PLACENTA 



611 



limited disc-shaped area covered by the thick . 

 part of the trophoblastic ectoderm where the distal 

 portion of the allantois coalesces with it (Fig. 166). 

 The membrane thus formed (chorion) develops vascular 

 processes or septa the chorionic villi, which are 



.c 



ys 



FIG. 1 66. A Rabbit embryo and blastodermic vesicle (" yolk-sac ") at the end of 

 the tenth day. The embryo is represented in surface view from the right side, 

 the course of the enteric canal being indicated by the broad dotted line ; the 

 blastodermic vesicle is shown in median longitudinal section. The greater part 

 of the tail has been removed, (x 7\.) 



an', pro-amnion ; a.x. cavity of amnion, between the inner or true amnion and 

 the embryo ; c. extra-embryonic portion of ccelome ; e. trophoblastic ectoderm ; 

 e' '. thickened part of e by which the blastodermic vesicle is attached to the 

 uterus, and from which the development of the foetal part of the placenta 

 proceeds ; ei. auditory vesicle ; ek. ectodermal villi ; gf, gt, gh. enteron ; h. 

 endoderm ; ol. eye ; r. heart ; si. circular marginal vessel of area vasculosa ; 

 ta. cavity of allantois ; ys. cavity of " yolk-sac." (From Marshall, in part 

 after Van Beneden and Julin.) 



received into depressions the uterine crypts in the 

 thickened placental folds of mucous membrane on the 

 dorsal wall of the uterus which constitute the maternal 

 portion of the placenta (Figs. 167 and 168). The foetal 

 portion of the placenta with its villi is supplied with 



