276 ABSORPTION LYMPH AND CHYLE. 



and the vessels are filled with colorless lymph during the intervals of diges- 

 tion. In many situations the lymphatics present in their course little, solid 

 structures, called lymphatic glands, although, as regards structure and office, 

 they are not true glandular organs. The smallest capillary lymphatics have 

 a diameter of about -g-J^ of an inch (83 /*). This may be taken as their aver- 

 age diameter in the primitive plexus. This plexus, when the vessels are 

 abundant, as they are in certain parts of the cutaneous surface, resembles an 

 ordinary plexus of capillary blood-vessels, except that the walls of the vessels 



FIG. 83. Lymphatic plexus, showing tlie endothelium (.Belaieft'j. 



are thinner and their diameter is greater. The vessels are lined by enclo- 

 thelial cells, the borders of which are brought into view by the action of sil- 

 ver nitrate, as is shown in Fig. 83. 



The smallest lymphatic vessels are by far the most abundant. They are 

 arranged in the form of a fine plexus, very superficially situated in the skin. 

 A second plexus exists just beneath the skin, composed of vessels of much 

 greater diameter. The skin is thus enclosed between two plexuses of capil- 

 lary lymphatics. A plexus analogous to the superficial plexus of the skin is 

 found just beneath the surface of the mucous membranes. These may, in- 

 deed, be classed with the superficial lymphatics. The deep lymphatics are 

 much larger and less abundant, and their origin is less easily made out. 

 These accompany the deeper veins in their course. They receive the lymph 

 from the superficial vessels. 



No valvular arrangement is found in the smallest lymphatics ; but the 

 vessels coming from the primitive plexuses, as well as the large vessels, con- 

 tain valves in great numbers. These valves, being so closely set in the ves- 

 sels, give to them, when filled with injection, a peculiar and characteristic 

 beaded appearance. 



