FEACTUEES OF THE HUMEEUS. 85 



muscular action. It will then be detached from its base, but its 

 displacement is slight, owing to the hold upon it exerted by the 

 coraco-acromial and coraco-clavicular ligaments, which are 

 seldom torn. 



The rarity of fracture of the body of the scapula is due to its 

 free mobility, and its close investiture by the supraspinatus, 

 infraspinatus, and subscapularis muscles. Separation of the 

 fragments is but small, and crepitus may be difficult to elicit, 

 because of the position of the same muscles. 



In a fracture through the neck of the scapula, which is the 

 constricted portion internal to the glenoid fossa, the coracbid 

 process will be attached to the outer, smaller fragment. 

 Hence the fragment will be drawn downwards by the pectoralis 

 minor, the biceps and coraco-brachialis, and if the coraco- 

 clavicular and coraco-acromial ligaments are torn, there will be 

 a distinct lengthening of the arm. 



Fractures of the Humerus. Fracture of the surgical neck. 

 The surgical neck of the humerus is the one which is most 

 commonly the seat of fracture, partly on account of its being a 

 weak part of the bone, but chiefly because in certain positions of 

 the upper extremity it is subjected to a very considerable strain, 

 as, for instance, when the arm is abducted. The bone breaks as 

 a rule between the base of the tuberosities and the upper part of 

 the insertions of the latissimus dorsi and the teres major muscles. 

 When the lesion has occurred, there is generally a very charac- 

 teristic displacement of the fragments occasioned by the action of 

 muscles. The upper fragment is abducted by the supraspinatus 

 and externally rotated by the infraspinatus and the teres minor. 

 The lower fragment has its upper end drawn upwards by all the 

 muscles running in a vertical direction, namely the biceps, the 

 deltoid, the coraco-brachialis, and the triceps. It is also adducted 

 by those which have a more or less horizontal direction, namely, 

 the pectoralis major, the latissimus dorsi, and the teres major. 

 In addition, there may be some forward displacement by the 

 action of the great pectoral muscle. If the two fragments remain 

 in apposition as sometimes happens, it is probable that the long 



