ANATOMY OF THE LACTEAL AND LYMPHATIC SYSTEM. 435 



the superficial and deep portions of the right arm, the right 

 half of the chest, and the mammary gland, with a few vessels 

 from the lungs, pass into the great lymphatic duct (ductus 

 lymphaticus dexter), which empties into the venous system 

 at the junction of the right subclavian with the internal 

 jugular. This vessel is about an inch in length and from 

 one-twelfth to one-eighth of an inch in diameter. It is pro- 

 vided with a pair of semilunar valves at its opening into 

 the veins, which effectually prevent the ingress of blood. 



The vessels from the inferior extremities, and those from 

 the lower portions of the trunk, the pelvic viscera, and the 

 abdominal organs, generally pass into the thoracic duct. In 

 their course, all of the lymphatics pass through the small, 

 flattened, oval bodies, called the lymphatic glands, which are 

 so abundant in the groin, the axilla, the pelvis, and some 

 other parts. From two to six vessels, called the vasa affer- 

 entia, enter these bodies, having first broken up into a num- 

 ber of smaller vessels just before they pass in. They pass 

 out by a number of small vessels which unite to form one, 

 two, or three trunks, generally of larger size than the vasa 

 afferentia. The vessels which thus .emerge from the glands 

 are called vasa efferentia. 



The lymphatics of the small intestine, called lacteals, pass 

 from the intestine between the folds of the mesentery to 

 empty, sometimes by one, and sometimes by four or five 

 trunks, into the receptaculum chyli. In their course, the 

 lacteals pass through several sets of lymphatic glands, which 

 are here called mesenteric glands. 



The thoracic duct, into which the great majority of the 

 lymphatic vessels empty, is a vessel with exceedingly delicate 

 walls, and about the size of a goose-quill. It commences by a 

 dilatation more or less marked, called the receptaculum chyli. 

 This is situated upon the second lumbar vertebra. The canal 

 passes upward in the median line for the inferior half of its 

 length. It then inclines to the left side, forms a semicircu- 

 lar curve something like the arch of the aorta, and empties at 



