420 PROCEEDINGS OF THE ACADEMY OF [May, 



The Anterior Arteries. 



The origin of the great arterial trunks — the pulmonary, aortic 

 arches, primary carotid, and right subclavian — has already been 

 given and the distribution of the pulmonary arteries and aortic 

 arches has been described, so that it now remains to describe the 

 distribution of the right subclavian, fig. 4, Sc.d, and the primary 

 carotid, capr. 



The right subclavian, Sc.d., since it has an independent origin 

 from the heart, instead of arising as a branch of the primary carotid, 

 will he described first. After leaving the heart it passes cephalad 

 and laterad and gives off the following branches in order, beginning 

 at the heart: an oesophageal artery, oe, a small, caudally directed 

 vessel carrying blood to the posterior region of the oesophagus. Close 

 to the oesophageal arises another small, caudally directed vessel, 

 the pleural artery, plu, extending to the pleura and possibly to the 

 pericardium. From the same region as the preceding two arteries, 

 but extending cephalad along the trachea and oesophagus, arises the 

 much larger branch of the right subclavian, the right collateralis 

 colli, cc, whose course and distribution will be described later. 



Close to the distal side of the collateralis colli arises the very 

 small thyroid artery, th, leading to the oval thyroid gland that lies 

 against the ventral surface of the trachea a short distance anterior 

 to the heart. 



A short distance distal to the thyroid artery the subclavian gives 

 off a fairly large artery, the internal mammary, im^ (shown too large 

 in the figure), that passes to the inner surface of the ribs near the 

 sternum and lies parallel to the vein of the same name, described 

 above. 



A short distance distal to the internal mammary arises an artery 

 of about the same diameter, the vertebral, v,^; it passes dorsad and 

 caudad to the region of the thoracic vertebrae. 



After giving off the five vessels just described, the subclavian 

 artery passes into the shoulder where it divides into three main 

 branches: (a) the subscapular, sc^, going to the skin and muscles of 

 the shoulder; (b) the thoracic, t\ carrying blood to the posterior 

 muscles of the shoulder and to the posterior region of the upper 

 arm; (c) the brachial, br^ which is really the continuation of the 

 subclavian and is the chief artery of the anterior appendage. 



After sending several branches to the upper arm the brachial 

 divides, in the region of the elbow, into two main vessels, the radial, 



