CHAP. XXVI.] THE ABSOKBENT VESSELS. 271 



undoubtedly concerned in the absorption of a part at least of the 

 nutrient matters of the food their contents (chyle) after a meal 

 being of a milky appearance whence their name, vasa lactea, 

 given to them in 1622 by their discoverer, Asellius. The lymphatics 

 (and the lacteals during fasting) contain a pellucid fluid the 

 lymph. 



The lacteals originate in the mucous membrane of the intestines, 

 especially in the villi, and form a network with close meshes in the 

 submucous areolar tissue. There are also more superficial ones 

 between the peritoneum and muscular coat, which take a more 

 longitudinal course, and join the other on the mesentery. They 

 then pass in great numbers between the layers of the mesentery 

 towards its root, anastomosing with one another and traversing 

 glandular organs, the mesenteric glands, in their way to the right 

 side of the aorta, where they all finally discharge themselves into 

 an elongated pouch common to them and to the lymphatics of 

 the parts below termed the receptaculum chyli. From this the 

 thoracic duct leads upwards to the left subclavian vein. 



The receptaculum is usually from an inch to an inch and a half 

 in length, and from a quarter to three-eighths of an inch in 

 diameter. The thoracic duct, which is continued upwards from it, 

 lies in the chest between the aorta and vena azygos, then inclines 

 behind the arch of the aorta to the left side, and empties itself into 

 the upper and back part of the left subclavian vein close to the 

 internal jugular vein, its orifice being defended by two valves. The 

 thoracic duct is about an eighth of an inch or more wide, becomes 

 more narrow up to the sixth dorsal vertebra, and again dilates 

 opposite the third. It frequently divides into branches which 

 reunite and sometimes opens into the subclavian vein by two or 

 even three separate trunks. 



The lymphatic vessels of the upper and lower extremities form 

 two sets, a deep one accompanying the deep blood-vessels, and a 

 superficial one running in the deeper layer of the superficial fascia. 

 These sets anastomose and pass in common to the trunk by the 

 groin and axilla, where numerous glands occur upon them. (1) 

 Those of the lower extremities after passing under Poupart's 

 ligament, follow the great blood-vessels, are joined by others from 

 the pelvis, loins, and abdominal walls and viscera, and open into 

 the receptaculum chyli by from four to six large trunks. Very 

 numerous glands succeed each other in their course, forming an 

 irregular chain. The thoracic duct is joined by lymphatics from 

 the left side of the walls of the chest, and from the heart and left 



