452 THE PHYSIOLOGY OF REPRODUCTION 



situated one on each side of the groove corresponding to the insertion 

 of the inesonietrium; nl- r hn;;,l,,l folds, the smallest, opposite the 

 mesometnuni : ,,;-/>/>< ,<fal folds, intermediate in position and size 

 1 26). Each fold is divided by transverse fissures into rectangular 

 j, the <,,/, As of Hollard. At the onset of pregnancy two of 

 these an-as on the placental folds, placed one on either side of the 

 mesonietrial groove, hypertrophy and form the maternal part of the 

 fmuie discoid placenta (Hischo'ff 1 ), which is thus bi-lohed (Fig. 127). 

 The folds of the mucosa are essentially increased areas of the mucosal 

 connective tissue, hut 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 blastocyst. 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 2 ). By the 

 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. 3 They persist till at least 

 mid-pregnancy, and are probably 



absorbed by the trophoblast overlying the yolk-sac. In the placental 

 Iol>e8 the epithelial cells proliferate and fill up the superficial culs-de- 

 sac of the mucous membrane. The glands are as yet unchanged, and 

 the increased blood supply leads to a free secretion which is usually 

 considered to 1*> added to the albumen-layer, and then to be absorbed 

 by the trophoblast. There is no appreciable transudation of lymph 

 such as occurs in Ruminants. 



Kn; liiT. Transverse section of a 

 seven days' gestation sac of the 

 rabbit (Chipman). The placental 

 folds ;i-t>n**int'fx) are large (a): 

 tin- muscular walls of the sac 

 are thin. 



iiotf. Entwietelvng <le* Kaninchen-Eie, Braunschweig, 1842. 

 - riiipumi. "< >l>-''i vatimis on the Placenta of the Babbit, with Special 

 enoe t<> the Present T of (ilycogen, Fat, and Iron," Lab. Rep., Hot/. 

 <'<>U. /'hi/*., Kdinliurgh, vol. viii., 1 903. The development of the placenta is 

 carefully tra<-.-<l in a complete age-series of pregnant rabbits and admirably 

 tiumvtl Ky many plioto-micrographa. The account as given here is based 

 mainly on ('hipiiiaii's monograph, but the phraseology is sometimes changed. 



I lammond suggests that these may l)e detached cells from the tropho- 

 blast. < '/. Hammond, "On the Causes Responsible for the Developmental Progress 

 of the Mammary (Hands in the Rabbit," Proc. Roy. Soc., B., vol. Ixxxix., 1917. 



