CH. XVIII.] 



LYMPHATICS. 



22 3 



The principal vessels of the lymphatic system are, in structure, 

 like small thin-walled veins, provided with numerous valves. The 

 beaded appearance of the lymphatic vessels shown in figs. 227 

 and 228 is due to the presence of these valves. They com- 

 mence in fine microscopic lymph-capillaries, in the organs and 



Fig. 228. Lymphatic vessels of the head and neck and the upper part of the trunk 

 (Mascagni). J. The chest and pericardium have been opened on the left side, and 

 the left mamma detached and thrown outwards over the left arm. so as to expose a 

 great part of its deep surface. The principal lymphatic vessels and glands are shown 

 on the side of the head and face oxid in the neck, axilla, and mediastinum. Between 

 the left internal jugular vein and the common carotid artery, the upper ascending part 

 of the t)ii>r.iri<' dud marked i, and above this, and descending to 2, the arch and last 

 part of the duct. The termination of the upper lymphatics of the diaphragm in the 

 tnediaxtinal glands, as well as the cardiac and the deep mammary lymphatic!), is also 

 liown. 



tissues of the body, and they end in two trunks which open 

 into the large veins near the heart (fig. 226). The fluid which 

 they contain, unlike the blood, passes only in one direction, 

 namely, from the fine branches to the trunk, and so to the 

 large veins, on entering which it is mingled with the stream 

 of blood and forms part of its constituents. In fig. 226 the 



