CHAPTER XXVIL 



SEROUS MEMBRANES. 

 BY E. KLEIN. 



THE serous membranes in general are composed of an endo- 

 thelium and a basement membrane or matrix, with lymphatics, 

 bloodvessels, and nerves. 



A. ENDOTHELIUM. 



The free surface of all serous membranes is covered by 'a 

 single layer of cells. The mesentery, the serous portion of the 

 diaphragm, and in part the external lamina of the pericardium, 

 have an epithelium on both sides ; whilst the parietal portion 

 of the peritoneum, pleura, and dura mater have only a layer on 

 that side that is turned towards the cavity of the sacs they 

 form. As regards the external lamina of the pericardium, the 

 cell investment is by no means complete, though in Rabbits, 

 Cats, and new-born children it extends over a large, and in 

 Guinea-pigs over the greater portion of the external surface. 



Boehm (1) only admits the presence of a cell investment to 

 the dura mater in the Rabbit. In the Triton and Frog, inter- 

 vening between non-ciliated epithelial cells, on the parietal 

 portion of the peritoneum, on the mesentery, and in the last- 

 named animals, also on the abdominal surface of the wall (2) 

 of the cisterna magna, isolated, small, ciliated, tesselated cells 

 occur, together with groups of such cells. 



The isolated cells are moderately flat, and possess a rounded 

 or oblong, often excentrically situated, nucleus, the thickness 

 of which often exceeds that of the cell, generally causing the 



