432 THE PHYSIOLOGY OF REPRODUCTION 



structureless membrane with no trace of nuclei, while the uterine 

 mucosa in this region is thrown into folds and covered with a high 

 columnar epithelium which is very active. The secretion is apparently 

 transmitted by transfusion through the membranous wall, and is 

 found inside the sac. At full time this part of the mucosa shows 

 signs of great degeneration, resembling the pulpe diffluente of Duval 

 in the guinea-pig (Assheton). The inter - glandular cells also 

 hypertrophy like the connective tissue cells of Rodents. 



The development and structure of the placenta of the sheep have 

 been described at some length because the formation of the special 

 nutriment for the foetus has received close attention in that 

 animal. 1 



C.ow. In the cow (Fig. 117) the placenta has essentially the same 

 form as in the sheep, but the interlocking is not so firm. On separation 

 of the maternal and foetal parts of the cotyledons, the former are 

 found to comprise the larger part. In the fully developed sheep's 

 placenta the foetal parts constitute the main mass of the cotyledon. 

 The various stages of development have not been completely investi- 

 gated, but one other difference has been noted, viz/ the absence of 

 lacuiue of maternal blood at the bases of the villi (Ledermann 2 ). 



The chorionic sac extends into both uterine cornua. 



The inter-cotyledonary trophoblast is avillous in the sheep and 

 cow. In the giraffe, however, there are rows and clusters of villi in 

 addition to the cotyledonary villi. Simple villi between the cotyledons 

 are also found in Ccrvus, Orcas, and Tetraceros? 



The Uterine Milk 



The existence of a nutritive juice in the uterus of Ruminants 

 during pregnancy has been recognised since the days of Harvey. He 

 spoke of an albuminous fluid, which might be squeezed out from the 

 cotyledons of the placenta, as a source of nutriment for the foetus. 

 As to its origin, he says in one of his Letters : " It might be transported 

 by the uterine arteries and distilled into the uterus." The fluid was 

 first called uterine milk by Needham in 1667. Haller described it as 

 a secretion of the utricular glands, and this view was supported by 

 Bischoff, Sharpey, and others, who considered it the immediate store 



1 For the above account of the development and structure of the sheep's 

 placenta, we are largely indebted to the important memoir of Assheton. Differ- 

 ing in many respects from previous descriptions, it alone brings forward evidence 

 that the Ungulate placenta may be "secondarily simplified" in Hubrecht's 

 sense (see Quar. Jour. Micr. Science, ] 908). 



2 Ledermann, " Ueber den Ban der Cotyledonen im Uterus von Bos, etc.," 

 Inaug.-Dis., Berlin, 1903. 



3 Turner, "On the F<etal Membrane of the Eland (Oreas canna)" Jour, of 

 Anat. and Pkys., vol. xiv., 1879. Weldon, " Note on the Placentation of 

 Tetraceros quadricomis" Proc. Zool. #oc., 1884. 



