FCETAL NUTRITION: THE PLACENTA 431 



and there is no free space, such as is described in the mare, between 

 them and the villi. The sub-epithelial tissue is represented in the 

 non-pregnant uterus' by a thin layer of dense connective tissue, with 

 localised thickenings in the burrs. With the onset of pregnancy 

 occur an infiltration of lymph between the more superficial celis 

 of the sub-epithelial layer, and an increase in the number and size 

 of the blood- capillaries and lymphatics. Thus the layer becomes 

 spongy and swells up around the foetal villi, producing the cotyle- 

 donary interdigitation. At the fundus of the crypts the lining cells 



m.y Tr Ic. 



FIG. 116. Section through the base of a fti'tal villus and the apices of two inter- 

 crypt columns. Sheep. The surfaces of the columns are traversed by 

 large blood-vessels, which later rupture and form the blood-extravasations. 

 (Assheton.) 



T>; Trophoblast dipping into crypt ; /<, inter-crypt column ; M.V, maternal 



blood-vessel. 



become syncytial. At the apices of the inter-en jit columns lacuna- 

 of maternal blood are formed by repeated small lui'innn-liairt's t'nun 

 the superficial capillaries (Fig. 116). 



In the inter-cotyledonary area, the epithelium, whether <>r imt it 

 'degenerates over large areas in the early stages as Assheton suppose^ 

 is later healthy and vigorous. There is no formation of a spongy 

 layer in the sub-epithelial tissue as in the burrs. But a great change 

 occurs in the glands, which are wholly inter-cotyledonary in position. 

 They increase in length and complexity, and secrete actively. T< \\ ; mis 

 the end of pregnancy, however, the greater part of the uterine glands 

 is destroyed, but the surface epithelium still secretes. At' the upper 

 end of each horn the w r all of the blastocyst forms a crumpled 



