234 



EMBRTOLOGY. 



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. 



Tig. 135a — uterus of a Cow laid open, in the middle of the period of JJjg Rumi- 



gestation. From Balfour, ^fter Colin. 



V, Vagina ; U, uterus ; Ch, chorion ; C, cotyledons of the uterus ; C, foetal nantS, in which 



cotyledons. , i i i j. i 



the blastoder- 

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

 special typ e 

 (fig. 135a). On u, 



their chorion 

 {Ch) have been 

 developed very 

 many small 

 fcetal placentae 

 {C^),whichhere 

 are also called 

 cotyledons. The 

 number of the 

 latter is ex- 

 ceedingly vari- 

 able in the 

 difierent 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. 13Sb.— Cotyledon of a Cow, the foetal and maternal parts half 

 detached from each other. Af bar Colin, from Balfour. 



■14, Uterus; C, maternal part ■ of the cotyledon (placenta uterina); 

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

 (chorion frondosum or placenta foetalis). 



