THE TERMINAL LYMPH VESSELS. 997 



mediastinum, through which it ascends, lying anterior to the vertebral column and 

 to the right of the median plane, to the level of the fifth thoracic vertebra ; it then 

 crosses somewhat abruptly from the right to the left of the median plane, and 

 ascends through the superior mediastinum to the root of the neck, where it turns 

 laterally, between the vertebral and common carotid arteries, and it terminates, at 

 the medial border of the left scalenus anterior, by joining the left innominate vein 

 at its commencement. 



Length and Diameter. The total length of the duct averages about 45 cm. (18 

 inches). It is dilated at both its origin and termination. As a rule it is narrowest 

 opposite the fifth thoracic vertebra, but its calibre is very variable, and sometimes 

 the thoracic portion is broken up into a series of anastomosing channels. The 

 widest portion of the tube is usually the cisterna, but occasionally that dilatation 

 is entirely absent. The duct is provided with several valves, formed by semilunar 

 folds of the tunica intima, arranged in pairs, and the most perfect of them is 

 situated at or near the orifice of communication with the left innominate vein. 



Relations. In the abdomen the cisterna chyli lies anterior to the upper two lumbar 

 vertebrae and the corresponding lumbar arteries, between the aorta on the left and the 

 vena azygos and the right crus of the diaphragm on the right. In ike posterior 

 mediastinum the thoracic duct is separated from the vertebral column and the anterior 

 longitudinal ligament by the right aortic intercostal arteries and the transverse parts of 

 the hemiazygos and accessory hemiazygos veins ; it is covered, in front, in the lower part 

 of its extent by the right pleural sac, and in the upper part by the oesophagus ; to its 

 right is the vena azygos, and to its left the descending aorta. In the superior mediasti- 

 num it passes forwards from the vertebral column, and it is separated from the left 

 longus colli muscle by a mass of fatty tissue ; the oesophagus lies in front of it in that 

 region, but the left margin of the duct projects beyond the oesophagus, and is in relation 

 anteriorly, and from below upwards, with the termination of the arch of the aorta, the 

 left subclavian artery and the pleura. As the duct enters the root of the neck it passes 

 behind the left common carotid artery, whilst to its right and somewhat anterior is the 

 oesophagus, and the left pleura is still in association with its left border. 



At the root of the neck it arches laterally above the apex of the pleura sac and the 

 first part of the left subclavian artery. It passes anterior to the vertebral artery and 

 vein, the roots of the inferior thyreoid, transverse cervical, and transverse scapular 

 arteries, the medial border of the scalenus anterior and the left phrenic nerve, and 

 posterior to the left carotid sheath and its contents. 



Tributaries. -- The cisterna chyli commonly receives five tributaries. (1) 

 Truncus Intestinalis. The intestinal trunk, which is formed by the efferents of 

 mesenteric and upper pre-aortic glands, and which conveys lymph from the lower 

 and anterior part of the liver, the stomach, the small intestine, the spleen, and the 

 pancreas. (2) Two trunci lumbales, one on each side ; they are formed by the 

 efferents of the lumbar glands. They carry lymph from the lower extremities, 

 from the deep portions of the abdominal and pelvic walls, the large intestine and 

 the pelvic viscera, and from the kidneys, suprarenal glands, and genital glands. 

 (3) Two descending lymphatic trunks, one on each side, each of which is formed by 

 the efferent vessels from the corresponding lower intercostal glands ; these descend 

 to the cisterna through the aortic opening of the diaphragm. Occasionally they 

 unite to form a single trunk, and in others they, or the tributaries from which 

 they are usually formed, open directly into the thoracic duct (Figs. 797, 798). 



In its course through the posterior mediastinum the thoracic duct receives 

 efferents from the upper and posterior part of the liver, and from the posterior 

 mediastinal and cesophageal glands ; the latter carry lymph from the oesophagus, 

 the pericardium, and the left side of the thoracic wall. 



In the superior mediastinum the vessels which open into it are derived from 

 the upper left intercostal glands ; it receives lymph also from the heart and left 

 lung by efferents from the left peritracheo-bronchial glands and the intertracheo- 

 bronchial glands, but the efferents of those glands may unite with the internal 

 mammary lymphatic to form a common trunk which may open either into the 

 thoracic duct or into the innominate vein. In the superior mediastinum, there- 

 fore, it may receive lymph from the upper and median part of the abdominal wall, 



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