130 



tion of their possible relation to the nutrition of the embryo I 

 must defer to the physiological part of this paper. 



The blood vessels which permeate the subepithelial tissue are 

 lined by a simple flat eudothelium. Round the whole is a layer 

 of circular muscles which at the root of the mesometrium tends 

 to become irregular aud broken up; here there are to be found 

 numerous connective tissue cells and among them the iron-con- 

 taining cells already mentioned; next cotne lymph spaces aud outside 

 all is a layer of longitudinal muscles, and the peritoneal epithelium. 



After parturition the tissue is exceedingly loose, the cells being 

 widely separate from one another; but at other times it is more 

 compact, and if fertilization has taken place, the cells become 

 more and more crowded together, preparatory to undergoing that 

 intense proliferation which occurs immediately before, and during 

 the fixation of the embryo. 



At about the sixth day, when the embryo is still free, the fol- 

 lowing changes begin. First the subepithelial cells become crowded 

 together and flattened round the lumen of the uterus, round the 

 glands, and round the blood vessels. Secondly, the embryo is 

 found situated in a small depression or pit on the anti-mesometric 

 side of the uterus lumen. The epithelium which lines this pit is 

 already beginning to degenerate, and the degeneration first sets 

 in those portions of it against which the trophoblast of the embryo 

 lies. All the stages of this process may be successively studied 

 by passing from the normal epithelium, by which the ordinary 

 lumeu of the uterus is still lined, down the side of the pit. 

 The cells become first cubical, and then flattened, their nuclei be- 

 come rounded and more intensely stained while the chromatin 

 becomes aggregated into irregular masses, and the small fat-globules 

 appear to run together into larger ones (the increase in size of 

 the fat-globules may be also due to fatty degeneration); ulti- 

 mately the cells become detached, and drop into the lumen of 

 the embryonic pit. (Pigs. 13 — 15). 



Extensive changes are at the same time taking place in the 

 subepithelial tissue, which is now everywhere, but more especially 





