Ffi:TAL NUTRITION: THE PLACENTA 431 



and there is no free space, such as is clescrilied in the mare, Ijetween 

 them and the villi. Tlie sub-e[)ithehal tissue is represented in the 

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

 localised thickenings in the linrrs. Witli the onset of ])regnancy 

 occur an infiltration of lymph between the more superficial cells 

 of the sulj-epithelial layer, and an increase in the uumljer and size 

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

 spongy and swells up around the foetal \'illi, pr(jducing tlie cotyle- 

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



Fig. 116. — Section through the ba.se of a f(etal villus and the apices of two inter- 

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

 large blood-vessels, which latei- rupture and form the lilood-extraA'asations. 

 (Assheton.) 



Tr, Tiophobla.st dipping into crypt ; 1<:, inter-crypt column ; ;/(.(■, maternal 



blood-vessel. 



become syncytial. At the apices of the inter-crypt columns lacunte 

 of maternal blood are formed b}- repeated small luemorrhages from 

 the superficial capillaries (Fig. 110). 



In the iirter-cotyledonary area, the epithelium, whether or )iot it 

 degenerates over large areas in the early stages as Assheton supposes, 

 is later health}' and vigorous. There is no formation of a spongy 

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

 occurs in the glands, which are wholly intei-C(it)dedonary in position. 

 They increase in length and complexity, and secrete activel}'. Towards 

 the end of pregnancy, howevei', the greater pait of the uterine glands 

 is destroyed, but the surface epithelium still secretes. At the \ipper 

 end of each Inirn the wall of the blast(jcyst forms a crumpled 



