230 



Dr. D. Ferrier. 



[May 10, 



and a repetition of the stimulation experiments which I have made, 

 have revealed an error in the enumeration of the roots of the brachial 

 plexus, which, in common with Professor Yeo, I wish to correct. What 

 we took for the first dorsal nerve has proved in reality to be the 

 second dorsal. Hence the results of the experiments must be read as 

 applying to the spinal nerves from the second dorsal to the fifth 

 cervical respectively, instead of from the first dorsal to the fourth 

 cervical, as stated in our paper. 



The anterior division of the second dorsal nerve in the monkey, 

 apparently invariably, gives a well developed communicating branch 

 to the first dorsal, besides giving off the second intercostal nerve and 

 a branch to the stellate or inferior cervical ganglion of the sympa- 

 thetic. 



The three branches, as seen in a dissection made for me by Mr. 

 Brooks, seem pretty equal in size, and all come off from the main 

 trunk together. 



The brachial plexus in man is not usually, in text-books of ana- 

 tomy, considered as deriving any of its component roots below the 

 first dorsal. In " Quain's Anatomy" (9th ed., p. 619), however, a 

 branch from the second to the first dorsal is given as a variety. On 

 this subject Dr. >D. J. Cunningham has published a note in the 

 "Journal of Anatomy and Physiology," vol. xi, Part III, p. 539, 1877. 

 Dr. Allen Thomson having mentioned to him that he had«n<one or 

 two occasions seen such a communicating branch in man, he in- 

 vestigated the point, with the result of finding a communicating 

 branch from the second to the first dorsal in twenty-seven out of 

 thirty-seven dissections. Of the ten cases where it was not fountl, 

 five were so complicated by previous interference in the dissecting- 

 room or by pleuritic adhesions and thickenings, that they may be con- 

 sidered as doubtful. But, even including these, it appears that the 

 second dorsal sends a communicating branch to the first in seventy- 

 three per cent, of the cases. Hence it should be considered as more than 

 *a mere variety. If a perfect homology exists between the roots of the 

 plexus in man and the monkey, the second dorsal root would be the one 

 presiding over the intrinsic muscles of the hand. Presumably in 

 those cases where it is not found, its functions are represented in 

 the first dorsal. 



Dilator Nerve of the Iris. — Professor Yeo and I mentioned in our 

 paper ($ujp. cit.) that in one case in which we directed special attention 

 to the pupil, stimulation of the anterior roots from the first dorsal to 

 the fourth cervical — in reality from the -second dorsal to the fifth 

 cervical — caused no change in the pupil, though the movements of 

 the limb occurred with regularity. 



I have isince investigated this point during the course of another 

 research on which I have been for some time engaged. I have 



