442 THE RABBIT. 



carried away by efferent vessels which open into the uterine 

 veins. 



The foetal or allantoic vessels, aa, pass between the several 

 lobules to their outer ends, and then return as thin-walled 

 capillaries, which pass through the lobules, lying between the 

 tubules into which these are divided ; on reaching the inner 

 surface of the uterus the capillaries open into the allantoic veins, 

 VA, which return the blood from the placenta to the embryo. 



In the later stages, from the twenty-fifth to the thirtieth day, 

 the chief changes consist in the gradual thinning of the parti- 

 tions separating the foetal and maternal streams in the lobules. 

 The ectoplacental wall becomes gradually absorbed, more and 

 more completely, until ultimately, according to Duval, a single 

 layer of epithelial cells, the endothelial wall of the foetal capil- 

 lary, is alone left between the two streams of blood. 



The changes that occur in the deeper, or submucous part 

 of the placenta require further notice. In the early stages 

 (Fig. 169), the submucous layer is very thick, and the ecto- 

 placenta very thin. By the nineteenth day (Fig. 170) the two 

 have become of about equal thickness. From this time the 

 submucous layer is the thinner of the two, and towards the 

 close of gestation it becomes comparatively insignificant. 



The chief changes that occur in the submucous layer during 

 these later stages are : — a still further dilatation of the capillary 

 vessels ; an increase in the decidual cells surrounding the capil- 

 laries ; and the appearance in the subglandular region of a layer 

 of special cells, spoken of as glycogenous cells. These latter 

 are large, roundish, or ovoid vesicular bodies, each consisting of 

 an outer capsule and a central multinucleate protoplasmic body,, 

 from which strands of protoplasm radiate outwards to the cap- 

 sule. In the meshes between the strands lie faintly glistening 

 glycogen masses. Each of these glycogenous cells is said to be 

 formed by the fusion of a number, from three to six, of origi- 

 nally separate cells. 



The perivascular and glycogenous cells are probably to be- 

 regarded as having some function in connection with the ela- 

 boration, or preparation, of the maternal blood, before it is sent 

 to the placenta for the nourishment of the embryo. The blood 



