Dunn, Innervation of the Thigh in the Frog. 219 



Summary. 



1. The innervation of the thigh in the American frog, 

 Rana virescens, shows no marked variation from that of the 

 European frog, Rana esculenta. 



2. An enumeration of all the nerve fibers concerned in 

 innervating the hind legs reveals only a slight numerical inequal- 

 ity for the two sides. 



3. The nerve fibers concerned in the innervation of the 

 skin and muscles of the thigh are more numerous and of greater 

 average caliber than those innervating the remainder of the leg. 

 Hence in the leg of the frog the fibers of greater diameter run 

 the shorter course, 



4. The nerve fibers to the muscles of the thigh surpass 

 both in number and average diameter those which supply the 

 skin of the thigh. 



5. From the results of enumeration we conclude that of 

 the fibers which innervate the thigh about 8 fo divide, one divi- 

 sion passing in the main trunk of the sciatic nerve at least to 

 the level S^ (Fig. H). distal to the last branch of the sciatic 

 nerve. Direct observation reveals some large fibers dividing 

 dichotomously where the branches from the sciatic to the thigh 

 are given off. They are sufficient in number to render the ex- 

 planation probably correct. 



6. The cutaneous nerve fibers of the thigh bear to the 

 cutaneous area which they supply a relation of one fiber to each 

 1. 1 3- 1. 58 square millimeter of this area. 



Section I. Gross Anatomy of the Muscular and Cutaneous 

 Nerves of the Thigh. 



The muscles and skin of the thigh in Rana virescens are 

 innervated by branches from the crural and sciatic nerves, and 

 thus derive their fibers from the Vllth, Vlllth, and IXth 

 spinal nerves.^ 



^ Gaupp numbers the spinal nerves from II to XI, beginning the enumera- 

 tion with the Hypoglossal as the second ?,'p'ma.\ nerve, because of its exit between 

 the first and second vertebrae. See Gaupp's edition, Ecker's und Wiedersheim's 

 Anatomic des Frosches, Part II, p. 156. 



