436 



THE BABBIT. 



uterus; and the third pair, or obplacental folds, lie opposite 

 the placental folds, along the free or unattached border of the 

 uterus. 



It is from the mesometrial, or placental, folds alone that the 

 maternal part of the placenta is derived : the periplacental and 



Fig. 168. — A transverse section across the uterus, with the contained blasto- 

 dermic vesicle, of a Babbit at the end of the seventh day. (In part 

 after Duval.) x 12. 



Tj, epiblaat of blastodermic vesicle. 'E'K., thickened epiblast of embryonal area.- 

 G-TJ, uterine glands. H, hypoblast of blastodermic vesicle. MI, outer or longitudinal 

 muscles of the wall of the uterus. MK, inner or circular muscles of the wall of the- 

 uterus. MM, mesometrium, or mesenterial fold connecting the uterus with the dorsal 

 wall of the abdomen. PK, placental fold of uterus. PM, periplacental fold of uterus. 

 PR, median cleft between the two placental folds. ITG, dilated capillaries of submucous 

 layer of uterus. YS, yolk-sac. 



obplacental folds undergo considerable changes, but do not take 

 any direct part in the formation of the placenta. 



On the seventh day the blastodermic vesicles are spaced out 

 along the uterus, and the swellings or loculi of the uterus, indi- 

 cating their position, are well marked externally. 



The blastodermic vesicle, the structure of which at this stage 



