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 ; 



7, 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 



