THE FCETUS. 



'901 



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

 opens directly into the vena portas ; the junction of the two vessels giving 

 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 FCETUS OPENED ON THE LEFT SIDE TO SHOW THE COURSE OF THE UMBILICAL 

 VESSELS IN THE BODY. 



A, Umbilical cord ; B, Umbilical vein ; C, Umbilical artery ; D, Bladder ; E, Testicle \ 

 F, 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 dnctus 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. 



DIFFERENTIAL CHARACTERS IN THE ANNEXES OF THE FCETUS OF OTHER THAN SOLIPED 



ANIMALS. 



1. KUMIXANTS. Placenta. The 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 insufficient 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 



