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2. The Thoractic Duct
FIG. 599 - The thoracic and right lymphatic ducts. 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 crus 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 pericardium, 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 superior 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 prevertebral 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 commencement, is about equal in diameter to a goose-quill, but it diminishes considerably 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 a plexiform interlacement. It occasionally divides at its upper part into two branches, right and left; the left ending in the usual manner, while the right opens into the right subclavian vein, in connection with the right lymphatic duct. The thoracic duct has several valves; at its termination it is provided with a pair, the free borders of which are turned toward the vein, so as to prevent the passage of venous blood into the duct. The cisterna chyli (receptaculum chyli) (Fig. 600) receives the two lumbar lymphatic trunks, right and left, and the intestinal lymphatic trunk. The lumbar trunks are formed by the union of the efferent vessels from the lateral aortic lymph glands. They receive the lymph from the lower limbs, from the walls and viscera of the pelvis, from the kidneys and suprarenal glands and the deep lymphatics of the greater part of the abdominal wall. The intestinal trunk receives the lymph from the stomach and intestine, from the pancreas and spleen, and from the lower and front part of the liver. Tributaries.—Opening into the commencement of the thoracic duct, on either side, is a descending trunk from the posterior intercostal lymph glands of the lower six or seven intercostal spaces. In the thorax the duct is joined, on either side, by a trunk which drains the upper lumbar lymph glands and pierces the crus of the diaphragm. It also receives the efferents from the posterior mediastinal lymph glands and from the posterior intercostal lymph glands of the upper six left spaces. In the neck it is joined by the left jugular and left subclavian trunks, and sometimes by the left bronchomediastinal trunk; the last-named, however, usually opens independently into the junction of the left subclavian and internal jugular veins. The right lymphatic duct (ductus lymphaticus dexter) (Fig. 601), about 1.25 cm. in length, courses along the medial border of the Scalenus anterior at the root of the neck and ends in the right subclavian vein, at its angle of junction with the right internal jugular vein. Its orifice is guarded by two semilunar valves, which prevent the passage of venous blood into the duct. Tributaries.—The right lymphatic duct receives the lymph from the right side of the head and neck through the right jugular trunk; from the right upper extremity through the right subclavian trunk; from the right side of the thorax, right lung, right side of the heart, and part of the convex surface of the liver, through the right bronchomediastinal trunk. These three collecting trunks frequently open separately in the angle of union of the two veins. 
FIG. 600 - Modes of origin of thoracic duct. (Poirier and Charpy.) a. Thoracic duct. a’. Cisterna chyli. b, c’ Efferent trunks from lateral aortic glands. d. An efferent vessel which pierces the left crus of the diaphragm. e. f. Lateral aortic glands. h. Retroaortic glands. i. Intestinal trunk. j. Descending branch from intercostal lymphatics. 
FIG. 601 - Terminal collecting trunks of right side. a. Jugular trunk. b. Subclavian trunk. c. Bronchomediastinal trunk. d. Right lymphatic trunk. e. Gland of internal mammary chain. f. Gland of deep cervical chain. (Poirier and Charpy.)
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