LYMPHATIC GLANDS. 



121 



chyle, but where they took 

 it and what became of it he 

 did not know. 



Eustachius, in 1564, dis- 

 covered in the horse the 

 thoracic duct, which he 

 called vena alba thoracica, 

 the white vein of the chest, 

 not knowing its use. Wes- 

 lingius, in 1649, found 

 that the chyle vessels or 

 lacteals of Aselius, termin- 

 ated in the thoracic duct. 

 By the labors of Monro, 

 Hunter, with others, and 

 especially Mascagni, the 

 lymphatic vessels have been 

 demonstrated as extending 

 to almost every part of the 

 body, the only parts in 

 which they have not been 

 seen are the brain, spinal 

 marrow, ball of the eye, and 

 placenta. The lymphatics 

 have been considered as an 

 appendage to the venous 

 system. They resemble the 

 veins in having the same 

 structure, though their coats are more delicate. Like 

 veins, they have numerous valves which give them a 

 knotted appearance. Their currents are in the same di- 

 rection, and terminate in veins. But they differ from 

 veins in passing through glands, in being less tortuous, 



FIG. 18 represents the formation and course of the thoracic duct. 



a Termination of thoracic duct. 6 Its separation into two ducts, which again 

 unite, c Lower end of duct, d Left azygos vein, e Right azygos. / Inter- 

 costal veins entering right azygos. g h i j Correspond to numerous lacteals 

 and lymphatics, which go to form the commencement of the thoracic duct. 



