A NOTE ON THE SIGNIFICANCE OF THE SIZE OF 

 NERVE FIBERS IN FISHES/ 



By C. JuDSON Herrick. 



The observations upon the relation between diameter and 

 distribution of nerve fibers in the frog, reported upon by Miss 

 Dunn ('02), call to mind certain facts which came under my 

 notice in the prosecution of my researches on the nerve com- 

 ponents of fishes and which may serve to supplement as well as 

 to verify her observations. 



The eye-muscle nerves of Menidia I have found (see Sec- 

 tion 9 of the work cited in the appended bibliography) to con- 

 tain both typical coarse motor fibers and also very fine fibers 

 which leave the brain bound up in the same root with the 

 others, but terminate peripherally on a different set of muscle 

 fibers. All of the extrinsic eye-muscles have, in addition to 

 the usual large muscle fibers, a large number of very small 

 ones. These latter are, for the most part, segregated into a 

 separate slip, which may have a slightly different origin from 

 the main muscular mass. The finer nerve fibers can be sepa- 

 rately followed from the superficial origin of the nerve to their 

 insertion in the muscle and the separation of the finer muscle 

 fibers from the coarse ones makes it easy to determine the 

 exact distribution of the two kinds of nerve fibers. To quote 

 from the work just cited (p. 389), "In the case of each of the 

 six eye-muscles of which we have just been treating, the side 

 along which the finer fibers of its nerve run contains much 

 smaller muscle fibers than those which make up the body of the 

 muscle, the diameter of these small muscle fibers often being 

 no greater than that of a large nerve fiber. The smaller 



'Studies from the Neurological Laboratory of Denison University, No.XVI. 



