126 NORMAL HISTOLOGY AND ORGANOGRAPHY. 



therefore, histologically, resemble the blood-capil- 

 laries. They are not so well defined but represent 

 rather irregular cavities with numerous constrictions. 

 These capillaries, according to one theory, form a 

 closed system and open only into the larger vessels. 



Fig. 90. From a human lymph gland. At a are seen the con- 

 centrically arranged cells of the lymph nodules (fixation with Flem 

 ming's fluid) (Bohm and Davidoff). 



Another theory is that at their origin they communi- 

 cate with intercellular spaces. 



2. Lymphatic Vessels. These accompany blood- 

 vessels and have very thin walls. Ultimately they 

 drain into the large thoracic lymph duct or the short 

 right lymphatic duct; each finally opens into the 

 venous system at the junction of the subclavian and 

 jugular veins. The thoracic duct begins with the 

 receptaculum chili, just below the diaphragm and a 

 little to the right of the vertebrae, passes upward into 

 the thorax to open into the venous system on the 



