Gravid Uterus.] 
This fuggeds an important advice to pra&itioners, to be 
cautious of pulling the rope to ex trad the placenta when 
they feel the fenfation of its fplitting as it were into two 
divifions, which will proportionally weaken its refinance, 
and render it liable to be ruptured with a very flight de¬ 
gree of force in pulling. 
The placenta, cake, or after-birth, is a thick, foft, vaf- 
cular, mafs, connected to the uterus on one fide, and to the 
umbilical cord on the other. It differs in fliape and iize; 
it is thickell: at the centre, and gradually becomes thinner 
towards the edges, where the membranes go off all round, 
making a complete bag or involucrum to fuiround the 
waters, funis, and child. Its fubftance is chiefly vafcu- 
lar, and probably in fome degree glandular. The ramifi¬ 
cations of the veffels are very minute, w hich are unravelled 
by maceration, and, when injedted, exhibit a molt beau¬ 
tiful appearance, refembling the bufhy tops of a tree.^ It 
has an external convex, and an internal concave, (urface. 
The former is divided into a number ot final 1 lobes and 
fifibres, by means of which its adhefion to the uterus is 
more firmly (beared. This lobulated appearance is mod 
remarkable when the cake has been rafhly feparated from 
the uterus; for the membrana decidua, or connecting mem¬ 
brane between it and the uterus, being then torn, the mod 
violent and alarming hemorrhages frequently enfue. d he 
internal concave furface of the placenta is in contadt with 
with the chorion, and that with the amnios. From its 
internal fubdance arife innumerable ramifications of veins 
and arteries, which inofculate and anadomofe with one 
another ; and at lad the different branches unite, and form 
the funis umbilicalis. The after-birth may adhere to 
every part of the internal furface of the uterus, as at the 
poderior and anterior, fuperior and lateral, parts ; and 
fometirrifcs, though more rarely, part of the cake extends 
over the orificium uteri; from w hence, w hen the orifice 
begins to dilate, the mod frightful and dangerous flood¬ 
ings arife. But the mod common place ol attachment of 
the cake is from the fuperior part of the cervix to the 
fundus. Twins, triplets, &c. have their placenta, fome- 
times feparate, and fometimes adhering together. When 
the placentae adhere, they have generally the chorion in 
common ; but each foetus has its didindt amnios. They 
are commonly joined together, either by an intervening 
membrane, or by the furfaces being contiguous to one ano¬ 
ther; and fometimes the veffels of the one cake anadomofe 
with thofe of the other. The human placenta, according 
to Dr. Hunter, and others who believe that the child is 
nouridied by a fecreted liquor, is compofed of two didindi 
fydems of parts, a fpongy or cellular, and a vafcular (ub- 
(tance; the fpongy or cellular part, formed by the deci¬ 
dua, being derived from the mother, the more internal 
vafcular part belonging entirely to the foetus; but, accord¬ 
ing to thofe who are of opinion that a real circulation is 
carried on between the mother and the child, the placenta 
is chiefly compofed of veffels which are connected by the 
common cellular fubdance. 
The membranes confid, externally, of two layers of 
the fpongy chorion, called decidua , and decidua rejlexa ; 
internally, of the true chorion, and the amnios. They 
form a pretty drong bag, commencing at the edge of the 
cake, going round the whole circumference, and lining the 
internal furface of the womb. When feparated from the 
uterus, this membranous bag is (lender and yielding, and 
its texture is readily dedroyed by the impulfe of the con¬ 
tained fluid, the preffure of the child, or of the Anger in 
touching ; but in its natural date, while it lines the womb, 
and is in clofe contadt with its furface, the membranous 
bag is tough and drong, fo as to give a confiderable degree 
of reddance. It is alio drengthened in proportion to the 
different layers of which it is compofed, whofe dructure 
we (hall proceed to explain more particularly. 
i. The membrana decidua , or that lamella of the fpongy 
falfe chorion which is in immediate contadt with the ute¬ 
rus, is originally very thick and (pcngy, and exceedingly 
vafcular, particularly where it approaches the placenta. 
651 
At fird, there is a fmall intervening fpace between it and 
the ovum, which is filled with a quantity of gelatinous 
fubdance. It gradually becomes more and more attenua¬ 
ted by dretching, and approaches nearer to the decidua 
redexa ; and about the fifth month the two layers come 
in contact, and adhere (o as to become apparently one 
membrane. 
2. The decidua rejlexa, in its drudture and appearance, 
is (imilar to the former, being rough, fleecy, and vafcular, 
on its external furface. In advanced geftation, it adheres 
intimately to the former membrane, and is with difficulty 
feparated from it. The decidua reflexa becomes thicker 
and more vafcular as it approaches the placenta, and is 
then blended with its fubdance, condituting the cellular 
or maternal part of the cake, as it is termed by Dr. Hunter. 
The other or more internal part belongs to the foetus, and 
is dyled the J'cetal part of the placenta. The double deci¬ 
dua is opaque in comparifon of the other membrane ; the 
blood-vedels are derived from the uterus, and can be rea¬ 
dily traced into it. Dr. Hunter fuppoles that the double 
decidua lines the uterus nearly in the fame manner as the 
peritonaeum does the cavity of the abdomen, and that the 
ovum is inclofed within its duplicature. 
3. The true chorion , or that connedted with the amnios, 
is the firmed, fmoothed, and mod tranfparent, of all the 
membranes, except the amnios; and, when feparated from 
it, has a cundderable degree of tranfparency. It adheres 
clofely to the internal furface of the cake, which it covers 
immediately under the amnios, and gives al(o a coat to the 
umbilical cord. It is connected to the amnios by means of 
a gelatinous fubdance, and is eadly feparated from it. 
4. The amnios, or internal membrane, forms the exter¬ 
nal coat of the umbilical cord. This lateral lamella of the 
membranous bag is the mod thin, attenuated, and tranfpa¬ 
rent, of the whole; and its veffels are fo delicate, that they 
can hardly be difeovered: their diameters are fo fmall as 
to be incapable, in their natural date, of admitting glo¬ 
bules of red blood. It is, however, firmer and fironger 
than the chorion, and gives the greated reddance in the 
breaking of the membranes. The fmall bag, called vefi- 
cula umbilicalis, formerly deferibed, and only confpicuous 
in the early months from its (filiation, is placed between 
the amnios and chorion, near the attachment of the cord ; 
and, from the colour of its contents, has been iwdakeafor 
the urachus: but there is no allantois in the human ftib- 
jedt. The allantois in quadrupeds is an oblong membra¬ 
nous fac, or pouch, placed between the chorion and amnios. 
This membrane communicates with the urachus, which in 
brutes is open, and tranfmits the urine from the bladder 
to the allantois. 
5. The waters are contained within the amnios, and are 
called the liquor amnii. They are pared, cleared, and mod 
limpid, in the fird months; acquiring a colour, and becom¬ 
ing fomewhat ropy, towards the latter end. They vary in 
different fubjebts, both in confidence and quantity; and, 
after a certain period, they proportionally diminilh as the 
woman advances in her pregnancy. This liquor does nor, 
in any refpebt, refemble the white of an egg; it is gene¬ 
rally faltiih, and therefore unfit for the nutrition of the 
child : fome of it may perhaps be abforbed by the foetus, 
but the child is chiefly nouridied by the navel-dring'. 
Water is fometimes collected between the chorion and 
amnios, or between the lameilie of the chorion. This is 
called the falfe water. It is generally in much fmaller 
quantity than the true water ; and, without detriment to 
the woman, may flow at any time of pregnancy. 
The foetus is commodioufly adapted to the cavity of the 
uterus, and deferibes an oblong or oval figure ; its feveral 
parts being collebted together in fuch a manner as to oc¬ 
cupy the lead podible fpace. The fpine is rounded, the 
head reclines, and die knees are drawn up to the belly, 
while the heels are drawn backwards towards the breech, 
and the hands and arms are folded upwards and down¬ 
ward-:. The head of the child is generally downwards. 
This does not proceed, as was commonly alleged, from the 
funts 
ANATOMY. 
