ABSORPTION. 



215 



freely with adjoining vessels. The diameter of a lymph-vessel 

 varies from i to 2 mm. After the lymphatics have emerged from 

 the lymph -capillaries they acquire three distinct coats, each of which 

 possesses definite histologic features. 



The internal coat is composed of a delicate lamina of longitudinally 

 disposed elastic fibers covered with a layer of flattened nucleated 

 endothelial cells with wavy outlines. 



The middle coat consists of white fibrous tissue arranged longi- 



-LYMPH-VESSELS AND LYMPH-GLANDS OF THE HEAD AND NECK. (From 

 Gould's Dictionary,} 



tudinally and of non-striated muscle and elastic fibers arranged 

 transversely. 



The external coat consists of practically the same structures, though 

 the ^muscle-fibers are longitudinally disposed. 



f The lymphatics are provided with valves which are so numerou^ 

 and located at such short intervals as to give the vessels a beaded 

 appearance. ^ These valves are arranged inrjairs and consist of two 

 semilunar folds with their concavities directed toward the larger 

 vessels. They are formed by a reduplication of the lining membrane, 



