THE LYMPHATIC SYSTEM. 317 



place incessantly throughout the body, are intimately connected 

 with the action of the great absorbent or lymphatic system of ves- 

 sels, which is to be considered as secondary or complementary to 

 that of the sanguiferous circulation. 



The lymphatics may be regarded as a system of vessels, com- 

 mencing in the substance of the various tissues and organs, and 

 endowed with the property of absorbing certain of their ingredi- 

 ents. Their commencement has been demonstrated by injections, 

 more particularly in the membranous parts of the body ; viz., in 

 the skin, the mucous membranes, the serous and synovial surfaces, 

 and the inner tunic of the arteries and veins. They originate in 

 these situations by vascular networks, not very unlike those of the 

 capillary bloodvessels. Notwithstanding this resemblance in form 

 between the capillary plexuses of the lymphatics and the blood- 

 vessels, it is most probable that they are anatomically distinct from 

 each other. It has been supposed, at various times, that there 

 might be communications between them, and even that the lymph- 

 atic plexus might be a direct continuation of that originating from 

 the smaller arteries ; but this has never been demonstrated, and it 

 is now almost universally conceded that the anatomical evidence is 

 in favor of a complete separation between the two vascular systems. 



Commencing in this way in the substance of the tissues, by a 

 vascular network, the minute lymphatics unite gradually with each 

 other to form larger vessels ; and, after continuing their course for 

 a certain distance from without inward, they enter and are distri- 

 buted to the substance of the lymphatic glands. According to M. 

 Colin, 1 beside the more minute and convoluted vessels in each gland, 

 there are always some larger branches which pass directly through 

 its substance, from the afferent to the efferent vessels ; so that only 

 a portion of the lymph is distributed to its ultimate glandular 

 plexus. This portion, however, in passing through the organ, is 

 evidently subjected to some glandular influence, which may serve 

 to modify its composition. 



After passing through these glandular organs, the lymphatic 

 vessels unite into two great trunks (Fig. 43) : the thoracic duct, which 

 collects the fluid from the absorbents of the lower extremities, the 

 intestines and other abdominal organs, the chest, the left upper 

 extremity, and the left side of the head and neck, and terminates 

 in the left subclavian vein, at the junction of the internal jugular ; 

 and the right lymphatic duct, which collects the fluid from the right 



1 Physiologic comparer des Animaux domestiques, Paris, 185H, vol. ii. p. 68. 



