558 



E!£Er.rcLoaY. 



scattered evenly over the chorion, so that the placenta is diffuse** 

 (Huxley). In carnivora the villi are collected in a mass v/hich ' 

 assumes the form of a belt, surrounding the chorion, aod hence 

 called a zonary placenta. In rodentia . the placenta is discoid, 

 the villi being assembled in a more or less circular mass. 



The placenta is found in most orders of mammals, and in tnem 

 alone ; its presence or absence has led to the separation of the ' 

 class mammalia into a placental and an implacental division. 



Fio. 216. 



. FcBtus of the Cow, with Its membranes, o a, Placenta ; 6 6, Chorion with the Allantois adherent 

 to its inner surface ; cc, Amnion seen through outer covering ; d, foetus seen through its covcrines. 



UMBILICAL CORD. 



This structure is the medium of connection between the foetus 

 and the placenta, reaching from the latter to the umbilical open- 

 ing in the linea alba. It consists mainly of the umbilical vessels, 

 one vein, and two arteries, and superiorly contcins the urachus, 

 a foetal tube continuous with the bladder. 



