CHAP. XII.] THE VASCULAR SYSTEM. 143 



The lymphatics, having attained a certain size, do not unite 

 into larger and larger trunks, but continue of the same diameter 

 until they finally enter two trunks or ducts through which their 

 contents are poured into the veins. The lymphatics from the 

 right arm, and right side of the head, neck, and upper part of 

 the trunk, enter the right lymphatic duct. The vessels from 

 the rest of the body, including the lacteals, or lymphatics of the 

 intestines, enter the thoracic duct. As we have stated else- 

 where (page 127), these ducts pour their contents into the blood 

 at the junction of the internal jugular and subclavian veins. 



The lymph, like the blood in the veins, is returned from the 

 limbs and viscera by a deep and by a superficial set of vessels. 

 In their course from origin to termination most of the lym- 

 phatics pass through small masses of tissue, called lymphatic 

 glands, a description of which will be given later on. 



The thoracic duct. The thoracic duct, from fifteen to eigh- 

 teen inches (381 to 457 mm.) long in the adult, extends from 

 the second lumbar vertebra to the root of the neck. It lies in 

 front of the bodies of the vertebrae gradually inclining towards 

 the left until, when on a level with the seventh cervical verte- 

 bra, it turns outwards and arches downwards and forwards to 

 terminate in the angle formed by the junction of the left inter- 

 nal jugular and subclavian veins. The size is usually compared 

 to that of a goose quill. It 'is dilated below where it receives 

 the lymphatics from the lower limbs and the chyle from the 

 lacteals, the dilatation being known as the receptaculum chyli, 

 receptacle of the chyle. The duct is provided with valves, 

 and in other respects closely resembles the larger lymphatics 

 in structure. It is often alternately contracted and enlarged 

 at irregular intervals. 



The right lymphatic duct is a short vessel usually from a quar- 

 ter to half an inch (6.3 to 12.7 mm.) in length. It pours its 

 contents into the blood at the junction of the right internal 

 jugular and subclavian veins. 



The lymph. The lymph is blood minus certain constituents. 

 When examined with the microscope, it is seen to consist of a 

 clear liquid with corpuscles floating in it. The liquid part 

 resembles the plasma of the blood in its composition, except 

 that it contains relatively more water and less solids. It clots 

 when removed from the body, though not so firmly as the 



