68 



Diseases of the Genital Organs 



type, the fundamental structure is essentially the same in 

 all species. In the cotyledonal placentae of ruminants, the 

 tufts, longer and far more elaborately branched, sink cor- 

 respondingly deeply into the placental crypts of the endo- 

 metrium. The chorionic tufts have in detail their counter- 

 part in the crypts into which they project. The ultimate 



Fig. 36 — Necrotic Tips of Fetal Sacs, Swine. 



/, /a. Necrotic embryos in totally necrosed fetal sacs ; 2, 2, normal 



embryos within amnion, the allantois having been opened ; 



4, necrotic tip of allantois. 



chorionic tufts consist of capillary walls with a single epi- 

 thelial layer, while the corresponding maternal crypt con- 

 sists also of capillary loops with a single, delicate, epithelial 

 layer. The fetal and maternal capillaries remain perma- 

 nently separate and the two delicate epithelial layers perma- 

 nently separate the maternal from the fetal blood. All nu- 

 triment and waste products exchanged between the mother 

 and the fetus must pass through these two epithelial bar- 

 riers, which together constitute the placental filter. Through 



