308 JoURNfAL OF COMPARATIVE NEUROLOGY. 



nished control results for this third set of observations. The 

 fourth level was at the ankle. At this point four trunks, Ti, 

 T2, Pi, and P2, the subdivisions of the tibial and peroneal 

 nerves, were sectioned. 



The branches to the thigh and to the shank were sectioned 

 as close as possible to their points of separation from the main 

 trunks, as is indicated in P'igure 2. 



2. Methods of observation. 



The methods of observation followed in this work varied 

 but slightly from those used in the preceding study, Dunn, 

 1900. As soon as possible after the frog was chloroformed 

 and its weight and length ascertained, the nerve tissue at the 

 chosen levels was laid bare, the overlying tissues being so care- 

 fully separated that the nerve tissue was undisturbed. Into the 

 cup-like cavity of the surrounding tissues was dropped a small 

 portion of a one per cent, solution of osmic acid. This 

 hardening agent fixed the undisturbed tissue, and made possible 

 a later removal and further fixation of it. After this prelimi- 

 nary fixation of from fifteen to thirty minutes the tissues were 

 carefully lifted into a capsule containing one per cent, osmic 

 acid solution and the capsule placed in a darkened chamber for 

 twenty-four hours. After the expiration of this period and an 

 additional three hours of washing in distilled water, the material 

 was carried through increasing percentages of alcohol, cleared 

 in xylol and embedded in paraffin. 



The sections were cut in ribbons by a Minot microtome to 

 a thickness of three and one-third micra, and, after being spread 

 by gentle heat, were fastened to the slides with albumen fixa- 

 tive. Thorough drying was followed by a second clearing in 

 xylol, after which the sections were mounted in colophonium 

 under thin cover glasses. 



a. Enumeration. The fibers in the sections of the main 

 trunks were enumerated by the "photographic method" which 

 has been used and described by Dr. Hardesty, 1899. 



For the thigh and shank branches the "net method" was 

 adopted. 



