376 SUBCLAVIAN ARTERIES. 



the same time anastomosing with the epigastric artery. It also supplies twigs to the 

 broad muscles of the belly, to the skin, and to the diaphragm ; and one runs forwards 

 upon the side and front of the xiphoid cartilage, where it anastomoses with that of 

 the opposite side. 



PECULIARITIES. The internal mammary is occasionally found connected at its 

 origin with the thyroid axis, or with the scapular arteries these being detached 

 from the thyroid. It occasionally springs from the second or third part of the sub- 

 clavian artery (the latter being the more frequent position of the two). In very rare 

 instances it has been found arising from the axillary, the innominate, or the aorta. 



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 with the pleura. The internal mammary artery may likewise furnish a 

 bronchial branch. 



IV. SUPERIOR INTERCOSTAL AND DEEP CERVICAL ARTERIES. 



THE SUPERIOR INTERCOSTAL 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 

 iieck 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. 



PECULIARITIES. 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 

 corresponding transverse processes of the dorsal vertebrae ; 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 trans- 

 verse processes of the vertebrae 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 

 subclavian artery, arises in most cases from the superior intercostal. Re- 

 sembling the posterior branch of an aortic intercostal artery, it generally 

 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 transverse 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 communi- 

 cate with those given outwards by the vertebral artery, whilst others 

 ascend to anastomose with the cervical branch of the occipital artery. 



PECULIARITIES. Origin. The deep cervical artery sometimes arises from the sub- 

 clavian, and more rarely from the posterior scapular. It is not unfrequently supple- 

 mented by a branch turning 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. 



