THE MUSCULO-SPIRAL (OR RADIAL) NERVE 145 



brachial vessels until it arrives at the point where the deep humeral 

 artery is given off from the brachial. Here the nerve disappears from 

 view by passing in front of the large head of the triceps extensor cubiti 

 muscle and between this muscle and the brachialis anticus. It accom- 

 panies the branch of the deep humeral artery round the musculo-spiral 

 groove, where the nerve will be found lying on the posterior border of 

 the brachialis anticus muscle. By following the muscle named the 

 nerve gains the front of the elbow joint. In this situation it will be 

 found to be deeply placed between the extensor metacarpi magnus 

 outwardly and the brachialis anticus inwardly, in company with the 

 anterior radial artery. The remainder of its course is in an almost 

 v^ertical direction along the anterior aspect of the shaft of the radius, 

 where it is covered by the extensor pedis muscle, and its ultimate 

 termination is in the extensor metacarpi obliquus muscle, which muscle 

 it supplies, and before entering which it splits up into two filaments. 



During its course the musculo-spiral nerve gives off the following 

 branches :— 



(i) A thick but short branch is given off before the nerve disap- 

 pears in front of the caput magnum. This divides into branches which 

 take an upward direction, pass round the common tendon of insertion 

 of the teres major and latissimus dorsi muscles, and penetrate the great 

 head of the triceps extensor cubiti, and branches which descend and 

 terminate either in the caput medium or parvum, or in the lower portion 

 of the caput magnum. 



(2) Another branch, which is long and slender, is given off before the 

 nerve passes behind the humerus. This nerve runs to supply the scapulo- 

 ulnaris muscle, which it enters on its inner aspect. 



(3) Whilst the nerve is twisting round the back of the arm it gives 

 off filaments which supply the middle head of the triceps, and also the 

 anconeus muscle, and in addition a number of small filaments which 

 descend the anterior aspect of the arm subcutaneously. 



(4) When it reaches the front of the limb, large branches are given 



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