226 Journal of Comparative Neurology. 



common North American frogs, so that beginning students might 

 not be entirely dependent upon the description of the European 

 forms which appear in the books most hkely to be consulted. 



Section II. Number and Size of the Nerve Fibers inner- 

 vating THE Thigh. 



A. Introdtiction. 



The thigh region was selected as the one most available 

 for the. numerical comparison of nerve fibers because the muscle 

 masses are of sufficient volume to make the study of their in- 

 nervation simple, and the nerves, both muscular and cutaneous, 

 can be identified with comparative ease. Possible comparison 

 with results already obtained through investigations in this lab- 

 oratory made a complete study of the distribution of all the 

 fibers of the lumbo-sacral plexus very desirable. This involved 

 so much labor that the attention was confined for the time be- 

 ing to the innervation of the thigh alone. 



The entire series of observations to determine the number 

 and size of the nerve fibers was first carried through on the nerves 

 of the left and right thighs of one frog (Sex, female. Length, 

 20. 5 cm. Weight, 49. 7 grams) with the expectation that the re- 

 sults from the two sides would serve as mutual controls. The 

 numerical results, although symmetrical for the two sides, were 

 in some particulars so unexpected that a second series of enum- 

 erations was made to test the accuracy of the first series. In 

 the second frog (Sex, female. Length, 20.5 cm. Weight, 45.4 

 grams) the innervation for both the right and the left thighs 

 was studied. This second series of observations confirmed the 

 numerical results of the first series. The determination of areas 

 was not undertaken in the investigations upon the second frog. 



I. Levels at which the computations were made. 



The levels at which the computations to determine the 

 number and area of the fibers were made, are indicated in 

 Figure II, by the interruptions in the continuity of the 

 nerve branches. The nerve designations correspond to those 

 already used in Figure I, and Tables I and II, with the excep- 



