THE COMMON CAROTID ARTERY 707 



The left coronary artery is much larger than the right one; it gives off a branch 

 which descends in the intermediate groove, and terminates by running downward 

 in the right longitudinal groove. The right coronary artery, after emerging from 

 the interval between the right auricle and the pulmonary artery, divides into 

 branches which are distributed to the wall of the right ventricle. 

 1 The brachiocephalic trunk (anterior aorta) is usually four or five inches (ca. 

 10-12 cm.) in length. 



The brachial arteries give off in the thorax the following branches: 



1. A common trunk for the dorsal, deep cervical, and vertebral arteries. 



(1) The subcostal artery commonly arises separately and runs forward along 

 the sides of the bodies of the vertebra. It supplies the second to the fifth inter- 

 costal arteries. 



(2) The dorsal artery is relatively small. It usually ascends in front of the 

 first costo-vertebral joint, and is distributed as in the horse. It gives off the first 

 intercostal artery. 



(3) The deep cervical artery may arise from a common stem (Truncus vertebro- 

 cervicalis) with the vertebral, or may constitute a branch of that artery. It passes 

 up between transverse processes of the first thoracic and last cervical vertebra, or be- 

 tween the sixth and seventh cervical, and is distributed as in the horse. 



(4) The vertebral artery passes along the neck as in the horse to the inter- 

 vertebral foramen between the second and third cervical vertebrae, gives off a 

 muscular branch, and enters the vertebral canal (Fig. 594). It runs forward on 

 the floor of the canal — connected with its fellow by two or three transverse anas- 

 tomoses — and divides in the atlas into two branches. The smaller medial division 

 (cerebrospinal artery). passes forward to the floor of the cranium and concurs with 

 the condyloid artery and branches of the internal maxillary in the formation of a 

 large rete mirabile. The large lateral branch emerges through the intervertebral 

 foramen of the atlas and ramifies in the muscles of the neck in that region, com- 

 pensating for the smallness of the branches of the occipital artery. It also sends a 

 branch to the rete mirabile. The collateral branches detached to the cervical mus- 

 cles are large and compensate for the small size of the deep cervical artery. The 

 spinal branches pass through the intervertebral foramina, divide into anterior and 

 posterior branches, and form two longitudinal trunks which are connected by cross- 

 branches so as to form irregular polygonal figures. 



2. The internal thoracic artery presents no remarkable features. 



3. The inferior cervical artery corresponds usually to the ascending branch of 

 that vessel in the horse. 



4. The external thoracic artery is large and usually gives off a branch which is 

 equivalent to the descending branch of the inferior cervical artery of the horse. 



THE COMMON CAROTID ARTERY 



The carotid arteries usually arise from a common trunk about two inches (ca. 

 5 cm.) in length, but in exceptional cases are given off separately from the brachio- 

 cephalic. Each pursues a course similar to that of the horse, and is accompanied 

 by the small internal jugular vein, but is separated from the external jugular vein 

 by the omo-hyoid and sterno-mastoid muscles. It divides at the digastricus into 

 occipital, external maxillary, and external carotid arteries. In addition to tracheal, 

 CESophageal, and muscular branches, it gives off the thyroid, laryngeal and inferior 

 parotid arteries. The thyroid artery (A. thyreoidea cranialis) bends around the 

 anterior end of the thyroid gland, in which it ramifies. The accessory thyroid 

 artery is usually absent. The laryngeal artery may arise with the thyroid. 



1. The occipital artery is relatively small. It gives off the following: 



