226 THE LYMPHATIC SYSTEM 



subarachnoid space (see Coverings of Brain and Spinal 

 Cord), whereupon it is taken up by the lymphatic 

 vessels. 



Lymph Capillaries. These are the connecting 

 vessels between the lymph spaces and the lymphatic 

 vessels proper. They are thin-walled vessels, which 

 consist of a single layer of endothelial cells. They 

 are arranged in plexuses interwoven with the blood 

 capillaries, and can be easily distinguished from them 

 by their larger size and irregular expansJons. 



The blood capillaries, in relation with the lymph 

 capillaries, permit of a transudation of the nutritive 

 elements of the blood through their thin walls, and at 

 the same time assist in the reabsorption of a portion 

 of this transudate and waste products resulting from 

 metabolism. 



The Lymphatic Vessels. They are arranged into 

 a superficial and deep set. The superficial set pass 

 just beneath the skin and follow the course of the 

 superficial veins, some pierce the fascia to communi- 

 cate with the deep set. These drain the surfaces of 

 the head, neck, trunk, and extremities. The deep 

 set follow the course of the deeper bloodvessels, and 

 drain the adjacent tissues. In the interior of the 

 trunk the lymphatics are found in the submucous 

 layer of the mucous membrane of the alimentary 

 canal and respiratory apparatus, also the genito- 

 urinary tract kidney, bladder, etc. 



The lymphatic vessels are seen as a net-work of 

 minute vessels, larger than the capillary vessels, in 

 the above-mentioned tissues and organs. The lymph 

 is conveyed through these lymph capillaries to larger 

 .vessels called lymphatics, which pass to small glandular 

 bodies called lymph nodes or lymphatic glands. 



The deep lymphatic vessels have the same origin 

 as the superficial set, but are fewer in number and 

 larger. They also drain into the lymph nodes. 



The lymph vessels are composed of three coats: 



