146 THE SURGICAL ANATOMY OF THE HORSE 



off which supply the extensor metacarpi magnus, the extensor pedis, and 

 the extensor suffraginis. These branches are given off at the front of 

 the elbow joint, where the musculo-spiral nerve is placed between the 

 brachialis anticus and extensor metacarpi magnus. 



(5) A small branch is given off which runs between the extensor 

 pedis muscle and the radius, and near the radio-ulnar arch it enters the 

 flexor metacarpi externus muscle, which it supplies. 



Summarising the distribution of this nerve, therefore, we find that 

 it supplies the flexor metacarpi externus muscle, the extensor muscles of 

 the elbow, the extensors of the knee, fetlock and inter-phalangeal joints, 

 and in addition is a sensory nerve to the skin covering the anterior 

 aspect of the upper portion of the limb. 



MUSCULO-SPIRAL OR RADIAL PARALYSIS 



Severe lameness due to paralysis of the musculo-spiral nerve is by no 

 means infrequent. The paralysis may be partial or complete. The 

 disease was first described by MoUer more than thirty years ago. Several 

 theories have been set forth as to the causation. Some observers main- 

 tained that it was an affection of the muscles themselves, citing in some 

 cases the caput muscles, and in others the extensors of the knee, fetlock, 

 and interphalangeal joints. Attention was, however, drawn to the fact 

 that the pathological changes were always confined to the muscles 

 supplied by the musculo-spiral nerve, with the result that it was con- 

 cluded that the changes in the muscles were secondary to an affection of 

 the nerve itself, a conclusion which has been amply justified by sub- 

 sequent observations. 



Cases of temporary paralysis of the triceps extensor cubiti muscle 

 have been observed to occur after casting for a prolonged period of time. 

 It will be remembered from our superficial examination that this 

 muscle forms a rounded bulging elevation. This in some animals is 



