228 Journal of Comparative Neurology. 



Special sections were made of all the cutaneous subdivisions of 

 these main branches of the sciatic nerve at the levels where 

 their character as cutaneous nerves could first be recognized. 



2. Methods of observation. 



The frog was chloroformed and its length and weight ascer- 

 tained. The ovarian tissue was removed and weighed, and its 

 weight deducted from the total weight. The length was meas- 

 ured from the tip of the nose to the end of the longest digit. 

 After division and retraction of the skin, the superficial muscles 

 were separated sufficiently to bring the nerve trunks into view 

 but not so widely as to put on tension the nerve branches sup- 

 plying the muscles. Upon the nerve tissue thus exposed a so- 

 lution of osmic acid, i%, was dropped. A certain portion of 

 the solution was retained in the cavity formed by the retracted 

 tissues, and fresh solution was added from time to time until 

 fifteen or twenty minutes of exposure to the action of the reagent 

 assured the fixation of the tissue in its normal condition. The 

 portions selected, indicated in Figure II, were now carefully 

 removed, and, after being placed in i fo osmic acid, were left 

 in a dark chamber for twenty-four hours. At the expiration of 

 that time the material was washed in distilled water for two 

 hours. After dehydrating in increasing percentages of alcohol 

 and clearing in xylol, the material was embedded in paraffin by 

 the usual process, care being exercised to identify in every in- 

 stance the proximal and distal ends of each portion. 



The sections were cut with the Minot microtome to a thick- 

 ness of 3^ micra, fastened to the slide with albumen fixative, 

 cleared in xylol and mounted in colophonium. 



a. Enumeration. Two methods were used for enumerating 

 the nerve fibers. 



The "net method " was employed for all sections of an 

 area small enough to present the entire surface in the field under 

 a magnification of 460 diameters. 



The photographic method was found to be more satisfac- 

 tory for all larger sections. This method has already been de- 



