234 



EMBRYOLOGY. 



c 1 



for it. But in the interest of a more precise definition it is advisable 



^2 to use the name 



only in the re- 

 stricted sense 

 in which it has 

 been employed 

 in this chapter, 

 and in other 

 cases to speak 

 of a villous 

 membrane or 

 chorion only. 

 The forma- 

 tion of the pla- 

 centa presents 

 in its details 

 important mo- 

 difications. 



Tig. 135a.-TJterus of a Cow laid open, in the middle of the period of Tha 7?,, * 

 gestation. From BALFOUR, after COLIN. lhe -ttumi- 



V, Vagina ; U, uterus ; Ch, chorion ; C\ cotyledons of the uterus ; C 2 , total nants, in which 

 cotyledons. 



the blastoder- 



mic vesicle is drawn out into two tips, as in the Pig, present a 

 special typ e 

 (fig.!35a). On w 

 their chorion 

 (Ch) have been 

 developed very 

 many small 

 foetal placentae 

 ((7 2 ),whichhere 

 are also called 

 cotyledons. The 

 number of the 

 latter is ex- 

 ceedingly vari- 

 able in the 

 different spe- 

 cies, from sixty 



Fig. 135b. Cotyledon of a Cow, the foatal and maternal parts half 

 detached from each other. After COLIN, from BALFOUR. 



u, Uterus; C l , maternal part of the cotyledon (placenta uterina); 

 Ch, chorion of the embryo; C*. foetal part of the cotyledon 

 (chorion frondosum or placenta foetalis). 



to one hundred 

 in the Sheep 

 and Cow, and only from five to six in the Doe. They are united with 



