174 VERTEBRATE ZOOLOGY 



Each of the innominate arteries, after a course of about a 

 quarter of an inch, divides into two vessels,— the carotid artery, 

 which runs directly forward to the head, and the subclavian 

 artery. This latter artery is very short; it gives off the small 

 internal mammary artery, and almost at once divides into the 

 brachial artery, which runs to the shoulder and supplies the wing, 

 and the pectoral artery, which supplies the pectoral muscles. 



Follow the carotid artery forward. Carefully separate the oesoph- 

 agus, with the crop, from the organs among which it lies; note 

 the large blood vessels which go to the crop. Note the two long 

 thymus glands, which lie, one on each side of the trachea, along 

 almost the entire length of the neck ; they have the appearance 

 of fat. Lying near the trachea also, on each side, are the cervical 

 artery, the large jugular vein, and the vagus nerve, the last of 

 which appears as a white cord ; do not dissect them yet. 



The carotid artery runs just beneath the jugular vein, about 

 half an inch, and then gives off two branches : the vertebral ar- 

 tery, which passes medially to the vertebrarterial canal of the 

 cervical vertebrae, in which it runs to the brain, and the cervical 

 artery, which accompanies the vagus and the jugular vein to 

 the head. 



In the angle between the carotid and the cervical artery on 

 each side lies the small thyroid gland. 



The main trunks of the two carotids now converge toward the 

 median plane and pass through the muscles of the neck to a 

 groove in the ventral surface of the center of the cervical vertebra, 

 along which they run forward. Near the head they diverge, and 

 each, passing to its own side, soon divides into two arteries : the 

 external carotid, which supplies the outer portions of the head, 

 and the internal carotid, which goes to the brain. 



Study the subclavian artery and its branches. One of the latter, 

 the internal mammary artery, passes backward along the inner 

 surface of the ribs. Follow the brachial and pectoral arteries, and 

 study their branching. 



Issuing from the right ventricle is the pulmonary artery; it 

 divides at once into the right and left pulmonaries, which lie di- 

 rectly dorsal to the innominate arteries and go to the lungs. 



