F(ETUS, 
The amnion is firm, thin, transparent, and 
possessing no visible vessels. It immediately 
includes the liquor amnii and child. The 
chorion lies outside of the amnion, and ad- 
heres to it ; it is transparent, very thin and 
tender, and adheres externally to the deci- 
dua. 
The decidua is an efflorescence of the in- 
ternal coat of the uterus, produced after 
conception, in order to adapt the womb for 
the ovum, which is to enter it. It is shed 
after every birth, or miscarriage, with the 
other membranes; and hence its name. 
It is thicker, but more delicate and tender 
than the amnion or chorion. It contains 
several blood vessels, which are best seen in 
recently discharged secundines. It adheres 
closely to the uterus on one side, and to the 
chorion on the other. The laceration of the 
vessels, which this membrane receives 
from the uterus, accounts for the hemorrhage 
which follows its separation. At the edge 
of the placenta it divides into two layers, 
which pass over the two surfaces of that 
organ, and form its uterine portion. 
The liquor amnii is the fluid immediately 
surrounding the body of the child, and so 
called from the membrane enclosing it. Its 
usual quantity is about two pints. It is a 
clear, transparent fluid. 
The child, while in the uterus, is naturally 
contracted into an oval form, adapted to 
the figure and circumstances of its habita- 
tion. The vertex of the head makes one 
end of the oval, and the nates the other. 
One side or edge of the oval is formed by 
the occiput, the back part of the neck, and 
the incurvated trunk ; the other is made by 
the forehead and the mass of contracted 
and conglomerated limbs. The chin is close 
to the breast, the trunk bended forwards, 
the knees close to the fore parts of the by- 
pochoridia, the legs drawn to the back parts 
of the thighs, and the upper extremities 
contracted into the vacant space betwixt 
the forehead and knees. The more or less 
compact form of the child depends on the 
quantity of liquor amnii; when that is 
small, the uterus moulds the child into va- 
rious forms, and often produces deformities 
of the limbs. The head is placed down- 
wards with respect to the mother, and the 
nates upwards. 
The usual weight of the child at the time 
of birth is from five to eight pounds: of 
several thousands weighed at the British 
Lying-in Hospital, the largest weighed 11 lb. 
Soz. the smallest was above 4 lb. 
The head, upper part of the trunk, and 
upper extremities, are very large when 
compared with the lower parts of the body. 
The surface of the skin is covered pretty 
generally with a crust of a white sebaceous 
matter. 
Peculiarities in the Structure of the Foetus. 
These are on the whole numerous ; but 
we shall briefly enumerate the most impor- 
tant only. 
The first which claim our attention are 
some points respecting the heart and large 
blood-vessels ; which we may suppose ab- 
solutely necessary to the life of the child, 
while it draws nourishment from the mo- 
ther, and cannot enjoy respiration. As the 
foetus in utero cannot breathe, the circula- 
tion of its blood through the lungs would be 
useless : hence that fluid can go from the 
right to the left side of the heart by means 
of an opening called the foramen ovale, 
and placed between the two auricles, 
and of a communicating canal from the 
pulmonary artery to the aorta, called duc- 
tus arteriosus. The umbilical arteries are 
continuations of the internal iliacs, taking 
the blood from the child to the placenta; 
from which it is brought back by the um- 
bilical vein, and circulated through the 
liver. , 
The lungs are small and compact ; and as 
they have not yet received air, they are 
specifically heavier than water. This is an 
important point, and is usually referred to 
in trials for child-murder, in order to deter- 
mine whether the child was born alive or 
no. If the lungs sink in water, it is con- 
sidered a still-born case ; and if they float, 
the probable inference is, that the child has 
breathed, but it would be a very rash con- 
clusion that it had, therefore, been murder- 
ed. Much caution and consideration of 
concomitant circumstances must be em- 
ployed in making use of this proof. Putre- 
faction will disengage air that may make 
the lungs float. 
The thymus gland, in the chest, is very 
large in the foetus ; it gradually shrinks 
after birth, until it entirely disappears. 
Its use is unknown. 
The pupil of the eye is shut until the 
seventh or eighth month, by a thin pellicle 
called membrana pupillaris. As a general 
observation, the eye and ear are very per- 
fect at the time of birth, and almost as large 
as they ever will be. (N.B. This does not 
apply to the external ear.) 
The small intestines have no valvul’.e 
conniventes. The large are filled with a 
