CHAP. IX.] 



THE VASCULAR SYSTEM. 



105 



share in returning the blood, especially from the distal portion 

 of the limb. The deep veins accompany the arteries, and are 

 called by the same names. Both 

 sets are provided with valves, and 

 terminate in the subclavian vein. 



The blood from the spine, walls 

 of thorax, and abdomen is chiefly 

 returned by the right and left azygos 

 veins, which are longitudinal vessels 

 resting against the thoracic portion 

 of the spinal column. They com- 

 municate below with the inferior 

 vena cava, and terminate above in the 

 superior vena cava : they thus form a 

 supplementary channel by which blood 

 can be conveyed from the lower part 

 of the body to the heart in case of 

 obstruction in the inferior vena cava. 



The innominate veins, commencing 

 on each side by the union of the sub- 

 clavian and internal jugular, behind 

 the inner end of the clavicle, 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 innominate 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 or descending vena cava 



is formed by the union of the right OF LoWEB EXTREMITY. i, veins 

 and left innominate veins. It is about of the foot; 2 internal ~&* 



, vein ; 3, superficial veins of calf ; 



three inches long, and opens into the 4> superficial veins of thigh, 

 right auricle, opposite the third rib. 



The blood from the lower limbs is also returned by a super- 

 ficial and deep set of veins. They are more abundantly supplied 



_ S(JPEEFICIAL 



