The Vascular System 217 
esophageal artery, oe, a small, caudally directed 
vessel carrying blood to the posterior region of the 
cesophagus. 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 ‘cesophagus, 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 vertebre. 
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 
