SUBCLAVIAN ARTERY. 77 



part of its course the artery rests on the surface of the first rib, which is 

 interposed between it and the pleura. 



Veins. The arch of the subclavian vein is close to the artery, not being 

 separated by muscle, but lies commonly at a lower level. The external 

 jugular vein crosses it near the scalenus muscle; and the suprascapular 

 and transverse cervical brandies, which enter the jugular, form sometimes 

 a plexus over the third part of the artery. 



Nerves. The 'large cords of the brachial plexus are placed above and 

 close to the vessel ; and the small nerve of the subclavius crosses it about 

 the middle. Superficial to the cervical fascia lie the descending cutaneous 

 branches of the cervical plexus. 



Peculiarities* The artery may spring as a separate trunk from the arch 

 of the aorta ; and in such a deviation the vessel takes a deeper place than 

 usual to reach the scaleni muscles. 



It has been before said (p. 66)' that the subclavian may be in front of 

 the scalenus or in its fibres ; and that it may be placed one inch and a half 

 above the level of the clavicle. 



Branches of subclavian. Usually there are four chief branches on the 

 subclavian artery. Three branches arise from the first part of the arterial 

 trunk ; one (vertebral) ascends to the head ; another (internal mammary) 

 descends to the chest ; and the remaining one (thyroid axis) is a short 

 thick trunk, which furnishes branches inwards and outwards to the thyroid 

 body and shoulder. These arise commonly near the scalenus muscle, so 

 as to leave an interval at the origin free from offsets. This interval varies 

 in length from half an inch to an inch in the greater number of cases ; and 

 its extremes range from somewhat less than half an inch to an inch and 

 three quarters. But in some instances the branches are scattered over the 

 first part of the artery (Quain). 1 



The fourth branch (superior intercostal) arises beneath the anterior 

 scalenus from the second part of the artery, and gives off the deep cervical 

 branch ; a small spinal artery conies sometimes from this part of the trunk. 



If there is a branch present on the third part of the artery, it is com- 

 monly the posterior scapular ; if more than one, this same branch with 

 the external mammary ; and if more than two, an offset belonging to the 

 thyroid axis will be added. 



The vertebral artery is generally the first and largest branch of the sub- 

 clavian, and arises from the upper and posterior part. Ascending between 

 the contiguous borders of the scalenus and longus colli muscles, this branch 

 enters the aperture in the lateral mass of the sixth cervical vertebra, and 

 is continued upwards to the skull through the foramina in the other cervical 

 vertebrae. Before the artery enters its aperture it is partly concealed by 

 the internal jugular vein, and passes beneath the thyroid artery ; it is ac- 

 companied by branches of the sympathetic nerve, and supplies small mus- 

 cular offsets. Its course and distribution will be given afterwards. 



The vertebral vein issues with its accompanying artery, to which it is 

 superficial in the neck, and is directed over the subclavian artery to join 

 the subclavian vein ; it receives the deep cervical vein, and the branch 

 that accompanies the ascending cervical artery. 



The internal mammary branch leaves the lower part of the subclavian 



1 The student is referred for fuller information respecting the peculiarities of 

 the vessel, and the practical applications to be deduced from them, to the original 

 and valuable work on the Anatomy of the Arteries of the Human Body, by Richard 

 Quain, F.R.S. 



