298 THE LYMPHATIC SYSTEM, BY F. v. RECKLINGHAUSEN. 



The difference in the amount of these two pressures consti- 

 tutes an essential factor in the production of the movement of 

 the lymph ; so that the greater the difference, the more rapid 

 is the movement. The lymphatic vascular system borrows its 

 contents, as well as the impulsive force under which they move, 

 from the blood vascular system ; and in so far it may be re- 

 garded as an appendage of, or as an accessory closed system 

 to, the blood vascular apparatus. 



The dependency of the lymphatic system on the bloodves- 

 sels is indicated by the circumstance that, as a general rule, the 

 lymphatic system in any organ is so much the more strongly 

 developed in proportion as its supply of bloodvessels (mucous 

 and serous membranes, skin, glands) is more abundant; but there 

 are also organs characterised by a peculiar richness in lymphatic 

 vessels, which are at the same time especially adapted for ab- 

 sorption (gastric and intestinal mucous membrane, central ten- 

 don of the diaphragm). 



The entire lymphatic system may be divided into two sec- 

 tions ; the first containing the fluid which, immediately after 

 its escape from the bloodvessels, circulates around the several 

 elements of the organs, the interstitial serous spaces ; and, 

 secondly, the system of the efferent canals, the proper lympha- 

 tic vessels. This second section will be here first described, 

 because its structure is much more accurately known. 



The efferent canals, or lymphatic vessels, ordinarily agree in 

 their form, arrangement, and in the structure of their walls 

 with the bloodvessels. In the greater number of organs they 

 form plexuses, which are so much the more close, the more 

 abundantly the tissues are supplied with bloodvessels : more- 

 over they only occur in association with bloodvessels ; and 

 those tissues which are destitute of bloodvessels, like the cor- 

 nea, vitreous humour, and epithelial tissues, possess also no 

 proper lymphatics. Like the bloodvessels, they generally form 

 cylindrical tubes, and only in certain regions, hereafter to be 

 described, present the characters of fissures or lacunse, under 

 which condition, however, they not unfrequently form investing 

 sheaths for different organs. The lymph vessels may be dis- 

 tinguished for the purposes of description into the smallest 

 branches, the capillaries which are intercalated between the 



