234 



EMBRYOLOGY. 



C' 



c" 



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



-2 to use the name 



/ yy> only in the re- 



stricted sense 

 in which it has 

 been employed 

 in this chapter, 

 and in other 

 cases to speak 

 of a vi lions 

 membrane or 

 chorion only. 

 The forma- 

 tion of the pla- 

 centa presents 

 in its details 

 important mo- 

 difications. 



Fig. 135a. TTterus of a Cow laid open, in the middle of the period of TVi T}im 



gestation. From BALFOUR, after COLIN. 



V, Vagina ; U, uterus ; Ch, chorion ; C", cotyledons of the uterus ; C*, foetal nants, in which 



cotyledons. , , , , 



the blastoder- 



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

 special typ e 

 (fig. 135a). On 

 their chorion 

 (Ch) have been 

 developed very 

 many small 

 foatal placentae 

 (C 2 ), which here 

 are also called 

 cotyledons. The 

 number of the 

 latter is ex- 

 ceedingly vari- 

 able in the 

 different spe- 

 cies, from sixty 

 to one hundred 

 in the Sheep 

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



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

 detached from each other. After COLIN, from BALFOUR. 



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

 Ch, chorion of the embryo ; C 3 , foatal part of the cotyledon 

 (chorion frondosum or placenta foetalis). 



