ANATOMY 0F THE LACTEAL AND LYMPHATIC VESSELS. 279 



strated in great abundance. Lymphatics have been demonstrated taking 

 their origin in the voluntary muscles, the diaphragm, the heart and the non- 

 striated muscular coats of the hollow viscera, although their investigation in 

 these situations is difficult. 



Lymphatics are found coming from the lungs in great numbers. These 

 arise in the walls of the air-cells and surround each pulmonary lobule with a 

 close plexus. The deep vessels follow the course of the bronchial tubes, 

 passing through the bronchial glands and the glands at the bifurcation of the 

 trachea, to empty into the thoracic duct and the great lymphatic duct of the 

 right side. 



In the glandular system, including the ductless glands, and in the ovaries, 

 the lymphatic vessels are, as a rule, more abundant than in any other parts 

 of the body. They are especially abundant in the testicles, the ovaries, the 

 liver and the kidneys. 



The lymphatic vessels from the superficial and deep portions of the head 

 and face on the right side, and those from 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 lym- 

 phaticus dexter, which empties into the venous system at the junction of 

 the right subclavian with the internal jugular. This vessel is about an inch 

 (25'4 mm.) in length and one-twelfth to one-eighth of an inch (2 to 3 mm.) 

 in diameter. It is provided 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, the abdominal organs generally and the left half 

 of the body above the abdomen empty 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 in some other parts. Two to six vessels, called the 

 vasa afferentia, penetrate each gland, having first broken up into a number 

 of smaller vessels just before they enter. 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 intes- 

 tine 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 most of the lymphatic vessels empty, is a 

 vessel with very delicate walls and about the size of a goose-quill. It begins 

 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 semicircular curve something like the arch of the aorta, and 

 empties at the junction of the left subclavian with the internal jugular vein. 



