CHAP. XI.] THE VASCULAB SYSTEM. 121 



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 from the intestines, 

 enter the thoracic duct. As we have stated elsewhere (page 

 105), 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 long in the adult, extends from the second lum- 

 bar 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 vertebra, it 

 turns outward and arches downwards and forwards to terminate 

 in the angle formed by the junction of the left internal jugular 

 and subclavian veins. The size is usually compared to that of 

 a goose quill. It is dilated below where it receives the lym- 

 phatics from the lower limbs and the chyle , from the lacteals, 

 the dilatation being known as the receptaculum chyli, recep- 

 tacle of the chyle. The duct is provided with valves, and in 

 other respects closely resembles the larger lymphatics in struc- 

 ture. 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 in length. It pours its contents into the 

 blood at the junction of the right internal jugular and sub- 

 clavian 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 



