422 THE PHYSIOLOGY OF REPRODUCTION 



bi-lobed (Fig. 101). The folds of the mucosa are essentially 

 increased areas of the mucosal connective tissue, but they differ 

 from the cotyledons of Ruminants in having glands. 



On the entrance of a fertilised ovum into the uterus, the 

 folds, especially the ob-placental, become shortened, and a 

 localised actual cavity appears which is occupied by the blasto- 

 cyst. At the same time there is a marked hyperplasia of the 

 cellular connective tissue of the placental and peri-placental 

 folds, leading to a thickening of their bases (Chipman 1 ). By the 



FIG. 101. Transverse section of a seven days' gestation sac of the rabbit 

 (Chipman). The placental folds (coussinets) are large (a) ; the muscular 

 walls of the sac are thin. 



sixth day, the capillaries are also increased in these regions. 

 In the ob-placental folds appear enormous giant-cells, derived 

 by a process of " degenerative hypertrophy " from the 

 epithelium of the surface and glands. They persist till the 

 fourteenth day, and are probably absorbed by the trophoblast 

 overlying the yolk-sac. In the placental lobes the epithelial 



1 Chipman, " Observations on the Placenta of the Rabbit, with Special 

 Reference to the Presence of Glycogen, Fat and Iron," Laboratory Reports, 

 Roy. Coll. Phys., Edinburgh, vol. viii., 1903. The development of the 

 placenta is carefully traced in a complete age-series of pregnant rabbits 

 and admirably figured .by many photo-micrographs. The account as given 

 here is based mainly on Chipman's monograph, but the phraseology is some- 

 times changed. 



