THE COMMON CAROTID ARTERY 635 



branches detach small twigs to the transversus thoracis, pleura, and pericardium, 

 and pass out between the costal cartilages as perforating branches (Rami perfor- 

 antes) to supply the pectoral muscles and skin, anastomosing with the external tho- 

 racic artery. A very small pericardiaco-phrenic artery (A. pericardiaco-phrenica) 

 ascends in the mediastinum on the left side, in the caval fold of pleura on the right 

 side; it supplies fine twigs to the pericardium and pleura and accompanies the 

 phrenic nerve to the diaphragm. In the young subject it gives small branches, 

 the thymic arteries (Aa. thymicse), to the thymus gland. The musculo-phrenic 

 or asternal artery (A. musculophrenica) passes along the groove between the eighth 

 and ninth costal cartilages and continues along the costal attachment of the trans- 

 versus abdominis (Fig. 275). It gives off intercostal branches which anastomose 

 wath those descending from the thoracic aorta, and twigs to the diaphragm and 

 transversus abdominis. The anterior abdominal artery (A. epigastrica cranialis) 

 is the direct continuation of the internal thoracic. It passes between the ninth 

 costal cartilage and the xiphoid cartilage, runs backward on the abdominal surface 

 of the rectus abdominis, and then becomes embedded in the muscle (Fig. 590). 

 It supplies the ventral wall of the abdomen and anastomoses with the posterior 

 abdominal artery. 



5. The external thoracic artery (A. thoracica externa) is given off from the 

 ventral aspect of the brachial, usually at the medial surface or anterior border of 

 the first rib. It turns around the first rib ventral to the brachial vein (when given 

 off within the thorax), and passes backward under cover of the deep pectoral muscle; 

 it is continued as a small vessel in the cutaneous muscle, where it accompanies the 

 external thoracic vein. It gives branches to the pectoral muscles and the axillary 

 lymph glands and terminates in the cutaneous muscle and the skin of the ventral 

 wall of the abdomen. 



This artery varies in origin and size. Not rarely it arises from the internal thoracic or 

 from the brachial outside of the thorax. In other cases it arises by a common trunk with the 

 inferior cervical. It may be very small or even absent, in which case the perforating branches 

 of the internal thoracic compensate. 



6. The inferior cervical artery (Truncus omo-cervicalis) arises usually from 

 the dorsal surface of the brachial artery opposite the first rib or where that vessel 

 winds around the rib. It is directed downward and a little forward across the 

 lateral surface of the terminal part of the jugular vein and the deep face of the 

 scalenus among the posterior cervical lymph glands, and divides into ascending and 

 descending branches. The ascending branch (A. cervicalis ascendens) passes 

 upward and forward along the lateral surface of the jugular vein, then turns sharply 

 backward and runs upward along the anterior border of the anterior deep pectoral 

 muscle, between the omo-hyoideus and brachiocephalicus and in relation to the 

 prescapular lymph glands; it gives branches to these muscles and the posterior 

 cervical and prescapular lymph glands. The descending branch (A. transversa 

 scapulae) passes ventro-laterally across the surface of the anterior deep pectoral and 

 then runs in the groove between the anterior superficial pectoral muscle and the 

 brachiocephalicus in company with the cephalic vein. It supplies branches to these 

 muscles and the skin of the breast.^ 



THE COMMON CAROTID ARTERY 



The two common carotid arteries arise from the brachiocephalic artery by a 

 common trunk. This stem, the truncus bicaroticus, is detached from the medial 

 face of the brachiocephalic opposite the first rib and passes forward medially on the 

 ventral face of the trachea. It is related ventrally to the posterior cervical lymph 

 glands, the terminal parts of the jugular veins, and the anterior vena cava, and 

 1 In rare cases the two branches arise separately. 



