THE VASCULAR SYSTEM. 



'53 



fore its junction with the subclavian. The opening is 

 guarded by a valve which prevents the blood from enter- 

 ing the lymphatic trunk. 



The thoracic duct (Fig. 80) is the largest vessel of the 

 lymphatic system, but is usually invisible unless injected. 

 It extends from the region of the kidneys on the dorsal 



FIG. 81. PHOTOGRAPH OF LYMPHATIC CAPILLARIES INJECTED WITH BERLIN 

 BLUE. They lie immediately beneath the skin on the outer aspect 

 of the ear. 



a, Point of injection; the black area is Berlin blue lying in the connec- 

 tive-tissue spaces from which the capillaries arise; n, injection es- 

 caped from ruptured vessel. 



aspect of the body cavity, along the left side of the spinal 

 column, to its opening into the external jugular vein near 

 where the latter joins the subclavian vein. The caudal end 



