FOETAL NUTRITION : THE PLACENTA 399 



In the inter-eotyledonary area, the epithelium, whether or 

 not it degenerates over large areas in the early stages as 

 Assheton supposes, 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. Towards the end of 



my. Tr Ic. 



FIG. 91. Section through the base of a fcetal 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-extravasa- 

 tions. (Assheton.) 



Tr, trophoblast dipping into crypt ; /r, inter-crypt column ; m.v, maternal 



blood-vessel. 



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 wall of the blastocyst forms a 

 crumpled 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- 



