1897 Human Embryology 22

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Minot CS. Human Embryology. (1897) London: The Macmillan Company.

Human Embryology: Introduction | The Uterus | General Outline of Human Development | The Genital Products | History of the Genoblasts and the Theory of Sex | The Germ-Layers | Segmentation | Primitive Streak | Mesoderm and the Coelom | Germ-Layers General Remarks | The Embryo | The Medullary Groove, Notochord and Neurenteric Canals | Coelom Divisions; Mesenchyma Origin | Blood, Blood-Vessels and Heart Origin | Urogenital System Origin | The Archenteron and the Gill Clefts | Germinal Area, the Embryo and its Appendages | The Foetal Appendages | Chorion | Amnion and Proamnion | The Yolk Sack, Allantois and Umbilical Cord | Placenta | The Foetus | Growth and External Development Embryo and Foetus | Mesenchymal Tissues | Skeleton and Limbs | Muscular System | Splanchnocoele and Diaphragm | Urogenital System | Transformations of the Heart and Blood-Vessels | The Epidermal System | Mouth Cavity and Face | The Nervous System | Sense Organs | Entodermal Canal | Figures | References | Embryology History

Note - this online text is only at a very early draft stage and contains many errors from the original scanning.
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Chapter XXII. Splanchnocoele and Diaphragm=

The history of the splanchnoccele of the head has already been given as fully as our present knowled^ permits, see p. 201, and except of that part which forms the pericardium. In this chapter the subdivision of the main ventral coelom or splanchnoccele into the pericardial, pleural, and abdominal cavities, and in connection therewith the development of the diaphragm, is described. It is to be remembered that the coelomatic cavities of the gill arches are possibly part of the splanchnocale. Development of the Septum Transversum.— The term septum transversnm was first introduced by Wilhelm His in his description of his embryoM (" Anat4>mie menscblicher Embrj-onen," Heft !.)■ Our present knowledge of its formation and metamorphoses rests chieflv upon the investigations of His, /.c, Heft III., also 81.1, and of Ed. Ravn, 89.2.


The septum transversum is the primary partition across the bodv, the heart being on the cranial side, the abdomen on the caudal side of the partition ; while above it the coelom forms a passage on each side of the median plane; these passages become the pleural cavi1 ties. The septum is quite thick; ' it includes the anlage of liver; by . , / it all theveins-maketheirentranco

fPal -r-RJ into the heart; later on the anlages of the supra-ronal capsules also appear in it; it is itself the anlage of both the diaphragm and of the membrane seimrating the pericardial and pleural cavities of the adult. The character and general relations of the aeptum can be underst^xxi from Fig. 'i'>9. The sep^ tum divides the pericardial cav . -.-, __ieriV'W(iriun(tj ity, p.c, from the main abdominal

S.'?n'JSi£;l^rJ.^\bifi»™Zl cavity, .16. r; the heart is sup .c. Titeiiiue reio. posed to be in great part removed.


The septum appears to be much enlarged by the growth of the liver, which at the stage represented has bewme, as it were, an appendage, Li, of the septum proper, which may be conveniently defined as the layer of connective tissue next the pericardial sac. Above the septum is the small paseage, PI, into which the lung, Pnl, is beginning to project, and which tecomes the pleural cavity of the adult ; at this stage it is termed the recessits parietalis dorsalis by Hia. It will be recalled, that the coelom forms originally two splanchDOCcelic cavities; in the region of the heart the partition disappears, leaving a single peri cardial cavity ; in the abdomen the partition (ventral mesentery) below the intestine disappears, so that the two cavities are brought into communication, while on the dorsal side of the septum the jiartition remains ; but the two pleural splauchnocceles always are distinct and never communicate directly with one another. The arrangement of the veins ia important. The jugular, v.j, coming ' from the head, and the cardinal, coming from the rump (Wolffian botly), unite on the doi-sal side of the cephalic end of the pleural cavity into a single stem, the ductus Cuvieri (future veva cava superior), which passes in the somatopleure around the outside of the pleural cavity to join the other veins in the dorsal part of the septum. The ductus Cuvieri, D.C, is just at the boundary of the pericardial and pleural cavities, and its growth is the essential factor in shutting the opening. The umbilical vein, Uiii. i', joins the ductus just as it enters the septum. The vitelline or omphalo-mesaraic veins enter the septum nearer the median line; the four veins which are thus unitett form the large sinus reuniens (see Chapter XXIV.) from which the blood is poured into the heart.


The origin of the septum in mammals has been studied as yet only in the rabbit by Uskow, 83. 1, His, and Ravn. The following description is based on Ra^-n's 89.2, Vii-V-i'.i. The head, H, of the embrjo early grows forwanl. Fig. 2li(), so as to intrude upon the region of the proamnion. Pro. A, and hence, as will l)e evident by an inspection' of the figure, the head is bounded in front and at the sides by the proamnion, and therefore the coelom of the head cannot communicate with the extra - embryonic coelom directly. Around the edge of the proamnion runs the omphalo-mesaraic vein, oin.v, the continuation of wliich is the anlago of the heart, Ht: on the double origin of the rabbit's heart, see p. 227. The vein projects considerably alM>ve the level of the splanchnopleure in which it runs, and this projection gradually increases until the wall of the vein reaches to iiiama. After "Ed. ri and unites with the overlying somatopleui'c, and tlius divides the cxelom into two parts, thi etalis dorsalis, r./t.il., and the reces.aus parietalis ventralis, r.p.v. This division is confined to the region of communication between the pericantial cavity, P, and the remaining coelom, as indicated by the position of the reference letters r.p.d, and r.p.v. A cross-section of a little older stage with the vorderdarm just closing is represented in Fig. 2C}1, and will help to elucidate the disposition of the parts. The ventral recessns early becomes closed at its hinder extremity and is therehy converted into a third pocket of the pericardial coelom, whicn His has described under the name of the , \ bursa panetalis. The bursse sub\sequently become merged with the u pericardial cavity. The dorsal reces3US, Fig. 201, r.p.d., is the aniage of the pleural cavity and persists for some no j«i-R-h itEmhn^F«hc«,da *»"!« onen at both ends. The parHait DajB, with Eieten r TwpTtB 8om tition dividing the two recessi from

v.ar card loai vein t p d m-psmw pa One another, and Containing the omani"»w or'ihB*iwBrir^'tr' iweMua i.^' phalo-mesaralc veins, is the aniage of djulu ' Aft?"Rft ^' P*™'^"* " * t'^" It't^ral portions of septum trans' *" ^er8lIm (Cadiat'-s floinoii m^soder miqtie, KdlHker's inesocardium laterale, Uskow's Vern-adutungabriicke) .


By the further growth of the embryo the head lengthens and with it the median heart formed by the union of the two heart anlages. The splanchnopleuric wall at fo, Fig. 14C, bounds not only the opening of the voruenlarm into the yoft-sac, but also the posterior wall of the pericardial cavity, and is the aniage of the median portion of the septum transversum. As the liver is developed at the hind end of the vorderdarm it has to grow out into this wall, and consequently contributes to the thickening of the septum tran»versum. The septum is further expanded by the development of the remaining veins, (jugulars, cardinals, and umbilicals), which are all ultimately unite*! with the omphalo-mesaraics to constitute the great sinus reunieiis.


In brief: the septum transversum includes the median part of the splanchnopleuric wall separating the pericardial cavity from the neck of the yolk-sac, and the two lateral parts resulting from the two upgrowths of the splaiichnopleure to carry the omphalo-inesaraic or vitelline veins to the hejirt. It is, therefore, entirely a product of the splanchnopleure.


Separation of the Pleural and Pericardial Cavities.— The septum transversum witamtes the two cavities as soon as it is formed, and in the adult the primitive arrangement is easily traced in part; despite the great expansion of the pulmiinarj' ctelom. The septum leaves, however, a direct communication open as shown in Fig. "-JSfl, whei-e the ducts of Cuvier. D.C, descTend from the dorsal to the ventral side. The figure further shows that the septum is oblique, so that the iwricardial cavity in [mrt imderlies the pleunil ravitv. As development prt^^resses, the thnv cavitiew jill cx{>and. jmd more and more of the i)ericanlial cavity comes t<"> lie on tiie vftitrdl side of the pleural cavities, letiving a part of the septum transversum as a partition, which. i)f course, runs as far lieiidwiii-d as the ductus Cuvieri, D.C. This iNirtitimi early l)ecom('s thin, and is the •membraiHi jtleiiro-perivanlittni which was iwrtly described by F.T. Schmidt, 70.1, and Uskow, 88.1, and morfe fully by His, 81.1, 313, and Ravn, 89.2, 136. The anterior passage is closed by the growth of the ductus Cuvieri, which, like all the chief veins of the embryo, has an enormous size ; it causes, therefore, a projection which ultimately shuts the passage to the pericardium completely. Exactly at what time the shutting oflF occurs is not stated, but probably during the fifth week in the human embi^^o, and in the rabbit by the fifteenth day. The separation of the pleural from the abdominal cavity takes place much later.


Expansion of the Pleural Cavities. — Concerning the gradual enlargement of the pleural cavities very little is known beyond the fact that they enlarge at the same rate as the lungs. In the rabbit at fifteen days they are together about half as large as the pericardial cavity.


As stated above, the primitive pleural cavity is on the dorsal side of the septum, and the cephalic limit of the septum is marked by the ductus Cuvieri, or future vena cava superior. Part of the septum is used to develop the pleuro-pericardial membrane, while the remainder, which includes the hepatic attachment, develops into the diaphragm ; beyond the caudal boundary of the septum the lungs never project. These considerations show that the pleural cavities lie entirely within the territory of the septum, and that their expansion takes place within the septum. This conception renders it necessarj to regard the thorax of the adult as chiefly occupied by the distended septum transversum, and involves important changes in our morphological notions concerning the adult condition.


Mesocardium, Mediastinum, and Mesentery. — These membranes are the remains of the tissue which originally divides the coelom of one side from that of the other. The tissue disappears for the most part around the heart, so that the pericardial cavity is continuous on both the dorsal and ventral sides of the heart. In the abdomen this continuity is established only on the ventral, not on the dorsal, side of the intestinal canal, and the tissue between the two lateral coeloms remains to form a very thin membrane, the mesentery, by which the intestine is attached to the median dorsal wall of the abdomen. Between the two pleural cavities the tissue remains, forming a thick partition, the mediastinum. Concerning the genesis of these membranes little is known.


Sac of the Omentum and Foramen of Winslow. * — In the chick soon after the lungs have grown out from the oesophagus, and just when the first forking has begun, the abdominal coelom is found to form two blind diverticula lined by well-marked mesothelium and extending until they come into direct contact with the pulmonary entoderm. Of these diverticula I have found no mention. Similar ones have been observed in the rabbit by Ravn, 89.2, 139; their formation is connected with the prolongation of the ridge of mesoderm on the side of the oesophagus. The ridge on the left side, and with it the diverticulum, disappears very early, but that on the right side persists and enlarges, the vena cava inferior being developed within it, on which account Ravn terms it the *' vena cava Falfe.^' This fold extends down into the aMomen ; the coelomatic diverticulum between it and the intestinal canal, Fig. 203, is the "rficessns superior sacci omenti " of W, His {" Anat. nienscttl. Enibryonen," Heft I., p. G5). While thi» growth of the "vena cava Falte" is taking place t^e stomach has bc«n developing its great bend to the left as indicated by the dotted lines in Fig. 'ZGi, carrying with it, of course, the nieai^astrium and mesentery of the duodenum, and thus forming a sac, the entrance to which in partially closed by the vena cava Falte. The sac is the Htuciis omenti, the entrance to it is the fnramert of Win.'tloir, F. W. The saccus is bounilod on the dorsal side and on the left by the mesoga.strium; on the ventral side by the stomach, the position of which at a level nearer the observer may lx> ea.sily im^ineil from the figure; and on the right hv the vena cava Falte, v.e.i.

  • Compare also chapter xxix.


In the rabbit, accortling to Ra\'n, 80.2, 14(;-U7, the anterior end of the recessus. Fig. 'Iwi, becomes separated, as a closed sac, about the ALwr ru>. n. Seventeenth daj", and forms a cavity

between the cesopbagns and the fo< called lobus inferior inediaHs of the right lung, and persists in the adult. A similar cavity {Sihleim-ieheide) is found also in rats and mice, and is presumably developed in the same wiiy. Rjivn thinks it probable that an homologous cavity is present in the human embryo, but aborts.

Separation of the Pleural and Abdominal Cavities. — This takes place much later than the separation of the pleural and pericardial cavities, for it is not effected in the rabbit until the seventeenth day, and Kiilliker reconls that it had not taken pljice in a twomonths' human embrj-o. This agrees with the fact that the separation takes place only in the mammals, not in other vertebrates. Rai.ni, 89.2, 147, is the only investigator who has attempted to follow out the pnH»S8 accurately, A fold is formed. Fig. "iOJ, which lies obliquely l«>tween the lungs and the Wolffian Ixwly on each side, and which in the rabbit at fifteen days is found to somewhat contract the oi)eiiing between the pleural aiid abdominal cavities ; the fold extends almost if not completely around the opening, making as it were a circular shelf. Another factor, as pointtnl out by His. is the expansion of the liver. I have ol)scrved also, in studying Profes^ior His' embryo Zw,* that the anlage of the supra-renal capsule had appeared in the septum transversum on the ventral side of, and close to, the peritonea) opening ()f the pleural cavity, so that the conclusion was inevitable that the final factor in completing the closure of the opening was the growth of the supra-renal capsule.


Diaphragm. — The diaphnigm (Ztverchfell) is developed from that portion of the septum transversum which intervenes between the pericardial and abdominal cavities, and from the fold which shuts oflf the connection of the pleural cavities with the abdominal. The veins pass through the diaphragm to the heart, and to the area around the veins the liver is permanently attached ; it is out of the remainder of the diaphragm that the muscular part and the centrum tendineum are developed, but concerning their development no observations whatever arc known to me.


Lining Membranes of the Splanchnocoele. — These membranes are the pericardial, pleural, and peritoneal. They each consist of a layer of specialized connective tissue and the mesothelium, which is foimd in the adult to have lost its primitive character of a cuboidal epithelium and to have become a thin layer or endothelium. Concerning the manner in which the transformation is effected, there are few reliable observations — compare Chapter XXIX.


The Supra-renal Capsules

It is onlv with considerable hesitation that I have decided to treat the pupra-renal capsules as organs developed in the septum transversum on the ventral side of the pleuro-peritoneal opening. I have made observations which lead me to think this view necessary from the facts of development, but I have not been able hitherto to continue the research to a satisfact<^r\^ conclusion. As the kidney grows forward until it reaches the dorsal pillars of the diaphragm, the supra-renals would come in juxtaposition with the upper end of the kidneys, whether the capsules began their development on the dorsal side of the pleuro-peritoneal opening or on the ventral side, for in the latter case the closure of the opening would bring the capsules near the kidneys. At present I am inclined to the belief that the mesenchj^mal portion of the suprarenals arises on the ventral side of the opening and the sympathetic portion on the dors^il side. That this view is right is confirmed by the observation that the capsule lies entirely on the ventral side of the kidney in the hmnan embrj- o at two months and at three.

Mesenchymal Anlage. — The mesothelium in the region of the vena cava inferior and septum transversum throws off cells to contribute to the mosenchyma. Janosik, 83.1, who observed this proC(?ss at the point where the supra-renals develop in mammals, conchided that it was a si>ecial process and that the supra-renal capsules must, therefore, be considered as derivatives of the peritoneum. The recognition since then of the genetic relation of the whole mosenchyma to mesothelium renders it unnecessary to assume a sj^ecial relation for a single mesenchymal organ. The same criticism applies also to Weldon, 85.1, who, having observed the prcxluction of mesenchyma from the mesothelium of the nephrotomes, or segmental vesicles, in lizards and sharks, concludes that there is a special genetic relation between the supra-renals and the segmental organs. In reptiles, soon after the vena cava is formed, there appears on each side of that vein a small cluster of crowded mesenchymal cells (Max Braun, 82.1), which increases quite rapidly; the cells of the cluster gradually arrange themselves in cords which become more and more twisted and united ; numerous bUxxi-vessels are early developed between the cells, probably by ingrowth from the adjacent Wolffian bodies. The nearness of the first trace of the supra-renals to the vena cava has also been noted by Gottschau, 83. 1, by Mitsukuri, 82. 1, and Weldon, 85. 1. In the rabbit the first distinct trace of crowding of the cells and of their enlargement to form the anlage of the rupra-renals may bo seen on the twelfth day ; on the fourteenth day the anlages are well marked (Mitsukuri, 82. 1) ; by the sixteenth day the sympathetic anlage is surrounded by the mesench}Tnal. In the sheep (Gottschau, 83.1, 441)) the anlage can be recognized in embryos \) mm. long ; it is in contact with the sympathetic ganglion tissue in embrj^os of 11 mm. and in those of 13 mm. has become quite sharply defined against the surrounding mesencliyma. In the pig the first trace is seen in li mm. embryos according to Gottschau, 83.1, 452.

Balfour, 81.3, homologies the mesenchymal anlage with the .socalled inter-renal bodies of elasmobranchs.


Sympathetic Anlage. — On the dorsal 8idt> and somewhat toward the median lino of each mesenchymal anlage appear a cluster of small cells, which are stained brown by bichromate of }K)tassium, as first observed by M. Braun, 82.1, 25, in reptile embryos. These cells are derived from the chain of sympathetic ganglia, and are characterized by being smaller and more granular and by having smaller nuclei than the cells of the mesenchymal anlage. I have noticed that in specimens colored with alum-cochineal they stand out conspicuously owing to their deeper staining. In rabbits of fourteen days, the sympathetic anlage has become very distinct and hfis increased in size, and in those of sixteen days it is found surrounding the mesenchymal supra-renal and more or less separat^^d from the ganglion proper. At this time traces of young ganglion cells and of nerv'e-fibres are said to be clearly recognized. F. M. Balfour, 81.3, and in his " Comparative Embryolog}'," II., (104, homologizes the sympathetic anlage with the so-called "true supra-renals" of elasmobranchs, bodies which develop from the sympathetic ganglia. According to Balfour (monograph of Ehismobranclis, ** Works," I., 472), who greatly extended Semper's okservations, 76.2, in shark embryos in Balfour's stiige L the ganglia of the symj)athetic chain are partially divided into two parts: one the future ganglion pro})er, the other the anlage of the supra-renal, which receives a direct artery from the aorta. By stage O these supra-renal anlages have acquircnl a distinct mesenchymal investment, which j^'netrates into their interior and dividers it, especially in the case of the anterior anlage?s, into a number of distinct alveoli. B>^stiigc Q, the cells arc differentiated into larger (ganglionic?) cells and smaller ones, which Balfour holds to form the true supra-renal tissue.


The observations thus far made indicate that the sym})athetic anlage is derived from a series of spinal ganglia, which give off a series of supra-renal parts; these piirts remain distinct in elasmtn branchs, but fuse into (jne mass on each side in amniotii. Rudimentary ganglion cells arise, but soon abort.


Union and Ultimate Fate of the Two Anlages.— The ra3Benchj-mal and sympathetic portions very soon come into contact (pheepof 11mm., nihbitsoftht) fourteenth (lay). At first, in amniota iit least, the sympathetic anlage grows most rapidly and partially surrounds the mesenchymal portion, but soon the relations are reversed and gradually the mesenchymal portion completely invests the sympathetic part, but for some time there remains a hilus on the inner side toward the i)OSterior end of the organ. Fig. 2611 shows a transverse section of the left suprarenal taken about the middle of the body from a rabbit embryo of twenty-six days. The cortex it already made up of distinct cell groups which, however, are not yet differentiated into the adult cortical and medullary zones. Capillaries are well formed between the adjacent cell-groups, The sympathetic portion, syin, is divided into irregular groups of cells, which etaiu readily and are u situated exclusively in the central region ; between these groups are relatively large blood-vessels, r. The connective tissue has formed a sheath, s, around the organ. cuvity Af sr M uukur Mitsukuri statcs that the masses

£ ner\ous origin are now full of distinct ganglion cells, supported in a connective-tissue framework; scattered among the lai^r cells are smaller cells." This may be regarded as |)erhaps the Sauropsidan condition, since according to HansRabl, 91.1, the two supra-renal tissues persist in birds throughout life, interlaceil with one another.


Mitsukuri believed that the medulla of the adult capsules arises from the sympathetic anlage, but Gottschau, 83. 1, showed that this was not the csise, though he failed to ascertain wliat became of the sj'm[iathetic nias-ses. By a considerable series of obae^^■ations on the supra-renid caisules of human embryos, I have ascertained that there are groups of ceils which gradually disapjiear and take no part in the prtKluction of the adult organ. The colls are in clusters in the central portion of the organ and stain very readily, so that they stand out conspicuously in the sect ions. In appearance they resemble the cells assigned to a s>'mpathetic origin in the rabbit, and I should feel no doubt that they aro the same wei-e it not that I fail to find them in enibr>-os of the second month, so that if they are really of syinttathetic origin then the union of the two anlages must take place at a considerably later stage in man than in other animals. Th^e groups of celLi are readily seen in the three-months' embryo, but tn the four-months' embryo they are disappearing and many of the clusters are hollow, their cavities being filled with what is apparently a I'oiiguluiii: by the seventh month the clusters have, so far as I have hitherto nbserveil, entirely disappeared. That both the cortex and medulla of the adult organ are formed in man fn»m the mewnchymal cells, as Gottfichaii, 83.1, showi-d was the rase in several mammals, is, I think, beyond qiiestiun. The vordH of cells are at first uuifonii throughout, but I find that t<nvard the end of the second month the cells of the cords multiply and become smaller, while at the same time the cords assume a more radial position and reguUr arrangement around the i>eripliery ; there is thus developed a cortex, characterized by radiating, small-celleii cords and a iimhilla, characterize*! by irregular, large-celled cords. In the cortex the conia are wide and contain numerous cells; toward the interior the cortls break up into small ones, which pursue the same radial course and consist of cells which gradually increase in size towanl the centre of the organ. The cords are marked off by wide capillaries, with distinct endothelial walls, between which and the supra-renal cords there appears to be no connective tissue, although in the medulla there is more or less connective tissue developtnl early around the ves.'wls, Pig. 2*1-;. It seonis to ints that the cortex grows at the ox]M'iise of the iiiedullji, the deep-lying large cells dividing into smaller ones. The medulla of a four-months' end)rvo is represented in Fig. 'H'A.


Fig. 9M. — Supra-renc Mini* Collprtlon, No. 31.


The cords of supra-renal cells are very irregular and often connected ti^fether, but are readilj- seen to be dinvtly wntiniKius with the corticjii cords. The nie<hd]iiry conls are much more widely separate] than those of the cortex from ime another, the siiaces 1«tween them being filled with tomiective tissue and hloixl-vesscls, none of which have any adventitial or muscular walls. The gresit Tariety of apix-arances presented by the cells uf the cords is indicated in the figure; large and small, regularly and irregularly shaped, uninucleate and multinucleate, light-stained and darklystained cells lie jumbled together without obvious law of arrangement. The significance of this strange picture is imknown. It should be noted that the nuclei of the cord-cells are all, or nearly all, decidedly larger than those of the adjacent connective tissue. As development proceeds the cells l^ecome gradually more uniform in appearance, and offer by the seventh month little variety ; also the continuity of the cords is lessened in the medulla and the blood-vessels become larger. It is evident that there is no fundamental diflFerence between cortex and medulla — in the former the cords have a radial trend, in the latter thej' run irregularl}' ; the medulla is also characterized by having larger supra-renal cells and a richer blood supply. Form and Size of tne Supra-renals. — The supra-renal capsules have at first a rounded form and lie on the ventral side of the cephalic end of the kidney. Probably about the third month they begin to spread on to the doreal side of the kidney, the head end of which they invest like a cap. The capsules grow at first very rapidly, afterward more slowly, and as the kidneys grow more steadily the relative size of the capsules compared with the kidneys passes through striking changes.



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Pages where the terms "Historic Textbook" and "Historic Embryology" appear on this site, and sections within pages where this disclaimer appears, indicate that the content and scientific understanding are specific to the time of publication. This means that while some scientific descriptions are still accurate, the terminology and interpretation of the developmental mechanisms reflect the understanding at the time of original publication and those of the preceding periods, these terms and interpretations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)


Human Embryology: Introduction | The Uterus | General Outline of Human Development | The Genital Products | History of the Genoblasts and the Theory of Sex | The Germ-Layers | Segmentation | Primitive Streak | Mesoderm and the Coelom | Germ-Layers General Remarks | The Embryo | The Medullary Groove, Notochord and Neurenteric Canals | Coelom Divisions; Mesenchyma Origin | Blood, Blood-Vessels and Heart Origin | Urogenital System Origin | The Archenteron and the Gill Clefts | Germinal Area, the Embryo and its Appendages | The Foetal Appendages | Chorion | Amnion and Proamnion | The Yolk Sack, Allantois and Umbilical Cord | Placenta | The Foetus | Growth and External Development Embryo and Foetus | Mesenchymal Tissues | Skeleton and Limbs | Muscular System | Splanchnocoele and Diaphragm | Urogenital System | Transformations of the Heart and Blood-Vessels | The Epidermal System | Mouth Cavity and Face | The Nervous System | Sense Organs | Entodermal Canal | Figures | References | Embryology History



Cite this page: Hill, M.A. (2018, April 25) Embryology 1897 Human Embryology 22. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/1897_Human_Embryology_22

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