THE FOETUS. 



901 



covered by thepentoneum, and arrives at the liver, into which it enters and 

 opens directly mto the vena portae ; the junction of the two vessels siving 

 rise to a single canal from which proceed the hepatic veins. In other 

 animals than Solipeds, this vessel gives off a particular trunk of somewhat 



Fig. 428. 



A FCETDS OPENED ON THE LEFT SIDE TO SHOW THE COURSE OE THE UMBILICAL 

 VESSELS IN THE BODY. 



A, Umbilical cord ; B, Umbilical vein ; c, Umbilical artery ; b, Bladder ; E, Testicle j 

 r, Kidney; G, Spleen; H, Liver; I, Intestine, J, Lung; K, Heart; L, Pulmonary 

 artery ; M, Ductus arteriosus ; N, Thymus gland. 



considerable volume, which passes directly to the posterior vena cava, 

 forming what is named the ductus venosus (Figs. 429, 430). 



Such are the umbilical vessels, and it will be seen that they form a part 

 of the circulatory system of the young creature which will be more com- 

 pletely studied hereafter. ^ 



DIFFEEBNTLIL CHAKACTEBS IN THE ANNEXES OP THE FCETUS OP OTHER THAN SOLIPED 



ANIMALS. 



1. KuMiN'ANTS. — Tlacenta. — Tlie placental apparatus of the Cow is not uniformly 

 spread over the outer surface of the chorion, but is constituted by a variable number of 

 vascular bodies about sixty on an average, disseminated here and there, and dovetailed by 

 reciprocal penetration of prominences and cavities, into analogous bodies on the inner 

 surface of the uterus, designated cotyledons. These are only thickened points of the 

 mucous membrane, the follicles of which are enormously enlarged. They exist, we have 

 seen, before gestation; but observation demonstrates that they may be afterwards formed 

 or entirely renewed, especially in those cases in which accidental circumstances have 

 rendered those present insufBoient for their office. The largest are found in the body of 

 the uterus ; in the cornua they are smaller as they are nearer the extremity. Their 

 form is generally elliptical, and they are attached to the uterine surface by a wide mucous 

 60 



