Paper - Development of the human coelom (1901)

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Mall FP. Development of the human coelom. (1901) Ref. Handb. Med. Sci. 3: 171-189. PDF

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This historic 1901 paper by Franklin Mall described development of the embryonic cavities using several early embryos from the later Carnegie Collection: 2, 6, 9, 10, 22, 34, 45, 48

See also: Mall FP. Comparative development of the coelom. (1901) Ref. Handb. Med. Sci. 3: 166-171. PDF
Note that due to the original formatting of this historic paper, where figures are inserted within the text, significant reformatting is required of this early online draft.
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Coelom Links: Introduction | Lecture - Week 3 Development | Lecture - Mesoderm Development | Placenta - Membranes | Category:Coelomic Cavity
Historic Embryology - Coelomic Cavity  
1891 peritoneal | 1897 human coelom | 1910 Coelom and Diaphragm | 1924 serous
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Pages where the terms "Historic" (textbooks, papers, people, recommendations) 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, interpretations and recommendations may not reflect our current scientific understanding.     (More? Embryology History | Historic Embryology Papers)

Development of the Human Coelom

Franklin Mall (1911)


Unfortunately, there are no data regarding the beginning of the coelom in the human embryo, and in all probability none will ever be found. The smallest human described until recently is that described by Reichert.' It was obtained from a woman wdio had committed suicide, on account of pregnane}', fortj'-one da3's after the beginning of the last menstrual pei'iod. It ivas therefore presumably about thirteen days old. This ovum, which is jiictured in every text-book, was 5.5 X 3.3 mm. in diameter, was surrounded by a zone of villi leaving two poles bare, and contained in its interior a mass of cells measuring 1.5 X 1-75 mm. All the space between this inner mass and the chorion is the ca^lom, and regarding its origin we can no more than speculate.

During the last few years five other huiuan ova, about as large as Reichcrt's, have been cut into sections, thus permitting a more careful study of their contents.- The dimensions and approximate ages of these embrj'os ai'e given in the talilc in the tirst coluinn of the following ]tage.

It is noticeable that in the embryos just mentioned the size of the whole egg docs not correspond with the .size of the embryo, nor with its age. I do not think that this gieat variation iu the size of the chorionic vesicle is altogether due to the method of hardening the specimen. Just at this time the growth of the choi'ion is precocious, as is also the case in the dog," rabbit, and monkey *

The papers by Bischoff and by Selenka are worthy of the most cai-eful study by every, and I take the liberty of rearrangim;' some of Bischolf's data on the


Coeloiii. Coelom.


Tablk or YouxG Human Ota.



Sieffenbeek van Kenkelom

Mall (No. XI.)


Von Spee <v. H.)

Von Spee ((ile. ).

Mall (No. XII.)

His IL<r.l

Von Sjiee


Diameter of embrvonic

vesieie, millimetres.

0.19 X ?

.;32o X ? 1.5 X i.n

1.75 X 1.5 1.84 X 1.083


2.15 :• 2

2.150 X 3

3 X 4



of ovum.


0.3 X 5.5 X 10 X 5.5 X 6 X

1.5 i-^


4.5 8.5 8



Time between flrst lapsed period and abortion.

13 davs.

14 '■ 12* " 12* "

13 " 12 "

14 "

15 "

These are all of the authentic young human ova I can collect from the literature giving all of their "measurements as well as the menstrual history of the mother. In both of von Spee's cases the time between the abortion and the end of the last period is given ; in embryo V. H. the time is given as " exactly five weeks," while in embryo (lie. five weeks " is given. If we estimate the duration of menstruation as tlve days and its frequency twenty-eight days, then the time between the first lapsed period and the abortion is twelve days, as I have given it in the table.

development of the dog. His ob.servations are very e.xtensive, and give us the basis for our present ideas of tlie passage of the ovum into the uterine tube after fertilization. Unfortunatel}', they were made before the time of sectioning specimens, j'et they are luore complete than most researches relating to this subject published since his time.

The portion I tabulate relates to the size of the embryonic mass or vesicle, the size of the ovum, and its approximate age. As far as I have been able to determine, these data taken from the dog are still the most important ones with which we can compare the human ovum. Embiyologists are accustomed to state that the age of a human ovum is to be reckoned from the beginning of the first lapsed period, and I think that Bischoff's observation upon the size and growth of the dog's ovum corroborates this view. He found that the ova left the ovary during the rutting period, but the exact date could never be determined. Neither did the time of copulation determine the ovulation. As a rule, it took twenty-four hours or less after copulation for the spermatozoa to reach the ovary, and about the same time is required for tlie ovum to reach the beginning of the uterine tube after ovulation. So if ovulation and copulation took place at the same time, fertilization of the ovum could not take place until twenty -four hours later.

BischofE in his taljles often rates the age of an ovum from the first or from the last copulation, or from the beginning or from the end of the rutting period. I have attempted to tabulate his specimens from all four of dates, but in none of the attempts did the size of the ova correspond with their respective dates. Often eggs of a given date were smaller and developed to a less degree than ova presumably younger. After much difficulty I finally constructed a table in which the size of the ovum and its age correspond. A ntunber of the ova published by Bischoff were obtained from the same animal by removing half of the uterus at one time and the remaining half the next day. In each half a number of ova were found, and they were usually of al)out the same .stage of development. By this nrethod of procedure it is possible to determine very accurately the growth of the ovum from one stage to one twenty-four hfjurs later. So, by gradually plodding through the specimens published by Bischoff, it was possible for me to correct his data completely. It is remarkable, as the table shows, how slowly the development takes place in the early stages, and about ten days are recjuired before the ovum is 1 mm. in diameter. On the fifteenth or sixteenth day the ovum is about as large as the human ovum described by Reichert (see table).

Similar results can also be obtained from the various papers published on the rabbit's embryo. Its development, however, is considerably more rapid than the dog's as the period of gestati(jn is but thirty days.


Table of Age and Size of the Dog's Otum. (Compiled from Bishoff.t



of ovum,


Diameter of embryonic

mass, millimetres.


1 day

0.15 .14 .14 M .IB .18 .20 .21 .28 .30



3! 4. 5. 5. ti.

' '.if! .16 .34 .4:3 .5




1 cell

2 davs

2 cells.

3 ■•

4 "

4 "

13 "

64 "



H "

9 "


10 "

11 "

12 "

13 "

14 " .

15 "

16 "

l(ii^ '■

It has been somew'hat difficult to compile this table, as Bischoff's measurements are all given In Paris lines. My measurements are taken in great pait from his figures, and I think that these are very accurate.

Recently Selenka has given some of his results relating to the development of the monkey. The most valuable specimen relating to the earlj' development of higher animals was unfortunately lost, but its age and dimensions are preserved for us, and are of value in the determination of the age of human ova. The ovum came from a monkey kept in confinement which was killed eight days after copulation. If we estimate one or two days required before fertilization, this ovum cannot be over seven days old. This suggests that the earlj' stage of this variety of monkey is developed more rapidly than that of the dog.

Developmext of the Moxket.


of ovum,


Diameter of embryonic

vesicle, milUmetres.

Semnopithecus maurus

1.5 6 5 10

3 *

Semnopithecus prulnosus

fercocebus cvnomolgus ......


24 t

The pictures Selenka gives indicate that the development of a monkey's ovum is identical with that of the human ovum. At anv rate, the few specimens Selenka publishes give results which are equal to the great number of speciTuens of human ova which have been published. This only Indicates that many of the interesting problems relating to early human development will probably be solved by the study of the monkey's ovum. There is but little doubt now that young monkeys' ova will soon be obtained for study.

Not an embryonic vesicle, but only a disc. + Neurenteric canal present.

Material E.mploted.

During the last few years I have obtained a number of young human embryos from physicians in different portions of the United "States, and "lo them I am under all obligation for the present studvaswell as for soiire others which are to follow. Nearly all of the specimens which I give in a table are well preserved, and a number of them are preserved excellently. All of the specimens were stained in alum carmine, and with the exception of Nos. XVII., XLIIL, and LVII. were cut transversely. These three were cut into .sagittal sections.

All of the specimens were hardened in alcohol, the value of which method I have repeatedly emphasized to my friends, and do continue to emphasize to those who may preserve speciiuens for my use in the future.*

Embryologists usually recommended that human embryos should he hardened by phirmg them in dilute alcohol and then gradually Increasuig the strength of the alcohol. It has been my experience that by this treatment the specimen is injured by maceration due to the


Coelom. Coeloin.

List of Embryos Studieij.


Length OF Millimetres.

V. B.*

N. B.

XI ...

■ ji'.i 5. 3

ih' '

17 17 18 18 18 1(1 19..5 3U SS 24 24 28 80 130


13 14 14 17 15 10 18 18 18 20

2(i ' ' 19

00 HO

Dr. Klttredge, Nasliim, N. H. Dr. Ellis, Elkton, Md. Pruf. His, Leipsic, German.v. Ur. Williiiins, Baltimore, Md. Dr. Douglas, Nashville, Tenn. Dr. C. (-1. Miller, Baltimore, Md.







Dr. Williams, Baltimore, Md.




Dr. Booker, Baltimore, Md. Dr. Bitter, Bi'ooklyn, N. Y. Dr. Evcleshvmer, Chicago, 111.









Dr. Wills, Los Angeles, Cal. Dr. Cottrell, Louisville, Ky. Dr. Sewall, Denver, Col. Dr. Booker. Baltimore, Md. Dr. Snively, Wayneshoro, Penn, Dr. Howard, Cleveland, < )hio. Dr. C. 0. Miller, Baltimore, Md.

X . . . .

Dr. W. S. Miller, Madison, Wis.


XXXIV .... XLVIII ....

Dr. Douglas, Nashville, Tenu.

Dr. Ellis, Elkton, Md.

Dr. Wilson, Worcester, Mass.

V. B. andN. B, indicate the length ot the embryo measured from the vertex to the breech and from the nape ol the neck to the breech, respectively.

Nearly all of the embryos were drawn or photographed to scale and then carefully cut into sections from 10 to 50 jj. thick. I find that for purposes of reconstruction it is a mistake to cut the sections very thin. Yet in small specimens, as Nos. XI. and XII., the specimens were cut thin to permit of careful cytological studies also. In most of the specimens photographs or an additional series of sections were made of the chorion and amnion in order to study the variation of tliese structures.

Embryos XL,' XII., and II.' were completely reconstructed in wax by the method of Born. Nos. IX., VI., and X. were reconstructed in part by Born's method and finished by His's method of reconstruction. The abdominal viscei-aof Nos. VI., IX., X., XXXIV., XLV., and XLVIII. were modelled by Born's method.'

The mechanical portion of reconstruction has been simplified to a great extent by a special apparatus used in the Anatomical Laboratory,' which enables us to cmploy a modeller. The sections are projected upon a screen, to which the wax plate is attached. By working in a dark room with this apparatus it is easy to direct a modeller to draw the outlines accurately. He can then . cut them out, and all that remains to be done is to pile the pieces and then blend them.

The Ccelom in Young Ova.

All of the young human ova which have been described contain within them a cavity, lined with mesoderm; this is the coelom, bounded by the somatopleure on the outside and by the splanchnopleure on the inside. This arrangement, as shown by a number of diagrams by recent authors, is very unlike the appearance of the blastodermic membranes of many of the lower mammals, and it is necessary, therefore, that we should revise our

weak alcohol. A few years ago I emphasized the fact that the whole ovum should be placed in a large quantity ol strong alcohol as soon as possible. It should be handled us little as possible before hardening it, thus preventing mechanical in.1ury. By leaving the ovum closed the alcohol must first penetrate the chorionic and amniotic fluids before it reaches the embryo, and thus, without placing the embryo first in weak alcohol, it naturally passes through the successive dilutions of alcohol before it is completely hardened.

It is very in,1urious to these delicate specimens to be wrapped m cotton before thev are sent by mail or express. A perfect method is to place the preserved specimen in a bottle filled completely with alcohol, thus imitating the condition of a foetus in utero. If there is no air or cotton in the bottle containing the embryo it is almost impossible to iniure the embryo by shaking it. ,,,„,.

Since i have emphasized this method of preparation (.lohns Hopkins Hospital Bulletin, 1893), I have obtained a number of specimens excellent in every respect. These specimens are not distorted, nor macerated, nor shrunken.

conception of the formation of the amnion in the human embryo.'"

The ova recently published by Peters and by Graf Spee indicate that the amnion must be formed very early, and, since it is completed before the medullary grooves begin, we must admit now that it is formed much the .same as it is in many rodents, i.e., by apparent inversion of the membrane. When Bischolf " first described inversion of the membrane in guinea-jngs it seemed like a paradox, but, .since the comparative methods of study have been introduced, inversion onlj' means that the amnion is completed before the medullary groove begins to form. This alteration of the development of the amnion and the medullary groove makes the body of the embryo develop on a concave surface instead of on a convex one, thus apparently making the embryo inverted, as is the case in the guinea-pig.

Closely associated with inversion of the blastodermic membrane is the formation of an tidditional layer of cells, discovered by Kauber,^ the importance of which has been emphasized by Selenka and others. Rauber's layer is so marked in the rabbit that it was at first believed to be the true ectoderm. The fate of Rauber's layer has not been stifflciently studied to interpret it completely, and our ideas regarding it will not improbably require some revision. In many rodents Rauber's layer becomes markedly thickened on one side of the ovum, forming a support, or Trdger, for the ovum. The relation of Rauber's layer to the Trager is shown beautifully by Selenka " on Plate XVI. of his monograph.

The questi(m which interests us here is whether the inversion of the blastodermic membrane as well as the discovery of Rauber's laj'eraids us in advancing a theory of the development of the germ layers of the human embryo, and thus in turn to explain the large ccelom as found in all of tlie earliest human ova. I realize fully that any such effort will not be final, yet I believe that it will aid us to understand better the relation of the membranes as found in the human ovum.

In looking over the illustrations of the development of animals closely related to man, one is struck with the similarity of the arrangement of the membranes to those described for the human ovum by Peters and by Graf Spec. One must compare only plates XXXV. -XXXVIII. of Selenkf/s" paper with the two plates accompanying Graf Spec's '= to be convinced that the early development of monkeys is almost identical with that of man. Yet Selenka's researches on monkeys do not help us a great deal; they only show us that the monkoy's development is like that of man. In monkeys we have also the precocious chorion and the early amnion and the large coelom between the umbilical vesicle and the chorion. The marked difference is that the amnion is attached to the chorion along its dorsal side, while in the human embryo this is only the case along the posterior end of the amnion. The attachment of the amnion along the chorion suggests that the embryonic jilate separated from the exterior of the ovum along this point, as Selenka thinks he observed in a very young ovum onl_v 1.5 mm. in diameter. Unfortunately, the most valuable specimen was injured in its preparation,'" and Selenka did not trust himself to give any illustrations of it.

With the amnion attached at its dorsal end to the chorion, we understand why the entodermal end of the allantois must growaroimdau angle to reach the chorion (Selenka, Plate XXXVII. , Fig. 5). Somewhat the same arrangement has been descrilDed by Graf Spec in his embryo Gle., but the curve is by no means as marked, indicating that the attachment of the embryo to the chorion is along its posterior end, as shown by His '* in liis well-known diagram of the formation of the amnion.

Regarding the very early stages of monkeys and man it is better tliat we make comparisons with animals most nearly related to them, and now we have careful studies of the very early stages of Chiroptera at our disposal. I believe that Selenka's" study of the development of Pteropus edulis gives us the key for the comparison of the formation of the blastodermic membranes in mam 173




mals. Recent investigatiims by Duval •" ou different families of Cliiroptera appear t<i confirm tlie work of Selenl^a on Pteropus.

In order to illustrate these points more clearly I Lave made diagrams of three of Seleuka's figures of Pteropus.

Figs. 1413-111.5.— Diagrams of the Devriopinent. of Ptpnjpus Ediilis, aftPr Selenka Fig- 14131s Selenka's Fig. 2; Fig. 1414, Selenka's Fig. .') ; Fig, 141.5, Scipnka's Fig. 9. It. Raulinr's layer; P. placenta; ec. eftoderm ; rii, entoderm; i-li, chorion; am, amnion; » r umbilical vesicle; iiics, mesoderm; me, <'a-lom ; al), allantols, with ihe arrow indicating the direction of Its future development.

Fig. 1413 is from an ovum covered conijiletely with two layers of cells, between which at one pule of the egg there is a mass of scattered cells destined to become the permanent ectoderm. The outer layer of cells has a tendency to grow into the form of villi over the embryonic disc, while on ^

the opposite side of the egg it is composed of but a single layer of cells. Since this outer layer remains well separated from the body of the embryo throughout its development, and since it holds the same position to t)je egg that Hauber's layer does in the rodents, I believe it to "be identical with Kauber's layer, and shall S|ieak of it as such. According to Duvid this Rauber's layer ilisapjiears over the embryonic disc in the Cliiroptera much as in the development of the ralibit ;ind the field mouse. This does not necessarily contradict Selenka's observations on Pti'i"opus, for the house mouse begins to develop like the held mouse, but continues during the early stages in the same manner as Pteropus does.

In the next stage the ectuderm has been converted into a hollow mass of cells. Fig.

1414, rather by a process of absorption than bj' an invagination, as I have expressed it in the diagram. The entoderm lines the wdiole interior of the egg, and surrounds the ectoderm of the amniotic cfvitj-. The ectoderm of the exterior of the egg, Rauber's layer, is again thickened over the embryonic mass to form the placenta, as Selcnka calls it, or the Trd'ier, if we ^\ere discu.ssing rodent embr5'ology.

In the next stage, as expressed in Fig. 1415, the mesoderm is beginning to form, and has extended completely over the amnion and partly over the umbilical vesicle. The entoderm has retracted itself and touches the ectoderm ; onlj- the chorda dorsalis is yet to form. Between the amnion and the placenta, or the Trager portion of Rauber's layer, there is a marked space, and the mesoderm does not come in contact with it. The allantois grows as a bag into this space and attaches itself to the thickened part of the ectoderm, as shown by GiJhre -' in his figures. In the Fig. 3 accompanying Gijhre's paper he shows the vesicular allantois attached to the support of the chorion (black portion of mj' Fig. 1415) leaving on either .side of the embryo a ccelom. The allantois carries the mesoderm and vessels to the villi of the chorion, and these in turn are embedded in the decidua of the uterus. In so doing the ectoderm of the chorion receives a second layer of epithelium, and I believe that this must account for the two layers of epithelium we have on the chorionic villi of the human ovum. There has been much written ou the subject of the double layer of epithelial cells of the human chorion, and I think that a glance at Gohie's Figs. 3 and 4, ou Pteropus, as well as at Selenka's Figs. 11 and 1'3 (Plate XXXV.) and Fig. 6 (Plate XXXVII.) on monkeys, will decide this question more definitely than all the many discussions on the hu-. man chorion put together have done. Having now selected from Selcnka diagrams and descriptions of the development of the germ layers of Pteropus, it is easier for me to give a jthiusible explana

Fio. 141S. Figs 141(1 n. 14ls -Hypothetical stages of the Early Development of the Human Ontm.

., Iliiubers layer; ec, ectoderm oi, entodenn ; mo, mesoderm ; iir, umhllical

vesicle; cot', ca'lom ; ((K, position of allantois.




tiuii of thebegiuuiugof tlieca-loin in the human embryo. If the diagram I have given in Fig. 1415 is eompared with Scleulia's Figs. 5 and 11 (Plate XXXV.) antl Fig. 5 (Plate XXXVll.) of the monkey, as well as with the sections of young human ova piililished by Graf Spec"- and > by mj'self," one is struck with the great similarity of the two groups of figures.

Fig. 142(5, given further on, is a diagrammatic outline of a longitudinal section of a young human enil)ryo jiublished recently by Graf Spee. It is the one marked v. II. in the table of J'oung human ova given in tlie beginning of this paper. When, now, this section is c<impared wilh the transverse section of Pteropus, in Fig. 1415, the only marked difference is that the umbilical vesicle in Pteropus has retracted, in order to make the arrangement of the membranes as given for the human embryo in Fig. 1426.

In order to make the connection complete, I give hvpothetical stages in Figs. 1416, 1417, and 141S. "Fig. 1416 represents the human ovum in the two layer stage. The outer layer, or Rauber's layer, is complete as in the rodents and in Pteropus. The inner layer, or entoderm, is also complete. Between the two is the endiryonic shield, or ectoderm of the future embryo. The next tigure, 1417,


FiCr. 1118.— Diagram ol a Patbological Ovum whiob Represents an Early Hypotbetlcal Stage.

shows the beginning of the mesoderm developing toward the tail end of the embryo, as this is the positii>n of the primitive streak, and as "the head fold of the amnion in many embryos is often invested only with ec'toderm and entoderm. A stage later. Fig. 141S, finds the mesoderm enveloping the umbilical vesicle completely, and also partly lini'ng the outer layer, R, of the ovum. The cavity lietween" the two is the ccelom. At the tail end of tlie endjryonio disc the mesoderm of the somatopleure and splan'clmopleure are still united, and mai'k the place of the formation of the rudimentary allantois.

Having carried the development of the human ovum to this stage by means of hypothetical stages, based upon the develofsmeut of Pteropus, I can now continue the description of the development based upon observation.

Abnormal Om. — Teratologists are accustomed to view a group of abnormal states as arrested development, and in recent years a number of abnormal Imman ova have been studied by His," by Giacomiui,-^ and others. Frequently in the' development of an ovum the embryo is destroyed completely, or, according to Giacomini, may wander out of the ovum. In these cases the ova are aborted. Frequently, however, a portion of the embryo is not developed, or it dies and the remaining portion develops for a time, and then the ovum is aborted. I have now in my collection a beautiful example of an ovum of apparently normal structure, the interior of which is lined completely with an amnion, and in place of an embryo there is only an umbilical cord. The ovum was aborted fifty-four days after the first lapsed period, and was 30 mm. in diameter. The cord was 2 mm. in diameter and 9 mm. long. Its embryonic end seemed to be cut off abruptly, and was covered with a small mass

of round cells. 1 give this example f)nly to show that the end)ryo may be entirely wanting with a perfect coi'd and membranes.



cxxxiv .,









CXXX . . . . CXLVII.. CXLIII . .

Dimensions of

.'4 ■ V, ill IS


i(i 17 ; 40;

1.5 X III ; JO -■■ 27



, :!o

I ■ li • i;

II • 3

I..-) ■ 1

I ■ 6 1.5

■i y i.i:

.■|..'> ,- :!.;■ 4 ■ 3,-- 1..-)


P J 3?





!;i da

41 ■ 4:i ■

71 '



■r, da

14 da

Amnion formed. Amnion partly form

Partial amnion.

Multiple anniion.

Xti amnion.

A large per cent, of young ova wdiich come into the embrj-oiogist's hands are abnormal. According to Professor His' experience over half of the ova less than three weeks olil are abnormal, w Idle of those of four and five weeks one-quarter are abnormal. In my collection the per cent, of almormal embryos is not as high. No. XIII. is His' Embryo XLIV., "which is frequently descrilicd in the books as a normal specimen, but which unfortunately is an abnormal one. My interpretations of the vesicular forms'" is that the fibrous degeneration overtook the embryonic vesicle after it had reached the stage of Graf Spec's embryo v. H., my Fig. 1426.

Nos. XXI. and LVIIL came to me as pei'fect specimens both having been hardened imopened, the first in strong formalin aird the second in strong alcohol. No. XXI. was still enclosed in its dccidua, and appeared to be a normal specimen until it had been cut into serial sections. The embryonic vesicle proved to be very large, and was composed throughout of two layers, an inner one giving all the appearance of the entodei-m and an outer giving all the appearance of the mesoderm of the umliilical vesicle of j-oung embryos. The mesodermal layer contained within it islands of blood cells, as are also present in normal specimens. The wdiole vesicle was connected to the chorion with a mass of mesodermal cells somewhat as shown in the diagrammatic Fig. 1419. The chorion and dccidua appeared to be normal.

No. LVm. showed considerable change in the mesoderm of the vesicle and chorion, giving somewhat the appearance of fibroid degeneration lich in cells. The chorion was attached to the vesicle by a strong pedicle, as shown in Fig. 1419. The vesicle itself was composed of two layers, aniuner and continuous one composed of one layer of cells, and an outer and thickened layer appearing like the mesoderm of the chorion. There were no indications of blood islands. In addition to these two layers there was a third layer fairly well marked near the pedicle and between the vesicle and the chorion. With the exception of the allantois canal, Fig. 1419 is a diagram of this specimen.

Giacomini" has described a niunber of similar vesicles, and he expressly states that the vesicles had the structure of the umbilical vesicle, but tliat there was no trace of the aiunion present in any of them. A number of other vesicular forms have lieen described, and in general they all appear much like the two specimens I have given.

I do not think that it is rash to assei't that these vesicles represent an arrested development of an earlier stage, which, due to impaired nutrition, or whatever it might have been, simply allowed the embryonic vesicle to keep on expanding. That this expansion can keep on is already shown in the simple enlargement of the chorion after the embryo is distorted or wanting altogether. We have in these S]iecimens a thin chorion with atrophic villi, and why can we nothave an exjjanded and atrophic


C«eloni. Cceloiu.


embryonic vesicle if its development is impaired? In tliis way I view specimen No. LVIII. It represents a much earlier stage, which has simply e.vpanded and was

Fig. 1430.— Diagrdmmatic Section of Hall ol the Human Ovum No. XI. Enlarged 10 times. The villi are drawn only on the upper side, ec. Ectoderm ; au entoderm ; 7Hf'.v, mesoderm ; ui\ umbilical vesicle : coc, coelom ; all, allantois ; a. amnion.

ultimately aborted. In No. LVIII. the embryonic vesicle must have ceased its further development a week or so before the abortion, about the time the cojlom was beginning to develop. At that time the fibrous degeneration enclosed the embryonic vesicle as well as extended around the whole chorion into all of its villi. This, then, arrested the further development of the embryo, and the embr^'onic vesicle simply continued to expand.

This idea is further strengthened by another ovum whose history I published on several occasions several years ago.* The specimen is a good one, having been preserved fairl}' well, and it has every indication of being normal. Since the specimen has been in my hands I have studied it over and over again, have photographed many of the sections, and have resconstructcd it. At first it was veryditflcult for me to interpret it, but finally it appears to me that something definite can be said regarding the arrangement of the membranes and their relation to older as well as to the pathological and presumably younger specimens.*

Eiithryo No. XI. — "The woman, from whom the specimen was (jlitained, is twenty-five years old, menstruates regularly every four weeks, the periods lasting from four to five days. She gave birtli to a child September 19t.h, 1892, and had the fii'St recurrence of menstrutition I)eceMil)er 19tli. Tlie second ]ieriod followed on January 'Jfith, ami was very profuse; it lasti'd mitil Peb luary 1st. The next period should have begun about February 32d, but on account of its lapsing the patient concluded that she was pregnant, and called' at my ofiice

An extensive description of the pathology of early human eiiihryos is given by me in the "Contributions to the Medical Sciences," Johns Hopkins Hospital Reports, viil. i.\., Baltiujore, V.U\.


a few days later. I did not examine her, but asked her to remain quiet and await developments as I thought possible that she might be pregnant. On the evening of March 1st she fell and sprained herself, and during the ■ same night had a scanty flow. The flow recurred each day, and on the 7th of March she passed the ovum. It was kept in a cool, moist cloth for twenty hours, and when it came into my hands was at once placed in a large quantity of sixty-per-eent. alcohol." f

The ovum is very large for its age, having a long diameter of 10 mm. and a short diameter of 7 mm. It is covered with villi only around its greatest circumference, having two spots without villi, as was the case with Reichert's ovum. The villi of the chorion are from 0.5 to 0.7 mm. long and are branched.

Upon opening the chorion it was found that the germinal vesicle was situated just opposite the edge of the zone of villi. About it was much coagulated albumen, magma reticulare, which I did not remove, and therefore could not obtain good camera drawings. The portion of the chorion to which the vesicle was attached was cut out and stained with alum cochineal and cleared in oil, but even after this treatment it was impossible to obtain any clear picture. The specimen was next embedded in paraffin and cut into sections 10 /j. thick. The .series proved to Ije perfect. From the sections a reconstruction was made in wax, and the accompanying Fig. 1420 is a sagittal section of it.

The dimensions of the different portions of the vesicle are as follows:

Diameter of stem 0.4 mm.

Length of stem 0.4 "

Length of vesicle 1..5 "

Width of vesicle 1.0 "

Length of invagination 0.8 *'

Width of invagination 0.5 "

Diameter of opening of invagination 0.03 "

The sections and reconstruction show that the embryonic vesicle is attached to the chorion by means of a stem. The greater part of the vesicle itself is composed of two layers, ectoderm and mesoderm. In the neighborhood of the eml)r3-onic stem there is a third outer layer which shows all of the characteristics of the eeto


Fir.s. 1421-U3.-i.-Sections Nos. 4;i, .53, «s, SO, and 89 through the Embryonic Vesicle of Embryo No. XI. Enlarged ;il times. The entoderm is a heavy line, the ectoderm is striated, and the mesoderm dotted, a. Amnion ; X, cavity of the umbilical vesicle e.xtending into the f the vesicle ; fi, Rauber's layer as the ectoderm of the chorion.

derm. Just beside the attachment of the vesicle to the stem there is a sharp, deep and narrow invagination of all thi-ee embrj^onic membranes, which I have interpi-eted as tlie foi-mation of the amnion. The arrangement of

+ Letter from Dr. Kittredge, April 27th, 1893.




this invagination is fully pictured in Figs. 1421 to 1435, Within the stem there is a sharply defined allantois which communicates with the cavity of the vesicle just below the cavity of the ectoderm, the ectodermal plate of the invagination is very broad but not of ecjual thickness throughout its whole extent. It extends to the outside of the vesicle and ends quite abruptly in the neighborhood of the stem. The blood-vessscls of th(^ mesodermal layer extend to the stem but do not enter it, nor are there any blood-vessels in the chorion.

Since the first publication of this specimen, embryos both normal and pathological have been studied, all of which indicate more and more that this specimen must belong to the pathological class. The other pathological specimens of my collection as well as the perfect normal specimen described recently by Peters all speak for this conclusion. Yet the' presence of all three blastodermic membranes in No. XL, with blood islands in the mesoderm, and an allantois in the embrycmic stem, indicate that this specimen cannot be far from the normal, but represents the earliest changes in the blastodermic membranes in a specimen of the Peters stage under pathological conditions.

The next stages in the development of the embryonic vesicle are taken from Graf Spec, and they are of importance to ehicidate the changes which take place preparatory to the formation of the body cavit}'. In Fig. 1426, which represents the younger embryo, the anmion is still surrounded completely with mesoderm, as in embryo No. XI. , represented in Fig. 1420. The mesoderm crosses the median line, as the sections given by Graf Spee " show. The dorsal side of the amnion is covered with a very thick layer of mesoderm, as the closure of the amnion in embryo No. XI. would suggest.

From the stage represented in Fig. 1426 it is easy to pass to the older embryo represented in Fig. 1427. Now the body of the embryo is well marked, the neural folds are just beginning, and the ncurenteric canal has just been formed. Tlie chorda dorsalis is not yet separated from the entoderm, and the blood islands encircle completelj' the umbilical vesicle and have nearly reached the head end of the body of the embryo preparatory to the formation of the heart.

In my earlier studies I was inclined to believe that embrAfo XI., Fig. 1420, to be normal, but the recent publication of a normal human ovum younger than Reicherfs, by Peters, makes this view improbable. Now we muSt view the opening in the amnion in XI. as a secondary rupture, for in the Peters embrj'o, which is so much smaller than any yet seen, and the amnion is closed. Furthermore, Selenka has just described a small ovum of the gibbon in which the amnion is still connected with the epithelial covering of the chorion and almost communicates with the exterior of the ovum. These observations practically set to rest this difficult question. The amnion arises directly from the exterior of the ovum, closes at once, and then the embryo forms within it. There is, therefore, apparent inversion of the germ layers.

In these two ova described by von Spee, the coelom is much of the same form it was in embryo No. XI., Fig. 1420, and therefore needs no special comment. Yet around the head end of embrj'o Gle. there is a marked accumulation of mesoderm into which the heart is to grow. In the illustrations of the section of this embryo Graf Spee ^" pictures spaces in the mesoderm which he believes to be portions of the body cavity of the embryo, that is, the cavity of the muscle plates, pericardial cavity or peritoneal cavity. It is impossible to determine definitely which portion of the bodj' cavity these spaces represent, but I do not feel inclined to believe that what he marks pericardial cavity in Fig. 143,5 can possibly represent it, for we are to look for the pericardial cavity between the junction of the pharynx and umbilical vesicle Vol. hi.— 12

and (he head end of the embryo. This portion of the embryo is marked II in my Fig. 1427, and falls anterior to von Spec's Fig. 16. Von Spec's Fig. 16 is the twentvf(nu-tli section of the embryo, beginning at the head, while Ills Fi'j;. 23 is the eighty-first section.

The various small sjiaecs in different portions of t)ie mesoderm cannot be; viewed as the real origin of the body c a V i t i e s without further discussion. In the von Spee endiryo V. II. there are indications already of small spaces in the mesoderm at

Fig. 1428.

Fig. 1427.

Figs. 1426 and 1427.— LoiiKitudiual Sections of Two Young Human Ova. (After Grat Spee.) Enlarged 10 times. Fig. 142li, Embryo v. H. ; Fig. 1427, Embryo Gle. Just half of the chorion is drawn, and the villi are outlined only over a portion of the ovum. TV, Rauber's layer ; a, amniotic cavity ; u v, umbilical vesicle ; en, entoderm ; mcs, mesoderm ; all, allantois ; c, chorda ; n c, neurentic canal ; if, position of heart.

the border of the ectoderm of the embryo. Similar spaces are described by Bonnet for the sheep and by Selenka^' for the monkey. While von Spee and Bonnet believe that these spaces belong to the ccelom, Selenka simply designates them heart, or vascular.

The blood-vessels are intimately associated with the ccelom in their early development, and it is easy to be led into error without an abundance of material. Drasch"^ recently has again emphasized this relation. He has shown in the chick that the blood islands are separated from one another by a nimiberof clcsed spaces filled only with a fluid. These spaces soon flow together to form the large slit-like coelom of birds. The same condition of things has been shown to be true, but from a very different method, by Budge. ^^ He injected the blastoderm of the chick, and showed that the coelom was composed of a network of spaces, which graduall}- flowed together into the large coelom surrounding the embryo.

Of course in the young human embryos we have at our disposal this stage of the process has long passed, but there is no reason why a remnant of it should not exist at the point of union of the umbilical vesicle with the body. The reason I question von Spec's interpretation of these small spaces in the mesoderm in embryo Gle. is that I believe that all, or certainly nearly all, of the body cavity is formed by an incorporation of the extra-embryonic Ctt'lom within the embryo. What I have observed in human embryos as well as in the injected specimens of Budge shows that this must be true. These small spaces in the mesoderm of the body may belong to the muscle plates and the early blood-vessels, and certainly cannot play any great part in the development of the body cavity. There is no doubt whatever that the whole peritoneal cavity is simply pinched off from the coelom of the outside of the bod}', and it is highly probable that




tlie perieardiiil cavity and pleural cavities ure formed in tlie same vjny. The anterioi' mesentery of tlie intestine has never existed in the Iniman embiyo, and it is therefore needless to explain its mode of disappearance.

My statements are based in gi-eat part im embryos Nos. III. "and XII., and since No. XII. is such a perfect speci


no. 1428.— Outline Drawing of a Sagittal Section of the Model of Embryo No. Xtl. Enlarged .50 times. The heavy line Is the aorta. The muscle plates are nuuihered for occipital, cervical, and dorsal regions, respectively. The mesoderm is striated. am. Amnion ; a, border between forebrain and midbrain ; x and x\ extent of closure of spinal canal ; 8. Seessel's pocket : c/j, chorda ; // and Jj\ first and second branchial pockets ; o v, otic vesicle ; m, mouth : T, thyroid ; H, pericardial space ; 2-Jh, pharynx ; cnt. entoderm : S T, septum transversum ; (, liver; n c, neurenteric canal ; alU allantois.

men it is well for me to describe it in greater detail. The embryo is about the same age as KoUmann's^' embryo Bulle. wliicli unfortunately was never fully published. No. III. is an embryo given me by Professor His. This embryo had been torn from the umbilical vesicle, and was inpired in different portions of the bfidy. Yet the head end of it is fairly well preserved, and it is of value in determining the growth of tlie body walls covering the heart.

Eiiihrjin .'./ //////. Long. — Thehistory of embryo No. XII. is as follr)\vs: "The woman from wliom the ovum was obtained is twenty-three years of age and has been married for three yeai's. Slie is a very intelligent woman, and her statements are reliable. Her menstrual periods recur every thirty days. She had been married some time befoie she liecame pregnant, and after passing two )ieriods aborlcd July 6tli, iK!)!!. She was unwell the 5th of October and again on the 7tli of November, this last period lasting ti vo days. She jiassed her next period and on Decemlier IHth aborted the ovum."*

The ovum was hardened in strong alcohol without opening it first, and when it came into my hands its

• Letter from Dr. Ellis, January 7th, 1S94.

dimensions were 18 X 18 X 8 mm., that is, it was sliglitly flattened. It was ccmipletely covered with long villi. It was carefully opened, care having been taken not to injure the embryo in any way. The ccelom was filled with a clear fluid, and manj' firm slireds of a fibrinlike body which obscured tlie embryonic vesicle gi-eatly. With much difficult}- the embryo could be outlined, and these drawings proved to be of great service in making the reconstruction. The portion of the chorion to wliich the embr}-!) was attached and the embryo were stained in carmine and endjedded in paraffin. The wdiole was cut into sections, at right angles to the bodj', 10 /j thick.

Every other section was enlarged 100 times and drawn on wax plates 2 mm. thick, and from them the model of the embryo was made. The model gives the whole central nervous system, the entoderm throughout its extent, the blood-vessels, and the muscle ])lates.

The shape of the neural tube is given in the diagrammatic outline. It was closed only along the middle of the body, being open in front down to the beginning of the fourth muscle plate. From the beginning of the fourth plate to the be.ginning of the fourteenth it was closed, and from there on again it was open. In the figure the portions between .t and x' indicate to what extent the tube is closed. In Figs. 1429 and 1430 the tidje is nearlj' closed, while in Fig. 1432 the tail end of the tube is just beginning to .separate from the ectoderm. The cephalic end of the tube already clearlj- outlines the forebrain. the mid-brain, and the hind-brain; the constriction. Fig. 1428, a, indicates tlie junction between the first two. On the ventral side of the fore-brain there are two marked jiockets, one on either side, just behind the neuropore, which are no doubt the primarj- optic vesicles. It shows that in the human embryo these are fully outlined before the brain lias separated itself from the ectoderm. Farther behind, very near the dorsal median line and about in the middle of the head, there is a short pocket of tliiekencd ectoderm, the otic vesicle. Toward the hinder end of the embryo the spinal cord communicates b^v means of a soliil band of cells with the entoderm (Fig. 1432). At no point in this communication is there a canal, so it must be viewed as the last remnant of the nciirenterie canal. The location is opposite the twelfth mu.scle plate, or in the neighborhood of what will later on be the position of the tirst rib. The chorda dorsalis extends to the neurenteric canal, but not beyond it. There is no chorda in the tail end of the embryo.

Throughout the central nervous system, immediately about the central canal, there are many karyokinetic figures, showing that the specimen was excellently preserved. In the greatei- ]iort^on of the neural lube the tissue is already marked by two zones, a central one rich in nuclei, and a peri]iheral containing none. This corresponds with the deseriptiou already made familiar to us by His.

The general shape of the whole central nervous system is very unlike that of any other young human embryo ever jiiiblished. It circumscribes the greater portion of a cii-cle, while in the other human embryos of this size it makes more of a straight line. I think that it is pi'obable that this specimen represents the normal, as it was not injiired nor handled in any way before it was cut into sections.

The entoderm, as the figures show, is already divided into fore-gut. mid-gut, and liind-gut. The" fore-gut makes the pharynx, from which there' ai-e four diverticula



Coeloiii. Cwloiii.

ou the (lovsiil side, one on the vential side, and two near the nioith. The four on the dorsal side mark the tirst two branchial pockets ou either side ot the embryo; the two in trout are Seessel's pocket and the entodcrmal portion of the mouth; while the one on the ventral side of the pharynx is the beginning- of the luediau portion of the thyroid gland (Fig. 14'J9, 0 At the junction of the pharynx with the umbilical vesicle there is a large diverticulum into the septum trausversuni (Fig. 1430 0. the beginning of the liver.

Within the tail end of the embryo, behind the neurenterio canal, the hind-gut is enlarged considerably, and from it the entodcrmal canal of the allantois arises.

The whole umbilical vesicle is covered with bloodvessels which communicate wilh the veins and arteries of the embryo. Near the (U'igin of the liver there are two veins which collect the blood frcmi the umbilical vesicle and then cuter the heart. These are the omphalomesenteric veins. They with a number of their branches arc sho^vn in sections in Fig. 1430, r. The heart itself is broken, but there is enough of it left to show that it is bent upon itself and contains a large cavity at the point where the veins entered it. From the heart two arteries arise and pass in front of the first branchial pocket, and each follows the course as shown in black in the reconstruction. The aortas do not unite, but each sends a number of segmental branches to the umbilical vesicle along the tail end of the embryo. These are, of course, temporary ; they may be callecl collectively the omphalomesenteric arteries. As the permanent omphalomesenteric artery arises more al30i-al than any of these, it is easy to understand that most of them must degenerate.

The sections show that there are fourteen muscle plates, all of which are hollow and do not in any way conununicate with the body cavity in general. Kollmann, who described an embryo of this same age, numbers them from before backward, but I tiiink that they can be designated more definitely. Froriep ^ showed that in all amniotic vertebrates there were a number of muscle plates and dorsal ganglia formed in the occipital region, and studied their fate in the chick and in the cow's embryo. Piatt ■" has also followed the order of the origin of the muscle plate in the chick, and found that the first division of the mesoderm was between the third and fourth occipital plates. The first three or four of these segments communicate in the chick, according to Dexter, 3" with the ca'lom, and Bonnet °nias found also that the same is tr\ie in the sheep. Bonnet's figures (compare his Plate IV.) show that a sheep's embryo of the same stage as embryo XII. has muscle plates much more sharply outlined than the human. In order to locate the muscle plates more definitely I have made every effort to count the spinal ganglia in embryo XII., but with no definite result. It is impossible for me to define the spinal ganglia, as often they are represented by a tew cells only, then again as a band of cells they extend over several segments. The same is true m the occipital region. Had I been able to number them definitely it would still have been impossible to number the muscle plates from them, for His-"" has shown that there is an occipital ganglion in the human embryo as well as in the lower animals.

The fact that the muscle plates reach to the otic vesicle in embryo XII as well as in Kollmann's embryo Bulle, indicate that the first plates must belong to the occipital reo-ion and I have found that there are three occipital mSscle. plates in embryo No. II.-" Jloreover, there is every indication of a degeneration of the first two plates in XII so on this account I am inclined to number them as they'are numbered in Fig. 1428. I do not think that any of them ever communicate with the pericardial cavity as Bonnet found them in the sheep. The cavities in all of the other plates are small, and they are separated by a large mass of mesoderm from the cadom. Ihis all confirms my view. , , ^ ^,

The chorda extends from Seessel's pocket to the neu renteric canal. , , , t i„

There are also a few segmental ducts, some completely

and some jtartly sejiarated from the e<'toderm, as was the case ill Kollinaim's embryo. The ducts are small, and extend over one or two .sections only, and oec-asionally one of them is arising at several dillerent [Kiinls between a given two .segments. They are [iresent on both sides between the first and second cervical segments, second and third segments, third and fourth segments, fourth and filth segments, and only on the leftside in the region of the fifth and sixth cervical segments.

The cceloni of this embryo is especially instructive. A sagittal .section of the embryo and ovum is given in Fig. 1433. This embryo, wdien drawn connected with the ovum, is very similar to Graf Slice's embryo Gle. as shown in Fig. 1437. It is very easy for us to conceive the von Spec embryo converted into this embryo, for about all the change that is necessary is that the embryo grow somcwdiat and bend upon itself. In so doing the attachment of the umbilical vesicle becomes smaller as the amnion encircles the body of the embryo more. The

FKi. U32.

FifiS. 1429-U:S3.— Sections tliinuRli Embryo No. XH., as indiciit^d by the Lines In Fif?. 1428. Enlurju'd .^)0 tiiiu^s. The blai-lv is tlie cu'Iom within the body. O' and (*■', J'irst and third occipital muscle plates ; C and (;", first and eighth cervical muscle plates; 7J', tlrst dorsal muscle plate ; a, aorta ; v, omphalomesenteric vein ; *, thyroid ; J, liver; jili, jiharynx; i, intestine ; ii iiiembrana reiini'ens.

neurenteric canal ; MH,

position of the neurenteric canal, the shape of the allantois, and the formation of the pericardial cavity, all show that I he curving must be a normal one.

Nearly all other young embryos of tliis stage, or a little older, wdiich have been published show ;i straighter body or even a curve in the opposite direction. I have also in


Coeloni. Cwloin.


my collection two embryos of tliis stage, Nos. I. and XV., which had been taken out of tlie chorion and torn from the umbilical vesicle^ and both of them are straight

Fig. 1433.— Sagittal Section o( ttie Ovum with Embryo No. XII. Attached. Enlarged 10 times. Cue, Ccelom ; u v, umbilical vesicle ■ all, allantois ; MP, medullary plate.

like Kollmann's embryo Bulle and Hi.s's" embryo L. It is difficult to conceive how my embryo XII. could possibly be torn out of its membranes without straightening it. We need only recall our experience in hardening embryos of lower animals to be reminded how easily a curved embryo is straightened when it is handled the least bit roughly before it is hardened.

His, in his great monograph on human embryos, emphasizes a curve in the back of the embryo just the reverse of the one given in Fig. 1433. I refer to embryos Sch., BE., andLg,, as well as to Minot's embryo 195. «  The fact that this inverted bend in the back is not constant (His's Rf., for instance), and that it occurs at the time when any tension upon the umbilical vesicle could produce it, makes me believe that it is an artifact. This view was suggested to me a number of j^ears ago, when I was removing young dogs' embryos from the uterus, and unwittingly distorted a number of them in this very way before they were hardened. The middle of the back i.s the weakest jjart (jf the embryo's body, and the umbilical vesicle is attached to it. Under these conditions tlie simple weight of the vesicle is sufficient to bend tlie back of th(^ embryo as pictvircd by His.

To retiirn to the ctelom. At tlie liiuder end of the embryo the C(elom dips into the l)ody overlapping tlie hiiidgut in the neighborlioHd of the ncurenteric canal, as shown in Fig 1433. This cavity eoimnniiicates with its fellow on the ojiposite side 'through an opening lietween the umbilical vesicle and the allantois, marked in Fig. 143a. This communication has already

been described bj' Ills'" for an embryo somewhat older. If, now, the point in Fig. 1438 is approximated toward NO, with a flexion of the embryo at the same time, this communication is easily explained. In other words, as the hind-gut is being separated from the umbilical vesicle, a groove-like portion of the coelom is also included in the body of the embryo. At the hinder portion of the embryo, on either side, the coelomic grooves extend deeper into the body of the embryo, and communicate with each other around the aboral side of the stem of the umbilical ve.sicle. This communication is shown well by His in Fig. I, B, Plate VI. of his "Atlas," as well as in the same figure, page 299 of Minot's "Embryology." Excellent profile views showing this point are given in all the embryos figured on Plate IX. of His's " Atlas. "

I emphasize this point in order to exclude the ventral mesentery for this portion of the embryo. The fact that this mesentery could never have existed in the human embryo is also proved by a careful examination of His's models of human embryos made by Ziegler.

As we pass toward the head in embryo XII. the coelomic groove communicates freely with the extra-embryonic coelom until the region of the membrana reuniens is reached. This is shown in Fig. 1431, 3fB, with the membrana reuniens complete on one side, but not yet united on the other. The membrana reuniens extends up to the heart, and separates the pericardial cavity from the extra-embryonic coelom, then crosses the ventral median line to return on tlie opposite side of the embryo. Throughout the extent of the membrana reuniens there is a great increase of mesodermal tissue, which encircles completely the beginning of the liver, as Fig. 1430 shows. A portion of this mesodermal tissue has been described by His as the septum transversum.- According to His only that portion of the mesodermal tissue is septum transversum which lies between the posterior part of the pericardial cavity (Parietelhdhle), the wall of the intestine, and the point where the veins enter the heart. It extends across the body, and has within it the beginning of the liver. In transverse section this region is shown in Fig. 1430. Now the pericardial cavity communicates by means of a long canal on either side, with the peritoneal cavity, and the omphalomesenteric vein hangs into this, attached to a kind of mesentery, as Fig. 1430 shows. Lower down, near the communication (Fig. 1431), there is an indication of the beginning of the umbilical vein, which unites with the omphalomesenteric vein through the membrana reuniens. The two canals which communicate with the extra-embryonic cadom are the pleural cavities, and the membrana reuniens aids to separate them from the peritoneal.

All of the tissues from the diaphragm to the opening

. , .. , . - .,^. ..,„^vi,,... pockets:

V, pleural lavity ; m ?•, membrana reuniens : vim, omphalomesenteric vein, which is expressed tlie'ilmbli?carveslcle*^°'"'""° "" l""'™***" '"'S"*' '^^^ 'eft body cavities on the ventral side of

of tlie liver duct into the duodenum arise from the septum transversum and the membrana reuniens; the stomach from the fore-gut, the liver from the liver diverticulum, and the diaphragm from the septum transversum and the membrana reuniens. The Cuvierian duct must also




have arisen in the membrana reunieus, in ordei- to pass around tlie outside of the body cavity to reach tlie cardinal and jugular veins, as pictured by His-'* for the human eml)r3'o.

In the further development of the pleural and pericardial cavities the Cuvierian veins give us our best landmark, as they define the i)oint where the pleural cavity is to be separated from the pericardial. And it really seems as if the greater portion of the diaphragm is formed from the portion of the septum transversum on the ventral side of the vein and from the membrana reuniens, rather than from the portion immediately in front of the intestine. In other words, there is a horseshoe shaped ridge of tissue around the neck of the embryo to the ventral side of the pericardial and pleural cavities and parallel to them. The median portion is composed of the septum transversum, and each wing of the alwe is the membrana revmiens, one on either side of tlie embryo. Its general direction in this stage is parallel with the long axis of the embryo, and within each wing there is an om]5halomesenteric vein.

Origin of Pericardial Cavity. — With the pericardial cavity opening into the extra-embryonic ca>lom on either side as a basis, it is possible to trace back the pericardial cavity to its origin. Figs. 1428 and 1436 show that the ventral wall of the pericardial cavitj' is composed mostly of mesoderm. This is the portion of the membrana reuniens which is composed of mesoderm, as the sections. Figs. 1480 and 1431, show. An earlier stage is shown in the diagrammatic Fig. 1435. It is taken from embryo No. III. In this specimen, since the ectoderm of the amnion has not reached completely around the body, as both the sagittal and sections show (Figs. 1435 and 1437), it is evident that the pericardial space is first covered on the ventral side with mesoderm and later the ectodei'm is added when the amnion begins to close over the head. In enrbryo HI. the canals communicating between the pericardial space and the extra-embryonic coelom are not as long as in embryo XII., and the ventral walls of the pericardial space are composed wholl}' of mesoderm. This indicates that the growth of this wall was lirst by a union of tlie mesoderm, which was followed by the ectoderm of the amnion to complete tlie liody wall. The process is shown in Figs. 1434 to 143(i. Fig. 1434 is a hypothetical stage between Graf Spec's emliryo Gle. and my embryo No. HI. As the process from Graf Spec's embryo continues, the blood-vessels reach the body to form the heart, as indicated by the outlines marked » in Fig. 1434. The mesoderm of the amnion tlicn unites with that of the umbilical vesicle, and the first pericardial

space is formed. This is not wholly an imaginary stage, tor it is based upon Bonnet's observations upon the sheep,"" as well as Cadiat's upon the chick. ■'^ In a sagittal section of a sheep's embryo of about the same stage (Plate HI. , Figs. 16-20, c CB) Bonnet gives a similar fold, and after the pericardial walls are well formed he gives an illustration of a stage in which it still communicates with the extra-embryonic ccehim (Plate IV., Fig. 17, KC). With Graf Spec's embryo Gle. and with Bonnet's observations upon the sheep as a starting-point, it is not difficult to interpret Figs. 1434-1436.

Extension of the Amnion. — After the stage of embryo XII. is passed the amnion rapidly envelops the whole body and soon passes out over the cord. The next stage after No. XII. which I have studied is No. XIX. I have

Fig. 1437. ~ Section tbrough tSe Head of Embryo No. HI. Enlarged .5.5 times. Pli, Pharynx; H, heart. The arrow in the amniotic cavity indicates the direction of the future growth of the amnion to complete the ventral body wall.

very perfect photographs of this s])ecinicn, and the sections are all good, although the nervous system is macerated. The embryo has rotated in the amnion, throwing the cord to the right side with the left .side towaiil the

Fio. 1138.— Ovum and Embryo No. XIX. Enlarged .5 times. Just half of the oviun is shown, a, Arm ; /, leg ; H, heart ; u \\ umbilical vesicle : B, branchial arch.

observer. It would have been impos,sible to obtain a view of the right side of the embrj'O without cutting the cord. The outlines of this embryo and ovum are given in Fig. 1438. Two sections through tlie body are given in Figs. 1439 and 1440.

The amnion has become separated from the bodj' with the exception of the part about the cord and also that along the right side of the body, over the heart. The arrow in Fig. 1437 .shows how the amnion on that side is extended over the ventral body wall to make the condition shown in Fig. 1440. No doubt the cause of this is the rotation of the bodj^, throwing the cord to its right side and the amnion with it. In nearly all 3'oung embryos the cord is on the right side*" With the exception of the four instances mentioned below, the rotation lias always been so as to throw the left side of the body away from the chorion, and in all of these specimens the amnion must have swept over the body from left to right, as shown in the figures. I find a similar illustration by His in his great monograph.*"

Absence of a Ventral Mesentery. — After the septum transversum has been formed as it is in embryo XII., there is on its ventral side a pretty sharp groove, which indicates that the umbilical vesicle is being constricted at this point.

It is generally believed that the ventral mesentery of the intestine extends to the umbilicus, and that ultimately the round ligament of the liver represents its remnant after most of it lias disappeared. This theor}' is exjiressed by two diagrams in Minot's" Embryology," page 767. As the liver begins to grow, and while the heart is being pushed down m front of it, the ventral end of the septum transversum is turned down to the umliilicus. While this is taking place the stem of the umbilical vesicle becomes relativcl}' smaller and smaller, but there is no union between the umbilical vesicle and the septum transversum as expressed in Minot's diagram. The first stage of this jMOcess is shown in mj' Fig. 1436, and its successive stages are shown in His's "Atlas," Plate IX. In all six embryos pictured on that plate the successive stages are repre.sented, and in none of them is the um


Ceelom. Ceelom.


bilical vesicle attached to the septum transvcrsum to form a ventral mesentery. From these embryos of His we can pass to embryo XIX., in which the umbiUcal

Fig. U39.

FIG. 1440

Figs. 1439 and 1440.— Section through Enibrvo XIX. to Show the Attachment of the Amnion to the Side of the Body. Enlarged 25 times, ^m, Amnion; S, stomach ; fl", heart; e, cardinal vein ; », umbilical vein ; a, aorta.

vesicle communicates liy a round canal with the intestine, and the tube is completely encircled with a space Avhich extends to the liver, thus cutting off any possible ventral mesentery at that point. The same thing is shown, but in a later stage, in Fig. 1442, 0, but a new process has already taken place to complicate matters.

In embryo XII. there is just a beginning of an umbilical vein in the membrana rcuniens. In Kollmann's embryo the vein is more marked." The vein extends out into the somatopleure, far away from either the intestine or the median line. This same position is again shown in His's embryos BB. and Lr. on Plate IX. in his "Atlas." The left umbilical vein becomes the more prominent, and as the body wall is developed more and more it moves around toward the ventral median line. This movement takes place in common with the movement of the amnion over the body from left to right, as shown in Fig. 144U. In embryo No. II. , however, the liver has nearly reached the umbilicus, and tlie vein has almost moved around to tlie ventral median line, as shown both in the reconstruction and the sections (Figs. 1443, 1437-14.51). After the vein has moved around the body to its ventral surface, and after the liver moves away from tlie umbilicus up to the permanent diaphragm, it is easy to explain the formation of the round and broad ligaments of the liver as a secondary formation, but not as a remnant of a ventral mesentery. It miglit be called a portion of the septum transversum, as it is directly continuous with it. A ventral mesentery does exist between the abdominal walls and the liver, and extends only slightly below the liver. It is always .slightly to the left of the median line, and is in direct connection with the septum transversum (Fitr 1442, and ST). - \ b (Mom of Eiuhryo No. i/.— After tlie body cavity is beginning to separate from the cxtra-cmbryonie eielom, the next important stage is tlie one after the separation is complete, as from now on tlie adult body cavities are formed by a simple division and expansion of the cavities already within the bodv. This stage is represented in embryos XVllL, II., and IV. All of embryos are nearly of the same size, the successive stages lieiii"- in the order they arc given. No. XVIIl. is sonie\vliat"distorted in the middle of the body, while No. IV. is slightly

macerated. No. II. is a perfect specimen, and has been already described by me several years ago.* I shall confine my description of it to the bod.y cavitj'.

The external form of the embiyo within the ovum is given in Fig,

1441. The position of the umbilical vesicle, as well as the extent of the amnion and the relation of the umbilical vesicle and amnion to the chorion, are all given. The umbilical cord is large and lies on the left .side of the body, while in most embryos alreadj' published it is upon the right side. The cord is short, and midway between the embryo and its attachment to the chorion it .shows a decided enlargement. Tlie umbilical vesicle is large, measuring 5 X 7 mm., and is located between the liead end of the embryo and the chorion.

The amnion has not grown very much, still leaving a great space between it and the chorion, the extra-embrj'onic cadom (compare with Fig. 143S). Within it hangs this large umbilical vesicle, the lumen of which no longer connects with the alimentaiy canal. The separation is now complete. Around the stem of the vesicle the extra-embryonic ceelom communicates freely with the body cavit3-, as shown in Fig.

1442. This figure is from a reconstruction, and shows the general

extent of the body cavity within the embryo. It encircles the heart, and then extends to the lungs and over them and to tlie stomach, over the intestines, and out into the cord. A cast of the whole cavity is also given,

Fig. 1441.-pEmhryo No. II. Attached to the Chorion. Enlarged H times. Just half of the ovum is shown, o i\ Optic vesicle • U E, upper cxtreiidty ; L i,', lower extremity ; jY, nose ; I, II. Ill, branchial arches. . ■ i , . .

showing the slit on the dorsal side for the mesentery of the intestine, and the grooves on either side of this for the Wolffian bodies. There are also grooves in the cast



Coeloni. Coeloiii.

for the veins, and the place where the Cuvierian dnct enters the lieart is marked V. The sagittal section of

Fig. 1443.— Reconstrurtlon of Embryo No. II. Enlarged 17 times. 1 and X, Fifth and tenth cranial nerves ; 1. ;.', 3, and A, cast of the hranchial pockets ; 1 and s, first and eighth cervical nerves, from the fourth the phrenic arises ; 3-', twelftlidorsal ner\'e , A, auricle ; r, ventricle ; L, lung ; S, stomach ; P, pancreas ; TI D, Wolffian l)ody ; K, kidnev ; M, mesentery ; S T, septum transversum ; 0. openinfrs which communicate with the peritoneal cavity of the opposite side. The black Ime around the heart marks the pericardial cavity.

the peritoneal cavity is given in Fig. 1444. The striated line indicates where the cavity crosses the median line of the body, while the other lines outline the cavity be yond. Lp' outlines the lesser peritoneal cavity. Figs. 144,5-14.51 give the extent of the peritoneal cavity in different portions of the embryo, as indicated by the lines in Fig. 1442.

It is not difficult now to imagine the body cavity of embryo XII. converted into the one just described. In that embryo the heart is high in the neck on the oval and dorsal side of the septum transversum. In this embryo it is on the ventral and oral side of the septum transversum, but still above the eighth cervical nerve. The septum transversum has already received its nerve supply from the fourth cervical nerve, as pointed out in the early part of the century by von Baer. This movement of the septum transversum is accompanied by a movement of all the other organs on their way into the thorax and abdomen of the future individual. In the rotation the Cuvierian duet acts much as the fixed point about which the calom is bent. The figures all illustrate this beautifully. But as the heart has rolled over the liver, and the septum transversum has undergone a quarterrevolurion, the Cuvierian ducts and all have moved away from tlie head. This is by no means the end of the excursion of the septum transversum, as its dorsal end must move down and beyond the twelfth dorsal segment (compare Fig. 1442). , , ,

The pericardial cavity surrounds the whole heart, as the various figures show. The cavity is traversed only where the lari;e veins enter, .and where the aorta leaves the heart The cavity completely surrounds the bulbus

aorta? to its oi-igin (Figs. 144-1-1447) in the ventricle. On the dorsal side oT the heart the iierieardial cavity is .separated by a bridge for the transnii.ssion of the veins to the heart. Between the bulbus aortic and the entrance of the veins into the heart the pericardial cavity crosses the median line as three distinct openings, as expressed by the black areas in front of the tracliea in Fig. 1442. On the dorsal .side of the heart on either side of the lungs the ))ericardial cavitj' communicates with the pleural cavities by means of two openings (Fig. 1445), each of which is about 0.1 X 0.r> mm. in diameter. Farther on, the pleural cavities extend as two slits which encircle the lobes of the liver and separate them from the alimentary canal on the one hand and from the body wall on the other (Figs. 144(5-1449). The two pleural cavities do not communicate with each other around the lungs, leaving for them both a dorsal and a ventral mesentery.

This appearance of the co'lom about the lungs and the liver can be explained by the lungs and liver both growing into the two pleural cavities of embryo XII., and this has often made me think that the membrana reuniens of embryo XII. is the main origin of what is called septum transversum in embryo II. If this proves to be the case, then tlie lower end of the membrana reuniens will form the ventral end of the diaphragm, and not the reverse. A stage between embryos XII. and XVIII. (Fig. 1453) is required toelucidate this point.

In the neighborhood of the stomach the peritoneal cavity on either side of it has become asymmetrical, as Fig. 1448 shows. The mesentery has become bent to the left side, leaving a divcrriculum from the right side which extends oralward to the tip of the lung (Figs. 1446 and 1447) to form the beginning of the lesser peritoneal cavity.'^ Further aboralward the cavities become symmetrical again (Figs. 1449, 1450), and tiien unite along the ventral median hne, as shown in Fig. 1451. The ventral mesentery shown in Fig.


FIG. 1443.-Cast of the Body Cavity of Embryo No. II. Enlarged 22 times. A, Position of the aorta; V, position of the veiu ; M, position of the mesentery; W B, position of the Wolffian body; i, pericardial cavity ; L, cuelom over liver.


Cceloiii. Coeloiii.


lie termed the 'plevro-peruarditil nienihrane, containing the plirenic nerve and the pillars which form the dorsal end of the diaphragm. The pillars of Uskow have heeu termed the pleiiro-jjeritoneal membranes by Bracket, and as this term is more appropriate it should be adopted.

My own studies show that the pleuro-pericardial and pleuro-])crit(meal membranes arise from a common structure which grows from the lol)e of the liver along the dorsal wall of the ductus Cuvieri to the dorsal attachment of the mesocai-dium. Later it extends toward the head to complete the pleuro-pericardial membrane, and then toward the tail to complete the pleuro-peritoneal membrane. This structure, which I term the puhnoruiry

1450 docs not extend more Ihun a section or two beyond

the liver, and is separated by a marked opening from the stem of the umbilical vesicle in this embrj'o, as is shown in Fig. 1443, (see also No. XII., Fig. 1428, 0). On the ahoral side of the umbilical cord the peritoneal cavities of the two sides unite in both embryos again, marked 0' in both figures.

]JeTel(>ximent of the Diapliritcfin. — It has often been stated that the development of the diaphragm, especially in the human embryo, belongs to one of the most difficult problems of embryology, partly because of the difticulty of obtaining tiie necessary specimens and

partly because there are no tixed points from

which to calculate. In its development the

whole diaphragm wanders from the head to

the abdomen, forming as well as modifying

the structures and organs along the way.

So while von Baer'^ recognized that the diaphragm wandered in its development, picking up its nerve in so doing, a fairly clear

picture of tlie whole process was not given

until Cadiat,°'His,«» Uskow," and Ravn «-^

studied carefully the development of neck,

heart, lungs, and intestine. In .so doing His

especially recognized the anlage of the diaphragm in a mass of tissue located with the

heart amongst structures belonging to the

head and containing within it tlie veins to

the heart as well as the anlage of the liver.

This mass of tissue His termed the septum

trausversuni. His's studies were made upon the human [ ridge, giving rise to the pleuro-pericardial and pleuro-peri,>,..n,„,i r.f ^ „^..„,..;„„ „.,,! , jo^pjj) membrane, is located in the sagittal plane of the

Fio, 1444,— Outline of Coelom in Kniliryo No. II. in Sagittal Soi'tion. The striated line indii'ates that the coelom crosses the median line. P, Pericardial space ; p/, pleural cavity ; ( p, outline of lesser peritoneal cavity.

FIG. 1447.

Fig. 1448. Figs. 1447 and 1448.— Sections through Embryo No. II. a. Aorta • .f stomach • \ liver • w, umbilical vein ; x, bulbus aoitte ; ;i, heart ; Vv, omphalomesenteric vein ;' «i lesser

c. cijE-liac axis; Wolffian ' body ;

peritoneal cavity; /, foramen of Winslow w.((., Wolffian duct.

embryo, mainly by the method of reconstruction, and shortly after they were published Uskow made a very careful study of the fiu'ther growth of the septum transvcrsiim. Uskow recognizeil the great importance of two additional structures in the formation of the pericardium and adult diaphragm from the septum transversum: these

Fig. 144,5.

ui'.. r , l"^;r:^«'tl"'is throuKh Embryo No. II. at tlic 144„. Enlarfred .;.; times. VJ ,., Bnuliial ple.-ius ; ,l a.jrta pharynx ; h, heart ; ^ trachea ; o, .jc'sophaius vein ; V, (Juvierian duct.


FIG. 144i;.

j, jugular vein; (, lung

Points Indicated In Fig. «, hulhus aortLV ; )i/i, r c, cardinal

body cavity with cephaUc and caudarhorns on its dorsal side. The ductus Cuviei-i lies between these horns.

In following the fate of the septum transversum it is necessary to consider the division of the body cavity into the pericardial, pleural, and peritoneal cavities. According to His. the bodv cavitv is divided into the runeUdhhhle and Ibmrpfh'ihUn. The communication between these spaces he has also ternied the recessus parietalis. The parietal cavity from its earliest appearance contains the heart and is destined to form the perirardial cavity. This is the pericardial cadom. A portion of the recessus parietalis forms the pleural cavity; it surrounds the lung buds tliroughout its development and forms the pleural ccrlom. The remainder of the recessus ])anetalis to tlie oi-iiiin of the liver has developed in it the liver and stomach; this i.s added to the general peritoneal cavitv and may be termed the jieritoneal cadom. In the etirly embryos the whole cadom lies far out ot Its tiiial place; in embryo XII. nearly the entire ccelom lies in the region of the head and neck, arid in the furtlier development of these parts the cielom with the surrounding organs wanders away from the head to its permanent location. As long as the serous cavities arising from the ciploin are in the process of wandering and are not fully separated from one another they may be termed pleural, pericardial, and peritoneal cffilom; when they are fully established they form these cavities


Cocloin. Coeloiri.

In embryo XII., Fig. 1433, the eci-lom of tlic embryo forms a free space encircling the lieart and extending on eitlier side of the body over the <miplialomesenteric veins to tile root of tlie nmbilieal vesicle. This canal of eom

FiGS. 1449-1451. — Sections through Embryo No. II. a. Aorta; v.c, cardinal vein; o, omphalomesenteric vein ; p, pancreas ; (, intestine : h, bile duct ; l, liver ; /i, heart : u, umbilical vein ; ?n, mesentery ; tr./j., Wolflian body ; all, allantois.

munication has developed witliin it the lung, stomach, and liver, and throughout its earlier development it always measures in length about one-fourth of that of the body. The appearance of the lung and liver marks the subdivision of the Cffllom into the pleural and pei'itoueal ccelom. With the development of the liver, lung, and stomach the cadom containing them gradually dilates until the embryo is about 9 mm. long, when the containing canal evagiaates, so to speak, and turns the liver and stomach out'into the general peritoneal cavity. The Wolffian body, which occupies the dorsal wall of the canal, gradually" degenerates, and the lung takes its place. From these statements it is readily inferred that the canal extending from the pericardial ccelom, His's recessus parietalis, gives rise to the pleural cadomon its dorsal side and to the peritoneal ctelom on its ventral side. The line of division is formed by the pleuro-peritoneal membrane extending fi'om the ductus Cuvieri to the adrenal.

It is now no great task for me to give the development of the diaphragm in the human embryo, for I have at my dispo.sal excellent sections, as well as definite knowledge of the anatomy of the surrounding organs conti'ibuted by tlie above-mentioned authoi's.

While the embryo is still straight it is very easy to locate the various organs and their relations to one an

again on its dorsal side. At first the hiiigs are on the dorsal side of the heart, tlien on the lateral side, and finally also on the ventral side of it. At first the liver is on the aboral side of the septum transversum in the head of the embryo, then on the dorsal side of it in the cervical region of the embryo, then as the liver is descending in its excursion it is transferred to the ventral side of the septum and extends into tlie sacral region. At fli-st the Woltfian body extends high into the thoracic region of the embryo, but while it is degenerating and the diaphragm descends, the upjicr part of the posterior cardinal vein remains, while the lower part is incorporated wilh its vena cava infei-ior, as shown by Iloehstetter.«° As the Cuvierian ducts and cardinal vein descend into the thoi'ax, the segmental veins entering the cardinal veins are gradually shifted, so that veins which oi-iginally emptied into the posterior cardinal now empty into the anterior cardinal. While the whole process is taking place the arteries arising from the descending aorta also shift, as I have shown in a previous communication. »■* At that time my collection of human embryos was very limited, and if was necessarj' to include some observations on lower animals to prove my point, but now I can give a complete table of human embryos in which the point of origin of the cceliac axis is recorded.

Fig 14.53 —Section of a Chick to Show that the Body Cavity Communicates with the Extra-Embryonic Ccelom. Although the embryo has been injected, the injection masses a and c are not continuous.

Other, but through their shifting and the flexion and extension of the embryo the relations are constantly changing, and one must "not rely too much upon sections or else erroneous impressions will often be obtained. At first the heart is upon the oral and dorsal side of the septum transversum, then on its ventral side, and finally


Fig. 14.53.~Diagram to Show the Position of the Diaphragm. The numbers on the blocks indicate the embryos from which the diaphragms are taken. KO is His's embryo K : PP. the outline of the opening between the pleural and peritoneal cavity, which is Anally closed when the diaphragm reaches the tenth dorsal segment.


Coeloni, Ceelom.


Tablk Showing Point of Origin of Cceliao Axis.


Length In millimetres.

Origin of coellac a-xis.


2.1 2.1)



7.rt 13 U




Opposite 4th cervical nen'e.* 1st dorsal " + 2tl " " t

Hls's Embryo JI


No. II

4th "

Hls's Embryo A


tith " " § 10th

" IX

nth "

" XXII .

" nth "


12th " "



12th "

In the first two embryos the omphalomesenteric artery is noted, . and not the coellac a.xls. t Compare Fig. 15, PI. yl., His's "Atlas," with M4, I>1. vU. t Compare Fig. 35, PI. 11., Hls's "Atlas," with Fig. 1, PI. 1. S Compare Figs. 79 and 86, Hls's "Atlas," with Fig. 4, PI. 1.

Tile tabk' shows that the arteries arising from the ventral side of the aorta to siipplj'the stomach and intestines are constantly shifting until their definite origin is finally reached. In these specimens the omphalomesenteric artery is shitted ahead of the coellac axis. In embryo No. II. the omphalomesenteric artery has a double origin from the aorta, which indicates that this movement maj' be brought about by a new anastomosis forming, which is then followed by an occlusion of the old origin. At any rate it is impossible that the whole aorta shffts with the abdominal viscera, for it is bound to the vertebrre and muscle plates through the segmental arteries.

The various sections and the reconstruction of embiyo No. II. .show the pleural and pericardial cavities still communicating freel.y. The same is true in embryos XIX., XVIII., and IV. immediately after this stage there are no embryos in my collection, so I have no specimen in which the communications bet ween the pleural and pericardial c a v ities are just closing. In embryos VIII., v., IX., and XLIII, (Figs. 1453-145.5), the pleural and pericardial cavities are separate d, while the pleural

Fig. 14.54.— Keconstrurtion of Embryo No. IX. Enlargeil 17 times. S.T., Septum transyersum ; I/, hvcr: ,s', stomach; C, ca'ciiiri ; ir, WoUlla)! boilv ; fC, kidney; ;-;.:', doreal ganglia; o, oiiiplml.^iiiesenterlo artery. Tlie ventral mesentery of the liver is' dotteil, as it is only a thin membrane; .s.o'., suprarenal capsule; X, point of communlcatlou between pleural and peritoneal cavities.

and peritoneal still communicate. In the embryos with a vertex breech measurement exceeding 17 mm, the pleural and peritoneal have been se])arated completely.

The separation of the pleural from the pericardial cavity is dependent upon the complete development of the diaphragm. At first the septum transversum and the membrana reunicns arc on tlie ventral side of the pleural cavity, and both are still located within the head. As the septum transversum descends into the body it is next located on the dorsal side of the heart. In other words, the dorsal end of the septum transversum has not moved as rapidly as the ventral end, and thus the wliole mass of tissue has turned a quarter revolution. This is accompanied by the extreme flexion of the head, as represented in embryo No. II. At this time the septum transversum has descended to the lower part of the cervical region. Now the septum begins to turn in the other direction again, for with the development of the neck the ventral end of the .septum becomes the fixed point and the dorsal end moves more rapidly. The successive stages in the movement of the septum are best shown in the diagrammatic Fig. 1453.

Fig. 1454 shows the septum transversum on the ventral side of the stomach and the pleural cavity communicating with the peritoneal at the point A'. Tlie Wolffian body and the suprarenal capsule, wdiich is verjr large, have receded markedly, and the pleural cavity already forms a pocket on the dorsal side of them, A sagittal section through this region, somewhat distant from the median line, is given in Fig. 1457. A transverse section of the eiiibi-yo pictured in Fig. 14.54 is given in Fig. 1455. This section is just at the point above the opening, and shows the communication between its pleural and peritoneal cavities closed on one side, but open on the other. There is a ridge on the side of the cavity which projects between the lung and the liver and continues down to the suprarenal capsule. This ridge has been well described by Ravu,* who gives an excellent illustration of the opening with the ridge encircling it.

In all the embryos in which the pleural and peritoneal cavities still commtmicate, the vena cava does not j'et communicate with the posterior cardinal vein.

Fig. 1457 is from an embryo slightlv larger than the one from which Fig." 1454 was taken. The pleuro - peritoneal communication has just closed by the walls of the ridge having grown together; the extent and shape of the pleural cavitv is much as it is in Fig. 14.54. TheWolttianbodyis smaller, and the kidney and suprarenal capsule have come together.

The story, then, is brief: as the diaphragm descends, its dorsal end is in apposition with the suprarenal capsule, and finally, when the capsule approaches the twelfth rib, a ridge of tissue which also includes the capsule unites with a ridge from the septum transversum, and the opening is closed. These two ridges, however, are portions of one and the same ridge, as they form a circle and in section appear as two ridges. The circle is closed much tiftcr the fashion of tying uyt a bag.

All of the abdominal organs, with the exception of the kidney, descend ; and the descent is not completed until the pelvis is loniied to admit some of them. In the stages pietiired nearly all the small intestine lies in the imibilieal coi'd, as is the case in many mammalian embryos. In embryo X. (Fig. 1457) a large portion of the liver also projects into the cord. I have also observed a hernia of the liver in another embryo somewhat larger. I do not consider the form of embryo X. altogether normal, but this was not noticed until the reconstruction was complete.

Fig. 1455.— Section through the Point of Communication between the Pleural and Peritoneal Cavities In Embryo No. IX. Enlarged 15 times. 7, Seventh rlh ; L. lung; Li, liver; M, ventral mesentery ol liver ; o, aorta. The diaphragm Is complete on one side, X, while it is incomplete on the other.

Closely associated with the clo.sing of the pleuro-peritoneal opening is the development of the celiac ganglion. In these young embryos it is extremely large, and can be outlined already, while the septum transversum is still high in the thorax. As the septum descends, the vai'ious communicating branches of the nerves are caught up with the caliac ganglion and dragged along. This accounts for the high origin of the splanchnic nerve.

Fig. 1458 (embryo VI.) shows that all the tissues are becoming more definitely outlined, and the whole structure is tirmer than in embryo X. The organs of the abdomen are more tirmly clustered together, and the intestine has become more convoluted. The lung is much larger, and the pleural cavity extends to the ventral wall of the embryo, obscuring wholly the outline of the heart. In general it confirms everything given in Fig. 1457.

Minot *« has stated that the pleural cavities are to be considered a portion of the septum trans\-ersum, because they lie on the dorsal side of it. From what has already been said above it will be seen that I consider the septum ti-ansversum the mass of tissue between the pericardial cavity, the pleural cavities, and the opening between the two sides of the peritoneal cavity immediately below the liver, marked in Figs. 1428 and 1443. This tis.sue includes the mcmbrana reuniens, which is really the wings of the septum transversum as described by His. In my account I have employed the term membrana reuniens wherever

possible to av(jid confusion, and have usually employed the terms septum and primitive diaphragui as synonyms.

There are developed within the region of the septum transversum the whole liver, inchiding its ventral mesen tery, the Ics.ser peritoneal cavitj', tiie stomaeli, and the suprarenal capsule. This same legion whieii I have marked out by these tliree l)oundaries as the septum transversum is still sharply defined in the adult. Tlje point in Figs. 1428 and 1442 is still as definul)ly marked as ever by tlie iciund ligament, foramen of \\' inslow, and the duct pa.ssing from the liver to the duodenum. The round ligament is developed by the umbilical vein shifting around tlie side of the abdominal walls into the ventral mesentery of the liver, and then when the liver is retracted from the umbilical cord, the vein and mesentery lemain as the round and broad ligaments respectively.

J^'sner Peritoneal Ciinty. — I have already discussed the lesser peritoneal cavity in a separate paper,*' and find that I can eonfirni all that I have stated at that time. I can only add that the portion of it extending up under the lung degenerates, while the omental sac is growing rapidly. I have also found that it is extremely easy for the omentum to find itswayr over the large intestine. At the time this takes place the large intestine is in the median line, while the stomach and the omentum are on the left side of the body. After the intestine is retracted

Fig 1456.— Section through Embrvo No. XLIII. Enlarged 8 times. H, Hand; yl, auricle ; T, ventricle; i, lung; S T, septum transversum; P, phrenic nerve; (J, umhillcal vein; ,S', stomach; Tt. Wolffian body ; Or, ovary ; Am, amnion ; 1-U, ribs.

from the cord the c;ecum falls over to the right side of the body, wdiile the descending colon is shifted to the left side, and the omentum then comes to lie on the ventral side of the transverse colon.

Mepansioii oftheBady Ciirity and Obliteration of the E.rtra-Einbryoiiic C'odoin. — After the pleural and pericardial

cavities are separated from eacli other it is very easy to follow their further development. In embryo II., Fig. 1459, the heart is still ripright, and a transverse section of

cardial accounts for the location of the phrenic nerve in the adult. In Fig. 1459 the nerve passes to the septum transversum from the lateral body wall, and it is gradually separated from it by the descent of the septum and by the growth of the pleural cavity between the nerve and the body wall, thus locating the nerve in a membrane, as Figs. 1460 and 1461 will readily explain.

The expansion of the peritoneal cavity is by no means as simple. In it there are many bandsand mesenteries as well as a marked shifting of the organs. With the descent of the testis a portion of it is cut off to form the tunica vaginalis.

In embryo II. (2) the peritoneal cavity is extremely simple, as the figures show, — a simple cavity on each side communicating the one with the other by means of two openings, one above and one below the omphalomesenteric duct. Later, as the diaphragm descends more and more, the liver rotates, and its lobes soon fill the peritoneal cavity, while the intestine develops out into the core. The Wolffian bod}', sexual glands, and suprarenal capsule fill the dorsal side of the cavity and the rudimentary pelvis. The whole development of the intestine takes place within the cord, and finally it is drawn into the embryos when it is about 30 mm. in length. By what process this takes place I am unable to determine, but it must take place very rapidly, for I have never seen a human embryo in which it is only partly retracted. In the pig's embryo, however, I have found tlie stages in which the intestine is in process of retraction.

The liver now fills nearly the whole cavity, and extends down to the pelvis, and in embryo XXII. projects over the

1444). more

Fig. 14.5T.— Reconstruction of Embryo No. X. (10) Enlarged Stime.s. 1-12, Dorsal ganglia; S.C., suprarenal carsiilB; ir. Wolffian body: K, kidney, L, liver ; S, stomach ; C, csecum. The dotted area on the ventral side ol the liver Indicates the extent of the ventral mesentery of the liver.

it is also transverse to the lung. The pleural cavity lies wholly on the dorsal side of the pericardial (Fig. ' ' In the next stage, as the lungs descend more and the heart is tilted over so tiiat its base is toward the lung and its apex away from it, as in embryo IX., shown in Figs. 14.o4and 1460. The pericardial space has now become separated comjiletely from the pleural, although both have grown at about the same pace. From now on the pleural space grows moi-e rapidly than the pericardial, as shown in Fig. 1461. I have a number of embryos which represent intermediate stages between embryos IX. (9) and XXII. (22), and all of them confirm the idea that the pleural si)ace develops first and then is followeil by a growth of the lung. Fig. 1462, which is a section of embryo No. XLV. (45), shows a marked increase in the size of the lung, but the heart and pericardial space are of about the same size as in embryo XXII (22). A much later stage is shown in Fig. 1461 The scale of enlargement is only half that of Fig. 1463, and when this is considered it is again seen tliat the heart has not grown very much, but tlie lung has develoi)ed enfirmously.

It is therefore seen that at first the p<>rieardial cavity is on the oral side of tlx; pleural, tbc^n on the ventral side, and is finally enclosed by the pleural cavity growing over it.

The growth of the pleural cavity over the peri

Fig. 1458.— Reconstruction of Embryo No. VI. (6) Enlarged 8 times 1-lS Dorsal ganglia ; ,S.C., suprarenal capsule ; K. kidney ; TI', Wolffian body • S stomach; C, caecum; L, liver. The dotted urea "on the ventral side of 'the liver indicates the extent of the ventral mesentery.

ovary and is in contact witli the rectum. As tlic intestines are retracted from the cord tlie liver is rehitively higher and higher, for the expansion of the abdominal walls is now greater below the umbilical cord than before, giving more space in this region for the intestine which displaces the liver. In embryos XXXIV. (34) and XLVIII. (48) the intestine has been studied, and it was found that it is still located in the ventral portion of the peritoneal cavity, as there is no pelvic cavity large enough to hold &ny portion of it.

Figs. 1459 to 1461. — Outlines of the Pleural and Pencardial Cavities to Show Their Relative Position and Size. Enlarged 7 times. Fig. 1459, Embryo No. II. (2); Fig. 14B0, Embryo No. IX. (9); Fig. 1461, Embryo No. XXII. (22) H, position of heart; i, position of lung.

The extra-embryonic coelom has only a short existence, as it is already completely obliterated in embryo No. XXII. (22) This embryo came to me in an unopened ovum.

Fig 1462. — Outline of Pleural and Pericardial Cavities in Embryo No. XLV. (45) Enlarged T times.

and on this account is extremelv valuable for this purpose. This embryo is about six weeks old, so, reasoning from it, the union of the amnion and chorion takes place earlier than is generally believed. In embryo No. XLIIL. which is about five weeks old, the amnion has expanded over the whole embryo and has nearly reached the chorion

Fig 1463. — Outline of Pleural and Pericardial Cavities In Embryo No. XXXIV. (34) Enlarged 314 times. If, Position of heart; L, position of lung.

The earlier stages are given in the sagittal sections. They show that the amnion is nearest the chorion at the caudal end of the embryo in the earliest stages, and soon the two unite at this point. As the embryo grows, the union of amnion and chorion extends. At the end of the fourth week the extra-embryonic coelom is still very large; at the end of the fifth week the space between the embryo and chorion is divided equally between the amnion cavity and the coelom; at the end of six weeks the extra-embryonic coelom has disappeared.

Fig. 1464.— Embryo No. XXII. (22) Within the Ovum. Enlarged 3 diameters. The villi of chorion are outlined on one side ot the ovum only. The umbilical vesicle, u v, has become shifted around to the dorsal and right side of the embryo. Tlie outline is made from a photograph, and is correct in detail with the exception of the attachment of the chord to the chorion. This in reality attaches itself to the chorion immediately to the right of the embryo.

Franklin P. Mall.

Bibliographical References

1 Reichert: Abhandl. d. kgl. Akad. d. Wiss., Berlin, 1873.

2 Von Spee ; His's Archiv, 1889 ; Mall : Anatom. Anzeiger, 1893 ; Johns Hopkins Hospital Bulletin, 1893 ; von Spee : Hls's Archiv, 1896 ; Siegenbeek von Henkelom : Hls's Archiv, 1898 ; and Peters ; Einbtttung des mensch. Eies, 1899.

3 Bischoff: Entwicklungsgeschlchte des Hundes Eies, Braunschweig,

BischoiI: Entwicklungsgeschlchte des Kanincheu Eies, Braunschweig, 1843. » Selenka : Studien liber Entwicklungsgeschlchte der Thiere, Heft . 5, Wiesbaden, 1893.

• Mall : Anatom. Anz. viii.

' Mall : Journ. of Morph., vol. v.

8 Mall : His's Archiv, Supplement Band, 189/.

» Hoen ; Johns Hopkins Hospital Bulletin, 1896.

1" Mall : Journ. of Morph., vol. xli.

11 Bischoff : Entwlckl. d. Meerschweinschens, Giessen, 1853.

12 Rauber- Sitzungsber. d. Naturforscher (iesellsch,, Leipzig, 1875.

13 Selenka : Studien iiber Entwlckl. d. Thiere, Heft 3. 1884- ,^^ n Selenka : Studien, etc.. Heft .5, Erste und Zweite Halfte, 1891, 1892. 15 His's Archiv, 1889 and 1896.

"Selenka : Studien, 1891, p. 201.

" Graf Spee : His's Archiv, 1896, Taf. 1., Fig. 1.

8 His : Anat. mensch. Embryonen, Theil i., p. 171.

i» Selenka: Studien, 1893, p. 209.

" Duval : Jour, de I'Anatomle et de la Physiologic, 1895.

= 1 Gohre : Selenka's Studien. etc., 1893, p. 218.

2'^ (iral Spee : His's Archiv, B«0 and 1896.

S3 Mall • A Human Embrvo of the Second Week, Anatom. Anz., Bd. 8 and Early Human Embryos and the Mo(Je of their Preservation, Johns Hopkins Hospital Bulletin, 1893.

21 His Anatomie mensch. Embryonen, Heft 3, 1883, and Interna^ tionale Beitriige zur wissenschaftllchen Medicin, Bd. 1, 1891.

25 Giacomini : Ergebnisse der Anatomie und Entwicklungsgeschlchte, Bd. 4, 1895. The original papei-s of Giacomini are in the Archives Ital'iennes de Biologle, vols, xvtii.-xxli.

2« Mall : Contributions to the Medical Sciences, Johns Hopkins Hospital Reports, vol. ix., Baltimore, ISIOO. ^ x,., , a

" Giacomini : Ergebnisse d. Anat. u. Entwicklungsgesch., Bd. 4, S. 636.

2" Mall : Anatom. Anz., 1893, and Jdhns Hopkins Hospital Bulletin,

2» Von Spee : His's Archiv, IWIIJ, PL i.. Figs. 4, 5, S, and 10.

=»GratSpee: His's .Archiv, 1KHI).

" Bonnet: His's Archiv, IWi).

^-Selenka: Stiidien, etc., Taf. xxxviii.. Fig. 3.5.

=' Drasch : Anatom. Anz., Bd. 9.

" Budge : His's Archiv, 1887.

^= Kollmann : His's Archiv, Supplement Bd., 1&S9, PI. v.. Figs. 1 and 3 ; von Lenhossek : His's Archiv, 1891, PI. i. ; Kollmann : His's Archiv, 1891, PI. lii.. Fig. 3.

^* Froriep : His's Arciiiv, 188;i and 188(5.

^' Piatt : Bulletin ot the Museum of Comparative Zoology, vol. xvli.

3" Dexter: Anatonj. Anz., 189(1.

»» Bonnet: His's Archiv, 1889.

■I" His : Abhandl. d. siich. (Jesellsch. d. Wiss., Bd. xxiv.

■'^ See also Mall ; -lourn. of Morph., vol. v.

^' His : Anat. nu-nsch. Eniljryonen, PI. vi.

■" Minot : Human f;iiil)ryi>logy. New York, Fig. 169.

'^'^ His : Anat. mensch. Euihryonen, i., p. l~(i.

'• His: Anat. mensch. Emhryonen, i., p. 126.

•"His: His's Archiv, 1881, PI. xii.. Fig. 9. Also Anat. mensch. Emhryonen, PI. ix.. Figs. Hi-13, 11.

" Bonnet : His's Archiv, 1889.

■" Uadiat : Jour, de I'Anat. et de la Physiol., 18*^ PI. v.. Figs. 1, 3.

^"The exceptions have been published by Waldeyer : Studien des physiol. Inst, zu Breslau, 180,5 ; Janosfk : Arch. f. mik. Anat., Bd. :Hi : His; Anat. mensch. Emhryonen, PI. viii.. Figs. A 1-4 ; Mall: Journ. of Morph., vol. V.

" His : Anat. mensch. Embrv(men, PI. vi.. Fig. 3, No. 10.

^'Kollmann : His's Archiv, 1891, PI. ill.. Figs. 3, 3, 4. V. umbil.

"•^ Mall : Journ. of Morph., vol. v.

^^ Mall : Journ. of Morph., vol. v.

" Budge : His's Archiv, 18«0 and 1887.

^^ Drasch : Anatom. Anz., Bd. 9.

'^« Cadiat : Jour, de I'Anat. et de la Physiol., 1883, PI. v., Figs. 1 and 3.

^' Duval : Atlas d'Embryologie, PI. xxli., Fig. 354.

»* Von Baer : Entwlcklungsgeschichte, 1837. •

«» Cadiat : Journ. de I'Anat. et de la Physiol., 1878.

" His : Anat. mensch. Emhryonen, Th. i., 1880. " Uskow : Arch. f. mik. Anat., 1883.

«= Ravn : His's Archiv, 1889.

" Hochstetter : Morph. Jahr., Bd. 20, p. 5a3.

^ Mall : Journ. of Morph.. vol. v., p. 472. «= Kavn : His's Archiv, 1889, PI. x.. Fig. 16.

"* Minot : Human Embryology, p. 483. " Mall : Journ. of Morph., vol. v.

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