THE PLACENTA. 



439 



surface of the uterus, nor those of the outermost layer, next to 

 the circular muscles of the uterine wall. 



Fig. 169. — A transTerse section across the uterus and the contained blasto- 

 dermic vesicle of a Eabbit at the end of the ninth day. Cf. Figs. 14.'5 and 

 146, in which the blastodermic vesicle and embryo of this age are shown 

 in surface view and in sagittal section. (In part after Duval.) x 8. 



AN", side fold of the amnion. C, mesoblast of the upper wall of the blastodermic 

 vesicle, beyond the embryonal area. E, epiblast of the blastorlermic vesicle ; the u pper 

 reference is to the thickened epiblast of the placental area. GTJ, uterine glands. G-W, 

 modified uterine glandfe of placental region. H, hypoblast of blastodermic vesicle. MI, 

 outer or longitudinal muscles of the wall of the uterus. MK, inner or circular muscles of 

 the waU of the uterus. ]VEM, mesometrium. I3"G, neural groove of embryo, in trans- 

 verse section. PR, median cleft between the placental lobes of the uterus. SI, sinus 

 termiualis. TIC, capillaries of placental region, "with thickened perivascular walls. 

 U Jb, giant cells. UV, blood-vessels of uterus. TS, yolk-sac, or cavity of blastodermic 

 vesicle. 



During the tenth day, the ectoplacental epithelium increases 

 greatly in thickness, and becomes excavated by irregular chan- 

 nels or lacunae, which according to Duval open into the maternal 



