VITELLINE VEIN. 



YOLK sue WA 



'■.\ -r — VITELLINE ARTERY 

 '\\\\ ' ,'_ DUCT FROM YOLK SAC TO 

 INTESTINE 



UTERINE WALL 

 GLAND LUMEN 



ALLANTOIC ARTER 

 6ELLY STALK 

 ALLANTOIC VEIN 



Fio. 373. Placental relationships. (A) Placenta of Mustelus laevis. This is a yolk- 

 sac placenta, and the yolk sac tissues burrow into the wall of the uterus, invading the 

 uterine glands. It does not erode the endometrium, however, and therefore resembles the 

 placental conditions in the pig, shown in fig. 373B. It is essentially an epithelio-chorial 

 type of placenta. (Redrawn from Needham, 1942, Biochemistry and Morphogenesis, 

 Cambridge University Press, London.) (B) Placental relationships in the pig. The 



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