THE PLACENTA. 



44B 



uv 



MM 



PO 



PW 



uc 



PH 



YK 



AA 



W 



TS 



FIG. 170. A transverse section across the uterus and the contained embryo 

 of a Rabbit at the end of the nineteenth day. The embryo is cut trans- 

 versely, about the middle of the body, the section passing through the 

 yolk-stalk and allantoic stalk, x 3^. 



A, dorsal aorta of the embryo. AA, allantoic artery. AX, amnionic cavity, be- 

 tween the inner or true amnion and the embryo. CX, space between the 'inner 

 and outer layers of the amnion (cf. Fig. 148). GU, uterine glands of obplacental 

 region. H, hypobliist of upper or vascular Avail of yolk-sac. MI, outer or longitudinal 

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

 uterus. MM, mesoinetrium. NS, spinal cord of the embryo. NY, sympathetic nerve 

 cord. PH, lobule of placenta. PO, region along which the separation of the placenta 

 occurs at birth. PR, interplacental groove. P~W, snbplacentul cavity. SI, sinus 

 tenninalis. TA, cavity of the allantois (cf. Fig. 148). TS, stomach of embryo. UC. 

 dilated uterine.capillary, with thick perivascular wall. UP, uterine or maternal sinnsc- 

 of placenta. UV, blood-vessels of uterus. VA, allantoic vein. "W, liver of embryo. 

 YK. yolk-stalk. YL, dotted line representing the lower or non-vascular wall of the yolk- 

 sac, now completely absorbed. YS. cavitv of volk-sac, continuous with the uterine 

 cavity owing to absorption of the lower wall of the yolk-sac. 



