58 LABORATORY DIRECTIONS 



best Identified by the course it takes. In dissecting the veins 

 care must be used not to destroy the arteries, which in general 

 follow more or less the same course. Only the more important 

 arteries and veins are mentioned in this outline; if a more com- 

 plete description is desired consult Reigard and Jennings. 



1. Superior Vena Cava. — This large vein was mentioned 

 previously in the study of the heart. It returns blood from the 

 head, fore limbs, and cranial part of the body to the right auricle. 

 Just before entering the heart it is joined by the azygos vein. 



2. AzYGOS Vein.— This vessel, if traced backward from its 

 point of union with the superior vena cava, will be seen to pass 

 to the right and then backward into the abdomen, where it 

 originates from several small veins from the dorsal muscles. 

 The azygos receives a series of intercostal veins from the muscles 

 of the ribs. 



3. Internal Mammary Veins. — A pair of these carrying 

 blood from the ventral body wall and diaphragm run forward 

 on the inner surface of the sternum, unite, and enter the superior 

 vena cava on a level with the third rib. 



4. Innominate Veins. — These are the large veins that unite, 

 about on a level with the first rib, to form the superior vena cava. 

 Follow the left one. 



5. Vertebral Vein. — This appears to be a short vein enter- 

 ing the innominate on the dorsal side. Bringing blood from the 

 brain it passes through the foramina transversaria of the first 

 six cervical vertebrae before leaving the spinal column to join 

 the innominate. Do not try to trace it within the vertebral 

 column. 



6. Subclavian Vein. — This vein comes from the arm and 

 enters the innominate anterior to the first rib. Outside of the 

 thoracic cavity it is known as the axillary vein. Trace it to the 

 elbow. 



7. External Jugular Vein. — This unites with the sub- 

 clavian to form the innominate. It comes from the region of the 

 head. Several veins enter it. 



8. Internal Jugular Vein. — This vein enters the external 

 jugular just anterior to the point of union of external jugular 

 and subclavian. It arises from the occipital region and passes 

 posteriorly along the side of the trachea in company with the 



