1+8 THE SURGICAL ANATOMY OF THE HORSE 



The inferior primary divisions of the first and second dorsal nerves, 

 it will be remembered, contribute to the formation of the brachial 

 plexus, and to reach the plexus these roots twist round the anterior 

 border of the bone, where there will be found a groove on the bone tor 

 their accommodation between its upper and middle thirds. From these 

 roots the fibres of the musculo-spiral nerve are almost entirely derived, 

 and it is not difficult to conclude that fracture of the rib might injure, 

 and that the formation of a callus during the healing process would exert 

 undue pressure upon, the dorsal contributions to the plexus, leading to 

 paralysis of the nerve chiefly derived from them. It is much more 

 probably due to this than to injury to the plexus itself Moreover, we 

 find in these cases that the rib is usually fractured between the upper 

 and middle thirds. 



Recently a case showing typical symptoms of dropped elbow has 

 been recorded by Wolstenholme {Veterinary Record, January 12, 1907). 

 It was "a marked case of dropped elbow in a cart horse, which on post 

 mortem showed same to be due to a shallow abscess in the rear of and 

 in close proximity to the lower third of the near radius. There was 

 no fracture or other lesion of the first rib. The lesion above the knee 

 had been recognised and treated, but the 'dropping' of the elbow was 

 so marked, and the whole symptoms so typical of interference with the 

 nerve-supply, that it was thought possible that there might be a lesion 

 of the first rib." As Hunting pointed out, the position of the limb 

 was impossible without loss of power in the triceps extensor cubiti 

 muscle, or fracture of the olecranon process of the ulna. The post 

 mortem examination only revealed an abscess in the position stated, and 

 in this situation the lesion could have had no effect on the dropped elbow, 

 and may be looked upon as an accidental complication. This contention 

 is supported upon simple anatomical grounds. 



In complete paralysis there is relaxation of, and inability to contract, 

 all the muscles supplied by the nerve. The elbow is flexed, the knee is 

 slightly bent, and the fetlock and interphalangeal joints are kept in a 



