MUSCULO-SPIRAL OR RADIAL PARALYSIS 147 



extremely prominent, and is one of the parts of the body upon which 

 the ground exerts pressure when the animal is in the recumbent position. 

 It will be readily understood, therefore, that the inability of this 

 muscle in such cases is due rather to interference with the circulation 

 through it than to any affection of the nerve by which it is supplied — 

 a view which is supported by the fact that lameness quickly 

 disappears, particularly after exercise. 



Other cases of paralysis have been noted wherein all the muscles 

 supplied by the musculo-spiral nerve have not been affected. In these 

 cases the muscles usually affected have been found to be the large and 

 small heads of the triceps extensor cubiti. Again referring to our 

 description of the nerve, these cases will be readily understood, for in 

 them it is most probable that the whole nerve is not affected, but only 

 the first branch which we described, and which, as already stated, is 

 very short, and consequently is the most likely to be unduly stretched 

 when any great strain is thrown upon the parts. 



MoUer reports having observed a kind of epidemic of cases of radial 

 paralysis in 1887, and amongst them a number which were only partial 

 paralysis, as described above. No adequate explanation has been forth- 

 coming as to the existence of any peculiar contributory factor to the 

 occurrence of a large number of cases in a comparatively brief period of 

 time, but the probability is that this affection occurs with much greater 

 frequency than is accredited to it. 



We have in recent years been made acquainted with a definite cause 

 of radial paralysis, for which we are indebted to the oft and accurately 

 recorded observations of Hunting, Willis, and Rogers, who were the first 

 to associate the affection with fracture of the first rib. Cases have so 

 frequently been recorded since, that we are bound to admit that 

 although instances of the affection occasionally occur which are not 

 associated with the fracture, the rib is found to be fractured in by far 

 the greater number. Moreover, this theory of the causation is easily 

 and rationally explained. 



