Dunn, Innetvation of the Thigh in the Frog, 



227 



tion of S„ and S,, which have been added to indicate the 

 points of section of the sciatic nerve above and below its 

 branches. The levels were so selected as to include all the 

 fibers from the plexus lumbo-sacralis which innervate the skin 

 and muscles of the hind leg of the frog. 



FIGURE II. 

 From a dissection of the right plexus lumbo-sacralis of Rana virescens, 

 showing the primary branches of the Crural and Sciatic Nerves. The inter- 

 ruptions in the nerve branches mark the levels at which the computations for 

 the number and the size of the fibers were made. The designations are those 

 used in Figure I, and Tables I and II, with the exception of Si and S2 , which 

 are added to indicate the levels of section of the Sciatic Nerve above and below 

 its thigh branches. 



The crural nerve was sectioned just proximal to its 

 division into branches, and each branch was cut as close as was 

 practicable to its point of departure from the main trunk. 

 Sections of the sciatic nerve were made both proximal 

 and distal to its branches to the thigh, the latter being made 

 for the purpose of determining the number and size of the fibers 

 which pass to the shank and foot. The proximal sections was 

 made distal to the first branch of the sciatic nerve, the branch 

 to the plexus ischio-coccygeus, which does not contribute to 

 the innervation of the thigh. Each one of the branches of the 

 sciatic nerve, which contributes to the innervation of the thigh, 

 was cut close to its point of separation from the sciatic trunk. 



