apposition ; or, in other words, that the amnios ^^^ blastoderm, e'. a portion of the ex-
had the same connection with the embryo as ri^rbrrTxhlt^T^frrm:
the serous membranes with the viscera they miotic hoods, v. The vitelline membrane.
Messrs. Coste, Velpeau, and Bischoff have combated this view success-
fully, in my estimation, by contending for the existence, at all periods, of
the continuity we have just described, and
they cannot possibly admit an opinion which ^"^- ^i-
is founded solely on pathological alterations.
For my own part, after examining the
preparations of M. Coste, I can have no
doubt as to the little value of such asser-
Immediately after the amnios is formed,
the margins of the embryonic spot, and
especially its true extremities, become more
and more turned inwards, thereby aug-
menting the concavity which it previously
exhibited ; and at the bottom of the groove
thus constituted, the mucous lamina of the
blastoderm is observed to concur in forming
the intestinal canal, which is represented at
this early period by an elongated gutter,
elseif (getClientWidth() > 430)
communicating freely with the interior
cavity of the blastoderm. But, in propor-
tion as this constantly increasing inversion
of the lateral walls, and of the extremities
of the embryo, progresses, this communication becomes more and more
contracted, so that in a short time the intestinal cavity only connects with
the blastodermic vesicle by a contracted pedicle; and thenceforth, this
latter receives the name of the umbilical vesicle, and the vessels which ain
This figure shows the amnios almosl ounj-
pleted, and likewise the origin of the allan-
tois. 0. The umbilical vesicle. I. The Id
testines. e. The amnios, e'. The externa
layer of the blastoderm, or the non-vascular
choiiou. V. The vitelline membrane. C. The
amniotic hoods ready to close up. A. The
PR EG N A NX Y.
distributed to its vascular layer, consisting of two veins that enter, and an
artery that emerges from the embryo, are called the omph(ilo-mesent\jric ves-
sels. (Fig. 61.)
As the contraction of the ventral opening in the embryo, and the circuiu-
scription of the umbilical vesicle go on, we may observe at the inferior
part of the intestinal canal, just in the region where the bladder and rectum,
(luring the earlier days of embryonic life, are confounded under the name
)f cloaca; we observe, I repeat, the intestinal parietes to form there a slight
elevation. Now, this little tumor (Fig.
61) gradually elongates, so as to con-
stitute a minute vesicle, which commu-
nicates by its narrow pedicle with the
intestinal cavity ; this is the allantois,
which has been known for a long time
to exist in mammalia, but which M.
Coste was one of the first to detect in
the human ovum. The allantois is
scarcely formed before it is provided
both with venous and arterial vessels,
consisting of the two umbilical arteries,
and one umbilical vein ; the former
arising fi-om the primitive iliacs, the
latter going to the liver, as may be seen
This little vesicle passes through the
umbilicus at first alongside of the pedi-
cle belonging to the umbilical vesicle,
and soon undergoes a rajoid develop-
ment. The growth of the allantois and
its vessels is so rapid that it soon comes
into contact with the external membrane
of the ovum. In some animals, the
allantois comes into juxtaposition by
its base with only one point of the chorion, and becomes attached there ;
and then the terminal extremities of the umbilical vessels not only reach
this membrane, but even extend for the most part to the villosities devel-
oped on its external surface, and acquire there a considerable growth.
In others (see Figs. 62 and 63), the allantois spreads out like an umbrella
around the embryo and umbilical vesicle, and supplies itself to the whole
external face of the amnios, as well as to the internal one of the chorion, then
the two laminae are fused into each other in such a way as to leave no trace
of the allantois. (Figs. 62 and 63.)
The development of the allantois completes the essential part of the
ovum, although by reference to Fig. 55, Plate IV., it will now be found to
consist : 1, of the embryo ; 2, of a variable quantity of liquid in which it
irt'ims ; 3, of the amnios, already considerably distended, and forming a
Bheath to the parts that pass through the ventral aperture; 4, of the umbil-
ical vesicle situated between the amnios and chorion, whose delicate pedicle,
This figure shows the rapid progress of the
allantois, and how it spreads over tlie foetus, the
umbilical vesicle, and the amnios. This latter
begins to ensheathe the pedicle of the umbilical
vesicle and that of the allantois in such a way
as to form a commencement of the cord. The
vitelline membrane disappears more and more.
0. Thi; umbilical vesicle, e'. The amnios, e".
The SKternal layer of the blastoderm. C. The
point where the two hoods come into contact.
V. The vitelline membrane almost entirely atro-
phied. A. The allantois.
DEVELOPMENT OF THE HUMAN OVUM.
with the omphalo-mesenteric vessels
appertaining to it, however, still com-
municate with the intestinal cavity ;
5, the pedicle of the allantois vesicle
still charged with the umbilical ves-
sels ; 6, the space between the amnios
and chorion, partly occupied by the
umbilical vesicle, but principally
filled with a liquid called by M. Vel-
peau the reticulated or the vitrijorm
body, according to the degree of its
consistence; and 7, of the outer en-
velope, or the chorion.
The phenomena yet to be studied
have special reference to the enlarge-
ment of the ovum, and the develop-
ment of the embryo.
In this figure, the allantois has spread over li. =
whole internal surface of the ovum, and but very
slight traces are left of the continuity between the
amnios and that part of the external layer of tht
blastoderm which formed the non-vascular chorion •
the amnios incloses the umbilical cord more and
more. o. The umbilical vesicle, e'. The amniua
C. The point where the two hoods are fused into
each other, and form but a single membrane, k".
The external layer of the blastoderm. a. The
allantois. v. The vitelline membrane.
OP THE FCETAL APPENDAGES.
These comprise the allantoic, the umbilical vesicle, the amnion, and the
§ 1. Of the Allantoid Vesicle.
By the time the amnion has become a completely closed sac, a little
pyriform vesicle, which we have denominated the allantois, is observed,
about the tenth day, to spring from the inferior part of the intestinal canal,
and taking on a rapid growth soon becomes applied by its base to the in-
ternal surface of the chorion. The terminal branches of the two umbilical
arteries and vein, as previously stated, ramify on the walls of this vesicle ;
and hence the urachus, which is nothing else than the pedicle of the allan-
tois, is accompanied in its course by three blood-vessels (see Fig. 3, Plate
IV.), two of which (i i) are arterial, coming from the iliacs, and called the
umbilical arteries. They run to the chorion, where they ramify, and ulti-
mately reach the villi that form the foetal placenta. The third trunk is
venous, and is known as the umbilical vein.
The umbilical vein j leaves the right auricle of the heart at the point /,
and soon after receives the contents of the vena cava inferior^; it then
traverses the under surface of the liver m, to which it sends a copious vas-
cular supply, and, before passing this organ, receives the omphalo-mesenteric
vein at the point o; then, after leaving the liver, it gains the left sidr
of the abdomen between the walls of this cavity and the intestinal fold e;
Qext, by turning abruptly towards the umbilical cord, it gets to the lefl
side of the urachus, and accompanies the latter to the chorion, wheie it
follows the umbilical arteries into the villosities.
After the earliest periods of development are over, there is but a single
umbilical vein left, although during the first part of the embryonic exist-
ence two are met with, one upon each side of the urachus (and consequently
one for each umbilical artery). That on the right side becomes efface 1,
but its traces may still be found at the thirtieth or even the fortieth day ;
indeed, some such existed and were perceptible on the embryo I am now
When the umbilical vein has actually passed the liver, it gives off no
branches whatever, in its course along the urachus, nor does it divide and
subdivide until it reaches the chorion. But, in the earlier periods of ges-
tation, when the two exist, they are observed to spread over the walls of
the chest and abdomen in the form of a large vascular plexus, extending
as far as the vertebral column ; however, this new apparatus soon vanishes
and leaves no vestige of its former existence.
The body of the allantoid vesicle disappears very rapidly, and scarcely
a trace of it can possibly be found after the lapse of a few days from its
first appearance. In fact, nothing more is seen than a cord of variable
length, extending from the embryo to the chorion, and having the umbilical
vessels inclosed within it. This likewise becomes gradually atropliied in
such a way as to disappear altogether in the substance of the umbilical
cord ; nevertheless, a portion of it still persists in the abdominal cavity of
the embryo, forming there the cord subsequently known as the urachus ;
and just as this latter terminates in the rectum, it exhibits a small swelling
which is afterwards converted into the urinary bladder. We may remark,
in anticipation, that this rudimentary bladder communicates with the
rectum, and constitutes there that transitory cloaca, whose existence in
the human species may be positively verined by direct observation. It is
this early disappearance of the allantois which has induced some ovologists
to doubt its existence in the human race. It is exclusively destined to
bring the embryonic vessels into contact wdth the external membrane of
the ovum, whence they are soon placed in their proper relation with the
internal surface of the womb.
§ 2. Of the Umbilical Vesicle.
This vesicle is formed exclusively by the internal or mucous layer of the
blastoderm ; at first, it is very voluminous, occupying nearly the whole
cavity of the ovum, and communicating so freely with the intestinal cavity
as to form with it apparently but a single vesicle. But the gradual con-
traction of the ventral opening serves to separate the two, as we have already
demonstrated, leaving only a pedicle of variable thickness, according to tlie
size of this aperture.
The umbilical vesicle contains a yellowish-wLlte liquid often of a vitel-
line yellowness, in which numerous granules and fat globules are seen
floating. It seems to be formed of two laminae, between which the vessels
are distributed (see Robia, Journal de Physiologie, 1861). As the amnion
DEVELOPMENT OF THE HUMA.V OVUM. 189
b^coinfes developed, the vesicle is crowded by this membrane, and is ihen
found placed between the external face of the latter and the internal sur-
fiace of the chorion.
In consequence of the development of the allantois, the umbilical vesicle
loses much of its importance in the human species, as it so soon becomes
an organ of little value either to the growth of the ovum or the embryo :
and furthermore, it dwindles away speedily ; thus, during the first three
weeks, it is as large as an ordinary pea, but after the fourth, it begins to
collapse and diminish in size, and at six weeks subsequent to the concep-
tion, it does not exceed a coriander-seed in bulk ; then it remains stationary
for a time, not disappearing altogether until towards the fourth month. I
have observed it several times of later years on ova of three to three and
a half months, in which it generally still retained the volume and shape
of a small lentil, being of a yellowish color, and having its surface wrinkled.
However, I may remark, that its size appeared very variable in several ova
of the same age.
In proportion as the umbilical vesicle becomes atrophied, it is removed
farther and farther from the trunk of the embryo, in consequence of the
development of the amnion, and its pedicle is also elongated in a marked
manner ; thus, the latter is from two to six lines in length, being continuous
at one end with the intestine, and at the other with the vesicle by a kind
of an infundibuliform expansion. The pedicle is apparently separated into
two portions by the amnios, before the abdominal walls are completely
closed up ; one part lying between the spine, or rather the intestine, and
the spot afterwards occupied by the umbilicus, while the other remains
exterior to the abdomen. This pedicle is traversed by a small canal for the
first five or six weeks of its existence, and through it the fluid in the vesicle
may be pressed back into the intestine, but it is obliterated after that period.
About the same time, also, it becomes more and more delicate, and oftec
ruptures from its great elongation ; and its umbilical portion being lost in
the cord, can no longer be traced into the abdomen. When broken, the
vesicle may be found more or less removed from the root of the cord, and
lying between the chorion and amnion.
The umbilical vesicle has a rich vascular apparatus, the blood of which
is carried to and from the embryo by the intervention of two trunks, one
venous, the other arterial ; both, however, accompany the pedicle, and form
a constituent part of it. The first, n (see Fig. 3, PL IV.), called the ompha/o-
viesenteric vein, enters the abdomen, winds around the duodenum, and then
opens into the umbilical vein at the point o, just as the latter is emerging
from the liver. As it passes the duodenum, branches are given off to the
stomach and intestines, and when it discharges into the umbilical vein, it
sends a voluminous trunk to the liver. That portion which furnishes the
branches just described, persists in the adult under the name of the ventral
or hepatic-portal vein, whilst all the rest will disappear with the umbilical
vesicle and its pedicle.
The arterial trunk p, accompanying the pedicle, has been designated as
the omplialo-mesenteric artery. Arising from the aorta, it gains the summit
'A the intestinal convolution, and gives ofi" branches to the mesentery and
to tlie intestine itself; then it reaches the pedicle, and folloAvs the latter to
the umbilical vesicle, upon which it ultimately ran/ifies. The part that
supplies the mesentery is converted in the adult into a mesenteric artery,
all the rest being effaced. From all which, it appears that the vascular
system of the umbilical vesicle represents the primitive circulation in the
embryo, corresponding in it to the sanguiferous apparatus of the yolk of
fowls. Of course, these vessels will become atrophied with the organ to
which they belong.
The umbilical vesicle seems to be intended to serve as a reservoir for the
fluid designed to nourish the foetus during the first weeks of intra-uterine
§ 3. Of the Amnion.
The most internal membrane of the ovum, or the amnion, is formed by
the inner lamina of the fold., or the cephalic and caudal hoods which con-
stituted the external serous layer of the blastoderm surrounding the embryo.
Being continuous, as we have shown, with the margins of the ventral open-
ing, it seems at first to be attached by its middle part to the skin on the
The internal amniotic surface subsequently exhales a liquid into its cavity,
in which the embryo swims freely; hence the amnios constitutes a little sac
around the foetus, having smooth and transparent walls. Its inner surface
is bathed by the liquid inclosed in the cavity, whilst its external one i*
separated from the chorion by a space of variable size, which is likewise
filled with a fluid and the expansion of the allantoid vesicle.
Originally, this membrane w-as not concentric with the chorion ; but in
proportion as the development advances it presses back the exterior liquid
and the allantoid vesicle more and more, thereby condensing it, and finally
comes in contact with the external envelope of the ovum. Now, since it
adheres to the periphery of the umbilical opening, it must furnish, by such
an extension, a sort of membranous sheath to the pedicles of the allantoid
and the umbilical vesicles, as well as to their accompanying vessels, sur-
rounding them throughout their course from the umbilicus to the chorion;
and all the parts thus inclosed constitute what is called the umbilical cord;
whence it follows that the abdominal cavity itself must be in connection
with the canal represented by this cord, and consequently that the foetal
appendages may communicate with it through the route thus opened to
them. It is thus that the pedicle of the umbilical vesicle becomes united
to the ileo-coecal fold of intestine, whilst the allantois connects with the
rectum by the intervention of the urachus.
As we have just stated, the amnios is separated from the chorion during
the earlier weeks by a filled space, which space is larger in proportion a?
the )vum is the more recent. This extra-amniotic liquid forms a gelatinous
or albuminous mass, of a weblike arrangement, and having the umbilical
vesicle in its midst. The mass becomes more and more compact by pressure
of the amnion, which has a constant tendency to approach the chorion, thus
acquiring the aspect of a membrane (the membrana media of Bischoff),
which is situated between the chorion and the amnion, where, says this
DEVELOPMENT OF THE HUMAN" OVUM. 191
author, it may be readily distinguislied towards the end of pregnancy, as a
gelatinous, though continuous membrane. M. Velpeau gave it the name
of the vitriform or reticulated body, but Robin has shown its structure to be
identical with that of the allantoid vesicle. Velpeau was, therefore, correct
in regarding the reticulated body as the analogue of the allantoid, of whicli
it is really but the remains.
The amnion undergoes no important change during the ulterior develop-
ment of the ovum, nor does its texture. Of course, it would be more firm
and consistent, acquiring by time a greater resemblance to the serous mem-
branes, although it neither incloses nor possesses vessels at any period.
Nevertheless, says Duges, it probably has some openings, which permit the
waters, exhaled by the uterine capillaries, and received by the vessels of the
decidua and the villi of the chorion, to be diffused around the foetus ; but
this perspiration of the liquids secreted by the internal uterine surface, may
very possibly be a simple phenomenon of endosmosis.
§ 4. Waters of the Amnion.
The amniotic cavity is filled wdth a liquid, in "which the foetus is im-
mersed. At the commencement of pregnancy, this fluid is of slight density,
and more or less transparent and limpid, but towards term it becomes viscid,
unctuous, and more consistent than piire water : sometimes it is as clear as
serum ; at others, it is of a light yellow or greenish color. It frequently be-
comes lactescent, turbid, and interspersed with yellowish-gray, or even black
albuminous flakes ; again, in certain cases, it is strongly tinged with yellow,
when the membranes are ruptured, from the admixture of a quantity of
meconium ; it exhales a disagreeable odor, analogous to that of the sper-
matic fluid, and its taste is slightly saline.
The quantity of the amniotic fluid varies greatly ; thus, in the early
months it is, relatively to the foetus, more abundant, in proportion as the
embryo is younger. Riolan found four ounces in an ovum containing a
foetus of the size of an ant. • The weight of the foetus and that of the fluid
at the middle of gestation, are very nearly equal. Again, dating from this
period, the difference is generally in favor of the foetus, and the weight of
the latter at term is four or five times greater than the waters, which seldom
exceed a pound or a pound and a quarter ; consequently, if the assertion is
true, that the waters augment in their absolute quantity until term, it is
equally so to say they increase relatively to the foetus in the first, and
diminish in the second half of pregnancy. In fact, the variations in thi -
respect are infinite, even at the time of the accouchement.
According to the analysis of Vauquelin, 100 parts of amniotic liquor
consist : of water 98*8 ; of albumen, hydrochlorate of soda, phosiDhate of
lime, and lime, 1'2. The interesting question now arises: What is the
source of the amniotic fluid ? Some assert that it comes from the mother ;
others, that it is produced by the foetus. Chaussier, Meckel, and Beclard,
adopting an intermediate opinion, suppose that its secretion takes place
simultaneously from the female and her product.
Everything proves, says M. Velpeau, that the liquor amnii is the resull
of a transudation or of a simple exhalation, like the serum of the pleura.
pericardium, &€., and that this process requires no particular canals for its
accomplishment, being a phenomenon of pure vital imbibition.
According- to Burdach, the amniotic waters cannot be secreted by the
itetus, because they exist prior to its formation,' and therefore they must be
exclusiyely furnished by the internal uterine surface, and reach the cavity
of the amnios by traversing its walls. We also' believe, that the greater
part of this liquid comes from the mother's organs ; yet we must add that
it also contains certain products, secreted by the foetus: for instance, it is
frequently colored by some meconium, and besides, it is almost certain that
the urine may be discharged into the amniotic cavity during the latter
months of pregnancy. A few incontestable facts prove that such an evacua-
tion is necessary to the maintenance of foetal life : thus, Billard and T. W,
King record having seen cases of ruptured bladder, resulting from imper-
foration of the urethra ; and further, Desormeaux and P. Dubois have
observed an obliteration of this canal in two stillborn children, which had
given rise to an enormous distention of the bladder, ureters, and both kid-
neys ; indeed, the latter were found transformed into two raultilocular cyst?.
Similar facts have been presented before the Academy of Medicine by MM
Depaul and ]\Ioreau.
According to some authors, the principal use of these waters is to contri-
bute to the nutrition of the foetus, during at least a great part of gestation.
(See Xutrition of the Foetus.) However this may be, the waters of the am-
nios serve during pregnancy to maintain the insulation of the external foetal
parts before the skin becomes covered with the sebaceous coat hereafter to
be described ; to promote the active movements of the foetus and its develop-
ment, both of which would have been greatly incommoded without this
intervention, by the pressure of the uterine walls ; to protect the foetus from
all external viol-ence, and to afford it the means of conforming to the laws
of gravity. They likewise favor a uniform expansion of the womb, and
remove all pressure from the umbilical cord, thus assuring the integrity of
the foeto-placental circulation both during pregnancy and labor. In the
latter, they seem destined to guard the child from the violence of the uterine
contractions, which, without them, would certainly compromise its existence;
to aid in forming the amniotic bag, the engagement of which renders the
dilatation of the neck more uniform and easy ; to lubricate the pelvic canal,
and thus facilitate the descent of the foetus ; and lastly, they render manipu-
lations of every kind less difficult than they otherwise would be.
§ 5. Of the Chorion.
The chorion is the most external envelope of the ovum. Writers are by
no means unanimous in their views as to the elements of which it is com-
posed. Thus, some of them, as we have had occasion to state, suppose that
it is formed by the vitelline membrane, the external lamina of the blasto-
derm, and the allantoid vesicle, uniting to constitute a single layer. Accord-
ing to others, on the contrary, the vitelline membrane will disappear soon
^ It is onlj' necessary to recall our remarks on the development of the amnios to
refute this opinion.
DEVELOPMENT OF THE HUMAN OVUM. 193
after the doubling of the blastodermic vesicle, and the external lamina of
the latter, conjoined with the allantois, will then form the chorion.
[M. Robin's view of the subject is as follows: According to M. Coste, three