chap, xi.] THE SHOULDER-JOINT. 197 



the bone be carried a good deal forwards and inwards, 

 and the limb be abducted. When the head has left 

 the glenoid cavity abduction tends to bring the 

 external condyle nearer to the acromion, and these 

 are the two points between which the measurement is 

 usually taken. Thus the apparent length of the arm 

 depends mainly upon the degree of abduction of the 

 humerus, or the obliquity of the axis of the bone. 



2. Sufoglenoid. The head is below, and a 

 little in front of and internal to, its normal position. 

 It cannot go directly downwards, owing to the situa- 

 tion of the long head of the triceps, but escapes in 

 the interval between that muscle and the subscapularis. 

 The articular head rests on the anterior aspect of the 

 triangular surface just below the glenoid fossa that 

 gives origin to the triceps. The upper border of the 

 great tuberosity is in close relation with the lower 

 margin of the joint. It is generally stated, on the 

 authority of Malle, that the circumstance which pre- 

 vents the head of the bone from being drawn upwards 

 is the entirety of the anterior part of the capsule, the 

 rent being in the lower part only of that ligament. 

 The subscapularis muscle is much stretched or torn, 

 and the head usually lies beneath its tendon, and 

 upon some fibres of the disturbed muscle. The supra- 

 spinatus will be torn. The infraspinatus will be 

 stretched or torn, and the two teres muscles will not 

 be much affected unless there be considerable abduc- 

 tion of the arm. The coraco-brachialis and biceps will 

 be stretched, but owing to the amount of abduction 

 usually present the biceps tendon is but little deflected 

 from a straight line. The deltoid is greatly stretched, 

 and its tension serves to produce the extreme flatten- 

 ing of the shoulder, and the great abduction common 

 in this injury. Some lengthening is seldom absent, 

 although it is always modified by the abduction that 

 exists. 



