BLOOD-VESSELS OF THE NECK. 505 



vicular articulation ; thence it proceeds obliquely outward 

 to the inner margin of the scalenus anticus muscle, con- 

 stituting its first stage. It now passes between the scale- 

 nus anticus and scalenus medius, forming its second stage. 

 After emerging from these muscles it proceeds downward 

 and outward, beneath the clavicle, to the lower margin of 

 the first rib, forming its third stage, where it terminates 

 as subclavian, and becomes axillary. 



The right subclavian has anterior to it, in its first stage, 

 the internal jugular and subclavian veins, the pneumo- 

 gastric, phrenic, and cardiac nerves ; the sterno-mastoid, 

 sterno-hyoid and sterno-thyroid muscles. Behind are the 

 inferior laryngeal and sympathetic nerves, the vertebral 

 vein, and some cellular tissue and lymphatic glands. In its 

 second stage it lies between the scaleni muscles, separated 

 by the scalenus anticus from the subclavian vein and phrenic 

 nerve, and accompanied by the brachial plexus of nerves. 

 In the third stage the subclavian vein, the subclavian mus- 

 cle, and the clavicle are in front ; the brachial plexus and 

 the omo-hyoid are above and external, and behind are the 

 scalenus posticus and the first rib, while the skin, platysma, 

 and fascia form the superficial covering. 



The left subclavian differs from the right in having its 

 origin from the arch of the aorta ; in being longer ; in pur- 

 suing nearly a vertical course to the scaleni muscles ; in 

 having the pneumogastric running parallel with instead of 

 crossing it ; in not having the recurrent passing around it ', 

 in having the vena innominata, left carotid, left lung, and 

 pleura in front ; and in having the thoracic duct and lon- 

 gus colli muscle behind. In the second and third stages 

 the relations of the subclavian are nearly the same on both 

 sides. 



BRANCHES OF THE SUBCLAVIAN SUPPLYING THE NECK. 



The vertebral artery is the largest branch, and comes off 

 from the subclavian at its upper and posterior part. It then 

 ascends upon the vertebral column behind the inferior thy- 

 roid artery, and after a short course enters the foramen in 



