THE SUPERIOR INTERCOSTAL ARTERY. 429 



arising- from the axillary, the innominate, or the aorta. The trunk of the artery has been 

 seen to cross the front of the fifth or sixth costal cartilage. 



An unusual lateral branch, of considerable size, occasionally comes off from the upper 

 part of this artery, and passes downwards and outwards, crossing several of the ribs, on their 

 inner surface, about midway between the spine and sternum, or somewhat farther forwards. 

 The internal mammary artery may likewise furnish a bronchial branch. 



4. Superior intercostal artery (iv). This artery arises from the back part 

 of the subclavian, generally behind the anterior scalenus on the right side, and 

 immediately internal to that muscle on the left. Taking its course backwards and 

 at first slightly upwards, it speedily gives off the deep cervical branch, and then 

 bends downwards in front of the neck of the first rib, to be distributed in the first 

 and second intercostal spaces. On the neck of the first rib, the artery is situated 

 between the first thoracic ganglion of the sympathetic internally and the anterior 

 primary division of the first dorsal nerve externally. 



The branches of the first and second intercostal spaces are distributed in the 

 same way as the intercostal arteries derived from the aorta (p. 455), and that in the 

 second space is frequently joined by an offset from the first aortic intercostal. 



Varieties. The superior intercostal artery has been found, in a few instances, to proceed 

 from the vertebral artery or from the thyroid axis. It has also been observed to descend 

 between the necks of one or two ribs and the transverse processes of the corresponding 

 dorsal vertebra? ; and in one case, after arising from the vertebral artery, it passed in addition 

 through the foramen in the transverse process of the last cervical vertebra (R. Quain, pi. 22, 

 fig. 5). This artery is sometimes, though very rarely, wanting. On the other hand it may be 

 larger than usual, and supply three or even four spaces. It has been seen to furnish a lateral 

 branch descending on the inner surface of the ribs, similar to that occasionally derived from 

 the internal mammary artery (Blandin). 



The deep cervical artery (fig. 351, 6), often described as a separate branch 

 of the subclavian, arises in most cases from the superior intercostal. Resembling 

 the posterior branch of an aortic intercostal artery, it 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, where it ascends under cover of the 

 complexus muscle, and resting upon the semispinalis colli, to the level of the axis. 

 Its branches supply the surrounding muscles, and anastomose with offsets of the 

 vertebral, the cervical branch of the occipital, and the ascending cervical arteries. 

 A spinal branch enters the canal with the last cervical nerve. 



Varieties. The deep cervical artery sometimes arises separately from the subclavian ; 

 more rarely from the posterior scapular. It occasionally passes back between the sixth and 

 seventh cervical vertebra, and sometimes between the first and second dorsal, or even below 

 the second. It has been seen to pass between the first rib and the transverse process 

 of the first dorsal vertebra. This artery is not unfrequently supplemented by a branch 

 of the ascending cervical artery, turning backwards between two of the cervical trans- 

 verse processes ; or by an enlarged dorsal branch from the superior intercostal artery in 

 the first space ; or in rare instances by an offset from the posterior scapular or inferior thyroid 

 artery. 



SURGICAL ANATOMY OF THE SUBCLAVIAN ARTERIES. 



The depth of the subclavian artery, its intimate and numerous connections with 

 important parts, and the large size of its branches, render operations on this vessel peculiarly 

 difficult. 



The third division of the artery, situated beyond the anterior scalenus muscle, is the part 

 which is most favourably circumstanced for the application of a ligature, inasmuch as the 

 vessel is here nearest to the surface, and the spot selected is remote from the origin of the 

 large branches. The artery is generally easy of access above the clavicle while the 

 parts are in their natural position, but when they are displaced by an aneurism in the 

 axilla, the clavicle may be so much elevated by the tumour as to be placed in front of the 



