1 86 



Innominate Veins 



(p. 1 57). They pass out horizontally over the front of the external inter- 

 costal muscle, and behind the pleura. As the ribs slope downwards 

 the arteries soon reach the upper part of the space, where they run 

 between the intercostal muscles in the costal groove, the nerve being 

 below, and the vein above, the artery. 



Each intercostal artery gives off a collateral branch, which courses 

 along the lower border of the space. In front the arteries anastomose 

 with the internal mammary (p. 156). They also anastomose with the 

 superior intercostal and with branches of the axillary, and with the 

 epigastric and lumbar arteries, and, at the back of the space, with the 

 bronchial arteries. 



Each intercostal artery gives off a dorsal branch, and, in the female, 

 the third, fourth, and fifth send out branches to the mamma. 



Section through bottom of fourth dorsal vertebra. I, H, in, iv, ribs ; i, trachea ; 2, oesopha- 

 gus ; 3, superior cava ; 4 is placed between first and third parts of aortic arch. (BRAUNE.) 



The left innominate vein, 3 in., is formed behind the inner 

 end of the clavicle, in front of the beginning of the left carotid, by the 

 confluence of the subclavian and internal jugular veins ; lying on a 

 rather higher level than the transverse aorta, but sometimes overlap- 

 ping it, it is very near to the upper border of the manubrium, from 

 which it is separated by the sterno-hyoid and sterno-thyroid muscles 

 and the remains of the thymus gland. 



The right innominate vein, I in., begins behind the end of the 

 right clavicle, and descends by the outer side of the innominate artery ; 

 on its right side are pleura and lung. 



