THE NECK 127 



In order that the important nerves may not be injured, the 

 loose fat which lies on the floor of the triangle is best removed 

 by the finger, covered with gauze. 



In exposing the brachial plexus after injuries by gunshot 

 wounds, or in obstetrical paralysis, etc., the sterno-mastoid is 

 drawn forwards and the scalenus anterior is then brought into 

 view. If there is little scar tissue the nerves may be looked 

 for at the lateral border of the scalenus anterior, from behind 

 which they emerge. The prevertebral fascia must be incised, 

 and C. 5 is found about an inch above the posterior belly of the 

 omo-hyoid. But if much scar tissue is present it is easier and 

 safer to look for the supra-scapular nerve first. It will be found 

 by blunt dissection in the angle between the clavicle and the 

 anterior border of the trapezius, and it can then be traced medi- 

 ally to its origin from the upper trunk of the plexus, formed 

 by the union of C. 5 and C. 6. 



These nerves can be followed to the point where they emerge 

 from under cover of the scalenus anterior, and the lower nerves 

 of the plexus can then be identified. C. 8 and T. i unite to form 

 the lower trunk behind the scalenus anterior. This nerve trunk 

 generally lies just below the omo-hyoid and above the subclavian 

 artery, but sometimes it is found behind the artery, occupying 

 the posterior part of the subclavian groove on the upper surface 

 of the first rib. 



An oblique incision, running from the junction of the middle 

 and lower thirds of the posterior border of the sterno-mastoid 

 to the angle between the trapezius and the clavicle, may also 

 be used in the exposure of the brachial plexus. If necessary, 

 it may be prolonged across the clavicle, and the bone may be 

 divided temporarily. The external jugular vein is exposed and 

 ligatured, and the omo-hyoid is freed and retracted upwards or 

 downwards. 



If end to end union is found to be impossible after excision 

 of the scar tissue in a torn cervical nerve, the proximal end of 

 the injured nerve may be implanted directly into the next nerve 

 of the series. 



Bilateral Ulnar Paresis and Analgesia sometimes supervene if a person, 

 who usually sleeps on one or other side, falls asleep lying on his back. The 

 explanation is to be found in the close relationship between the first thoracic 

 nerve (or the lower trunk) and the first rib, for the weight of the shoulders 

 falling backwards is sufficient to cause pressure on the nerve. For a similar 

 reason, symptoms resembling those produced by a cervical rib (p. 100) may 

 occur in patients who are restricted to a dorsal decubitus after abdominal 



