ANATOMY OF SEROUS MEMBRANES. 149 



The omentum and the mediastinal pleura are constructed 

 in a perfectly similar manner. 



The omentum has lymphatic vessels, which in the neigh- 

 bourhood of the greater curvature of the stomach form an 

 abundant network. In the rest of the omentum, a few single 

 lymphatic trunks are found corresponding to the large blood 

 vascular trunks, and these are connected together by lateral 

 vessels. In the rabbit the lymphatic vessels in general are 

 abundant. In the guinea-pig, cat, dog, and monkey, larger 

 or smaller spots are found in the normal condition where the 

 endothelial cells are not pale plates, but have a youthful 

 appearance ; the individual cells are cubical, and consist of a 

 granular protoplasma enclosing a single, oblong, partly divided 

 or double nucleus. 



The trabecules of the fenestrated portion are in this respect 

 especially instructive ; spots may here be found where a pro- 

 liferation of the endothelium is clearly demonstrable, that is 

 to say, there may be seen budlike masses of various size, 

 consisting of young endothelial cells. The same appearances 

 are presented on and near the cords in the fatty lobules, which 

 contain the larger blood-vessels, and in nodular structures more 

 or less raised above the surface, which are partly connected 

 with the large Vascular cords, and partly occur isolated in the 

 fenestrated portions. The mesogastrium of the frog exhibits 

 the same phenomena, only that here the young endothelial 

 cells are ciliated.^ 



The endothelial cells have this character in every part where 

 true stomata or pseudo-stomata are to be found. This is the 

 case in the fenestrated omentum only near the pseudo-stomata, 

 in other parts both near the true and the pseudo-stomata. 

 In the rabbit the endothelium shows the same character in 

 certain moi'e or less clearly defined, flat, tablet-shaped struc- 

 tures, and in the cords containing the blood- and lymph- 

 vessels. 



The cellular structures of the connective-tissue of the 

 omentum may be, generally speaking, like those of the centrum 

 tendineum, separated into two layers. The one situated under 

 the endothelium consists of large flat branched cells which in 

 some parts lie closer together, and possess shorter and fewer 

 processes, and are even occasionally so closely set as to be sepa- 

 rated only by their cement lines. In the latter case we find 

 under the endothelium of the surface a more or less clearly 

 defined spot where treatment with silver produces the same 

 appearance as in the lymph-capillaries of the centrum ten- 

 dineum. It is, in fact, nothing but a lacuna, which as we 

 * See a notice by E. Klein in the last number of this Journal, 



