434 



Mr. W. P. Herringham. 



The nerve to the supinator brevis was traced thirteen times, in 

 every case to the 6th, but in five the 5th was not excluded. 



The two remaining divisions are the radial and the posterior in- 

 terosseous. The former was composed by the 6th alone thirteen 

 times, in seven of which the 5th was not excluded, twelve times it 

 was partly formed by the lower nerves. In all the seven cases when 

 the two lower nerves had been divided the 7th alone was found to 

 share in the radial. 



I was able in only one case to dissect the radial consisting of both 

 6th and 7th. In it the 6th supplied the ball and dorsum of the 

 thumb and the radial side of the index, while the 7th took the 

 remainder. 



The posterior interosseous was in seven cases formed by the lower 

 nerves entirely. In four it received also part of the upper nerves. 

 The question arose whether the 8th ever entered the muscles of the 

 forearm. Out of sixteen dissections, eleven foetal and five adult, 

 twelve of which four were adult showed the 8th to cease before the 

 forearm muscles were reached, four of which two were adult showed 

 the 8th coming round to the back of the arm. 



In two of these latter the 7th and 8th formed equal parts of the 

 posterior interosseous; in the other two cases the 8th gave so minute 

 a fibre to the nerve below the triceps that I could not trace it 

 separately. 



In several of these cases the 5th was not excluded from the 

 musculo-spiral, and must therefore be considered as a possible source 

 of the supply, but it must be remembered that the probability of its 

 taking part in the nerve is only, as before shown, nine in thirty-four, 

 and that when dissected in the nerve it was found only to enter the 

 short external cutaneous branch. 



These results show considerable variation in the distribution of the 

 nerve roots, although I do not think it is greater than in any other 

 of the structures of the body. But this variation is not extravagant. 

 If a type be composed from the foregoing materials and compared 

 with the varieties, it appears that if a muscle or a piece of skin is not 

 supplied by the typical nerve, the place is filled only by one of its 

 neighbours, not by a nerve far removed from it in the series. The 

 teres major usually supplied by the 6th is on occasion supplied by the 

 5th, and sometimes by the 7th, never by the 8th or 9th. 



Again, some muscles seem to bear definite relations to each other, 

 and their nerve supply seems also to vary solidly, so that the relative 

 position of the muscles judged by their nerve supply does not alter 

 although they be not served by the usual nerve. The best example 

 of this is in the three muscles which are attached along the inner 

 side of the bicipital groove, the subscapularis, teres major, and latis- 

 simus dorsi. The first is usually supplied by the 5th and 6th, the 



