316 DISLOCATIONS. 



recur, and the involved joint becomes more and more liable to it, 

 by repetition ; the remedial means described should not be 

 neglected. After the effects of the second blister have gone off, 

 tlio animal may be gradually put to work, or turned out to grass, 

 as the case may be. 



Dislocation of the Shoulder Joint. 



This injury is of extremely rare occurrence, although a good deal 

 lias been written about it. 



ANATOMY OF THE PARTS.— This is a ball-and-socket joint, formed by 

 the rounded head of the humerus and the shallow cavity which is on the 

 lower end of the shoulder blade (Scapula, Fig. 115). It possesses only one 

 ligament, the capsular ligament, which envelops it like a bag, open at both 

 ends, one end of which is attached round the cavity in the end of the 

 shoulder blade : while the other is fixed round the head of the humerus. 

 This capsular ligament loosely envelops the joint and allows the two arti- 

 culating surfaces the power of separating from each other to the extent of 

 nearly an inch. The stability of the joint is maintained by the muscles of 

 the part, which more or less serve the purpose of ligaments to it, and also 

 by the pressure of the atmosphere. 



DEFINITION.— The joint (Fig. 31, p. 59) here involved is 

 usually termed " the point of the shoulder," and is composed of 

 the lower end of the shoulder blade and the head of the humerus, 

 the latter being always found in this accident above, and to the 

 front of the former. The head of the humerus will also be usually 

 displaced to the outside of the end of the shoulder blade. 



CAUSE. — Taking into consideration the position of the bones 

 after this dislocation and the fact that the more the elbow joint 

 is bent and the shoulder joint straightened, the more easily can 

 the head of the humerus be displaced in a forward direction ; the 

 most likely position of the limb for this accident to occur in, is 

 when the fore arm is stretched forward. Hence, if a liorse falls, 

 for instance, in jumping or from '' slipping up," and comes down 

 on the ground with his fore arm stretched out to the front, with 

 or without the leg below the knee being doubled under it ; the 

 shock, being transmitted more or less vertically upwards through 

 the humerus, would naturally tend to force the head of that bone 

 out of the cavity (at the lower end of the shoulder blade) in which 

 it normally rests, and in a direction in front and above it. The 

 flexor brachii (Fig. 31) acts in preserving the stability, of the 

 shoulder joint by exerting a downward and backward pressure 

 on the head of the humerus. 



