FGETAL NUTRITION: THE PLACENTA 453 



by special characteristics of the uterine mucosa. They differ 

 from the cotyledonary burrs, however, in being proliferations 

 of the surface epithelium. Before the fertilised ova reach the 

 uterus, there are variations in thickness in the mucosa. It is 

 thin at the mesometrial and anti-mesometrial sections, but~ 

 thickened over the sides to form two cushions, in which the 

 blood-vessels are more numerous. No glands are present near 

 the mesometrium. They are collected on the opposite surface 

 and open into a longitudinal anti-mesometrial groove (Fig. 114). 



U.E. 



FIG. 115. Part of the anti-mesometrial wall of the uterus of Sorex 

 (Hubrecht). The proliferated epithelium is arranged in a radial fashion, 

 and later it forms a secondary crypt (Cr.), when the uterine epithelium 

 (U.E.) gives way over it. 



When the blastocysts reach the uterus, further changes 

 take place. Both the lateral regions increase in thickness by the 

 proliferation of connective tissue cells and the formation of new 

 vessels, while the anti-mesometrial part is widened out into a 

 concave bell-shaped surface into which the glands open. Then 

 the epithelium proliferates, first in the lateral cushions and 

 later in the concave area. In the former the proliferation 

 reaches a thickness of twelve to eighteen cells, and the new 

 elements pass in among the cells and vessels of the deeper 

 layers. In the allantoidean region, the bell-shaped area, the 

 proliferation also leads to a thick epithelial layer with vascular 

 channels between the cells. At intervals, however, the cells are 



