chap, xii.] THE ARM. 207 



case reported by Tillaux, where paralysis followed 

 some time after a fracture, the nerve was found 

 embedded in callus, and on cutting some of the 

 redundant mass away a good recovery followed. In 

 several instances the nerve has been paralysed by the 

 pressure of the head when a man has slept with his 

 head resting on the arm in the position of full 

 supination and abduction. It is said to be often 

 paralysed in Russian coachmen who fall asleep with 

 the reins wound round the upper arm. It has also 

 been frequently damaged by the pressure of badly 

 constructed crutches, especially those that afford no 

 proper support for the hand. Indeed, it is the nerve 

 most often affected in " crutch paralysis," the ulnar 

 being the trunk that suffers next in frequency. 



Fracture of the shaft of the humeriis is 

 usually due to direct violence. The shaft may, how- 

 ever be broken by indirect violence, and of all bones 

 the humerus is said to be the one most frequently 

 fractured by muscular action. As examples of the 

 latter may be noted the throwing of a ball, the 

 clutching at a support to prevent a fall, and the so- 

 called trial of strength known as "wrist turning." 

 When the bone is broken above the deltoid insertion 

 the lower fragment may be drawn upwards by the 

 biceps, triceps, and deltoid, and outwards by the last- 

 named muscle ; while the upper fragment is drawn 

 inwards by the muscles attached to the bicipital 

 groove. When the fracture is below the deltoid 

 insertion, the lower end of the upper fragment may 

 be carried outwards by that muscle, while the lower 

 fragment is drawn upwards to its inner side by the 

 biceps and triceps. The deformity, however, as a 

 rule depends much more upon the nature and direction 

 of the force that breaks the bone than upon any 

 muscular action. The displacements just noted may 

 be met with, but usually they are quite independent 



