690 journal of Comparative Neurology and Psychology. 



In the shank some deviation from the tabulated scheme is found 

 in the derivation from the I^. tibialis, before its division into Tl 

 and T2, of a small cutaneous branch, while a larger cutaneous 

 branch was given oif from Tl from which no cutaneous branch usually 

 arises. Two muscular branches were also found where one usually 

 is present. The upper branch of P2a in the left leg was not found, 

 because of anomalous branching or of faulty technique. The sub- 

 stituted number of nerve fibers in this case is marked by parentheses 

 wherever it is mentioned in the tables. 



ClIAKACTEK OF THE ]!*TeEVE BrANCHES^ MuSCULAK^ CuTAlSTEOUS OE 



Aeticulae, in which Medullated Neeve Fibees have 

 Deopped Out, and Compaeison with Coeeesponding Find- 

 ings FOE the Control, Feog IIB. 



The value of the present study for the frog depends largely on 

 the uniformity in the numbers of medullated nerve fibers for the cor- 

 responding trunks and branches on the two sides. This uniforaiity 

 was determined in the previous studies, Dunn, 1900, and 1902. 



These nerve trunks are made up of two groups of medullated 

 nerve fibers, those leaving the spinal cord by way of the ventral 

 roots, or ventral root fibers, and those connected with the dorsal 

 roots and spinal ganglia, or dorsal root fibers. The ventral root 

 fibers conduct impulses chiefly, if not entirely, away from the cen- 

 tral nervous system and are therefore named efferent nerve fibers. 

 The dorsal root fibers conduct impulses toward the central nervous 

 system and are termed afferent fibers. Either descriptive term is 

 used in this paper when referring to these two groups of nerve 

 fibers. 



The present inquiry determines not only the number of dorsal 

 root or afferent nerve fibers at various levels, remaining intact after 

 the severing of the ventral roots, but by a comparison of each pri- 

 mary branch with the corresponding branch of the opposite leg 

 shows us the approximate number of degenerated ventral root or 

 efferent fibers at each level. 



Counts of the medullated nerve fibers were made at selected levels 

 for the two legs. Fig. 1, repeated from page 307, Dunn, 1902, 



