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THE POPULAR SCIENCE MONTHLY 





as the nerves pass out from the spinal cord to reach the muscles 

 they again become separated and, as Ferrier and Yeo have dis- 

 covered, the motor roots which enter into the brachial plexus are 

 arranged with a view to definite co-ordinated movements. Now, 

 this plexus has been to me, and I think to many others, a perfect 

 perplexity, both in its anatomy and physiology. Yet, if we take 



it from the same 

 point of view as 

 we have taken the 

 motor centers, it 

 becomes compara- 

 tively simple. We 

 must not forget 

 that, although the 

 monkey is so much 

 like man that we 

 can draw most 

 useful deductions 

 regarding human 

 physiology from 

 experiments on 

 these animals, we 

 must not trans- 

 fer without more 

 ado the results of 

 these experiments 

 to man in their en- 

 tirety. We must 

 remember that 

 man, although for- 

 merly a frugivo- 

 rous and probably 

 more or less arboreal animal, is now very different from a monkey, 

 and experiments in the laboratory must be compared with and 

 corrected by those experiments which disease makes upon man in 

 producing localized palsies. I think it very probable that many 

 here would find it difficult to answer the question, What are the 

 movements which result in the monkey from stimulation of the 

 fifth cervical nerve ? — nor might he be able to remember them six 

 months hence even if he learned to-night that they consist in the 

 shoulder and arm being raised upward and backward, the humerus 

 rotated outward, the forearm flexed and supinated, the wrist ex- 

 tended, and the tips of the fingers flexed. But he would find it easy 

 enough to remember them, not for six months only, but for the 

 rest of his life, if he were told that they were simply those required 

 to raise the hand in such a way as to grasp an apple hanging 



Fig. 13. — Diagram of the Brachial Plexus. 



