234 



EMBRYOLOGY. 



Cb 



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



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. 



Fig. 135a.-Werus of a Cow laid open, in the middle of the period of TU fi /?>///;/ 



gestation. From BALFOOH, after COLIN. 



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



cotyledons. . , -11,1 



the blastoder- 



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

 special type 

 (fig. 135a). On u 

 their chorion 

 (Ch) have been 

 developed very 

 many small 

 foetal placentae 

 (<? 2 ),whichhere 

 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 part* half 

 detached from each other. After COLIN, from BAM 



u, Uterus ; C 1 , maternal part of the cotyledon (placenta nterina) ; 

 Ch, chorion of the embryo; C*, f ratal part of the cotyledon 

 (chorion frondosum or placenta f retails). 



