ANATOMY OF LYMPHATIC AND LACTEAL VESSELS 



245 



tive plexuses, the elasticity of the walls of the vessels renders their 

 diameter greatly dependent on the pressure of liquid in their interior. 

 Many anatomists have noticed that vessels which are hardly perceptible 

 while empty are capable of being dilated to the diameter of half a line 

 (about i millimeter) or more, returning to their original size so soon as 

 the distending liquid is 

 removed. 



In the lymphatics of 

 the skin, the only impor- 

 tant peculiarity not yet 

 mentioned is that the 

 vessels appear to be un- 

 equally distributed in dif- 

 ferent parts of the surface. 

 They are particularly 

 abundant in the scalp over 

 the biparietal suture, the 

 soles of the feet and the 

 palms of the hand, the fin- 

 gers at the lateral portion 

 of the last phalanges, and 

 the scrotum. In the me- 

 dian portion of the scro- 

 tum they attain their 

 highest degree of devel- 

 opment. They are also 

 found, though in less 

 number, originating from 

 around the median line on 

 the anterior and posterior 

 surface of the trunk, the 

 posterior median portion 



Of the extremities, the Fig- 55- Superficial lym- Fig. 56. Superficial lym- 

 , . ., phaties of the arm (Sappey). phatics of the leg (Sappev). 



skin over the mammae 



and around the orifices of the mucous passages. Lymphatic vessels 

 have been demonstrated in the anterior portion of the forearm, the 

 thigh and the leg, and in the middle portion of the face, although they 

 are demonstrated with difficulty in these situations. If they exist at all 

 in other portions of the cutaneous surface, they are not abundant. 



In the mucous membranes the lymphatics are very abundant. 

 Here are found, as in the skin, two distinct layers which enclose 

 between them the entire thickness of the mucous membrane. The 



