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 cesophagus 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. 
