The Vascular System 217 



(esophageal artery, oe, a small, caudally directed 

 vessel carrying blood to the posterior region of the 

 oesophagus. Close to the oesophageal arises an- 

 other 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 vertebras. 



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 



