Generation and Development. 391 



impregnation may be mentioned the great increase in the 

 elements of the muscular wall, enlargement of the broad 

 ligaments of the uterus, and the formation in the mucous 

 membrane of depressions, or ' crypts,' in which are lodged 

 the villi of the chorion. 



The Nutrition of the Embryo is in the first instance carried 

 out by the umbilical vesicle; later, when the membranes 

 are formed, and connected with the interior of the uterus, 

 nutrition is carried on by the interchange of material oc- 

 curring in the villi of the chorion, and the capillary vessels 

 surrounding the follicles or crypts in the uterine mucous 

 membrane. The capillary vessels of mother and foetus 

 here come in contact, though there is no communication 

 whatever between them ; carbonic anhydride passes through 

 the vessels from the foetus to the mother, and in return the 

 vessels of the latter give up oxygen to the foetal villi, by 

 which it is conveyed to the umbilical vessels, and so enters 

 the body of the foetus. 



Uterine Milk.— If the villi of the chorion be separated 

 from the tubular depressions of the mucous membrane of 

 the uterus, a milky fluid can be expressed, known as uterine 

 milk. This is particularly observable in separating the 

 foetal and maternal cotyledons. 



Uterine milk is of a white or rosy-white colour, creamy 

 consistence, and contains proteids, fat, and a small propor- 

 tion of ash. Examined microscopically it is found to con- 

 tain globules of fat, leucocytes, and rod-like crystals of 

 albumin-crystalloids, besides structureless masses of proteid 

 containing chromatin* The use of the fluid is described 

 by this authority as for the nourishment of the epithelial 

 cells of the chorion. 



Parturition.— The foetus having reached its full stage of 

 development, changes of an obscure nature take place, 

 which lead to it being expelled. Preparatory to this pro- 

 cess the foetus changes position ; for, from lying on its back 

 on the floor of the mare's abdomen, with its chin on its 

 chest, the fore-legs bent at the knee, and the hind-legs in 

 * Ellenberger, ' Physiologic' 



