of the corpora callosa (ordinates) in square centimeters. There is in general an increase in area of the cor- pus callosum with each increment of brain weight. There are, however, many individual exceptions. For instance, one Caucasian brain weighing about 1100 grams has a corpus callosum of about 8 square centimeters area, while another brain weighing about 1400 grams has a corpus callo- sum of about 6 square centimeters area. These are extreme instances, 384 Some Racial Peculiarities of the Negro Brain but there are other similar ones. Spitzka has measured the cross section “area of the corpus callosum in the brains of ten eminent men, and he finds the average area higher than in ordinary men. Their average brain weight was also greater than in ordinary men. The weight of Prof. Joseph Leidy’s brain was estimated to be 1545 grams or possibly more, and the corpus callosum measured 10.6 sq. cm. in sectional area. The symbol representing this brain may be found in Chart V and its unusual CAUCASIAN = O NEGRO ae MULATTO = © CHART V.—RKelation of the area of the cross section of the corpus callosum (ordinates) to brain weight (abscisse). The heavy black lines enclose the majority of the Negro symbols and exclude the majority of the Caucasian. position attracts immediate attention. This may be an exception to the rule that the cross section area of the corpus callosum varies directly with brain weight and at a proportionate rate, and exceptional size of the corpus callosum may mean exceptional intellectual activity. One of the Negro brains, however, had a corpus callosum with a cross section area of 9.1 square centimeters, which is nearly 2 square centimeters Go Or Robert Bennett Bean above the average Spitzka gives for the ten eminent men, and there is no reason to believe that this Negro had greater mental powers than any one of those eminent men, although he may have been an obscure genius. One Caucasian male brain in my series had a corpus callosum of 9.1 square centimeters cross section area, and eight other brains, six Caucasian male, one mulatto male, and one Negro male had areas between 8 and 9 square centimeters, and there is nothing to indicate that these brains were from exceptional men, although they may have been. The brain of a laboring man pictured by Retzius had a corpus callosum which measured 9.8 square centimeters in area. The brain weight was 1587 grams. The brains in my series with large callosa are invariably large. Of the ten brains mentioned above with large callosa each one weighed about 1500 grams (Table I). The racial distinction in the relation of brain weight to the area of the corpus callosum is not marked, but it is noticeable. To show this, lines are drawn on Chart V through the 7 square centimeter ordinate and through the 1300 gram abscissa, these lines being extended in a horizontal and in a vertical direction respec- tively, until they intersect. One-third of the brains represented below the horizontal line and to the left of the vertical line are Caucasian, and two-thirds are Negro. ‘Two-thirds of the brains represented above the horizontal line and to the right of the vertical line are Caucasian and one-third are Negro. A majority of the Negro brains are thus repre- sented within the lines and a majority of the Caucasian brains are repre- sented without the lines. It is a noteworthy fact that about half of the Caucasian brains represented within the lines are from women, or from the inmates of Bay View Pauper Asylum, a great many of whom are known to have had dementia—alcoholic, syphilitic, or senile. With them the brains of such noted men as Gyldens™ (No. 23), Siljestrém” (No. 25), a statesman * (No. 26), and Prof. Leidy “ (No. 27), are found. These men each had a large brain, or a large callosum, or both. Thir- teen Negro brains are found without the lines having a corpus callosum of more than 7 square centimeters area, and only eight have a brain weight of more than 1300 grams. These invariably give evidence of Caucasian characteristics. To be found outside of the lines are a mulatto; a Negro who had been instrumental in at least three, and possibly five, murders; a Negro accomplice of the latter; a Negro laborer from North Carolina; a Negro killed in a railroad wreck; and another the victim of a third-rail accident. The racial difference is really more marked than is apparent in the chart (V) because the class of Negroes from which bodies are ob- tained is comparatively better than the class from which Caucasian bodies are obtained, this being especially marked in the females of the two races. 29 386 Some Racial Pecuharities of the Negro Brain In dealing with the corpus callosum as a whole, it is found to be smaller in the Negro than in the Caucasian, just as the brain of the Negro is smaller than that of the Caucasian, and in about the same degree. The averages of brain weights and areas of the corpora callosa reveal interest- ing racial and sexual differences. ‘They are given in Table I?, with ratios made up from Table I. TABLE Ia. Tur RELATION OF THE AREA OF THE CORPUS CALLOSUM TO BRAIN WEIGHT- AVERAGES AND RATIOS. iets Goren Galleeaee Veal. Ratio. sq. cm. em. CAUCASIAN Ia G taeteleeicls ie leterstoiers 54 7.02 1302 54 Negro male ...... qaoccsdehons 50 6.27 1208 a2 Caucasian (female! in 3 vcicterc-1-- 14 6.40 1087 59 INEST ORLeTINAl eis cis)-cclcete tetas rect 26 5.68 1064 53 The average brain weight is greatest in the Caucasian male, least in the Negro female, and intermediate in the Negro male and the Caucasian female. The average cross section area of the corpus callosum is rela- tively the same, with the Negro male and the Caucasian female transposed in relation to each other. The ratio of area to weight is greatest in the Caucasian female, least in the Negro male, with the Negro female and the Caucasian male respectively a little higher than the Negro male; but. the ratio of the Caucasian female is hardly a fair one, because so few brains of this kind are examined, and they are from such varied sources, and with so many methods of preservation. The relation of the anterior and posterior lineal halves of the corpus callosum exhibits a greater racial difference. This is perceived by a glance at Chart VI, compiled from Table VI in a manner similar to that of the charts previously presented. The corpus callosum is divided into halves of equal length by a line per- pendicular to the brain axis, at a point intermediate between two lines. perpendicular to the brain axis, dropped from each end of the corpus callosum. It is hardly necessary to do more than point out the racial difference indicated in the chart, because it is so plain, even to a casual observer. There is not an absolute separation of the races, but there is a decided difference. In general, as the area of one end of the corpus callosum increases, the other increases also, but the increase in area of the anterior end is greater in the Caucasian than in the Negro, while the in- crease in the area of the posterior end is greater in the Negro than in the Robert Bennett Bean 387 Caucasian. The relative difference is noticed throughout. ‘The anterior end is relatively larger in the Caucasian, the posterior end is relatively Cuarr VI.—Relation of the anterior lineal half of the corpus callosum (ordinates) to the posterior lineal half (abscisse). The races are separated. larger in the Negro. This may be expressed in averages in a table made up from Table VI. 388 Some Racial Peculiarities of the Negro Brain TABLE VIa. RELATION OF THE AVERAGES OF THE AREAS OF THE ANTERIOR TO THE POSTERIOR LINEAL HALF OF THE CorPUS CALLOSUM. No. of Beatin Anterior. Posterior. Ratio. sq. cm. sq. cm. Caucasiangemalleammaocicdsiete 42 3.70 3.04 122 : 100 INGPTOSMale armen coe crsn ket 62 3.06 3.02 101 : 100 Caucasian wfemalewenn.o..ceece 9 Oeil 2.87 110 : 100 Negro: femaletrayaceoscccciece 25 2.86 2.86 100 : 100 Each end of the corpus callosum is larger in the Caucasian male than in the Negro male or in the others. Likewise the Caucasian female is larger than the Negro female, the anterior end is larger than the Negro male, the posterior end being smaller than the Negro male and about the same size as the Negro female. The anterior end of the corpus callo- sum is small in the Negro male, and smaller in the Negro female. It is large in the Caucasian female and larger in the Caucasian male. The posterior end is about the same size in each sex, but smaller in the female than in the male, so that the anterior end shows a racial and sexual dif- ference, while the posterior end shows a sexual difference only. This can be located more definitely than in the two lineal halves of the corpus cal- losum. Comparing the genu and the splenium, leaving aside the inter- mediate portion of the corpus callosum, a distinct racial difference is found similar to that just discussed. Chart VII taken from Table VII gives a graphic picture of the essential differences, which are about the same as those found in Chart VI. To prepare this chart, the corpus callosum is divided into four parts, six-tenths (.6) anteriorly being sep- arated from four-tenths (.4) posteriorly, and each of these two parts be- ing divided in half. This is done by using lines perpendicular to the brain axis, and parallel to lines used in preparing for measurements for Table VI. This gives the splenium two-tenths of the total lineal length of the corpus callosum anterior to the splenium a narrow part, which I call the isthmus, two-tenths of the total length; anterior to this the body, three-tenths of the total length. These divisions are shown in Figures 92 and 9». Several brains are broken through the fissure of Ro- lando and the break invariably passes through the isthmus. The conclu- sion is that the body of the corpus callosum contains the fibers connecting the motor areas of the two hemispheres, and the isthmus and splenium contain the fibers connecting the sensory areas of the two hemispheres, and all areas posterior to these. Eliminating the isthmus and body must leave the fibers that more definitely connect the association centers and Robert Bennett Bean. 389 Cuarr VII.—Relation of the area of the genu (ordinates) to the area of the Splenium (abscisse). The races are further separated. ” 390 Some Racial Peculiarities of the Negro Brain to special sense centers in the two hemispheres. Flechsig ” indicates that part of the centers for smell may lie in the gyri recti, which are larger in the Negro than in the Caucasian. The latter is evidently true from what we know about the sense of smell in the Negro, and the size of the olfactory apparatus in this race. If the fibers connecting the frontal lobes anterior to the motor area are contained in the genu, and a greater number of the fibers in the genu connect the olfactory lobes in the Negro than in the Caucasian, then the genu of the Negro should be larger. But it is really smaller. Consequently the fibers connecting the anterior associa- tion centers must be less in the Negro than is indicated by the size of the genu. Comparing the areas of the genu and splenium must give an ap- proximate comparison of the anterior and posterior association centers. They are compared in the two races in Chart VII, made up from Table VII. A more definite racial difference is seen in this chart than in Charts I and II where the association centers are contrasted from brain outlines. A glance at Chart VII convinces that the genu is relatively and absolutely larger in the Caucasian than in the Negro. This may also be expressed in a table of averages taken from Table VII. TABLE VIIa. THE RELATION OF THE AVERAGES OF THE AREAS OF THE GENU AND SPLENIUM, ETc., IN SQ. CM. Number Ratio Ratio f (0) Genu. Body. Isthmus. Splen- Genu to Body to Brains. ium Splenium. Isthmus. Caucasian male ..... By vastly ALD 94 1.72 158:100 160: 100 INGgrommale- 252... -- 60 2.12 1.33 81 1.76 120 : 100 164 : 100 Caucasian female .... 17 2.41 1.36 Se 61 ASO LOO AS oaO0 Negro female ....... 25 1.98 Ua aries ale (ey = lala 2X0 AUS LOK) The genu is absolutely and relatively largest in the Caucasian male, absolutely and relatively smaller in the Caucasian female, absolutely and. relatively smaller still in the Negro male, and absolutely and relatively smallest in the Negro female. The relations of the splenium are the converse of this. The relation of the isthmus to the body is similar, but with less marked racial difference. Compare the relation of the ratios of the genu to the splenium in the males of the two races (158 : 120 = 131), with the relation of the ratios of the body to the isthmus (160 : 164 — 97), and a greater racial difference is evident in the former (131) than in the latter (97). This difference is also evident in the females of the two. races (150 :115==130. 155 :1603=97). ‘The relation of the ratios of the two-lineal halves of the corpus callosum (Table VI®) is 122 : 102 —119 in the males of the two races, and 110 :100 = 110 in Robert Bennett Bean 391 the females of the two races. Compare these results with the results ob- tained above and there appears a greater racial difference in the relation of the genu to the splenium than in the relation of the body to the isthmus, or in the relation of the anterior to the posterior lineal halves of the corpus callosum. This may be expressed in a table. TABLE VIIb. Tue RELATION OF THE RATIOS OF THE PARTS OF THE CORPUS CALLOSUM. Genu to Splenium. Body to Isthmus. Lineal Halves. ~ Negro Cauca- wee, Relation Cauca- Relation Cauca-— Relation and sian verre of sian, Nero : sian weere of Caucasian. Ratio. ‘ * Ratio. Ratio. * Ratio. Ratio. * Ratio. ITAL ees ss LDS 120 131 160 164 97 122 102 119 Females .... 150 alas) 130 io 160 97 110 100 110 The racial difference is greater in the “relation of the ratios” of the genu and the splenium (130) than it is in the “relation of the ratios ” of the body and the isthmus (97), or of the lineal halves ( 119, 110). The sexual difference is slight in the relation of the ratios of the genu to the splenium (131 : 130 = 101); it is more marked in the “relation of the ratios” of the anterior lineal half to the posterior lineal half (119: 110 = 108) ; and it is least marked in the “ relation of the ratios ” of the body to the isthmus (97 :97 = 100). In other words the above table may be interpreted as follows: The genu of the Caucasian female is larger in proportion to the size of the splenium than it is in the Negro female, and this difference is greater than the racial difference in the females in the proportion of the body to the isthmus, or the anterior lineal half to the posterior lineal half of the corpus callosum, the same difference being noticed in the relative sizes of these, but in a lesser de- gree. The same racial differences are found in the males, but they are not so marked. The splenium and genu, then, exhibit the most notice- able racial differences. The most striking sexual differences are found in the anterior and posterior lineal halves, the anterior in proportion to the posterior being larger in the males than in the females. The ratio of the body to the isthmus is greatest in the Negro male, least in the Caucasian female and intermediate in the Caucasian inale and Negro female. This may be explained by the relative muscular power of the four classes, the commissural fibers of the motor areas forming the body of the corpus callosum. The greatest racial differences being found out- side of the motor areas and their commissural fibers gives strong presump- tive evidence that the great racial difference lies in the relation of the anterior to thé posterior association center. CAUCASIAN NEGRO MULATTO Boo CHART VIII.—Relation of the area of the genu (ordinates) to brain weight (abscisse). The heavy black lines include the majority of the Negro symbols, and exclude the majority of the Caucasian. Cf. Chart V. With equal increments of brain weight there is a proportionate increase in area of the genu. Robert Bennett Bean 393 The genu is not only larger in the Caucasian than in the Negro, but the size of the genu bears a more or less definite relation to brain weight in both races, an increase in brain weight being accompanied by a corre- sponding increase in the size of the genu. The splenium does not bear so definite a relation to brain weight, although there may be a slight in- crease in the size of the splenium with increase in brain weight. These statements may be verified by examining Charts VIII and IX, compiled v7 Co) g q ole le q q q iC q ga 0 a es a is) © le ae os eae ee q ae = ° ic Q joo 14\00 1 fos) fo} 2 | a soo__é/00 7j00 eee ! Cuarr IX.—Relation of the area of the splenium (ordinates) to brain weight (abscisse). With equal increments of brain weight there is not a proportionate increase in the area of the splenium. from Tables I, I’ and VII. A more or less definite racial difference is noted in the charts, but it is not marked. In Chart VIII draw a line horizontally through the 2.60 square centimeter ordinate, and draw an- other line vertically through the 1300-gram abscissa until these two lines intersect, and continue them to the limits of the charts. Very few sym- bols representing Negro brains are found above and to the right of these if comp.Type © Comp. Type comp. TYPe Robert Bennett Bean. 395 Fig. 12. Types of the corpus callosum in the Caucasian male. Type I, 8 subjects; Type II, 7 subjects; Type III, 7 subjects; Type IV, 6 subjects; Type V, 4 subjects; composite Type made up of the others, 32 in all. One-half natural size. Fig. 18. Types of the corpus callosum in the Negro male. Type I, 18 sub- jects; Type II, 8 subjects; Type III, 10 subjects; Type IV, 9 subjects; Com- posite Type made up of the others, 45 in all. One-half natural size. Fic. 14. Types of the corpus callosum in the Caucasian female. Type I, 1 subject; Type II. 2 subjects; Type III, 1 subject; Type V, 1 subject; Com- posite Type made up of the others, 5 in all. One-half natural size. ¥ Fig. 15. Types of the corpus callosum in the Negro female. Type I, 5 sub- jects; Type II, 3 subjects; Type III, 6 subjects; Type IV, 5 subjects; Com- posite Type made up of the others, 19 in all. One-half natural size. Fic. 16. Composite types of both races and sexes. Type I, 22 subjects, 13 Negro and 9 Caucasian. Type II, 29 subjects, 21 Negro and 8 Caucasian. Type III, 22 subjects, 15 Negro and 7 Caucasian. Type IV, 28 subjects, 15 Negro and 13 Caucasian. One-half natural size. lines, which signifies that very few Negro brains are found with a brain weight of more than 1300 grams, or an area of the genu of more than 2.60 square centimeters. A majority of the symbols representing Cau- casian brains are found above and to the right of the lines, signifying that the majority of the Caucasian brains have a brain weight of more than 1300 grams, and an area of the genu exceeding 2.60 square centi- meters. The converse of these propositions is true. Few Caucasian brains have a brain weight of less than 1300 grams or an area of the genu less than 2.50 square centimeters, while the majority of the Negro brains are in this class. Compare Chart V with Chart VIII and a simi- larity is noticed, in fact they are nearly identical, but there is a more de- cided identity between the area of the genu and brain weight, than be- tween the area of the entire corpus callosum and brain weight. This is due to the less decided identity between the area of the splenium and brain weight. That the size of the genu and brain weight are closely related may be significant in the relation of brain weights in races and in distinguished individuals. CoMPosITtE 'T'YPES. The corpus callosum may be classified in types racially and sexually according to the size and shape of the outline of its cross section. One hundred and one selected cases are taken and composite outlines are made of each racial and sexual type, as, Caucasian male, 5 types; Negro male, 4 types; Caucasian female, 4 types; and Negro female, 4 types. Com- posites are made by selecting outlines similar in size and shape, and 2 396 Some Racial Peculiarities of the Negro Brain placing them over each other so that they coincide throughout as much as possible. The heaviest resulting outline is taken as the composite. Then the types are combined for each race in the same way, and finally the race types are combined. The types are represented in Figures 12 to 16. The type of brain varies with the type of corpus callosum, and the type of individual varies likewise. Caucasian male type.—There are five types of the corpus callosum in the Caucasian male, but these may be brought together into two groups. Types I, II and IV belong to the primary group, and Types III and V to the secondary group. The primary group represents the young and vigorous, the secondary represents the old and infirm. The corpus callosum representing Type I is a composite of eight cases. It is large in cross section, and every part is full and well developed. The splenium is of moderate size, the isthmus is not small, the body and genu are large and heavy. The type of brain to which this belongs is large, heavy (1400-1500 grams), and well rounded in all its outlines, approach- ing the dolichocephalic in shape. The frontal and temporal regions are large, the parietal and occipital regions are relatively not so large. The bodies from which these brains are taken are of men in the prime of life, from 40 to 50 years of age, and in apparently good physical condition, death coming rapidly or suddenly (pneumonia, heart disease, nephritis, galloping consumption, or accident), without great emaciation. The avy- erage height is 184 cm. (6 feet, $ inch), and the average weight is 73 kilo. (161 pounds). There is evidence of average intelligence and in- dividuality among these men. One was manager of a livery stable, another was an eccentric man who became alienated from his family on Long Island and wandered off with considerable money, drifted to Baltimore and died in the Bay View Pauper Asylum, while a third was the victim of a third-rail accident, and apparently a man of affairs. Two are noted as “blonde.” 'The others are not described as to color. Type II is a composite of seven cases. The cross section of the corpus callosum is longer and narrower than in Type I. The splenium is large, the isthmus is small, the body is of medium size, and the genu is large. The brains representing this type are of medium size (1300-1500 grams), high and narrow (dolichocephalic), and the outlines are squared—not so rounded as in Type I. The frontal and parietal regions are large, the temporal is of fair size, and the occipital hangs low and is long. The bodies from which these brains were removed were in a well nourished condition, death having resulted rapidly (pneumonia, nephritis, etc.) The men were in the prime of life—approaching old age, 40 to 60 years old, with an average height of 172 em. (5 feet 8 inches) and an average Robert Bennett Bean 397 weight of 75 kilo (165 pounds). ‘Two are noted as “ brunette.” One is a dark Scandinavian. No records are made of the intellectual condi- tion, or anything that would give a clue to it. Type III is a composite of seven cases. The cross section of the corpus callosum is long, narrow, and highly arched. The splenium is large, the isthmus and body small, and the genu large with a long beak. The brains of this type are small (1200 to 1350 grams), high, long (dolicho- cephalic), and oval in shape from the side and from above. The ventricles are large and full of fluid. The bodies from which the brains are ob- tained are emaciated, the majority weighing little more than 45 kilo. (100 pounds), death being the result of lingering disease (senility, asthenia, etc.). The men were old (60 to 80 years), with an average height of 168 cm. (5 feet 6 inches). There was evidence of dementia in two or three. Type IV is a composite of six cases. The cross section of the corpus callosum is short, of medium size, and not large anteriorly. The splenium is large, the isthmus is large, the body and genu are relatively small. The brains of this type are of medium size (1200 to 1500 grams), high, short, narrow, and boxlike in appearance, with full frontal and temporo- parietal regions. The men were of average height, 165 em. (5 feet 5 inches), of ages ranging from 15 to 75 years, and in weight varying from 50 to 80 kilo. (111 to 178 pounds). Two were Germans from Berlin. Type V is a composite of four cases. The cross section of the corpus callosum is long, and the arch is high and more curved than in any other type. The splenium is large, the isthmus thin, the body of medium size and the genau not large, but having a long pointed beak. The brains vary in weight from 1040 to 1520 grams. They are high, long and rounded in all outlines. The ventricles are large and distended as if by pressure from within. The bodies were in a fair state of nourishment. The men were old (60 to 75 years), and ranged in height from 157 to 186 cm. (5 feet 2 inches to 6 feet 1 inch). Caucasian female types——In general the female types are similar to the male types of the same number. So few cases are given that general- ization is inadmissible. Composite Caucasian types—The composite types are composites of all the Caucasian male types and of all the Caucasian female types. The most noticeable features of the corpus callosum of the Caucasian in com- parison with that of the Negro are the high arch, and the greater size of the anterior half of the corpus callosum in the Caucasian. The splenium is of good size in the Caucasian, but not so large as in the Negro, while the isthmus, body, and genu are larger than the same parts in the Negro. 9 398 Some Racial Peculiarities of the Negro Brain The sexual differences are slight. The cross section area is larger in the male than in the female Caucasian, but the splenium of the female is rela- tively larger than that of the male, the isthmus likewise, while the body is relatively smaller in the female, and the genu is relatively about the same size. (cf. Table VIII? et seq.) Negro male types.—There are four types of the cross section outlines of the corpus callosum in the Negro male. Type I is a composite of eighteen cases. This type is representative and characteristic of the Negro race. The cross section of the corpus callosum is small. The splenium is large and club shaped, the remainder of the corpus callosum is small, narrow, long, and slender. The brain weight is from 1000 to 1200 grams. The brains are short, with narrow frontal lobes, and wide, bulging parietal region. The mesial outline is oval. The bodies from which the brains are removed are well nourished and muscular. The average height is 162 cm. (5 feet 4 inches), and the average weight is 67 kilo (148 pounds). ‘The age limit is 20 to 40 years. This represents a familiar type of Negro, the low, heavy set, muscular, dark-skinned young Negro, with small head, having the parietal bosses prominent and the frontal region low, narrow and receding. This is the lowest order and most prevalent type of Negro. There is evidence of little foreign blood. This type represents the Guinea Coast Negro, from which the subjects are probably derived. A few may be representative of the Hottentot Negro type. . Type IIL is a composite of eight cases. The cross section of the corpus callosum is larger than Type I and the anterior end is better developed. The splenium is also large. This may be considered as a sub-type of the one above, with evidence of more mixture with a foreign element. The brains are larger, weighing from 1100 to 1300 grams. The characteris- tics of the type are otherwise similar to those of Type I. Type III is a composite of ten cases. The cross section of the corpus callosum is long and large. The splenium is large and club-shaped; the genu is large and round; the isthmus and body are long and narrow. The brains are long (dolichocephalic), high, and narrow in front, wide and bulging in the parietal region. The weight is from 1200 to 1400 grams. The bodies are in a fairly well nourished condition, death being rapid or sudden (accident, pneumonia, heart disease, etc.) The height averages 162 cm. (5 feet 4 inches), and the weight averages 63 kilo. (140 pounds). The men of this type are lighter skinned than those of Type I, and are built on broad lines in general. These are long armed, flat-footed, and loose-jointed individuals, not so compactly built or well knit as those of the previous types, and having long heads and faces, with high foreheads. Robert Bennett Bean 399 Unmistakable evidences of a previous mixture of other races with the Negro exist. Three are mulattoes. Three are accident cases. The ma- jority are between the ages of 50 and 80 years. This type represents the higher and better class of the Guinea Coast Negro. Type IV is a composite of nine cases. The cross section of the corpus callosum is long, large, and highly arched, resembling Type V in the male Caucasian. The splenium is large and regular in outline, tapering off gradually in the isthmus and body, which are long, curved, and smaller than the splenium. The genu is of medium size and has a long pointed beak. The brains are large, heavy (1300 to 1500 grams), long (dolichocephalic), and high in the frontal region. The frontal lobes are comparatively large and the parietal region is massive and bulging. The bodies are in a well nourished condition. The average weight is 72 kilo. (158 pounds), the average height is 175 cm. (5 feet 9 inches), and the age varies from about 40 to 70 years. This represents the tall, fair- skinned Negro (or mulatto), of the enterprising nature, but the mest dangerous of all characters to human society. Rape and murder aitach themselves here. Two of them were murderers, four Mulattoes, and the others exhibit traits of considerable Caucasian intermixture. This type represents the Kaffir Negro, probably a mixture of Semitic (Arab), Ha- mitic, and Negro at a remote period of time, the Zulus being the charac- teristic tribe of the Kaffir Negro. Negro female types——There are four female Negro types, which corre- spond in general to the four male Negro types. These may be combined into two groups for the two sexes alike. The primary group, composed of Types I and II, is the prevalent Negro type, being purer Negro than the secondary group, composed of Types III and IV, which is largely mixed with Caucasian. Type I is a composite of five cases. The cross section of the corpus callosum is short, wide, and compact. The splenium, isthmus, body and genu are relatively of good size. The brain is small, short, and boxlike in appearance. The brain weight is from 1000 to 1100 grams. The frontal lobes are small, narrow from side to side and from above downward. The parietal region is large, full, and bulging. The subjects are about 160 em. (5 feet 3 inches) average height, 50 to 54 kilo (110 to 120 pounds) average weight, and the age is from 20 to 30 years. They represent a class of young, stocky built, dark-skinned Negro women of the Guinea Coast Negro type. There is a trace of racial intermixture in some of them. Type II is a composite of three cases. The cross section of the corpus callosum is long, arched, and narrow. The splenium and venu are of 400 Some Racial Pecularities of the Negro Brain good size, the isthmus is not well marked, and the body is slender. The brain is slightly longer than in Type I, but is smaller, the smallest of all brains being in this type. The average weight is 995 grams. The subjects are taller (168 cm.—5 feet 6 inches), and weigh less (45 kilo.— 100 pounds or less) than those in Type I. These are probably of the Hottentot or Bosjeswoman type. Type IV is a composite of five cases. The cross section of the corpus callosum is long, straight and slender. The splenium is large and club- shaped, the isthmus is narrow, the body is long and narrow, and the genu is of good size. The brains are long and narrow (dolichocephalic). The frontal lobes are narrow, low, and long, the parietal lobes are large and prominent. The brain weight ranges from 1000 to 1200 grams. The subjects are in a fairly well nourished condition, weighing from 54 to 59 kilo. (120 to 130 pounds), and having a height of 165 cm. (5 feet 5 inches) average. These are the old women from 60 to 70 years of age, of medium height and weight and light-brown skin. There is evidence of a little white blood. This type is probably of Kaffir origin. Type III is a composite of six cases. The cross section of the corpus callosum is long, extremely thin and curved. The splenium is large and knob-shaped, the isthmus is narrow, the body long, narrow, and curved, and the genu small, with a long pointed beak. The brains are exceedingly long and narrow, and somewhat high in front. The frontal lobes are long, narrow, and thin, but high, the parietal lobes are full and bulging. The brain weight is from 1000 to 1100 grams. The subjects are low, fat and heavy. The average height is about 155 cm. (5 feet 1 inch), the average weight is 68 kilo. (150 pounds), and the age is from 30 to 50 years. This is the Negro “ mammiy,” who is so well known. We have here a fat, fair-skinned Negro woman, not tall, but of a voluptuous type. There is evidence of white intermixture. This type probably represents the better class of the Guinea Coast Negro. 'The female types conform to the type of the race more nearly than do the males. The latter show more markedly the traces of racial intermixture. The composite types for the Negro are made in the same manner as those for the Caucasian. 'The composite male and female are almost identical in shape, except that the splenium of the male is relatively larger than that of the female, just the opposite of what was found in the Caucasian. The cross section area in the male is altogether larger than in the female. Racia] differences are more marked. The cross section area of the corpus callosum is less in the Negro than in the Caucasian. The area of the posterior lineal half is relatively larger in the Negro, while the area of the anterior lineal half is relatively smaller. The Robert Bennett Bean 401 splenium is absolutely and relatively larger in the Negro than in the Caucasian, while the genu is relatively and absolutely smaller. The isthmus and body are relatively about the same size in the males of the two races, but in the females the isthmus is relatively smaller in the Negro, while the body is relatively larger. The hooked beak of the genu is larger in any case in the Caucasian, especially in the female. Composite types of both races and sexes.—There are four of these types made up as follows: Type I is a composite of Type II Negro male, and Type I of the others, twenty-two individual cases in all, thirteen Negro and nine Caucasian. The Caucasian traits predominate. This type represents the young, active, vigorous individuals. Type II is a com- posite of Types I Negro male, II Negro female and Caucasian female, and Type IV Caucasian male, twenty-nine individual cases in all, twenty- one Negro and eight Caucasian. The Negro traits predominate. This type represents the old and the passionate. Type III is a composite of Type II Caucasian male, and Type III Negro male and Type IV Negro female, twenty-one individual cases in all, fifteen Negro and seven Cau- casian. The Negro and Caucasian traits are well mixed. This is a Mu- latto type. Type IV is a composite of the remaining types, twenty-eight individual cases in all, fifteen Negro and thirteen Caucasian. This type represents the mentally dull, the demented, and the degraded. Whenever the number of Caucasian exceeds one-third of the whole number of cases in any type the Caucasian traits predominate. This may indicate a certain amount of Caucasian mixtures among the Negroes. The American Negro may be divided into two groups, each with subdi- visions.” The first group comprising the greater number of blacks, being represented by the Negro types I, II and ITI, and the second group, includ- ing only a comparatively small number, being represented by the Negro Type IV. The first group includes the Guinea Coast Negro and may he the few Hottentots in America, and is divided into three classes. First the Hottentot, or Bosjesman, having gray or old yellow skin resembling dirty varnished oak; low, dwarfed stature, either weak, or squat and mus- cular ; long, woolly hair, in small obliquely inserted tufts; very dark eyes, wide apart; extraordinarily broad, flat nose; large mouth, with thick, projecting, turned-out lips; enormous prognathism ; heads extremely doli- chocephalic; the smallest brains (900-1000 grams) of any human beings probably; and lastly, having the distinctive steatopyga and the tablier which are not always present. This class is comparatively rare. Sec- ondly, the low class Guinea Coast Negro, the most ancient and most class- ical Negro type, having a cool, velvety skin, glossy, and varying from a reddish, yellowish, or bluish black to jet black; low stature, well knit and 30 j 402 Some Racial Peculiarities of the Negro Brain muscular ; black hair and eyes; platyrrhine nose; thick lips; prognathous face; beautifully white, sound teeth; small square ears (Hrdlicka ™) ; long upper and short lower extremities; flat feet; heads dolichocephalic, or even approaching subbrachycephaly ; and brains weighing from 1000 to 1200 grams,—possibly more. This is the most prevalent class of Negro in the South. Thirdly, the high class Guinea Negro, similar to the low class, but developed along broader lines, and instead of being ugly, di- minutive, with large and squat limbs, and a round or short face, they are comparatively handsome, taller, with well-proportioned limbs and a long face. They exist in fairly large numbers in certain localities, but are much less prevalent than the low-class Guinea Negro. The second group is made up of Kaffirs and other Mulattoes, and Mulattoids, or Mulatto- hike individuals. The Kaffirs are represented by the Zulus in Virginia and North Carolina, being particularly noted for their height and intelli- gence. They have various shades of dark brown skin; very high stature, sim and well made; thick, woolly hair, and dark brown eyes; broad, flat nose, sometimes highly arched, Romanesque, or Arablike; thick lips; long, oval face; slight prognathism and platyrrhiny; long, high heads, with narrow foreheads, and median frontal protuberances; and large brains, weighing from 1300 to 1500 grams. They do not exist in great numbers except in certain sections, as in Virginia and North Carolina where they are fairly prevalent. The Mulattoes are such a heterogeneous conglomeration as to beggar description. Three classes do stand out dis- tinctly though. One is the large, yellow Mulatto with every feature mag- nified and like the Negro, tremendous frame, sometimes veritable giants, and a conspicuous bumptiousness and volubility. Another is the small, almost white Mulatto, with Caucasian features, neat, compact frame, and partaking of the qualities of the Caucasian mentally. A third is that pe- culiar mottled Mulatto or Mulattoid mentioned by Shaler.” There are all sorts of mixtures of all the classes mentioned above forming a not inconsiderable part of the Negro population. There may be a few other types of Negroes here and there, such as the Ethiopians, Papuans, Ne- gritos, and perhaps Australians, and one occasionally sees a red Negro, probably a Foulah from the heart of Africa in the region of the Soudan, or a Dahomian from near there, but these are so rare as to be inconsid- erable. A few mixed bloods with Indian characteristics are occasionally observed. This classification is slightly different from that given by Prof. Shaler,” but only in minor points. It does not differ materially from Tobinard’s™ classification of the Negro in the West and South of Africa, from which sections nearly all of the Negroes of America are supposed to have been brought. Robert Bennett Bean. 403 FoRAMEN OF MUNRO. The position of the foramen of Munro bears an interesting relation to the two ends of the curpus callosum and to the brain center, sexually and racially. Measurements are made on the brain axis, all points not on the axis being projected to it by lines perpendicular to the axis. The average of all measurements is represented in Table VIII in millimeters. In this table “Genu” and “Splenium” mean the anterior and posterior ends, respectively, of the corpus callosum. The “ Ratio” is the number preceding it divided by the length of the brain axis for that race and sex. The two hemispheres measure alike practically. A difference of one milli- meter in the numbers in the table is to be ignored. TABLE VIII. RELATIVE POSITIONS OF THE GENU, SPLENIUM, FORAMEN OF MUNRO, AND BRAIN CENTER. AVERAGES AND RATIOS. ar ghcas tans ls ee q aa! Ses 5 5 Fs ce HOS 3 Gey WSO Ce GSE sous et Gl see er a 3) cele Bic ag ees ooo ne On & O oe © Se oo og es 9 Caucasian male io... - 26 1550 18 107 750" 300) 44) 262 32° 1190 6s INGE TOM ALe! isrercie ele mele) - 22 Om Ge 95) 48) 28544 262s = 1905 6S Caticasian ftemalens ses zou bon i 05) 4292 ARIL * AXO) alts) all Negro female .......... 29) 186> 145 (90 43. 270) 43) 276, 29). 186. 156 The splenium is further from the brain center in the Negro than in the Caucasian, and it is further posterior in the female Negro than in the male. The foramen of Munro is nearer the brain center in the Negro than in the Caucasian and it is nearest in the female Negro. The genu is nearer the center in the Negro, and nearest in the female Negro. The splenium is further removed from the foramen of Munro in the female Negro than in any of the others. The genu is nearer the foramen of Munro in the females than in the males, there being no racial difference in either sex here. The corpus callosum and the foramen of Munro are both placed further posterior in the female Negro, indicating that more brain substance lies anterior to these structures in the female Negro than in the others. This corresponds to the findings in relation to the position of the fissure of Rolando. There is less brain substance anteriorly in the female Negro, the apparent discrepancy being due to the fact that the frontal lobes of the female Negro are long and slender. The male Negro has an intermediate position between the female Negro and the Caucas- sian in regard to the location of the corpus callosum and the foramen of Munro. 404 Some Racial Peculiarities of the Negro Brain BRAIN AXIS. The brain axis used in the measurements for this study is determined and located by three points, the inferior border of the splenium, the su- perior border of the anterior commissure and the foramen of Munro. A line is drawn on each outline of the mesial surface of each hemisphere 690 mn CAUCASIAN + O a NEGRO _. | S, aa ae po f H 13/00 Lag GRAM Cuart X.—Relation of the area of the brain outlines (ordinates) to brain weight (abscisse). The Caucasian is more variable, the Negro more con- stant. through these three points, to each extremity of the brain. This line is arbitrarily made to touch the lower border of the splenium and the upper border of the anterior commissure, and it passes through the foramen of Munro in 90% of the cases, and falls from 1 to 3 mm. below it in 10%. Robert Bennett Bean 405 The line passes through the longest diameter of the brain in 68% of the male Caucasian brains; 70% of the adult male Negro; none of the infant male Negro; 60% of the female Caucasian, and 334% of the female Negro. The line passes near the longest diameter, below in front and above behind, in 32% of the male Caucasian brains, 30% of the adult male Negro, 40% of the female Caucasian, 663% of the female Negro, and 100% of the infant male Negro. This gives a distinct gradation from the male Caucasian to the infant male Negro, the female Negro resembling most closely the infant type. In relation to the brain axis the infant has a larger amount of brain substance below the axis pos- teriorly, and a smaller amount below anteriorly, than is found in any of the others. When the brain axis does not exactly coincide with the long- est diameter of the brain, lines are drawn from the ends of the brain perpendicular to the axis, and in all cases the length of the axis between these lines coincides in length, practically, with the longest diameter of the brain. Refer to Figures 1 to 4 and 8 to 12 for evidence of these facts. The average distance between the lower border of the genu and the lower border of the frontal lobe is 22 mm. in the male Caucasian, 21 mm. in the male Negro, and 20 mm. in the female Negro. This difference, in connection with the extreme thinness of this part of the frontal lobe in the Negro, especially the Negro woman, indicates the frontal lobes to be even smaller than is apparent in the outlines, and by measurements taken from them. The brain axis is used because it is located definitely by three points that seem to be fairly constant in position, relatively; because it passes through the longest diameter of the brain in the majority of cases; be- cause it is a convenient line for measuring all parts of the brain in any position, thus facilitating speed and accuracy in brain measurements, and affording a just basis for comparison of any brain in the relation of its parts to each other and to other brains. By means of the brain axis a brain center is established which is constant within a small circle, and by a composite is shown to retain its position, relatively, in the brains meas- ured. It is located just above and anterior to the opening of the aque- duct of Sylvius into the third ventricle, a line drawn at an angle of 45° above the anterior end of the brain axis through the aqueduct of Sylvius passes through the brain center. It is just posterior to the gray commis- sure in the sulcus of Munro separating the alar from the basal lamina of the embryonic brain tube at a point that is perhaps as constant in posi- tion as any other during development. Shifting of the brain axis by ro- tation, antero-posteriorly or infero-superiorly, its usual variation when it changes, does not alter the position of the brain center. If its position 406 Some Racial Peculiarities of the Negro Brain is slightly altered by shifting the axis up and down, the relations to dif- ferent points remain the same. Shifting the position of the brain center forwards or backwards indicates altered relations of the anterior or pos- terior extremities of the brain outlines and is something to be desired as an indication of existing conditions. The brain center, then, is a com- paratively constant point and is a good one to use as a basis for all meas- urements of the brain. By means of the brain axis and the brain center, racial and sexual differences are demonstrated in the size and shape of the corpus callosum; in the position of the fissure of Rolando; in the amount of brain substance anterior and posterior to this fissure; in the relations of the foramen of Munro to the whole brain, to the whole cor- pus callosum, to the genu and the splenium, and the relation of these parts to one another and to other parts of the brain; and by means of the » brain axis and the brain center a system of notation is devised whereby any point anywhere about the brain may be located definitely and accu- rately. This may be done by representing the brain as a sphere, and us- ing degrees of latitude and longitude, in this way bringing everything to the brain center as a basis. The degrees of longitude may be represented by semicircles connecting the extremitis of the brain axis and extending over the surface of the brain in the direction of its long diameter. De- grees of latitude may be represented by lines joining the terminal points of radii drawn from the brain center to these semicircles. The anterior end of the brain axis represents the north pole, and the posterior end the south pole. The equator is represented by the outline of a vertical plane passing through the vertex of the brain and through the brain center at right angles to the brain axis, supposing the brain to be in its normal po- sition with the body standing erect in all this description. The brain axis will be horizontal under such conditions. A horizontal plane passing through the axis and the right hemisphere will cut a semicircle around the side of this hemisphere and this semicircle represents 0° longitude, which will be called L. 0°. Revolve this plane to the left and upward through a distance of 360° to its original position, and as it traverses the circle its different positions in the course of its transit will vary from 0° to 360°, any one of which may be located on the brain surface. Thus the mesial surface of each hemisphere above the axis will be L. 90°, the mesial surface below the axis will be L. 270°, the horizontal plane of the left hemisphere opposite L. 0° and similar to it will be L. 180°, and in- termediate planes likewise according to position. Jn like manner the planes of the outlines represented in Table IT will be L. 45° for the right hemi- sphere and L. 135° for the left. The degrees of latitude as radii from the brain center begin at the north pole and pass towards the vertex of Robert Bennett Bean 407 the brain through the equator above the axis, through the south pole and through the equator below the axis to the original position, describing a circle of 360°, the north pole being R. 0°, the south pole R. 180°, and intermediate points likewise. These radii are to be represented on any plane of Jongitude, and they may be placed so close together as to form a plane which will coincide with the anterior halves of L. 0° and L. 180° when the radii are R. 0°, with the equator above the axis when the radii are R. 90°, with the posterior halves of L. 0° and L. 180° when the radii are 180°, and with the equator below the axis when the radii are 270°. L. 0° and L. 360° are identical. R. 0° and R. 360° are identical. By combining the degrees of latitude and of longitude definite points may be located. For example, the vertex of the brain being at the central point of the equator above the axis will be L. 90° R. 90°, and the bifurcation (or junction) of the Crura cerebri will be about L. 270° R. 270°. ‘The point representing the right anterior association center as used in Table II would be L. 45° R. 45°, and a similar point in the left hemisphere would be L. 135° R. 45°. In this way any other point may be deter- mined. The brain center being located, the distance of any point from the brain center may be determined. Degrees of latitude are used instead of parallels of latitude in order to bring everything to the brain center as a basis. To sum up these: There is a north pole, the anterior end of the brain axis (R. 0°); there is a south pole, the posterior end of the brain axis (R. 180°) ; there is an equator circumscribing a plane which passes through the vertex of the brain and through the brain center at right angles to the brain axis; there are planes of latitude cutting sections of the brain from the periphery to the center beginning at the north pole and completing a circle by passing upward and backward to the south pole, and downward and forward from this point to the original position, the planes being represented by R. 0° to R. 360°; and there are planes of longitude cutting longitudinal sections of the brain, the planes passing from the horizontal plane of the right hemisphere upwards and to the left through a circle of 360° to the original position and being represented by L. 0° to L. 360° in their course. ADDENDA. Certain relevant subjects are not treated at length for various reasons, but are simply added as an appendix that anyone who is interested may examine, and take for what it is worth. Not much value is attached to these subjects, but there may be something of value and interest in them as discussed below. 408 Some Racial Peculiarities of the Negro Brain Brain WEIGHT. So many factors enter into brain weight that it is questionable whether discussion of the subject is profitable here. A few points will be touched on, however. The brain weight (Chart XI), actual or approximate, of seventy-nine Negro brains in the fresh state is given. The average for BRAIN WEIGHT CAUCASIAN NEGRO CHart XI.—Percentages of brain weight in the two races. fifty-one males is 1292 grams; the largest, 1560 grams; the smallest, 1010 grams. The average for twenty-eight females is 1108 grams; the largest, 1320 grams; the smallest, 910 grams. The brain weight, actual or approximate, of forty-six Caucasian brains in the fresh state is given. The average for thirty-seven males is 1341 grams; the largest, 1555 grams; the smallest, 1040 grams. The average for nine females is 1103 Robert Bennett Bean. 409 grams; the largest, 1275 grams; the smallest, 915 grams. The lot of brains includes a larger number from high-class Negroes than from high- class Caucasians, and a larger number from low-class Caucasians than from low-class Negroes, this being especially true in regard to the Negro males and the Caucasian females. This statement is based on the follow- ing facts: 1. There is a larger number of deaths resulting from acute illnesses and from accidents among the Negroes, giving a larger number of brains from normal individuals.” “ 2. That a larger number of Negro bodies are regularly disposed of to anatomists indicates less respect for the dead among Negroes, and it fol- lows that more of the better class of Negroes would be received, since the whites greatly outnumber the blacks in Baltimore. 3. It is weil known that only the lowest classes of whites are un- claimed, especially among the women, who are apt to be prostitutes, or depraved, or the like, while among Negroes it is known that even the better class neglect their dead unless provision has been made for their care after death. 4. It is a well attested fact that the Negroes are at present roaming over the country without fixed abode in greater numbers than the whites and this might result in many stray unclaimed bodies of the better class of Negroes being turned over to the anatomists, and finally, 5. Many Mulattoes and mixed bloods are included among the Negroes. So then the brain weights do not really represent the exact racial dif- ference between the Negro and the Caucasian, but do perhaps show that the low class Caucasian has a larger brain than a better class Negro. Many of the brains are from the senile, the demented, or those dying of wasting diseases, which would tend to make the average weight lower than among normal individuals. The total stature of the Caucasian ex- ceeds that of the Negro, and the total body weight is slightly greater in the Caucasian, the stature and body weight being greater in the males than in the females. The majority of the Caucasian males and Negro females were between the ages of 30 and 50, the majority of the others under 35 or over 45. The percentage curve of brain weight for the two races shows the greater number of Negro brains to be about 1100 to 1200 grams, the greater number of the Caucasian brains being 1300 grams and over, with a drop in the number of Negro brains at 1300 grams and an increase at 1400 grams, indicating a mixture of Caucasian and Negro in the largest brains. There are on record the weights of less than 100 Negro brains,” perhaps, with the exception of 380 weighed by Hunt and Russell,” who include Mulattoes and mixed bloods, as I have done. The 410 Some Racial Peculiarities of the Negro Brain average weight of twenty-two male Negro brains weighed by sundry men, at various times, in divers places with different systems of weights and under dissimilar conditions is 1256 grams; the largest, 1458 grams; the smallest, 1100 grams. The average weight of 10 female Negro brains under similar conditions is 980 grams; the largest, 1325 grams; the smallest, 738 grams. Waldeyer™ gives the average weight of twelve Ne- gro brains in the fresh state as 1148 grams; the largest, 1450 grams; the smallest 780 grams. Sandford B. Hunt*™” gives the average weight of 140 male Negro brains as 1331 grams; the largest, 1585 grams; the smallest, 1010 grams; the average of 240 male mixed bloods, Negro and white, 1285 grams; the largest, 1736 grams; the smallest, 980 grams. Hunt concludes by grouping the brains according to the estimated amount of white blood, that the weight varies directly in proportion to the amount of white blood. The mulattoes and those more than one-half white have brains nearly as large as the pure white and larger than the Negro, while those less than one-half white have smaller brains, those with the least amount of white blood having smaller brains than the pure Negro. Practically the same conclusion is reached by a similar classification of the male Negro brains I weighed. The average for the mulattoes is 1347 grams; for those one-fourth white, 1340 grams; for the one-eighth white, 1335 grams; for the one-sixteenth white, 1191 grams; but for the pure Negro 1157 grams. The difficulty about any such classification is that no two individuals may agree as to what constitutes the exact markings of the different grades. Only those Negroes should be considered pure that show no evidence of any previous crossing with another race at a previous time, perhaps the low-class Guinea Coast Negro representing this type in the brains studied. Certainly the high-class Guinea Coast Negro and the Kaffir (Zulu) show unmistakable evidence of a previous mingling of races. (Topinard).™ The conclusion is that the brain of the Negro is smaller than the brain of the white, the stature is also lower, and the body weight is less, and any crossing of the two races results in a brain weight relative to the proportion of white blood in the individual. The skull capacity of the Negro has been repeatedly demonstrated to be less than that of the Caucasian.” TEST TO DETERMINE RACE AND SEX OF BRAINS. When this work was undertaken I had handled comparatively few brains, so I examined about twenty and measured them in various ways before attempting to differentiate the Negro from the Caucasian brain, Robert Bennett Bean 411 or the male from the female. After that a record was kept of the guess made on each brain, except those I could recognize from previous hand- ling, before the race or sex was known, these being looked up afterwards, to determine the degree of accuracy possible in such a guess. The race was determined correctly 70 times, doubtfully 5 times, and incorrectly 5 times in 80 brains. The sex was determined correctly 69 times, doubt- fully once, and incorrectly 10 times. The race and sex were determined correctly 60 times, one or the other correctly 15 times, and incorrectly 5 times. Of the 5 incorrect guesses a Caucasian female brain was taken to 1200 Cuarr XIl.—Percentages of brain weight, in relation to stature and body weight combined. be a Negro male in one case (No. 1583), a Negro female in another (No. 1527) ; a Caucasian male brain was taken to be a Negro male in two cases (Nos. 1716 and 1749), but with one of these there was some doubt; and a Negro male was taken to be a Caucasian male in one case (No. 1707). Mulattoes partook of one type or, the other as a rule, sometimes resembling the Negro and sometimes the Caucasian more closely. CONCLUSIONS. 1. The brain of the American Negro is smaller than that of the American Caucasian, the difference being primarily in the frontal lobe, and it follows that the anterior association center is relatively and abso- lutely smaller. , id 412 Some Racial Peculiarities of the Negro Brain 2. The Negro brain can be distinguished from the Caucasian with a varying degree of accuracy according to the amount of admixture of white blood. > 3. ‘The area of the cross section of the corpus callosum varies with the brain weight. However, in the Negro its anterior half is relatively smaller than in the Caucasian, to correspond with the smaller anterior association center ; the genu is relatively larger and the splenium relatively smaller. 4. From the deduced difference between the functions of the anterior and posterior association centers and from the known characteristics of the two races the conclusion is that the Negro is more objective and the Caucasian more subjective. The Negro has the lower mental faculties (smell, sight, handicraftsmanship, body-sense, melody) well developed. the Caucasian the higher (self-control, will power, ethical and esthetic senses and reason). BIBLIOGRAPHY. 1. Barker, L. 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Sci., 1892. 414 57. 58. 59. 60. 61. 62. 63. 64. 65. 66. 67. 68. 69. 70. fly Some Racial Peculiarities of the Negro Brain Mortron.—Crania Americana, Philadelphia, 1839. Observations on the Size of the Brain in Various Races and Families of Man. Proc. Acad. Nat. Sci., IV, Philadelphia, 1848-9. Parker, A. J.—The Cerebral Convolutions of the Negro, Proc. Acad. Nat. Sci., Phila., 1879. Peacock, THos. B.—On the Weight of the Brain in the Negro. Memoirs read before the Anthropological Society of London, I, 1863-4. Deutsche Zeitschrift fiir Nervenheilkunde, XXVIII. PEARL, R.—Variation and Correlation in Brain Weight, Biometrika, 1905. PrRuNER Bey.—Mémoir de la Soc. d’Anthropologie, Paris, 1865, II. Rei, JoHn.—Tables of the Weights of some of the most important organs, ete. London and Edinburgh. Monthly Journal of Medical Science, III, 1843. Retzius, A.—Ethnologische Schriftian, Stockholm, 1864. Retzius.—Ueber das Gehirngewicht der Schweden. Biologische Unter- suchungen, N. Folge, IX, 1900. Biologische Untersuchungen, VIII, IX, X and XI. SaBIN, FLoRENcE R.—On Flechsig’s Investigations on the Brain. Johns Hopkins Hospital Bulletin, 1905. SCHWALBE.—Neurologie, S. 555, 556, und Rtidinger, Ein Beitrag zur Anat- omie der Affenspalte und der Interparictalfurche beim Menschen nach Race, Geschlecht und Individualitat. Beitrage zur Anatomie und Embryologie. Festgabe an Jacob Heanle. Bonn, 1882. SHALER.—The Negro Since the Civil War. Popular Science Monthly, WOES eel O00: Simon, E.—Philosophical Transactions, 1864. SmitTH, G. ELuiorr.—The Morphology of the Occipital Region of the Cere- bral Hemispheres in Man and the Apes. 9 Figures. Anatomische Anzeiger. Bd. 24. Journal of Anatomy and Physiology, XX XVII, 1903. SOMMERING, S. TH. V.—Ueber die korperliche Verschiedenheit des Negers vom Europaer, 1785. SpitzKA, E. A.—The Development of Man’s Great Brain, Connecticut Magazine, 1905. Proc. Ass. Am. Anat.—Am. Jour. Anat, IV. TIEDEMANN, F'rR.—Das Hirn des Negers mit dem des Europ. u. Orang- Utang. Verglichen. Folio, Heidelberg, 1837. On the Brain of the Negro Compared with that of the European and the Ourang Outang. Philosophical Transactions, CX XVI, Lon- don, 1836. TOPINARD, PAuL.—Revue d’Anthrop., II. Eléments d’Anthropologie Générale, 1885. TURNER.—On the Relations of the Convolutions of the Human Cerebrum to the Outer Surface of the Skull and Head. Jour. Anat. and Phys., VII. VircHow, RupotpH.—The Cranial Affinities of Man and the Ape, Bos- ton, Lee and Shephard, 1871. Archiy.*ftir Anthrop., IV, 1871. 82. 83. 84. Robert Bennett Bean 415 WaaGner, R.—Vorstudien des menschlischen Gehirns. Morphologie und ee des menschlichen Gehirns als Seelen- organ. WALDEYER.—Ueber einige Anthropologisch. bemerkbare Befund an Neger Gehirnen. Sitz. bei d. K. Preuss, Akad. d. Wissensch. Berlin, 1894. WELCKER.—Untersuchungen tiber Wachstum und Bau des menschlichen Schaedels, Leipzig, 1862. WerspacH, A.—Die Gewichts verhaltnisse der Gehrine ésterreichischer Volker. Archiv. fiir Anthropologie, I, 1866. Der Deutsche Weiberschadel. Archiv ftr Anthropologie, III, 1868. Witson, DanreL.—Brain Weight and Size in Relation to Relative Capac- ity of Races. Read before the American Association for the Ad- vancement of Science at Buffalo, N. Y., 1876. Also in Canadian Journal, Toronto, 1876. Wyman.—Proceedings of the Boston Soc. Nat. Hist., LX. Articles on Brain Weight. Nos. 2, 4, 7, Ord Owl 145 5; bz, 20,28; 29, 30, 31, 32, 33, 34, 35, 37, 38, 39, 40, 41, 42, 48, 47, 49, 51, 52, 53, 55, 59, 62, 65, 66, 68, 72, 74, 1. ela, TAS ehatell 103): Articles on Skull Capacity. Nos. 4, 5, 6, Hewes to, Ade25. (a0, 46; £1, 49, 54, 65, 66, 67, 68, 70, 75, 77 and 78. Articles on Form and Structure of Brain. INi@sy dl, By 6, IMS als, illo. 17. 18), 19, 215.223, 24,.25,.-26; 31, 33, 34, 35, 36, 44, 45, 48, 52, 56, 57, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, Ree Vals Ties Eiale7G)- Articles on Head Size and Brain Weight. Nos. 3, 8, 9, 14, 16, 21, 92, 23, 26, 27, 31, 36, 37, 41, 42, 50, 68, 69, 70, 76 and 77. Articles on Classes of Negroes. Nos. bo Gist alls Bap tudan ckeaeG, 29, 30, 32, 58, 62 and 68. APPENDIX. TABLES II TO VII. 416 Some Racial Peculiarities of the Negro Brain TABLE II—LENGTH OF THE RADII IN MILLIMETERS FROM THE DEGREE OUTLINE. ALSO DISTANCE OF FRONTAL AND OCCIPI CENTIMETER FROM EACH END OF THE BRAIN. DEGREES BE NEGRO MALE. LEFT SIDE. + Brain No. axis saad (1) 10° 20° 30° 40° 50° 60° 0° 80° 90° 100° 110° 120° 1189 176 86 89 87 84 80 75 71 70 68 68 72 75 76 1190 184 89 92 89 82 77 70 66 64 63 66 68 72 73 1456 164 75 82 81 vas 73 7 69 65 65 67 71 74 76 1466 180 89 90 89 84 78 73 71 69 69 69 71 73 75 1470 164 78 84 86 80 74 65 61 Ve 57 57 59 62 64 1472 154 62 78 76 75 71 66 62 60 59 61 64 69 72 1473 160 77 81 82 78 71 64 62 61 61 62 68 71 73 1476 164 79 84 83 78 75 70 67 65 65 67 70 73 75 1478 166 80 83 81 75 71 68 65 62 64 63 67 69 72 1480 180 86 91 90 85 79 74 73 73 73 76 80 80 83 1486 174 85 88 87 82 75 69 67 65 63 63 67 69 71 1492 164 83 85 82 78 71 68 64 63 62 63 66 70 74 1495 170 83 87 85 81 75 69 65 64 63 64 66 72 73 1497 170 79 85 85 82 76 70 63 63 61 60 63 66 wal 1502 164 76 84 86 84 80 74 69 66 65 64 65 67 70 1511 158 78 83 83 82 75 71 65 64 62 62 64 66 68 1519 160 74 78 79 75 70 66 64 64 63 65 69 73 75 1528 176 84 87 85 79 76 72 70 67 69 71 74 76 79 1530 158 7 78 77 74 68 64 61 61 61 62 65 67 69 15382 188 92 95 88 81 74 70 68 67 68 70 76 79 82 1533 160 77 82 84 80 76 69 65 62 61 61 63 65 68 1661 156 69 76 Ge 75 72 66 62 60 59 59 60 62 65 1680 166 78 84 84 80 73 67 65 62 60 61 62 63 67 1691 172 80 90 86 80 74 69 65 63 63 62 63 65 67 1699 166 75 83 85 83 78 71 67 63 62 62 65 68 70 1701 167 80 84 83 81 7 69 67 65 67 68 70 73 75 1704 177 85 92 90 84 78 72 69 67 68 69 71 73 75 1706 173 83 89 89 85 78 74 70 69 69 71 73 75 74 1709 181 88 92 89 84 77 73 71 71 68 70 71 74 75 1711 159 76 80 80 74 68 66 64 62 62 64 67 72 73 1713 171 75 86 87 83 80 73 69 67 67 69 73 77 80 1718 156 72 79 77 75 72 67 65 64 65 67 69 72 75 1727 180 86 91 91 84 79 74 67 64 62 61 62 66 70 1728 182 81 90 91 86 78 72 69 68 68 70 74 78 82 1731 176 80 88 88 84 78 74 72 72 71 75 78 81 83 1736 164 78 82 80 80 75 70 66 66 65 67 71 7 78 1738 173 7 84 86 85 78 73 68 64 61 62 65 67 69 2521 171 84 87 86 82 77 71 69 68 67 71 73 74 76 2522 171 86 87 85 82 77 72 70 67 67 69 71 7. 75 2524 165 81 82 83 79 73 69 68 68 68 70 72 73 73 2535 160 75 82 81 78 71 67 63 62 63 65 68 70 72 105 148 70 75 75 73 68 64 62 60 60 60 62 65 68 173 171 83 87 84 78 72 Avs. 43 168 80 85 84 ~=80 73 70 66 65 65 65 68 71 73 NEGRO FEMALE. LEFT SIDE. 1449 164 76 83 84 80 74 69 64 62 62 61 62 66 69 1459 162 81 83 78 74 67 64 60 59 57 58 60 65 68 1477 160 78 80 81 76 71 68 65 64 63 63 67 68 70 1479 162 82 82 82 77 72 67 64 60 61 63 65 65 69 1487 150 74 75 73 68 63 60 58 57 56 57 59 63 65 1493 166 80 §=68&3 83 78 71 66 61 60 59 ~3=B8 61 63 65 1500 154 77 78 75 72 66 62 57 57 57 59 61-62 64 1501 144 71 79 82 74 69 65 63 62 61 63 67 69 70 1515 164 80 80 78 74 71 66 64 62 62 63 66 70 69 1544 160 80 81 81 78 72 68 66 64 63 64 68 70 72 \ Robert Bennett Bean 417 BRAIN CENTER FOR EACH TEN DEGREES ON THE FORTY-FIVE- TAL LOBES BELOW THE AXIS OF THE BRAIN, MEASURED AT EACH GIN WITH 0° AT ANTERIOR END OF BRAIN AXIS. NEGRO MALE. LEFT SIDE,—(Continued across.) From anterior end. From posterior Index. end. associa- —-— "w——- a ition 130° 140° 150° 160° 170° 180° 1lem.2em. 38cm. 4cm. 5cm. lem. 2cm. 38cm. centers. 76 77 77 79 84 88 8 11 13 14 12 11 5 ae 93 75 76 77 79 85 92 5 8 10 11 11 12 12 we 89 77 79 79 80 82 80 7 11 12 13 10 6 3 a0 90 76 77 80 86 89 88 11 12 13 12 10 9 11 6 94 66 70 72 75 80 82 5 10 12 12 22, 15 ss 95 5 75 76 76 76 79 69 —2 1 5 8 ae 1 10 6 86 74 76 75 76 79 79 5 8 9 11 10 12 14 4 84 76 77 78 79 82 83 7 11 13 14 12 8 9 5 89 74 77 79 81 84 83 11 10 12 14 11 8 11 5 90 84 85 85 89 93 85 5 9 9 9 9 1 2 0 88 73 15 80 81 85 86 7 10 12 14 13 10 8 sie 94 76 77 78 79 80 82 8 18 15 16 14 18 18 5h 86 74 76 77 78 79 84 5 8 10 9 5 9 10 06 89 73 76 79 83 83 84 3 13 12 13 14 7 14 6 88 12 73 73 74 79 80 1 5 9 10 10 15 12 u 98 7 70 72 73 76 80 4 8 9 9 8 19 16 12 95 77 78 78 78 81 75 5 8 10 9 8 0 2 85 82 84 84 85 89 70 8 12 16 17 iis) Ps 1 88 71 72 75 75 78 77 5 8 9 10 10 5 6 1 88 83 84 87 91 95 88 15 18 17 15 14 5 9 1 83 70 72 75 76 78 79 4 7 10 10 14 a0 95 66 68 69 71 74 76 4 9 11 10 5 8 AG 95 70 73 75 77 81 84 5 7 10 11 10 Ul 10 os 96 71 77 79 81 83 86 5 8 (3) 15 9 11 12 12 97 73 75 76 77 80 81 il 5 7 9 6 9 10 5 95 76 77 78 80 83 82 6 11 14 14 14 9 3 89 77 78 82 84 87 85 5 8 9 10 ul ul 5 0 90 75 77 UG 80 86 85 5 8 10 11 9 4 4 94 79 79 81 83 87 91 8 11 12 13 14 16 14 94 76 79 78 80 78 68 6 11 12 12 1G} = 5 0 87 81 82 83 85 84 75 0 2 5 6 4 0 6 2 86 77 78 79 82 78 65 3 9 10 12 Ze 2 1 29 86 74 77 80 84 88 90 5 u 9 9 9 7 12 6 95 84 83 84 85 89 86 1 1 6 7 8 2 il os 84 84 84 85 87 88 71 6 9 9 10 101 0 —1 86 80 80 82 81 83 73 5 6 6 6 4 0 5 0 84 7. 75 75 77 82 83 2 6 9 11 11 14 i ce 98 78 81 81 85 86 72 4 9 12 13 9 —4 3 90 77 78 78 79 84 80 10 11 11 11 10 5 6 a 93 76 76 76 78 82 79 10 11 12 14 13 5 6 93 74 76 77 82 78 78 3 6 7 8 9 4 5 87 70 70 70 69 72 71 3 5 7 7 5 30 91 69 73 76 81 85 83 10 14 15 16 17 6 4 94 75 76 78 80 83 80 5 9 i) abt 10 6 8 3 90 NEGRO FEMALE. LEFT SIDE.—(Continued across.) 71 75 77 78 79 82 3 u 10 11 7 17 18 10 92 70 74 75 77 80 81 ul 12 14 17 17 2 3 sis 88 69 69 70 75 80 75 8 9 13 14 11 10 5 % 92 72 74 76 77 79 82 2 7 10 10 10 12 11 ne 92 67 69 70 71 74 74 9 12 14 16 15 8 9 89 68 72 76 79 82 78 8 11 12 12 10 1 5 Se 93 68 72 72 73 77 77 9 14 14 11 7 3 1 ye 86 70 7 69 67 68 71 8 11 11 10 ate 16 10 ae 90 69 70 73 77 83 80 8 9 12 11 6 7 4 is 92 1 74 75 75 76 77 80 4 9 11 8 11 15 7 91 Some Racial Peculiarities of the Negro Brain TABLE JI.—ContTinvueEp. No. 1593 1659 1678 1684 1685 1686 1695 1700 1715 1722 1730 163 Avs. 22 1189 1190 1453 1456 1466 1470 1472 1473 1476 1478 1480 1486 1492 1495 1497 1502 1511 1519 1528 1530 1532 1533 1661 1680 1691 1699 1701 1704 1706 1709 1711 1713 1718 1727 1728 1731 1736 1788 2521 2522 2524 2535 105 173 B.V.87 Avs. 45 Brain axis. 148 168 158 176 160 160 158 161 145 149 146 153 158 176 180 168 164 180 160 158 160 162 170 180 176 162 166 170 166 160 160 176 158 180 160 156 164 170 168 169 174 169 179 160 174 157 182 180 176 167 174 173 169 163 159 148 173 162 168 ITO MW OS Oe 89 “Its “10 IM © ~r “10 I-10 owooe 10° 79 81 80 87 86 NEGRO FEMALE. 20° 74 79 NEGRO MALE 86 90 85 79 80° 70 78 79 84 79 75 71 80 74 75 72 73 75 81 85 78 75 74 71 81 73 72 as LEFT SIDE. BOS 6098 709 62 60 60 68 66 64 71 66 63 72 69 68 69 63 61 68 66 65 62 59 59 70 66 65 61 58 57 68 65 65 63 59 58 62 57 55 66 62 61 RIGHT SIDE. 73 69 66 68 65 63 70 67 66 68 64 63 ath 75 72 67 62 60 67 62 59 64 63 61 68 65 65 61 63 63 70 67 66 71 67 65 64 63 61 71 67 66 72 69 68 67 64 63 67 65 64 68 65 64 76 73 72 70 66 65 70 67 66 70 66 62 61 62 62 65 62 57 65 61 60 7. 68 65 72 69 68 (Pe 68 66 70 68 67 74 71 69 70 67 66 70 66 65 65 63 62 74 67 62 74 68 64 73 69 67 71 69 68 73 68 65 71 69 68 70 68 67 val 70 68 68 65 63 62 63 60 71 67 66 71 68 66 70 66 64 80° 110° 120° 65 65 66 70 65 70 70 74 68 72 2 ae 68 70 70 73 58 61 70 gil 64 65 62 65 66 68 74 76 70 73 72 75 71 75 77 79 65 69 67 ral 71 76 69 72 70 73 73 77 72 76 69 1 71 73 72 74 68 72 68 71 - 74 76 78 80 69 72 76 80 66 70 69 rel 64 67 64 69 71 74 7 Ue! 72 76 74 76 74 76 72 74 730 18) 69 73 65 68 69 72 76 78 76 78 68 70 (Al 72 73 77 71 74 71 73 66 67 72 75 72 74 0) eet Robert Bennett Bean 419 NEGRO FEMALE. LEFT SIDE.—(Continued across.) From anterior end. From posterior Index end. associa- = ad = A, tion 130° 140° 150° 160° 170° 180° l1cm.2cm. 38cm. 4cm. 5cm. lem. 2cm. 38cm. centers. 65 65 66 71 75 70 12 13 12 10 ae 6 2 ts 92 71 74 76 79 83 82 7 12 12 13 11 8 13 ; 94 73 74 77 LL 75 76 0 3 6 7 50 138 11 5 94 77 79 81 83 85 88 0 5 9 9 7 8 12 fe 93 74 76 75 74 75 7 i 5 @ 8 11 11 15 9 87 72 74 76 78 82 69 9 13 12 all 7 —2 4 -—1 90 70 72 74 75 it 79 11 14 16 15 14 5 10 12 84 to 76 76 78 81 70 3 9 12 12 8 0 0 Ne 98 : 62 64 66 69 71 72 0 4 a 7 ae 12 us 95 72 73 72 72 78 74 —3 2 6 8 6 6 if 95 67 69 (2 74 72 69 —2 1 4 6 4 38 —1 90 66 68 70 ffl 71 76 2 8 10 11 7 20 19 87 70 72 73 75 77 77 5 8 10 10 9 9 9 7 91 NEGRO MALE. RIGHT SIDE.—(Continued across.) 76 76 77 80 86 88 9 14 16 18 17 4 11 9 90 75 78 80 81 85 88 3 6 10 11 iil 8 17 17 88 77 77 76 83 85 80 —2 3 tf 8 8 4 3 ots 88 77 78 79 82 84 73 4 10 13 14 12 0 3 85 82 81 83 87 91 85 8 13 15 16 16 2 9 8 94 tm 74 77 77 80 75 1 7 11 9 3 7 a0 89 74 (lif titi 74 78 79 1 7 11 10 13 15 8 87 77 78 78 Us 80 78 8 10 12 12 10 3 10 5 82 {iD 76 78 78 81 82 9 12 15 16 16 5 5 2 90 74 76 78 79 82 85 int 14 15 13 10 9 11 10 86 80 82 88 90 91 86 8 12 14 15 11 1 2 0 87 79 81 83 84 87 85 7 11 11 12 13 3 9 6 88 74 75 75 77 80 76 8 15 17 aly; 16 3 it 11 88 75 76 79 80 84 84 4 1 10 8 7 10 11 ae 91 (ME 79 81 81 85 85 1 6 9 10 8 12 14 93 74 74 75 75 81 81 8 14 15 15 13 4 9 5 88 72 72 73 74 78 80 6 10 11 11 11 ra 9 5 91 76 76 77 79 81 ate 6 8 8 7 7 -6 -4 -8 85 82 82 83 86 88 82 6 11 12 13 11 6 if 2: 91 74 76 75 76 80 73 Cie 10 9 8 2, 7 1 91 82 83 84 88 92 87 8 13 13 3 2 5 85 72 75 78 79 81 78 4 a 9 8 14 15 94 72 74 77 80 val ve 5 9 10 9 —9 —5 87 70 iP 76 ie 80 80 iG 10 12 12 12 14 12 49 92 70 75 79 80 80 85 6 10 19 19 ae) ea 20 17 88 77 77 78 79 81 81 4 8 11 11 8 6 8 89 78 78 78 82 84 83 4 9 11 12 ali! 6 14 91 77 79 82 88 89 76 5 9 10 10 10 —2 0 88 76 76 78 82 87 76 8 10 14 15 14 0 5 89 80 82 84 86 91 86 8 11 15 14 13 2 7 94 74 75 76 77 80 67 6 11 12 10 —2 3 90 80 81 82 82 84 86 2 5 8 10 10 13 9 84 75 77 78 80 80 70 7 ia 14 16 15 0 4 85 71 75 7 82 89 909 —2 1 5 10 11 7 15 15 98 74 76 79 82 85 91 —6 0 3 6 if 20 18 94 80 82 84 84 89 83 Uf 10 13 13 12 3 14 88 79 80 80 80 83 80 2 9 12 13 12 4 2 88 72 73 75 77 83 80 1 6 11 13 11 4 = 97 74 75 76 80 84 83 8 12 1) 15 12 9 12 95 79 80 82 82 84 80 8 10 12 13 12 0 3 88 75 76 7 79 82 71 7 10 11 13 14 3 10 94 73 73 76 77 80 76 2 4 8 10 8 7 13 89 69 70 71 70 73 66 —1 2 6 7 3 5 94 78 80 80 85 87 76 Ul 11 13 15 16 0 6 89 76 77 77 78 81 76 —4 2 6 9 7 6 f 90 76 77 78 80 83 80 5 8 11 Pye aly, 5 8 7 89 420 Some Racial Peculiarities of the Negro Brain TABLE I[I.—CoNTINUED. NEGRO FEMALE. RIGHT SIDR. + Brain No. “axis ee OS) 10° 20° «630° «€6©40°) = iB0°-—s«éaBOP—Cé‘Z-—s« BOP-—s«#—930-—s-:«1009-—s-:«110° 120° 1449 162 72 79 80 81 77 73 66 66 63 62 62 64 68 1459 164 81 82 79 73 68 66 62 61 60 61 64 66 70 1477 160 78 80 81 76 70 64 62 61 61 60 63 65 68 1479 162 78 81 82 79 73 69 66 64 62 63 66 68 71 1487 152 68 76 78 Ue 74 70 67 66 65 65 67 68 69 1493 166 79 81 77 75 69 65 63 62 61 62 63 66 69 1500 154 75 75 74 70 66 61 56 57 58 57 59 59 61 1501 142 71 72 74 75 72 68 65 63 63 65 67 69 70 1515 160 7 76 74 71 66 65 62 60 62 65 69 69 70 1544 160 74 81 81 79 74 69 67 66 65 67 70 73 74 1593 148 74 73 71 66 61 58 56 56 55 55 60 61 63 1659 168 81 82 81 74 68 63 60 60 59 61 63 65 70 1678 160 70 78 80 79 75 69 64 62 60 60 62 65 68 1684 176 82 90 88 84 76 69 63 60 60 60 61 65 68 1685 158 72 79 82 77 71 67 62 59 58 59 59 62 65 1686 160 79 80 82 78 72 69 66 66 67 69 70 72 74 1695 160 76 81 81 72 71 66 63 63 65 66 69 71 73 1700 161 72 82 83 80 75 70 66 65 69 67 69 70 72 1715 147 67 74 75 (al 65 62 60 59 57 56 58 60 62 1722 151 65 78 82 75 72 66 64 63 62 62 67 US 72 1730 149 65 75 75 72 67 62 59 59 58 59 63 65 66 163 148 69 79 82 76 71 66 62 60 61 61 65 66 68 vst Moore AEBS: va) 79 70 5 Leas G6) GS 62 cel. * 6216s. co meee CAUCASIAN MALE. LEFT SIDE. 1406 172 82 88 88 86 82 75 72 72 7p 70 72 75 V7 1455 172 86 86 82 78 75 73 69 68 68 69 68 70 70 1457 165 85 85 85 81 74 69 66 65 64 65 67 67 68 1458 174 85 87 85 82 Ue 73 71 70 70 7 73 75 76 1463 184 88 92 92 87 81 78 44 73 72 73 77 79 81 1469 172 85 86 85 81 78 73 69 67 66 66 68 71 71 1489 168 84 85 84 80 76 72 69 68 66 67 69 70 71 1490 173 87 88 85 81 7 74 73 74 74 74 74° 75 74 1496 174 82 88 88 84 79 73 70 67 65 65 65 68 70 1512 166 74 84 86 85 81 75 71 69 68 66 66 68 70 1514 170 85 86 84 80 75 74 72 70 70 71 72 72 73 1529 172 81 87 90 89 85 81 79 78 77 77 80 81 81 1538 162 81 80 79 7 68 66 65 62 62 63 64 66 69 1591 164 81 82 85 83 77 71 69 68 67 67 70 69 71 1682 170 75 86 89 85 82 76 72 69 67 65 67 69 ua! 1683 164 81 82 78 77 74 72 69 68 69 70 71 70 72 1690 170 82 87 87 83 77 74 72 70 69 69 70 72 72 1693 166 63 85 88 89 84 ue 74 71 67 66 66 67 69 1696 168 81 85 82 78 75 72 69 67 67 68 69 70 71 1702 164 73 82 84 82 76 72 70 66 64 64 66 68 69 1707 177 84 89 90 82 76 72 67 62 61 61 67 66 68 1708 169 82 85 83 80 75 72 71 68 66 66 67 68 69 1712 167 82 81 82 73 69 68 67 66 67 69 70 71 72 1716 165 81 85 82 76 71 69 66 65 67 69 71 70 71 1719 173 86 86 86 81 7 72 70 68 70 71 75 75 75 1723 161 72 81 81 77 75 70 69 68 68 68 69 70 74 1734 166 75 84 86 82 79 73 69 67 65 67 67 68 70 1748 185 89 93 92 90 84 82 77 75 77 77 as 78 79 1749 164 73 84 85 85 82 77 73 68 68 69 69 72 72 177 159 75 79 80 77 70 66 64 60 59 61 63 61 64 1G. 160 78 80 79 74 69 65 66 62 61 62 62 63 66 3G. 162 81 84 82 78 73 69 67 65 64 64 65 65 65 4G. 156 76 79 77 73 69 65 62 58 57 57 58 60 61 6G. 156 70 78 80 78 73 71 68 66 66 67 69 71 72 Avs. 34 168 80 85 85 81 76 72 70 68 67 65 66 70 71 130° 69 72 70 75 70 71 140° 74 74 150° 75 a io CrsT ee bo “ID I-17 I tor) Robert Bennett Bean NEGRO FEMALE, RIGHT SIDE.—(Continued across.) From posterior Index 160° 78 78 75 170° 80 81 77 78 84 84 83 87 90 84 84 84 84 83 82 87 79 79 86 83 85 82 84 180° 76 86 86 85 86 90 85 84 87 86 78 86 86 81 81 73 75 87 78 82 78 86 80 83 76 80 83 72 7 79 79 83 79 71 81 From anterior end. end. 421 associa- tion ———a4t——_7 lem. 2cm. 3em. 4cm. 5em. lem. 2cm. 3em. centers. _ eb HH = oO Nore SNoRF, WWONFK WOMT10D Co _ DoT © oo CORSO et Bee BOWAon HOMNSH CHE paR, ee New TWOANN ~I 7 14 8 = a = ornas$ He © an~t Oost or DOr OO 7 19 8 14 14 i 13 15 unt 6 17 9 16 9 16 12 11 11 14 9 ul 13 12 itz 5 10 10 12 19 1R| 17 15 9 15 18 15 9 19 10 17 9 15 12 9 13 13 9 10 14 17 5 13 11 8 11 11 8 9 10 14 14 7 14 Mw oOo NO BYOTH 14 4 13 7 10 Se | = De oT = OPONNT OOSNN = es long 10 —(Continued across. ) 12 19 11 18 16 11 15 18 15 10 19 10 15 8 10 16 15 5 16 11 10 17 21 15 15 11 10 11 7 12 13 16 16 iit 14 10 15 10 17 14 11 11 15 14 10 15 10 15 8 13 13 w 10 6 12 ~T He OT BO tay, one ite 22 Some Racial Peculiarities of the Negro Brain TABLE II.—ConrinvueEp. CAUCASIAN FEMALE. LEFT SIDE. INGE Brain AXIS. go 10° 20° 30° 40° 50° 60° 70° 80? 90° 100° 110° 120° 1510 170 80 85 84 79 72, 67 66 65 63 65 67 70 71 1522 150 70 76 76 72 68 65 62 61 59 60 60 62 65 1527 164 73 82 82 80 74 68 66 63 63 64 66 68 69 sie IX) Bay GE A GD GR GR GR GH TDG 1692 162 78 81 80 79 73 69 65 63 62 64 66 69 70 1697 156 75 78 77 72 68 63 60 58 58 59 60 61 62 2G. 156 75 78 77 74 69 64 63 62 61 62 62 63 64 5G. 150 67 76 71 67 64 63 59 58 58 59 61 62 Avs. 8 161 (> 81 80 77 71 67 64 62 61 62 63 66 67 1406 174 74 88 90 88 80 75 72 70 69 69 69 71 73 1455 172 86 86 81 78 75 74 71 70 (al 73 75 77 76 1457 165 75 85 86 78 72 68 67 66 65 65 67 68 69 1458 172 81 85 81 81 74 70 69 68 69 70 72 75 Uff 1463 182 84 91 93 89 86 83 81 78 73 74 76 79 79 1469 172 80 87 82 79 75 71 68 66 63 64 66 68 70 1489 166 78 84 83 80 75 72 69 67 66 67 68 70 74 1490 170 83 86 87 80 78 73 72 70 69 71 73 74 74 1496 174 82 88 91 88 84 81 aad 73 70 70 71 72 73 1512 170 81 86 91 87 82 74 68 66 65 64 67 68 tak 1514 168 84 84 83 78 74 73 71 70 6) 70 73 74 74 1529 172 82 88 85 84 78 75 73 72 71 71 75 76 78 1538 162 79 81 78 74 70 68 68 66 67 68 70 71 72 1591 162 69 82 85 83 79 74 72 72 69 68 71 71 72 1682 170 77 88 89 84 78 75 73 71 71 71 7 72 75 16838 164 80 82 79 76 (fil bas or) ~J a for) D> oo D> > OV > rs lor) or) or =o o 1690 170 82 86 87 83 79 ‘ 1693 166 65 82 87 87 84 78 76 74 74 73 7d 76 ig 1696 170 81 86 85 81 78 73 70 68 67 68 71 71 73 1702 160 70 80 81 79 75 72 70 68 65 65 66 68 69 1707 174 75 85 88 83 79 75 70 67 68 67 70 73 74 1708 170 80 84 85 81 77 74 72 71 70 70 71 72 73 1712 168 73 83 85 84 78 74 70 70 69 71 73 74 74 1716 162 77 81 81 78 74 7 69 68 68 69 72 74 75 1719 176 86 88 84 82 75 72 70 68 70 71 73 75 75 1723 163 75 81 82 80 75 73 71 71 69 69 72 73 73 1734 168 69 83 86 83 78 75 70 67 67 65 67 68 69 1748 183 90 92 91 88 84 80 77 75 76 75 76 78 80 1749 159 73 79 82 80 75 72 70 68 68 70 72 72 75 177 158 74 80 83 79 72 66 64 60 59 59 61 63 63 1G. 160 79 81 79 72 66 63 58 55 55 56 56 59 61 3G. 160 76 81 80 77 72 68 65 61 61 62 63 65 66 4G. 152 72 75 76 76 73 20 68 67 Cie) Gian 64 68 6G. 156 72 ie i 79 76 72 68 64 63 65 67 67 69 Avs. 34 167 78 84 84 81 77 73 70 68 65 65 69 71 72 CAUCASIAN FEMALE. RIGHT SIDE, 1510 168 84 85 84 81 73 71 69 69 66 67 70 72 72 1522 148 68 73 76 72 64 60 63 61 60 59 61 62 63 1527 160 75 81 81 80 74 * 68 65 62 62 65 66 70 69 1583 176 85 88 88 82 76 72 69 66 66 62 69 73 76 1692 164 80 83 83 79 73 69 66 64 62 62 65 68 71 1697 157 75 78 76 64 67 62 60 58 58 57 58 60 61 2G. 152 72 77 79 76 71 66 62 58 57 56 58 59 62 5G. 150 64 72 77 72 69 66 64 60 58 56 58 59 60 Avs. 8 160 75 80 81 76 71 67 65 62 61 61 63 65 67 Robert Bennett Bean. CAUCASIAN FEMALE, LEFT SIDE.—(Continued across.) From posterior Index From anterior end. 423 130° 140° 150° 160° 170° 180° Jem. 2em. 8em. 4cm. 5em. lem. 2em. 38cm. centers. 73 74 77 76 82 81 85 75 82 85 80 77 80 (peer [Sees bt - | oO aoa Beasts Bae HOWOM CNSAG NROwWN NHL ED CAUCASIAN FEMALE, RIGHT SIDE,—(Continued across.) 80 70 a = wo AOkKDS end. associa- — tion 9 11 13 13 8 9 4 93 10 12 12 7 8 3 ata 95 6 10 10 7 12 14 ae 95 8 11 11 7 2 14 10 93 14 16 17 16 6 10 6 93 12 13 13 ll -2 -—1 0 97 al 12 12 9 8 4 1 98 ‘ 6 9 9 8 —5 —5 se LOL 8 12 12 10 5 6 4 96 RIGHT SIDE.—(Continued across.) 4 8 10 101 11 10 9 98 20 21 18 8 3 11 8 93 9 12 12 12 2 Uf a 9o7 14 16 17 16 al 5 4 90 12 15 15 13 il 10 6 102 9 12 14 15 17 15 16 98 14 15 14 12 4 4 —1 93 13 15} 17 17 16 11 ws 97 10 13 12 12 4 10 10 105 7 10 10 ; . ‘i . : . : . H : ae u Pee eho cence stmt coAmerw SONI Ee a\S. ays ni ne & = S = & = S = 2 = & = SMCS Oe ree eS goer orale. m (Bs neue : es) = nD = wm = mn = n 72 wm a= n ° =) qi ro) re ro) q ro) q } q fo) =| fs) Z = 4 Ay =) eal pre} oD pYes} i a) o z Za = ioe] z 450 *B1IQ9J1OA 9} JO S9YOIB OY} JO UOTJBOYISSO JO OUI} OY} SUTATH “AT ATH VL Franklin P. Mall 451 find. this rib much more common in the embryo than we think it is,— possibly in 5% of the specimens. The arches—The arches of the vertebrae appear on the 57th day as two small granules of bone, one for the second vertebra and one for the eighth. On the next day these two points of ossification have increased on both sides of the embryo. In the cervical region the first and second arches are present on the right side and the first three arches are on the 77 TABLE V. Giving the times of ossification of the bodies of the vertebri. | INO serie d Jadnaccoces 202/274'263, b, 2/266:263, b, 1272/282/284/288, b|/M|N 300) O} S8|/806,c) Q'806,a306,b) P| R Mere thee ceciscicteiciieisiete 30) 31) 32 33) 34 34) 42) 54) 57 (69/70) 73/73/75) 75 (81/109 ie 105/110 INN SS oobos basbogdondG 56] 56 57) 58 58) 65) 73) 75 |8383) 858587) 87 (901100 105 (105110 loa. Pen llee 36 al Dolke Wlladiioo “We ae ae | hee phe Shr ie lWlske so lode bo WO he os Reyes Ih 8 Gay 5.. el est era |ieet ileal NOM eye eae Eat 3 6e es | ee ee * ok | * (IQ * fk * Em IKE aa Nee ne omc A ee Sco ee cal ee ap Cele |i cs ¥) |e) |e ge co feo [2] © FFL FOR] * fF] * * | * | & Gi he leo | eo i) £2 cS ee ey ep ce 4) Me ea ee ullet 1055 Foie | e3 || es es | ea yy toy ta IE * | & | & Tit * |e] xe] oe & fe] # ig fe] # fe] # * |e le 12.. aes |) te IS ee liye || ee Bale * | * | # ise xe] e |e] * & fe) # ig fe] * fe] x * |e] x& Bodies of | 14. rae je dal PRE * #& ik | * 0 * | x |* * Eat Se 3 the aps xi|alae| oe oo |e #19 | * fe] # * | # | # Vertebree | 16. | 2 eae 1%. | ee eee ie ee ee | ee ae le 18. w]e] ae] ok oe fe fe fe ie] oe fe] oe | ok | & | 19. #l*x]e| oe «i]t ie] « ie] x | & | & | 20. el ala)] « «i |x ie ie | x le | x * | * | * 2]. ele} e| # «fe |e ie le] & fe | x x | «| * 29 | PS |fes || e3 * ox ik | & le fe ES Esa eS FS eS) eS | 93. ES || ead) es |) C3 62 (E> Peay 3 ee S| es * || DAs ele] | oe oe fe | & be fe * * * oer |e Shae Allee ele le] oe oe tele te oe] oe fe] oe | oe | | & 6. | * | oe & fe | fe fe] oe fe | x | |2|* ee Sea (oe | * Se £ (| & |e be *” lk =] oe te aes lea er 2 os rene. | heer ee | ‘le | a # : | | left side. Lower down the 7th to the 10th arches inclusive are on the right side and the 8th to the 11th on the left side. In embryo 272 and J, all the arches are present to the 19th, 7. e., through the cervical and tho- racic region on both sides; on the 64th day they extend to the third lumbar vertebra. The next day they extend to the 13th vertebra only, and on the 72d day they reach to the 27th vertebra. From now on the ossification centers are irregular in number, fluctuating around the first sacral vertebra. A glance at Table IV shows that the lower vertebre vary in their appearance, corresponding somewhat with the condition found in the appearance of the ribs. Up to the 65th day the second arch is the largest in the cervical region 452 Ossification Centers in Human Embryos and the eighth or ninth, or both, in the upper thoracic region. This ap- pearance indicates that the arch first to appear is the largest for a con- siderable time after other arches appear, a conclusion which the earlier | anatomists deduced in studying the ossification centers of the ribs, arches and bodies of the vertebre. The bodies.—The bodies are present in large number in an embryo 58 days old, although none are present in another embryo of the same age as well as in a few excellent specimens a little younger. In this specimen (272) the bodies extend from the 10th to the 25th vertebra being very small above and below, the 19th, 20th and 21st being the largest. A specimen of the 65th day shows much the same appearance. They now extend more rapidly towards the head than into the sacrum, fluctuating in number on both ends of the spinal column. Until the 90th day the bodies on the 20th and 21st vertebra are the largest, indicating that these two bones were the first to ossify. At no time were accessory ossification centers seen nor were the bodies found to arise from two centers. Meckel made the same observation in 1815, but several writers since his time have spoken in favor of double ossification centers in the bodies of the vertebra, an idea much in vogue about the time of Haller. OSSIFICATION OF THE BONES OF THE ARM. The clavicle-—The ossification center for the clavicle is present in two, and uncertain in one, out of five embryos of the 39th day. In these specimens, as well as in older ones, the clavicle is clearly made up of two centers, a large one about .5 mm. in diameter near the median line and a smaller one (.2 mm. in diameter, and .5 mm. long) reaching something like a handle from the first, towards the shoulder joint. Together they are about a millimeter long. A few days later (No. 42) these two bones measure nearly 2 mm. together, the inner one, however, is much the larger, and fully separate from the outer one. Towards the 45th day the two centers blend, and a recent series of sections of an embryo 20 mm. long (No 240), which had been stained in iron hemotoxylin, shows them fairly well united. This specimen also shows the anlage of the clavicle as composed of a peculiar cartilage with a deposit of granules between the cells. The appearance is unlike that seen in the mandible or in the humerus. By the 49th day the two centers are fully united, and appear in a single bone 2 mm. long as is shown in an excellent specimen (No. 333). By the 55th day it is 3 mm. long; the 58th day, 5 mm.; the v5th day, 9 mm., and the 85th day, 12 mm. The humerus.—This bone appears on the 42d day as a very small cylin- 453 x|a| * | 4 * | 4 * xia} o* | ¥) * | ¥ * *)*| * *| =* * * * | * * *| * *) * ai«| * [# * | ¥ % ela] * | #) * | 4 # ela| * | a4 * | 4% ' * | * * *| * *| * | ik * *) =* *| * * | * * *|| * *| * = ela] * |*) * | 4 * oS || o* |) * | x * = *|*| * *| * x) * * | * * *) * *| 0; «|x| « |* * | 4 # e\/e| *« | # * | ¥ 4% q al ce # x) * | 4 * a= Eel lee el Ve 4 * *| # ay, # |e )-% |) 4) * | 4 4 rca | eae ae ||) A ae ise fo * | * # *| * *| oh * *| # * * | ¥ * { E54 eg tae, Sel Vad +| * #|«|o* | * 4) * | Vere GOT |06| 18 |L8| $8 OIL gor I8| 9h |9u) €2 YW) d2'908) 0)9°908) S| O % & % % * [arate SRA SOO Pee “4 KH E % % AO BG HOES Hid 6200 Had ed HAs “X FRE - REREKRKR EKER RRKR KKK HEHEHE KH KEKE REE KR RRR KKK KEKE HH HE HH HH xX EE HEE HHH KE KR HK x XK RK Ke Ke KH KH HH KH HK HR 1 | % | lx eR RRR ER HRHREHE EEE \ lee e HER KEEO 1 lax ee RRR ERE 1 | heserot Lene eeeeeeereee reese OGY Ole eR RE HE HEHE KR HH HE HHH i Qlax eee eee eR HE HEE 12 oO. a) Pod oS Ce) oO we ZB 3 “ULIB 94} JO SOMOG OY} JO UOTJBOYTSSO OY} JO OUNTy Ol} BuLATH ‘TIA ATAViL WUE sosuBleygd II sosue[eud I sosav[egd [edreovjO WL soeeeccescooos BINABOS = Bury teens eeeees eee SNIDRBY te eeeeeeeeeees sSnIOmUINnH ‘O[OIARTO ee eeee. ceeeeeeeeeeseees qyysue'T tent eeeeee ee eeee eens essere ONT 454 Ossification Centers in Human Embryos drical center, but half a millimeter in length. It grows quite rapidly, being 5 mm. long on the 58th day; 9 mm. on the 75th day; and 14 mm. on the 85th day. The radius and ulna.—The radius and tibia both arise on the 42d day, and the ulna appears a few days later. They are hollow cylinders, a millimeter long on the 56th day, and 3 mm. on the 58th day. From now on the ulna is always a little longer than the radius; on the 85th day they are 12 mm. long. Fic. 5. Hand of embryo No. 300 (73 mm. long), enlarged 3 diameters. Scapula.—tThe first center appears about the middle of the region of the spine as a small granule on the 55th day. By the 58th day it is 24 mm. in diameter, and on the 85th day it is 9 mm. long. Metacarpal.—The second and third metacarpal bones begin at the same time, for they are equally large in an embryo of the 57th day. On the next day (263, b, 1) small fourth and fifth metacarpal bones are also present, and in an embryo of the same age (272) the first one is added as a small crescent-shaped bone with the opening of the ring turned Franklin P. Mall 455 toward the volar side of the hand. On the 75th day these bones are 1 mm. long and on the 85th day they are 2 mm. long. Phalanges, I—The second and third bones of the first row of phalanges are present in an embryo 58 days old as two small crescent-shaped bones open toward the volar side of the hand. In an embryo two days older four of the bones of this row are present. On the 64th day and thereafter all five are present. On the 90th day they are 14 mm. long. Phalanges, II—The second row are the last of the phalanges to ap- pear. On the 75th day the center in the second phalanx is well formed and those of the third and fourth phalanges are each represented as two very small nuclei, the one on the radial side being a little longer than the one on the ulnar side. On the 83d day (N) a single center appears in the fifth phalanx. It is crescent-shaped with its closed side outwards, and its open side directed towards the radial side of the hand. It retains this form, growing only in size in embryos up to 105 days old. At this time each of the bones of this row is about half a millimeter long. Phalanges, IJ1J.—The first terminal phalanx is the first bone of the hand to appear, being present in an embryo of the 56th day. It is club- shaped being developed, unlike the rest of the phalanges, in connec- tive tissue. Immediately following the appearance of the first terminal phalanx the rest of the terminal phalanges appear, the fifth being very minute. Lambertz first demonstrated that these bones appear before any other bones of the hand, while Rambaud and Renault thought that they were the last of the phalanges to develop, and actually picture a hand of an embryo with the ossification centers present in the second, but not in the terminal row. Bade’s X-ray pictures are too hazy to give any clear idea regarding this point. OSSIFICATION OF THE BONES OF THE LEG. The femur.—tThe ossification center of the femur appears on the 42d day and grows gradually, being 1.5 mm. long on the 55th day. On the 58th day it is 4 mm. long, on the 75th, 8 and on the 85th 15 mm. long. Tibia and Fibula—The tibia appears on the 44th day and the fibula on the 55th day, at which time the former is about one millimeter long. Throughout the early development the tibia remains a little longer than the fibula, and about 25% shorter than the femur. Iliwm.—The center of the ilium appears a little anterior to its center on the 56th day, and by the 58th day it measures 2 mm. in diameter. It soon has a knob-like process on its posterior border which often appears as a small adjacent nucleus above the great ischiatic notch. By the 85th day the antero-posterior length of the center is 6 mm. Ossification Centers in Human Embryos 456 | ee lee on oe ee oe HEHEHE HH KH KKH HK HEHE X HHH HEH HH H Hee KHN KH HH KH K ~ | OITg0r <0r OLLGOT ¢Or RRR K RR KH HK H HK RHEE KRKHKRHK HK HHH HH * | 001 068898 * * * *| * *) | * *) 3% *| * # * *| | * * * HEE KSEHEEHEE E EE te ek ee Pee ee (001 Ise "| d Q'906 B'80E9 8 | { | ie 1/01 69 © 008) NW i lee eee RR HX le eee RREREE lee eH ERE HE x 0 4 6 61199 SSloPh Mc8% lhe ee Sal bes ah ey 8 Delbaere Olealbe uly wes Sail eeprene 0} | x * call eee | + Salle Bate | * ets Ieee ode no # * * Heke EER Sleaeceexe xx FE o& | BLS TA 'E9 99S sa ‘E9% I FLG 0g 606 sel ee oe * * * * * * Boy! (43 || 20 BON | 00 €€) 99 | V 61 9°96 ee eee ee eens BBOBEGDDSIG OOOO 09 0CO0 GRO DOO dy (15) (16) ee er) Itl sosuvlegq i cr ee cr i OD OD HG NOD HID CI CD Had QD HID i er) tee eee ee see eneee ee cr ai IT sosuvleyd j | ett ae ee ry a) rc Ce Ce id rs ey i ee iy Ce er) er a | [BS1B1 BIO er) ee ee ee ey Peete eee seen eSeeeeees TUNITY Sete eee eee eres BING prstateinfelevetiferatereroreKerelefeteleiarelele veee eee BIG, TEE e eee eee eee eee tee eee eens econ eeeesees INTIOM eee e ewes Cette wee eee ee See were eee eee cane seen wee ew eees 0.00.64: 0 FOOD OFO0 OG G06 OO OOON070 00950 9.0030 DODOLO COOK: re ht, ee ar ce) q}3u0', Ce er i) beet eee seers ONT ‘SOT OY JO SOUOd OY} JO UOTJBOYISSO JO OUIT} OY} SUTATYD ‘IA 2TAVL Franklin P. Mall AD Ischium.—This nucleus appears first on the 105th day in the body of the ischium. It is one millimeter in diameter in embryo R. Calcaneum (variation).—A nucleus one millimeter in diameter is in the middle of of this bone on both sides on the 65th day. It is not pres- ent in any of the older embryos. Metatarsal bone-—The second metatarsal bone is the first of this row to appear and is present as a small nucleus in an embryo 58 days old. In an embryo 60 days old the second, third and fourth metatarsal bones have begun to ossify and in a second embryo 58 days old all five bones Fic. 6. Foot of embryo No. 300 (73 mm. long), enlarged 3 diameters. are present, the second being the largest. On the 75th day they are about one, and on the 90th day about two millimeters long. My data correspond in time with those given by Quain, who states that the metatarsal ossify in the 8th or 9th week. Other anatomists find the time of their appearance all the way from 6 weeks (Gegenbaur) to 5 months (Schwegel). Hasselwander,” who has made an exhaustive study of the ossification of the bones of the foot, fixes the time of the appear- 1° Hasselwander, Zeit. f. Morph. u. Anthropol., 5, 1903. 458 Ossification Centers in Human Embryos ance of the metatarsal between the 9th and 10th weeks. Unfortunately Hasselwander does not give the crown-rump measurements of his speci- mens, making it difficult for me to estimate their age. However, I am in- clined to think that he has overestimated the ages of all of his embryos. Phalanges, 1—The center for the first bone of this row is present in an embryo 83 days old and all of them are present in another embryo of the same age. On the 85th day a specimen shows but the first and sec- ond bones. In the earliest stages the bones often appear as double centers, one on the dorsal side and one on the volar side of the bone. Soon two delicate half rings unite the primary centers to form the shaft which in the older embryos of my list is but half a millimeter long. Hassel- wander places the time for the appearance of this row all the way from 11 weeks to 4 months, the centers not being constant until the latter part of the 4th month.—The second row of phalanges is not ossified in any of my preparations. They appear shortly after the 110th day, according to Hasselwander, although the older French anatomists place the time much too early, Rambaud and Renault on the 45th day! Phalanges, I11.—The first terminal phalanx appears on the 58th day and is therefore one of the first bones of the foot to ossify, as was cor- rectly stated by Meckel nearly a century ago. After this time, in all the embryos studied, the first four of the terminal phalanges are present, while the fifth is not constant until the 90th day, although it is present in three younger embryos. Rambaud and Renault fix the time of ossifica- tion of the first four terminal phalanges in the 4th month, and the fifth after birth. It may be noted again that early ossification centers are best seen in Schultze specimens viewed in direct sunlight with a purple background, with a large lense which magnifies two or three diameters, in order that both eyes may be used. ‘The very earliest deposit of bone cannot be seen with certainty in ordinary serial sections stained with haematoxylin and eosin or with carmine. Much of the trouble in determining the time of ossification is due to the uncertainty regarding the age of the embryos studied. In my speci- mens the age is estimated in days by multiplying the square root of the crown-rump length in millimeters by 10. This measurement was made with great care, and is given each time with the age. If the calculations of embryologists are correct, my estimations of the age of the embryos cannot be out of the way more than a few days. Estimations of the age from the last menstrual period alone may be fully a month in error and are nearly always in need of correction. DESCRIPTION OF A 4-MM. HUMAN EMBRYO. J. L. BREMER. WitTH 16 TExt FIGURES. This embryo, series No. 714 of the Harvard Embryological Collection, noted as about three weeks old, is an excellent subject for study because of its good preservation and successful sectioning. Unfortunately the drawings of the whole embryo are inadequate, so that the sketch given here has been altered slightly to conform more accurately with the shape as we find it in the serial sections. The necessity for a part of this altera- tion may, of course, be due to shrinkage, but the form, as given in Fig. 7, is certainly at least approximately correct. This shows a large head, flexed sharply on the body, a curving back ending in a curled tail, twisted spirally to the right; a marked protuberance below the head for the heart, and an outgrowth for the fore limb. There is no trace of posterior limb. Appended to the ventral surface below the heart is the yolk-sac, represented here as cut irregularly, and at the right side of this, posteriorly, the body-stalk, cut near the chorion. Four pocket-like de- pressions, the gill clefts, lie behind a larger depression, the mouth. There is no surface marking to indicate the eye. Protuberances corres- ponding to the primitive segments are not shown in the original drawings, though plainly visible in a model of the rump region (Figs. 15, 16)— perhaps the irregularities of surface have increased, with shrinkage. There is no sign of distortion or injury. The embryo was preserved in 10 per cent formalin, imbedded in paraffin, and cut in a transverse plane. On microscopic examination the tissues are found to be excellently preserved; even the frequent mitotic figures in multiplying cells show clearly. In fact, by the histo- logical condition, as well as by the external appearances, we are led to believe that the specimen is normal, and yet the state of growth of some parts and the form of others do not agree with the descriptions of human embryos of the same size given by His and other investigators. The most notable difference is in the stage of growth of the nervous system. His describes the thickened medullary plates as having already, in an embryo of this size and general stage of development, been changed throughout their entire extent from a groove to a closed tube; but in AMERICAN JOURNAL OF ANATOMY.—VOL. V. thom Phary 1 ~ 3 = . 1. Models of Bra G ] x FI J. L. Bremer 461 this embryo the closure is incomplete in the anterior part of the head, and also for a considerable distance from the end of the tail, giving both an anterior and a posterior neuropore. This is the more interesting when we consider that in both the pig embryo and the rabbit embryo, Hic. 4: Fie. 5. Fic. 2, 3, 4 and 5. Sections through head. X 60. as described in Keibel’s Normentafeln, the closure of the medullary tube is completed only after the formation of the head and neck bends, as in this human embryo. 462 Description of a 4-mm. Human Embryo DESCRIPTION OF MODELS. MODEL OF BRAIN. This model is shown in side view in Fig. 1, and again in Fig. 6, there turned so as to be seen nearly from below. The fore brain is divided into two parts, one of which includes the anterior neuropore (marked by the rolled ectoderm, shown only where that of the brain joins that of the skin), the lateral pocket of the optic vesicle, and further from the anterior end on the ventral side the enlargement for the hypophysis, which fits between the two lobes of this gland arising from the pharynx. Fia. 6. Model of brain, seen from below. X 60. The relations of the pharyngeal and medullary portions of the hypophysis are shown in Fig. 3, the photograph of a section of this part of the embryo at this level. Of the other photographs of the brain, Fig. 4 represents a section of the anterior part of the hypophysis, showing its continuity with the cavity of the brain, and Fig. 5, a section passing through the optic vesicle and the anterior neuropore. The plane of sec- tion is shown by the line between the two pieces of the model. In this first portion of the fore brain there are, beside the anterior J. L. Bremer 463 neuropore, two other areas, shown in the model, where the ectoderm of brain and skin are continuous; one in the mouth region, and one behind (following the curve of the brain) the neuropore. Moreover just be- hind this last area there is a distinct prominence of the brain tube, not Fie. 7. Drawing of whole embryo. X 30. attached to the skin, which simulates a neural crest, as though for a pair of cranial ganglia. This of course must soon disappear, as no such pair of ganglia exists at a later period, but its presence is interesting as showing a tendency of this anterior portion of the brain to develop as do the more posterior portions. 464 Description of a 4-mm. Human Embryo Between this anterior part of the fore brain and the mid brain, not marked distinctly from either, is found a narrow strip of less caliber than the anterior portion, with no special prominence and no connec- tion with the ectoderm of the skin. A cross section of this is shown in Fig. 2. The mid brain, oceupying the head bend, is also without special in- terest, except that it is of smaller caliber than might be expected. It merges without line of demarcation into the hind brain. The hind brain is again divisible into two parts; one posterior, smooth, of nearly even caliber, merging gradually at the neck bend into the spinal cord; and one anterior, showing a further development. The roof of this anterior part is thin, has become shrunken and crumpled. As yet, however, there is no sign of a Varolian bend. Attached to the side, ventrally, are two Lt.um.art. Fig. 8. Section through body of embryo, near the cloaca. X 60. ganglia, one for the Trigeminal nerve, and one for the Acoustico-facial complex, in which there is only a faint indication of separation into distinct nerves. Behind this second ganglion, applied closely to it, hes the otocyst, a rounded hollow vesicle, close to the brain, but not touching it, and still attached externally to the ectoderm, a patch of which can be seen on its outer surface. Of the other cranial ganglia nothing is shown in the model, as they are represented only by diffuse groups of cells on each side of the hind brain, not yet divided into separate ganglia, and not attached to the brain wall. There is a peculiar notch in the floor of this part of the hind brain, shown in Fig. 1, between the two ganglia, bounded by two rounded prominences seen better in Fig. 6, the significance of which I do not know. On taking off the top part of the model, we find that the cavity of the hind brain is marked by a median ventral furrow. The sides are J. L. Bremer 465 smooth, except in the anterior portion, where there are distinct traces of neuromeres. ‘Toward the cord the cavity is compressed laterally, but there is no sign of a groove between the zones of His. Fig. 6 shows the wide open anterior neuropore, through which one can look into the hollow optic vesicles, and into the median cavity of the fore brain, which is seen to be a narrow slit, compressed laterally. The edges of the opening are broadly curved or rolling, with no demarca- tion to indicate where the future line of closure is to be. This is shown in section in Fig. 5. MODEL OF PHARYNX AND AORTIC ARCHES. The pharynx, of which the model is a cast, the shape of the cavity being represented, is shown in Fig. 1, in its proper relation to the brain. It consists of a broad body opening anteriorly into the mouth, the lateral extension of which, between the maxillary and mandibular processes, is represented as a cut surface. On the dorsal surface of this body, near the fore brain, are irregularities, chiefly two rounded ridges, one on each side of the median line, representing the out-pocketings for the pharyn- geal lobes of the hypophysis, as shown in Fig. 3, and explained above. Behind these, at the angle made by the roof of the pharynx correspond- ing to the curve made by the brain at the head bend, is a median ridge or point which is continuous with the notochord, and marks the anterior end of the latter. Toward the cesophagus, into which the body of the pharynx merges, the cavity becomes more and more compressed laterally, until it is an antero-posterior slit. From the sides of this main cavity three lateral out-pocketings project, the most dorsal one being divided into two smaller projections near the end. These represent the gill pouches, and diminish in size from before backward. The first two rapidly become compressed antero-posteriorly and end in blunt, more or less vertical ridges, while the third is more tapering, and the fourth ends in two distinct pointed branches. In the tissue between the opening of the mouth and the first gill pouch, and also between the first and second, and second and third gill pouches, run the first, second, and third aortic arches on each side, joined dorsally by the dorsal aortee, which make an impression on either side of the median line of the body of the pharynx, and then continue down- ward, beside and behind the esophagus. On the model, the aortic bulb is represented as cut off just above the standard; a cup-shaped chamber leads from this forward, and gives off on each side two vessels ; one pair of vessels forms the first aortic arches, a second pair divides 34 ; 466 Description of a 4-mm. Human Embryo into the second and third arches of each side. The connection between these last two pairs of arches and the aortic stem is very slender, com- pressed laterally, as though the arches had grown from the dorsal aorta and had only just united with the ventral aorte. Of the fourth and fifth aortic arches the only trace is the rim of the cup-shaped part of the ventral aorta, shown in the figure below the bend of the third aortic arch. No branches come from the dorsal aorte in the position of these fourth and fifth arches. The dorsal aorte are joined in a single median vessel for a considerable distance along the back; there is no trace of carotid branches from the first arches toward the head. MODEL OF HEART. An anterior view of the model of the heart is given in Fig. 9, the model is seen slightly from the right side. The most anterior portion is the large rounded aortic bulb (B. ao.), cut off just below its division into aortic arches as shown in the model of the pharynx. Continuous with this is the ventricle (Vent.) a large single chamber, beginning at a constriction marked by a groove on the outside (Gr.), extending down- ward on the left side, turning on itself to form the apex of the heart, and then tapering upward to merge with the aortic bulb. The walls of the ventricle are thick, smooth externally, but internally very irregular, with deep pockets ined by endothelium leading from the main chamber, rep- resenting the sinusoids of the heart. In the aortic bulb the walls be- come smooth internally; there is no sign of division into right and left ventricles. The left auricle (Lt. au.) is placed above the ventricle, marked from it externally by the groove. Its walls are thin and folded, probably by pressure, and internally the endothelium is smooth, with no pockets nor trabecule. The left and right auricles are joined near their upper ends anteriorly by a prominent ridge, enclosing a cavity, which extends downward, compressed antero-posteriorly, and opens by a nar- row channel into the ventricle to the left of the median line. Above this connection the right auricle rises dorsally to a rounded peak, not quite so high as the top of the left auricle, from which it is separated by the intestine (/n.), but, unlike the left auricle, the right extends far below the auriculo-ventricular canal as a spacious pouch, reaching almost to the level of the apex of the ventricle, and occupying a position behind and to the right of the aortic bulb and the lower part of the ventricle. Here, as in the left auricle, the walls are thin, smooth on both external and internal surfaces, and thrown into great folds. If this auricle were distended it could certainly contain a larger volume of blood than the J. i. Bremer 467 ventricle. This enormous right auricle is not, to my knowledge, figured im any model or drawing of human or other mammalian hearts of any stage, but conforms almost exactly to the Selachian heart. The blood enters the heart by way of the right auricle, from the sinus venosus, as is shown in Fig. 10. In this figure the heart is viewed from behind and slightly from the left side, and a portion of the model, the cee iew. dorsal wall of the sinus venosus, has been removed. The jugular veins from the head region and the umbilical veins from the body join on either side, on the left more anteriorly than on the right, and from this junction on each side an irregular sinus extends across the embryo, in- terrupted in places by bands of tissue (the cut end of one of which is seen in the figure) into which open dorsally the two vitelline veins. From this sinus venosus the blood passes to the right auricle by two sep- 468 Description of a 4-mm. Human Embryo arate openings (a and y). Here again this embryo differs from those previously described or modelled, in all of which a single channel leads from sinus venosus to right auricle. Dr. Minot has recorded separate openings into the heart for the cardinal and omphalo-mesaraic veins in the chick (Textbook, p. 282), but the double openings just described do not appear to be correlated with those in the bird. 4 ; ‘a re Lar Ai % Fig. 10. Model of heart, posterior view. X 90. The heart lies in the body cavity or ccelum, and is attached to the body wall by the sinus venosus, and to the intestinal tract by a short fold of mesenchyma. Fig. 10 shows also a portion of this intestinal tract; the mesodermal part has been partially dissected away from the entoderm in order to show the outgrowth destined to become the lung (Lu.). This outgrowth, situated at the level of the left auricle on the ventral side of J. L. Bremer 469 the intestine, where the pharynx is becoming narrowed to form the cesophagus, is rounded, irregular, and extends to right and left and eaudally. The right side of the outgrowth is the larger and extends further tailward, leaving the cesophagus at a more acute angle than the left, a reversal of the adult condition. There is no distinct trachea, as the cavity of the esophagus is continued directly into the cavities of the right and left lobes of this outgrowth. Fic. 11. Model of veins near heart, dorsal view. x 160. MODEL OF VEINS NEAR HEART. This model represents the venous channels as solid, and includes the junction in the sinus venosus of the three large pairs of veins, the jugular and the umbilical veins in the body wall, and the vitelline veins in the intestinal wall. The sinus venosus is shown as a cavity in the model of the heart, so that these two models overlap to a certain extent. Fig. 11 shows the model as seen from the dorsum of the embryo; Fig. 12 as seen from the left side; and Fig. 13 is a view taken from the caudal end of the embryo, and a little from the right side. The umbilical veins, entering the embryo by the body stalk, run in the 470 Description of a 4-mm. Human Embryo body wall forward, at a level ventral to the intestine, varying only slightly in diameter. At points differing slightly on the two sides, more an- teriorly and dorsally on the left, they join the two jugular veins and turn inward (on the left side also ventrally) as the sinus venosus. From each jugular vein, nearly at its junction with the umbilical vein, arises a small bud, the future posterior cardinal vein (P. card.). The Duct of Cuvier (D. C.), later a well marked trunk extending from the junction SeeRtvitave Jug. \ i je j mere: ae og Oe ‘gt ty) ey Ltvit.v. 2 & ft s \ Recut. y Fils Nye ; \ipl- 1 1 Shin 5 ' Lt!um.v. a P. card. Fic. 12. Model of veins near heart, from left side. X 160. of jugular and cardinal veins to the entrance of the umbilical veins, can in this embryo, then, scarcely be said to exist, so short and ill-defined is it. The sinus venosus is seen, as in the model of the heart, extending across the embryo, an irregular cavity subdivided by bands of mesen- chyma (represented in this cast as holes), and emptying anteriorly into the right auricle by two channels (Rt. au.). Into this sinus empty also the two vitelline veins (Vit. v.) one on each side of the intestine, at a level dorsal to the umbilical and jugular veins (Fig. 12). The vitelline veins, unlike the two other pairs modelled, vary greatly in caliber; they are small and rounded at their entrance into the sinus venosus, but more caudally spread into large channels, each with a mesial wall straight, J. L. Bremer 471 vertical, fitting closely the sides of the entodermic intestine, which lies between them (Figs. 11 and 13). The lateral wall of each vitelline vein ¢ is very irregular, giving off many branches, which join to form new longi- a) 3 2) 1 ' ' < 160. 13. Model of veins near heart, from caudal end Fia. Revit weeseee [EUAUITe Vere ‘ <= tudinal channels, the whole making an irregular plexus. The plexus from the right vitelline vein is more developed than that from the left, and has even acquired an opening of its own into the sinus venosus 42 Description of a 4-mm. Human Embryo (Figs. 11 and 15). From the plexus on each side -branches extend ven- trally, those on the right ending blindly, but one on the left side joining by a narrow channel (Figs. 12 and 13, x) with another venous plexus (V. pl.) extending across the median line, ventral to the intestine, and posterior or caudal to the sinus venosus, from which it is entirely free. This ventral plexus is in intimate relation with the liver, and will be spoken of more fully in the next section. Posterior to the outgrowth of these plexuses the vitelline veins divide into many branches which spread out over the yolk sac, into which the intestine soon opens. Cut ends of some of these branches may be seen in Fig. 13. MODEL OF THE LIVER. This model is seen from the caudal end, and a little from the right side in Fig. 14. The intestine is a large tube much compressed laterally, and the vertical right side is shown. From the ventral border of this tube hangs a large outgrowth, extending first ventrally, then laterally, then dorsally, composed of an irregular mass of entodermal cells, which tends to break up into cords, often anastomosing with each other. Only the right side of this mass has been modelled. The cavity of the intes- tine passes for a short distance into this mass, but without subdivision, so that all the cords and irregularities are solid. In the model a part of the left wall of the intestine has been cut away to allow a view of this cavity. It has been stated by other writers that the liver arises by cords of cells - which grow into the territory occupied by a large vein, pushing before them, and thus becoming invested by the endothelium, and forcing the blood to run in small, anastomosing channels, the sinusoids. This state- ment would not be true of this embryo, for the liver cords are found growing into mesenchyma, at a level ventral to the vitelline veins; in this same mesenchyma, however, we find the branches of the vitelline veins ramifying, and forming plexuses, and in certain places these plexuses come into intimate relation with the liver cords. These points of con- tact, where veins and liver actually touch, are marked in the model of the liver (Fig. 14, V.), and are seen to correspond with the anterior surfaces of the portion of the plexuses marked in the model of the veins (Fig. 13, li.). These two models might be fitted together, in which case we should find the intestine lying between the vertical, mesial walls of the two vitelline veins, the liver spreading in the same mesenchyma that contains the lateral and ventral venous plexuses, between the sinus J. L. Bremer 4°73 venosus in front and the ventral venous plexus behind; but the two models would come into actual contact only at the points marked and already noted. As both the liver and the venous plexuses continue to grow, they will come into contact over more and more of their extent, until finally the result of small, anastomosing channels, the endothelium of which is in close contact with the liver cords, will be produced. The method by which this result is attained is, however, in this embryo dif- ferent from that usually described; in the one case, the cords of liver cells push against the walls of a pre-existing large venous channel, and Fig. 14. Model of liver, from caudal end. X 160. by invaginating these walls, make finger-like trabeculee within this large space, yet separated from the cavity by the endothelium which invests them. ‘These cords then anastomose until the cavity of the vein is sub- divided into many smaller channels, the sinusoids, all lined by the origi- nal endothelium, and having for walls, beside this endothelium, the cords of liver cells. In this embryo, on the other hand, the cords of liver cells and the small branches from the vitelline veins are both pushing into the same mesenchyma, both growing rapidly, until, the mesenchyma re- maining small in amount, the whole enlarged mass will be made up practically of the veins and the liver cells, which by their continued growth must come into contact, the veins filling practically all the spaces 474 Description of a 4-mm. Human Embryo between the cords, and the thin endothelium becoming wrapped around the cords; and thus the adult condition will be reached. In this model is also shown the anlage of the pancreas. (Fig. 14, Pa.) It is a small, knob-like mass of cells, with no cavity, growing from the ventral border of the intestine just caudal to the liver outgrowth, but distinct from the latter. Further down the intestine (nine sections in the specimen) where it has begun to expand to the yolk sac, is found an- other, smaller mass of cells, growing also from the ventral border, which probably represents a second anlage of the pancreas; there is no sign of a dorsal anlage. The pancreas also, then, differs from those usually de- scribed, as it has probably two outgrowths, neither from the liver stalk, for the duct of Wirsung, and as yet no outgrowth to represent the duct of Santorini. There is no enlargement of the intestine above the liver for the stomach. MODEL OF THE TAIL END OF THE EMBRYO. This model has been photographed in two positions, once (Fig. 15) squarely from the right side, and again (Fig. 16) still from the right side, but also a little from behind. The left side of the model shows the surface of the embryo with the umbilical cord attached to it. os = = ae it ir a ps a Baie! : »? a PA ‘ Lire as ‘. 1 - > ae ; a+ i + + e 7. , = a e ‘ \ * t ‘* a 4 in > Ly a ah : \ en . wh aed, Phe @\ ' . i P| : My Ni xs I PROCEEDINGS OF THE ASSOCIATION OF AMERICAN ANATOMISTS. NINETEENTH: SESSION. August 6-10, 1905. The Nineteenth Session of the Association of American Anatomists was held in Geneva, Switzerland, August 6-10, 1905, in conjunction with the Anatomische Gesellschaft, the Anatomical Society of Great Britain: and Ireland, L’Association des Anatomistes of France and the Unione Zoologica of Italy; the jomt meeting of the societies constituting the First International Congress of Anatomy. . The Executive Committee of this Congress considered an invitation extended by the Executive Committee of the Assocjation of American Anatomists to hold the Second International Congress of Anatomy in Boston, Mass., in 1907, in conjunction with the International Zoological Congress. The Executive Committee of the First International Congress of Anatomy expressed its regret at being unable to accept this invitation, inasmuch as it had been previously decided to have the meetings of the International Congress of Anatomy occur not oftener than once in five years. Of the members of the American Association of Anatomy, there were present at the First International Congress of Anatomy :—KEdward Phelps Allis, Jr., (Milwaukee, Wis.), Elexious Thompson Bell (Univer- sity of Missouri), Frederic Henry Gerrish (Portland, Me.), Francis John Shepherd (Montreal, Canada), George L. Streeter (Johns Hopkins University). The members of the Association of American Anatomists participated in this Congress as follows :— CONCERNING THE DEVELOPMENT OF THE ACOUSTIC GANGLION IN THE HUMAN EMBRYO. By G. L. STREETER, Department of Anatomy, Johns Hopkins University. A study based on a series of wax models of the ear vesicle and acoustic ganglion, reconstructed from human embryos measuring respectively 4, 7, 9, 11, 14, 20, and 30 mm. in length. It was found that in the early AMERICAN JOURNAL OF ANATOMY.—VOL. V. 16 II Proceedings of the Association of American Anatomists stages the acoustic ganglion consists of an upper and lower division. On the ventral border of the latter a portion of the ganglion cells of this di- vision become massed together into a separate bud, and form the primitive ganglion cochlearis; in other words, the acoustic ganglion at this stage consists of an upper division entirely vestibular, and a lower division — partly vestibular and partly cochlear. As the differentiation proceeds the group of cells forming the cochlear ganglion continues to become more distinctly separated from the rest of the acoustic mass, and gradually as- sumes the spiral form, seen in the adult. The nervus cochlearis sprouts out from the ganglion cochlearis com- paratively late, and passes up along the median side of the acoustic mass, without joining with the nerves to the sacculus and the posterior ampulla. Contrary to the younger His, the author concludes that the nerves to the sacculus and posterior ampulla belong to the vestibular rather than the cochlear division of the acoustic nerve. PROCEEDINGS OF THE ASSOCIATION OF AMERICAN ANATOMISTS. TWENTIETH SESSION: In the Medical Building, Laboratories of Anatomy and Histology and Embryology, University of Michigan, Ann Arbor, Michigan, December 27, 28 and 29, 1905. At its business sessions the Association took the following actions: The minutes of the Secretary as printed in the American Journal of Anatomy, Vol. IV, No. 2, pages I-II, were approved. The Association received a communication from Prof. Burt G. Wilder, Chairman of the Committee on Brain Requests and Methods, stating that this committee had held one meeting, but were as yet not prepared to make a formal report. The committee asks to be continued. On motion this report was accepted and the committee continued. The permanent secretary of the American Association for the Advance- ment of Science, Doctor L. O. Howard, states that this association would be pleased to have the Association of American Anatomists meet in affili- ation with the A. A. A. 8S. during convocation week, 1906, in New York City. It was informally agreed that if the Association of American Anatomists should meet during convocation week (1906), they would in all probability meet in New York City. In response to a request from the secretary of the Committee of Ar- Proceedings of the Association of American Anatomists It rangements for the International Congress of Anatomy, the Association, on motion, appointed Dr. Charles C. Minot, as member—from the Asso- ciation of American Anatomists—of the Committee of Arrangements of the International Congress of Anatomy for 1910, with Dr. Franklin P. Mall, alternate. At the suggestion of the Executive Committee, the following distin- guished European anatomists were elected honorary members of this Association : Professor Ramon Y. Cajal, Professor of Normal Histology, Madrid, Spain. Professor Oscar Hertwig, Professor of Anatomy and Embryology, Berlin, Germany. Forty-six new members were elected. . The Committee on Nominations (Dr. Charles R. Bardeen, Prof. Simon H. Gage, Dr Robert J. Terry) made the following report: INDE TERESI hs oooh op ecooedns dhe Cosa PaNS FRANKLIN P. MALL. HORMHITSE VIGE-LTESUC CI Ge i ciens ho) cic) eterall= GEORGE A. PTERSOL. For Second Vice-President.............. RopertT R. BENSLEY. For Secretary and Treasurer..............-- G. CARL HUBER. For Members of Executive Committee. GEPAR TESS seul VEINO Deaiere ete pone cieretoiels Term expiring in 1908. JAMES PLAYFAIR MCMURRICH..... Term expiring in 1910. On motion the Secretary was instructed to cast a ballot for the officers recommended. Carried. + TREASURER’S REPORT FOR THE YEAR 1905. Balance. on hand, December 27, L904 wes «aside sldeirye ghee a ele ae ie $48.04 Motal receipts’ fort 90 be rieisas scrote s Aeeetatoraedecels atebt sy sete nd «cele 932.10 $980.14 $980.14 Expenditures for 1905: Expenses of Secretary for Philadelphia meeting, 1904.... 24.00 TorAmerican JOUrNAl (OL “AWALOMY. or cle oe ors 0.0 oie cies ono 794.50 To Ramon Guiteras, Secretary American National Com. IMpernavion als VWed st CONETESS miei. cis siercie ec sic) els