124 LYMPHATIC SYSTEM. 



np of endothelium and membrana propria. The tendon con- 

 sists of two Ia3 r ers, of which the one that is next the perito- 

 neum is formed of bundles of fibres which radiate from the 

 centre outwards ; the upper layer of bundles arranged circu- 

 larly. The bundles of each are separated from their neighbors 

 by splits or channels, of which there are two sets ; those 

 between the abdominal layers being designated the superficial, 

 those of the pleural, the deep interfascicular channels of the 

 centrum tendineum. The membrana propria of the peritoneum, 

 where it stretches over the superficial channels, possesses a 

 special fenestrated structure (found also in one or two situa- 

 tions elsewhere). Between the propria of the pleural side and 

 the tendons, large lymphatic vessels exist which form numer- 

 ous ramifications, and communicate with a network of capil- 

 laries. All of the larger vessels are provided with valves, 

 with their corresponding dilatations. The capillaries maybe 

 distinguished into those which lie in the pleural propria, and 

 have a more or less winding course, and those which are 

 straight and lie further from the pleural surface. The former 

 have saccular dilatations, which are called lymphatic sinuses. 

 The straight vessels are contained in the channels already 

 described, and may, therefore, be designated lymphatics of 

 the interfascicular channels. They may be further distin- 

 guished, according as they are contained in the peritoneal or 

 pleural layer, into superficial and deep. There are many 

 channels of both layers which do not contain them. The two 

 sets of vessels are in communication with each other. The 

 superficial interfascicular lymphatics pass, in the neighborhood 

 of the great vessels which perforate the centrum tendineum, 

 into winding lymphatic capillaries with saccular dilatations, 

 which are situated on the abdominal surface of the tendon, 

 where they form a network. On the other hand, the interfas- 

 cicular lymphatics freely communicate with the peritoneal 

 cavity by means of vertical channels, which, although the3 r for 

 the most part extend only to the radiating tymphatics of the 

 superficial layer, can also, in many instances, be seen to pass 

 directty to those contained in the deeper, i. e., the circular 

 channels. By these canals the endothelium of the lymphatics 

 is continuous with that of the peritoneum. The endothelial 

 element's which guard the orifices of each vertical canal (the 

 stoma) have the characters of young cells, and differ from 

 those which adjoin them in being more granular, smaller, and 

 polyhedric. It has been already indicated, in Chapter II., 

 that the endothelium which covers the channels consists of 

 smaller and apparently younger elements than those of the 

 general surface. These characters are much more marked in 

 the cells which surround and form the stomata. In diaphragms 

 which have been stained without brushing, they cannot be 



