Chap. XI] THE VASCULAR SYSTEM 205 



axillary artery and collects all the blood of the upper ex- 

 tremities. 



The subclavian vein. — This vein continues the axillary from 

 the first rib to the joint between the sternum and clavicle, where it 

 unites with the internal jugular to form the innominate vein. 



The innominate veins. — The innominate (brachio-cephalic) 

 veins, commencing on each side by the union of the subclavian 

 and internal jugular, transmit the blood returning from the head 

 and neck, the upper limbs, and a part of the thoracic wall ; they 

 end below by uniting to form the superior vena cava. Both in- 

 nominate veins are joined by many side tributaries : they also 

 receive, at the junction of the subclavian and internal jugular, the 

 lymph ; on the left side from the thoracic duct, and on the right 

 from the right lymphatic duct. 



The superior vena cava. — The superior, or descending, vena 

 cava, is formed by the union of the right and left innominate 

 veins, just behind the junction of the first right costal cartilage 

 with the sternum. It is about three inches (75 mm.) long, and 

 opens into the right auricle, opposite the third rib. 



Thoracic veins. — The great majority of the thoracic veins 

 follow the same course as the arteries, and bear the same names. 

 Two exceptions are the inferior vena cava and the azygos veins 

 which will be described later. 



Veins of the lower extremities. — The blood from the lower 

 limbs is also returned by a deep and a superficial set of veins. 

 They are more abundantly supplied with valves than the veins of 

 the upper limbs. 



The deep veins. — Below the knee the deep veins accompany 

 the arteries in pairs, as venae comites, and as in the upper limbs are 

 called by the same names. The veins from the foot empty into 

 anterior tibial and posterior tibial veins. They unite to form the 

 single popliteal vein, which is continued as the femoral and becomes 

 the external iliac. 



The superficial veins. — The internal or long saphenous and the 

 external or short saphenous are the two largest superficial veins. 



The internal saphenous extends from the ankle to within an 

 inch and a half (38 mm.) of the inguinal ligament. It lies along 

 the inner side of the leg and thigh and terminates in the femoral 

 vein. 



