Dunn, Inmruation of the ThigJi in the Frog. 241 



The second sciatic cutaneous branch, ramus cutaneus medi- 

 alis, has, for the left leg, 83 fibers in an area of .01 of a square 

 millimeter, and supplies an average area of 1 1 7 square micra 

 for each of its fibers. The average area for each fiber of the 

 same branch of the right thigh is 1 1 1 square micra. 



The totals for all the cutaneous fibers to the thigh. Table 

 XIII, show for the left thigh a total number of 871 fibers, a 

 total area of . 1 1 5 of a square millimeter and an average area of 

 132 square micra for each fiber. For the right side of the same 

 frog, the totals are approximately the same, giving an average 

 area of 133 square micra for each fiber. 



To compute the average area for the muscular fibers to the 

 thigh, the totals for the cutaneous thigh fibers were subtracted, 

 Table XIV, from the totals for all the branches to the thigh, 

 given in Table XI. The differences give the totals for the mus- 

 cular fibers. By this method we find that for the left thigh, 

 the muscular fibers number 1729, and have a section area of 

 .327 of a square millimeter. The average area for each of these 

 fibers is 189 square micra. The muscular branches for the 

 right thigh vary but slightly from those of the left thigh, and 

 give an average area of 184 square micra for each fiber. 



Hence we observe that the average area for each cutaneous 

 fiber to the thigh is somewhat less than the average area for all 

 the thigh fibers, and that a marked superiority in size is exhib- 

 ited by the muscular fibers when their average area is compared 

 with the average area for the cutaneous fibers. 



3. Average area for each fiber innervating the shank and foot. 



The measurements to determine the average area for each 

 fiber innervating the shank and foot were made upon a section 

 of the sciatic nerve at the level S,, Figure II, just distal to the 

 last of the sciatic thigh branches, since all the fibers to the 

 shank and foot run in the sciatic nerve. At that level in the 

 left sciatic nerve of frog B, we find, Table XII, 2974 fibers in 

 a section having an area of .371 of a square millimeter. By 

 process of division an average area of 125 square micra is de- 

 termined for each nerve fiber. The right sciatic nerve at the 



