392 THE SUBCLAVIAN ARTEEY. 



An unusual branch, of considerable size, occasionally comes off from it, and 

 passes downwards and outwards, crossing several of the ribs, on their inner 

 surface, in contact Vv-ith the pleura. The internal mammary artery may likewise 

 furnish a bronchial branch. 



4. — Superior Intercostal Artery. — This artery generally arises 

 from the upper and back part of the subclavian, behind the anterior 

 scalenus muscle on the right side, and immediately at the inner side of 

 the muscle on the left side. Taking its course backwards, it speedily 

 gives off the deep cervical branch (profunda cervicis), and bending 

 backwards and downwards in front of the neck of the first rib, ends in 

 one or two intercostal spaces : on the right side it more frequently 

 descends into the second space than on the left side. On the neck of 

 the first rib, the artery is situated on the outer side of the first dorsal 

 ganglion of the sympathetic nerve. 



Branches. — Besides giving off the deep cervical artery, the superior intercostal 

 gives branches to the first and second intercostal spaces. The branch to the first 

 space is similar in course and distribution to the aortic intercostals : that to the 

 second space usually joins with one from the first aortic intercostal. A small 

 offset is likewise sent backwards, through the first space, to the posterior spinal 

 muscles, and also a small one through the corresponding intervertebral foramen 

 to the spinal cord and its membranes. 



Varieties. — Origin. — The superior intercostal artery has been found, in a few 

 instances, to proceed from the vertebral artery or from the thyroid axis. 



Course. — It has been observed to pass between the necks of one or two ribs 

 and the con-esponding transverse processes of the dorsal vertebrce ; and a case has 

 been recorded in which, after arising from the vertebral artery, it descended 

 through the intertransverse foramen of the last cervical vertebra, and then 

 continued, as in the instances just mentioned, between the necks of the ribs and 

 the contiguous transverse processes of the vertebras of the back. (Quain on the 

 Arteries, plate 22, fig. 5.) The intercostal artery is sometimes, though very rarely, 

 wanting. 



The deep cervical artery, often described as a separate branch of the 

 Bubclavian artery, arises in most cases from the superior intercostal. 

 Eesembling the posterior branch of an aortic intercostal artery, it gene- 

 rally passes backwards in the interval between the transverse process 

 of the last cervical vertebra and the first rib, to reach the posterior 

 aspect of the neck. Here it ascends in the interval between the trans- 

 verse and spinous processes, as high as the second vertebra, under cover 

 of the complexus muscle, between this and the semi-spinalis colli. Some 

 of the branches communicate with those given outwards by the verte- 

 bral artery, Avhilst others ascend to anastomose with the cervical branch 

 of the occipital artery. 



Varieties.— ^;'?-/^(«. — The deep cervical artery sometimes arises from the sub- 

 clavian, and more rarely from the posterior scapular. It is not unfrcqucntly 

 supplemented by a branch tui-ning backwards from the ascending cervical artery 

 beneath the transverse process of the third cervical vertebra, or by another branch 

 from the superior intercostal, or, in some instances, by a twig from the posterior 

 scapular or inferior thyroid arteries. 



Course.— This artery occasionally passes back between the sixth and seventh 

 cervical vertebrae, and sometimes between the fii-st and second dorsal, or even 

 below the second. It has been seen to pass between the fii'st rib and the trans- 

 verse process which supports it. 



SURGICAL ANATOMY OF THE SUBCLAVIAN ARTERIES 

 The depth of the subclavian arteiy, its ultimate and varying connections with 



