NOURISHING MEMBRANES 



493 



With the naked eye, it can be seen that the entire inner surface of the 

 uterus is thrown into a series of flat circular flaps, or papillae, and a good- 

 sized blood vessel can be seen passing along the edge of each flap. The 

 true line of junction of the flap to the wall is always longitudinal, and it 

 can be seen at a glance that this surface amplification affords more than 

 double the original surface of the cavity. 



Sections taken transversely to the uterus, and consequently to the 

 papillae, show the flaps in cross section with the blood vessel in the outer 

 edge (Fig. 462, ^4). The body of the evagination is of loose connective 

 tissue and covered with a very thin stratified epithelium. In the base 



FIG. 462. Acanthias vulgaris; A, Diagrammatic figure of part of a section of the wall of the 

 pregnant oviduct (uterus), taken transversely to the length of the tube; bl, blood vessels; 

 ep, respiratory epithelium. Lower layers are connective tissue, and longitudinal and circu- 

 lar muscle layers covered by a layer of epithelium (peritoneum). Black lines in top of 

 papilla indicate the region which is shown under greater magnification in B. B, Small 

 portion of the wall which lies between the uterine fluid and the large blood vessel on edge 

 of a papilla; bl, blood capillaries in outer epithelium. A, X 20. B, X 500. 



of each papilla is another vessel, usually empty or with but a few red 

 blood corpuscles in its lumen. It is nearly as large as the arterial loop 

 out in the edge, and is the vein which returns the blood to the circulatory 

 system. 



The passage of the blood from the superficial loop of artery to the 

 lower and more internal vein is the interesting structural feature of the 

 tissue (Fig. 462, B). It does not flow through the body of the connective 

 tissue, which is barely supplied with circulation, but enters a plexus of 

 capillaries just under the stratified epithelium and so close to it that a 

 separating blood-vessel wall is hardly discernible. The blood appar- 

 ently flows in contact with, or even within, the epithelium, which is 

 weakly stratified. These channels proceed from the top of the papilla 



