524 ON THE REPRODUCTIVE SYSTEM IN ANIMALS. 
enter the urinary bladder. It would be inconsistent with the 
object of this paper to describe the foetal circulation. After the 
third month of utero-gestation, the umbilical cord forms the only 
connexion between the foetus and placenta. This cord consists of 
the umbilical vein and two umbilical arteries. The umbilical vein 
conveys arterial blood from the mother to the foetus, and the two 
umbilical arteries return the venous blood from the foetus to the 
placenta. Commencing where the umbilical vessels emerge from 
the body of the foetus, I shall describe the nature of the placental 
circulation in the cow. It has been already stated that two arteries 
and one vein constitute the cord; the cord is often of considerable 
length: at the place of its union with the amnion the vessels 
divide and subdivide into a certain number of branches, corre¬ 
sponding with the number of cotyledons, each receiving two vessels, 
an artery, and vein. When these enter the foetal part of the 
placenta, they form extremely minute vessels. The ramifications 
of the umbilical vein form fasciculi, or tufts, which are very 
minute loops that dip down, as it were, into the maternal blood, 
and, being furnished with absorbent powers, they abstract from the 
contents of the curling arteries the materials destined to the 
nutrition of the foetus. The umbilical arteries are divided and 
ramified throughout the placenta in a manner analogous to that 
now described; their tufts dip into the uterine vessels, where they 
perform the function of exhalents, or excretory ducts. Moreover, 
the capillary vessels of the umbilical veins and arteries anastomose 
freely together—hence the placental circulation, &c. The foetus 
commands a circulation, in one view, independent of the mother, 
its pulsations being double in number to that of the parent. The 
arterial blood is conveyed from the placenta along the umbilical 
vein, after having circulated through the body of the foetus, during 
which course it gives off all the elements it contains suitable for 
nutrition, and receives into its volume the effete matter discharged 
by the foetal system. It returns exhausted and impure, along the 
umbilical arteries, to the placenta, where a great part of it is 
absorbed by the uterine veins, and re-enters the circulation of the 
mother. A portion of it passes through the placental capillaries, 
in which it undergoes the renovating influence of the maternal 
blood, from which it is returned to the foetus in a state of purit)'. 
It is a truth that the heart of adult animals performs the double 
operation of a forcing and suction pump: the left side forcing the 
blood through every part of the body; the right side by its 
powerful suction drawing the blood from every vein in the body, 
and promoting absorption, not only in the veins themselves but in 
every orifice connected with them. It does not appear that any 
lymphatics have ever been traced to the placenta; neither, so far 
