MEDULLA TED NERVE FIBERS 431 



the largest had a diameter of thirteen micra, the remainder had a 

 diameter intermediate between thirteen and ten micra. Of the 

 second group, the smallest fibers had a diameter of four micra. 

 For comparison with these measurements the size of the central 

 fibers of the dorsal root was determined. The largest fibers in 

 the dorsal root of this Xth nerve had a mean diameter of eighteen 

 micra and the smallest fibers a mean diameter of less than two 

 micra. If the fibers under discussion are central fibers from the 

 dorsal root ganglion it follows that they are neither the largest 

 nor the smallest of the dorsal ganglion fibers, but are intermediate 

 in size. 



The preservation of these undegenerated medullated nerve 

 fibers after complete and prolonged separation of the ventral 

 root from the spinal cord, and their relations to other structures 

 in the ventral root seem sufficient evidence of the peripheral 

 location of their perikarya. If the validity of this evidence is 

 admitted the question of the location of the perikarya at once 

 arises. Peripheral nerve cells are foXind in the spinal ganglia 

 and in the sympathetic ganglia. I am inclined to interpret 

 the origin of this group of nerve fibers as from the spinal ganglia, 

 because of their relation to the structures within the ganglion. 

 If these fibers in the ventral root originate in sympathetic ganglia, 

 their central course must be by way of the peripheral portion of 

 the dorsal root, as careful search revealed no medullated nerve 

 fibers, large or small, entering the ventral root from the peripheral 

 nerve. The size, also, is greater than the size attributed to the 

 postganglionic medullated nerve fibers of Langley. Reference 

 has already been made to the close association of these fibers 

 with the perikarya at the periphery of the ganglion. 



For an interpretation of the functional significance of such 

 nerve fibers as have been noted in this frog it is necessary to 

 pass in review the findings of others who have noted the presence 

 of atypical fibers in the ventral or dorsal roots. 



Sherrington ('94) noted the presence of undegenerated med- 

 ullated nerve fibers in the lumbo-sacral roots of the monkey and 

 the cat. Sherrington interprets these ventral root fibers as 

 having their origin in the peripheral portion of the posterior 



