334 THE CIRCULATORY SYSTEM. 



of the aorta {a), somewhat to the left. It passes along the 

 aorta, gradually coming to lie more on its left side, and finally 

 leaves that vessel near the aortic arch. The duct continues 

 thence straight craniad along the left side of the oesophagus till 

 it reaches the external jugular vein at its junction with the sub- 

 clavian. In this region the thoracic duct usually unites with 

 the lymphatics coming from the head and arm, then enters the 

 external jugular vein, or the innominate at the point of union 

 of external jugular and subclavian. 



In its passage through the thorax the duct frequently 

 divides into two or three divisions which pass along parallel to 

 each other for a distance, then reunite. Such division into two 

 or three parts is especially frequent just before the union with 

 the jugular vein. The numerous valves in the thoracic duct 

 give it a beaded appearance. 



5. Lymphatics of the Pelvic Limbs. — A number of lym- 

 phatic vessels are formed on the dorsum and the sole of the 

 foot. These pass to the lateral side, forming a network on the 

 lateral and dorsal surface of the ankle-joint, and finally unite 

 into two main trunks which accompany the vena saphena parva. 

 In the popliteal space these enter the popliteal gland which 

 lies imbedded in the fat of that region. From the popliteal 

 gland one or two trunks accompany the superficial division of 

 the vena saphena parva across the lateral surface of the biceps 

 muscle, and finally thus reach the pelvic cavity. Here they 

 join the lymphatics of the pelvic region, which all pour their 

 lymph at last into the thoracic duct. Inguinal glands are 

 either very small or not present in the cat. 



The pelvic limbs have perhaps a deep system of lymphatics, 

 accompanying the deep veins ; if so, they are not easily 

 demonstrable. 



