THE NECK 131 



and passes backwards through the scalenus medius, emerging 

 on its lateral surface, under cover of the posterior belly of the 

 omo-hyoid. It disappears by passing between the levator 

 scapulae and the scalenus posterior. 



The Long Thoracic Nerve (of Bell) arises by three roots, 

 from C. 5, 6, and 7. The first root arises in common with the 

 dorsalis scapulae nerve, but separates from it in the scalenus 

 medius and appears on the surface of the muscle at a slightly 

 lower level. The second root also pierces the scalenus medius, 

 and unites with the first to form a common trunk, which runs 

 downwards to the axilla behind the main part of the plexus. 

 The root from C. 7 arises near the lateral border of the scalenus 

 medius, and enters the axilla before uniting with the rest of the 

 nerve. 



Both the dorsalis scapula and the long thoracic nerves lie behind 

 the prevertebral fascia, and, in removal of the poster o-inferior group 

 of the deep cervical lymph glands, they are in no danger so long as 

 the fascia is not disturbed. In operations in which the pre- 

 vertebral fascia requires to be opened, e.g. repair of brachial 

 plexus, these two nerves should be found and isolated as soon 

 as the fascia is incised. 



The Third Part of the Subclavian Artery commences 

 at the lateral border of the scalenus anterior, and extends down- 

 wards and laterally to the outer border of the first rib. Near 

 its termination, the artery lies completely behind the clavicle. 

 If pressure is exerted in a downward, medial, and backward 

 direction in the angle between the posterior border of the sterno- 

 mastoid and the clavicle, the subclavian artery can be compressed 

 against the first rib. 



In making the incision for the purpose of ligaturing this part 

 of the subclavian artery, the surgeon draws the skin down over 

 the clavicle and incises it along the bone. When the skin is 

 allowed to retract upwards, the deep fascia, which cannot be 

 drawn down with it, is found exposed but not incised, and 

 therefore there is no risk of injury to the underlying veins in 

 making the incision. After division of the deep fascia, the 

 external jugular vein is found as it crosses the artery to 

 join the subclavian vein. It receives the transverse cervical 

 and transverse scapular (supra-scapular) veins from the lateral 

 side, and these vessels, though often very large, must not be 

 mistaken for the subclavian vein, which lies at a lower level 

 and is under cover of the clavicle. The posterior belly of the 



