Dunn, hmervation of the Thigh in the Frog. 229 



scribed by Dr. Hardesty' as used in his enumeration of the 

 fibers forming the spinal nerves. 



In using both methods, special attention was given to the 

 recognition of the smallest medullated fibers, which so readily 

 escape observation under ordinary circumstances. 



b. Determination of areas. For the determination of the 

 areas of the sections whose fibers had been counted, drawings 

 at a magnification of 165 diameters were first made by the aid 

 of a camera lucida. The boundary line was located at the peri- 

 phery of the most external fibers and within the epineurium. 

 By this method the area measured was limited to that actually 

 occupied by the fibers, plus the space between the fibers. The 

 area covered by this camera drawing was determined by the 

 planimeter. This form of integrator for measuring the area of 

 a plane surface by carrying a pointer around its boundary and 

 reading the indications from a scale, furnishes a most convenient 

 instrument for determining the areas of nerve sections. 



On the basis of the magnification the true area of the sec- 

 tion was estimated. The estimate was controlled by the meas- 

 urements of diameters made directly on the section itself. 



B. Ntanber of Nerve Fibers. 

 The study of the number of nerve fibers supplying the 

 thigh in Rana virescens is based upon data obtained by an ex- 

 amination of two frogs, frog I^, Sex, female. Length 20.5 cm. 

 Weight, 49.7 grams, and frog C, Sex, female. Length, 20.5 cm. 

 Weight, 45.4 grams. A count was made at corresponding levels 

 for the two sides and the numbers given in the tables are the 

 result of actual enumeration. The tables dealing with numbers 

 alone are those from III to VII inclusive. The levels at which 

 sections and counts were made are illustrated and explained by 

 Figure II and the text accompanying that figure. 



I. Comparison of the number of nerve fibers for the right 

 and the left sides. 



The total number of nerve fibers innervating each leg is 

 nearly the same. In the case of frog B, the number for the left 



* The Number and Arrangement of the Fibers forming the Spinal Nerves 

 of the Frog (Rana virescens). Irving Hardesty. The Journal of Comparative 

 Neurology y Vol. IX, No. 2, 1899. 



