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. thymic), 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 
with 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 
seapul) 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 
ace 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 
ands, the terminal parts of the jugular véins, and the anterior vena cava, and 
1Tn rare cases the two branches arise separately. 
