318 DISLOCATIONS. 



off, the animal may be gradually put to work, or turned out to 

 grass, as the case may be. 



I have compiled the foregoing remarks on dislocation of the 

 patella chiefly from Peuch and Toussaint's " Chirurgie Veterinaire." 



Dislocation of the Shoulder Joint. 



This injury is of extremely rare occurrence, although a good 

 deal has 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 articulating 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. 



DEFTNITION.— 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, according to Moller, 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; we 

 may conclude that the most likely position of the limb for this 

 accident to occur in, is when the fore arm is stretched forward. 

 Hence, if a horse 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 of and above it. The flexor brachii (Fig. 31) acts in pre- 

 serving the stability of the shoulder joint by exerting a downward 

 and backward pressure on the head of the humerus. 



SYMPTOMS.— There will be marked deformity of the point of 

 the shoulder, as may be seen if it be compared with the other 



