120 ANATOMY AND PHYSIOLOGY FOR NURSES 



is cited as an agency in venous circulation, and that is 

 capillary attraction. Still another factor responsible for 

 the return of the venous blood to the heart is furnished by 

 thoracic aspiration. The following illustrations of the 

 venous system give a fair conception of the course of the 

 veins and shows their relation to the arterial system. 



The blood is of much darker color in the veins than in 

 the arteries. This change takes place during the passage 

 of the blood through the capillary system, and is depend- 

 ent upon the phenomena of combustion and the general 

 metamorphosis of the materials of the tissues, all of which 

 are in contact with the capillary system. 



The veins of the body are divided into two groups : those 

 that pass by way of the superior and those that empty into 

 the inferior vena cava. The blood from the lower ex- 

 tremities is brought by way of the inferior vena cava; the 

 blood from the brain, neck, and face passes through the 

 internal and the external jugular veins, which unite with 

 the venous trunk from the upper extremity to form the 

 superior vena cava. 



The external jugular vein starts at the angle of the 

 lower jaw and terminates in the subclavian vein. 



The internal jugular vein passes downward in 

 line with the common carotid, and unites with the sub- 

 clavian to form the innominate vein. 



The subclavian vein receives the blood from the 

 arm. The veins, with the exception of the superficial 

 branches, accompany the arteries in the same sheath. 

 The right and left azygos veins receive the blood 

 from the spine. 



The innominate veins unite in forming the superior 

 vena cava. The inferior vena cava is formed by the 

 union of the two common iliacs, which receive all the blood 

 from the deep and the superficial veins of the lower limbs. 

 The large vein of the leg is called the internal saphenous. 



