26-7 VETERINARY OBSTETRICS. 
The Umbilical Vesicle. 
This is a small, pear-shaped structure, which is 
only seen in the very early stages of foetal life. Its 
function is not very well understood, but it is believed 
to supply the foetus with nourishment until the 
membranes have assumed that function. By its narrow 
extremity, the umbilical vesicle is in contact with the 
small intestine of the foetus; and by its other or broad 
extremity, it is in contact with or rests upon the inner 
aspect of the chorion. As soon as the placental 
circulation is established, this structure commences to 
undergo atrophy, and all that remains of it at birth is a 
brownish colored fibrous cord. 
The PLACENTAL CIRCULATION, Or, as it is sometimes 
called, the ‘ vascularization,” varies in the foetus of 
different animals. 
In the Cow, as already stated, there are a large 
number of vascular processes in the pregnant animal, 
called cotyledons. These are in contact with the 
external surface of the chorion, and the blood of the 
parent is thus brought into close contact with the 
blood of the foetus at these situations. There is no 
direct continuity of the circulation, the blood of the 
parent being spread out in very small vessels on the 
surface of the maternal cotyledons, while that of the 
foetus is distributed in a similar manner, on the 
opposing surface of the chorion. Through the walls 
of these opposing vessels the exchange takes place. 
In the Mare, instead of the blood-vessels being 
found at certain parts, they are distributed all over the 
