THORACIC DUCT. 359 



sub-mucous tissue. From this areolar network the .acteal vessels proceed 

 to the mesenteric glands, and from thence to the thoracic duct, in which 

 they terminate. 



The Lymphatic glands of the large intestines are situated along the at- 

 tached margin of the intestine, in the meshes formed by the colic and 

 haemorrhoidal arteries previously to their distribution. The lymphatic 

 vessels take their course in two different directions ; those of the caecum, 

 ascending and transverse colon, after traversing their proper glands, pro- 

 ceed to the mesenteric, and those of the descending colon and rectum to 

 the lumbar glands. 



The Lymphatic vessels of the Iddney follow the direction of the blood- 

 vessels to the lumbar glands situated around the aorta and inferior vena 

 cava ; those of the supra-renal capsules, which are very large and nume- 

 rous, terminate in the real lymphatics. 



The Lymphatic vessels of the viscera of the pelvis terminate in the sacral 

 and lumbar glands. 



The Lymphatic vessels of the testicle take the course of the spermatic 

 cord in which they are of large size ; they terminate in the lumbar glands. 



THORACIC DUCT. 



The thoracic duct* commences in the abdomen, by a considerable and 

 somewhat triangular dilatation, the receptaculum chyli, which is situated 

 on the front of the body of the second lumbar vertebra, behind and be- 

 tween the aorta and inferior vena cava, and close to the tendon of the 

 right crus of the diaphragm. From the upper part of the receptaculum 

 chyli the thoracic duct ascends through the aortic opening of the dia- 

 phragm, and along the front of the vertebral column, lying between the 

 thoracic aorta and vena azygos, to the fourth dorsal vertebra. It then in- 

 clines to the left side, passes behind the arch of the aorta, and ascends by 

 the side of the oesophagus and behind the perpendicular portion of the 

 left subclavian artery to the root of the neck opposite the seventh cervical 

 vertebra, where it makes a sudden curve forwards and downwards, and 

 terminates at the point of junction of the left subclavian with the left in- 

 ternal jugular vein. 



The thoracic duct is equal in size to the diameter of a goose-quill at its 

 commencement from the receptaculum chyli, diminishes considerably in 

 diameter towards the middle of the posterior mediastinum, and again be- 

 comes dilated near its termination. At about the middle of the thorax it 

 frequently divides into two branches of equal size, which reunite after a 

 short course ; and sometimes it gives off several branches, which assume 

 a plexiform arrangement in this situation. Occasionally the thoracic duct 

 bifurcates at the upper part of the thorax into two branches, one of which 

 opens into the point of junction between the right subclavian and jugular 

 veins, while the other proceeds to the normal termination of the duct on 

 the left side. In rare instances the duct has been found to terminate ir 

 the vena azygos, which is its normal destination in some Mammalia. 



* The thoracic duct was discovered by Eustachius, in 1563, in the horse : he regarded 

 it as a vein, and called it the vena alba thoracis. The lacteals were first seen by Asel 

 Uu* in 1622, in the dog; and within the next ten years by Veslingius in man. 



