156 VERTEBRATE ZOOLOGY 



arteries, which go to the forelegs, and the right and left carotid 

 arteries, which go to the head. In the angle formed by the branch- 

 ing of these arteries lies the round thyroid gland. Next to the in- 

 nominate artery is the left aorta, which springs from the right side 

 of the ventricle and passes to the left side of the body. Next to it 

 and on the left is the pulmonary artery, which branches at once 

 into the right and left pulmonaries. 



After these arteries have been dissected free from the surround- 

 ing tissues, the right aorta will be seen beneath the innominate 

 artery, which is a branch of it ; it springs from the left side of the 

 ventricle and passes to the right side of the body. The right and 

 left pulmonaries will also be seen. The right and left aortas meet 

 on the dorsal side of the body cavity and form the dorsal aorta. 



Follow these arteries and their main branches, beginning with 

 the subclavian. 



The subclavian artery gives off several small branches, of which 

 one passes at once to the thyroid gland, one (the ascending cer- 

 vical) runs along the ventral side, and one (the superior cervical) 

 runs along the dorsal side of the neck and also supplies the muscles 

 of the pectoral girdle ; it then becomes the axillary artery, which 

 passes above the brachial nerve plexus, and finally, as the brachial 

 artery, goes to the leg. The axillary artery gives off a branch, the 

 internal mammary, which passes to the outer border of the cara- 

 pace and runs backward along it to the hinder part of the body, 

 where it anastomoses with the epigastric artery, a branch of the 

 dorsal aorta. 



The carotid artery is smaller than the subclavian, and may be 

 traced forward to the head. In the greater part of its course it lies 

 alongside the large vagus nerve, the much smaller sympathetic 

 nerve, and the internal jugular vein. The thymus glands will also 

 be seen ; they are a pair of loose, yellowish masses of tissue at the 

 base of the neck. 



Follow, now, the pulmonary artery and the aorta on the left side 

 of the animal. Push the stomach and left lobe of the liver to the 

 animal's right and trace the left pulmonary artery to the lung. 

 Note again the left pulmonary vein, and trace it from the lung to 

 the heart. Trace also the left aorta to its union on the dorsal side 



