The Minute Anatomy of the Brachial Plexus. 



427 



6th to reach the muscle. It is therefore quite distinct not only from 

 the musculo-cutaneous, but from the 5th and 6th also. I have found 

 this arrangement constant in the foetus in more than twelve consecu- 

 tive cases, in fact ever since I first recognised it. I have also seen it 

 in the adult. 



In one case, however, I found the muscle supplied not only by this 

 nerve from the 7th, but also by a fibre from the 6th in the musculo- 

 cutaneous. 



The rest of the musculo-cutaneous, or as should be said, the musculo- 

 cutaneous nerve proper, hardly ever contains any fibres other than 

 those of the 5th and 6th. In thirty-nine cases, twenty-one foetal and 

 eighteen adult, the 7th only contributed to the musculo-cutaneous 

 four times, twice in the foetus, and twice in the adult. Of these four 

 exceptions, in two the 7th could not be traced down the nerve, in a 

 third it ran to the short head of the biceps, and in the fourth, an 

 adult case, it entered the cutaneous branch only. 



Twenty- eight cases were examined to see if both 5th and 6th 

 entered the nerve. In twenty-seven this was found to be the fact, in 

 one, only the 5th was traced into it. 



In eight cases the 5th and 6th were traced down the nerve. Four 

 of these were foetal, and four were adcdt. The biceps was found to 

 be served by both 5th and 6th in seven instances, in one the 5th alone 

 was traced to the muscle. The brachialis anticus was supplied by 

 both the 5th and 6th in four cases, and by the 5th alone in four. 

 The cutaneous branch was found to contain fibres from both roots in 

 six cases ; in one it was formed by the 6th and 7th. The bundle 

 from the 5th was noted as very small in two cases, and in two more 

 was found to supply the skin over the outer condyle and the head of 

 the radius, the nerve in the forearm being wholly derived from the 

 6th root. In another case it ran down the forearm over the flexor 

 carpi radialis in front of the branches from the 6th. 



The remaining nerve given from the outer cord is the outer head of 

 the median. Into this the 5th does not enter. Thirty-one dissections 

 showed no exception to this rule. The supply of the 5th by its 

 anterior branch ends therefore with the musculo-cutaneous nerve. 



The median is formed by two heads ; into the outer the 6th and 

 7th always enter, while the inner is formed always by branches of the 

 8th and 9th, sometimes with the addition of some bundles of the 7th. 

 This variety depends upon whether the anterior branch of the 7th 

 bifurcates or goes wholly to the outer cord. In order to see whether 

 both 8th and 9th contribute to the median, twenty- eight dissections 

 were made, fourteen in infants, fourteen in adults. In one foetus, 

 and in one adult, no branch from the 9th was found. These two 

 were, however, the only exceptions to the rule that both roots send 

 fibres to the nerve. The median then is made of the 6th, 7th, 8th, 



