

690 ANGIOLOGY 



between them, are much larger than those of the capillary plexus. From these 

 net-works small vessels emerge, which pass, either to a neighboring gland, or to 

 join some larger lymphatic trunk. The deep lymphatic vessels, fewer in number, 

 but larger than the superficial, accompany the deep bloodvessels. Their mode of 

 origin is probably similar to that of the superficial vessels. The lymphatic vessels 

 of any part or organ exceed the veins in number, but in size they are much smaller. 

 Their anastomoses also, especially those of the large trunks, are more frequent, 

 and are effected by vessels equal in diameter to those which they connect, the con- 

 tinuous trunks retaining the same diameter. 



Hemolymph nodes or glands and hemal nodes which are so abundant in some 

 mammals are probably not present in man. 



Lymph. Lymph, found only in the closed lymphatic vessels, is a transparent, 

 colorless, or slightly yellow, watery fluid of specific gravity about 1.015; it closely 

 resembles the blood plasma, but is more dilute. When it is examined under the 

 microscope, leucocytes of the lymphocyte class are found floating in the transparent 

 fluid ; they are always increased in number after the passage of the lymph through 

 lymphoid tissue, as in lymph glands. Lymph should be distinguished from " tissue 

 fluid" 1 which is found outside the lymphatic vessels in the tissue spaces. 



THE THORACIC DUCT. 



The thoracic duct (ductus thoracicus) (Fig. 599) conveys the greater part of the 

 lymph and chyle into the blood. It is the common trunk of all the lymphatic 

 vessels of the body, excepting those on the right side of the head, neck, and thorax, 

 and right upper extremity, the right lung, right side of the heart, and the convex 

 surface of the liver. In the adult it varies in length from 38 to 45 cm. and extends 

 from the second lumbar vertebra to the root of the neck. It begins in the abdomen 

 by a triangular dilatation, the cisterna chyli, which is situated on the front of the 

 body of the second lumbar vertebra, to the right side of and behind the aorta, 

 by the side of the right cms of the diaphragm. It enters the thorax through the 

 aortic hiatus of the diaphragm, and ascends through the posterior mediastinal 

 cavity between the aorta and azygos vein. Behind it in this region are the vertebral 

 column, the right intercostal arteries, and the hemiazygos veins as they cross to 

 open into the azygos vein; in front of it are the diaphragm, esophagus, and peri- 

 cardium, the last being separated from it by a recess of the right pleural cavity. 

 Opposite the fifth thoracic vertebra, it inclines toward the left side, enters the supe- 

 rior mediastinal cavity, and ascends behind the aortic arch and the thoracic part 

 of the left subclavian artery and between the left side of the esophagus and the 

 left pleura, to the upper orifice of the thorax. Passing into the neck it forms an 

 arch which rises about 3 or 4 cm. above the clavicle and crosses anterior to the 

 subclavian artery, the vertebral artery and vein, and the thyrocervical trunk or 

 its branches. It also passes in front of the phrenic nerve and the medial border 

 of the Scalenus anterior, but is separated from these two structures by the pre- 

 vertebral fascia. In front of it are the left common carotid artery, vagus nerve, 

 and internal jugular vein; it ends by opening into the angle of junction of the left 

 subclavian vein with the left internal jugular vein. The thoracic duct, at its com- 

 mencement, is about equal in diameter to a goose-quill, but it diminishes consid- 

 erably in caliber in the middle of the thorax, and is again dilated just before its 

 termination. It is generally flexuous, and constricted at intervals so as to present 

 a varicose appearance. Not infrequently it divides in the middle of its course into 

 two vessels of unequal size which soon reunite, or into several branches which form 



: Sabin, Harvey Lecture, Series ix, New York, 1915-16. 



