PARALYSIS OF THE SUPRASCAPULAR NERVE 143 



where it curves round the coracoid border of the scapula. Violent 

 blows over this area such as the animal receives when colliding with 

 trees, door frames, or other firm objects, are very frequently the cause. 

 Another cause is undue tension thrown upon the nerve when the 

 shoulder becomes pressed forcibly backwards. Cases have also been 

 reported of paralysis of this nerve resulting from casting where the 

 subject has been kept down for a considerable length of time. 



It is upwards of a century since attention was first drawn to this 

 lameness, and it was attributed to various causes, but was most fre- 

 quently associated with some injury to the infraspinatus muscle or its 

 tendons of insertion. Gunther first ascertained that it was the result of 

 paralysis of this nerve. 



The first symptom which presents itself is loss of power in the 

 supraspinatus and infraspinatus muscles, which are supplied by this nerve. 

 Dollar in his translation of Moller's Surgery also includes the two teres 

 muscles. The teres major, however, derives its innervation from a 

 special nerve which leaves the brachial plexus in conjunction with the 

 circumflex nerve, whilst the circumflex nerve itself supplies the teres 

 minor. 



The attachments of the tendons of these muscles and the influence 

 which the muscles exert in maintaining the head of the humerus in 

 position in the glenoid cavity have already been explained. This 

 influence is now lost, and since these two tendons played the part of a 

 powerful external lateral ligament, the result is that when pressure is 

 placed upon the limb the humeral head rotates in the cavity, and since 

 the subscapularis and biceps are not affected, the head is pressed 

 outwards, a movement which is plainly visible and which is permitted 

 by the loose manner in which the only true ligament of the joint, 

 namely the capsular, is attached to the bones. This peculiar and 

 characteristic slipping out of position of the head of the humerus gave 

 rise to the term " shoulder slip." 



As the disease progresses we get atrophy of the two muscles lying in 



