31G 



ANATOMY OF VERTEBRATES. 



relations between the electrical, nervous, and muscular forces. It 

 may be convenient, therefore, to some readers to find here, in con- 

 nection with the nervous 

 207 system of the Butrachia, 



an account of the chief 

 modes of preparing it 

 for the purpose of such 

 experiments. Galvani 

 removed the skin from 

 the hinder part and limbs 

 of the frog, exposed the 

 lumbar plexus, leaving 

 it in connection with the 

 part of the spine from 

 which the nerves issued, 

 and cut away all the 

 parts save the trunks of 

 the sciatic nerves, be- 

 tween the spine, s, and 

 the hind limbs, A & B, 

 fig. 207. So prepared, 

 it is usually called ' Gal- 

 vani's frog.' 



The ' galvanoscopic leg,' fig. 207, C, is prepared by skinning it, 

 dissecting out the sciatic nerve from among the muscles at the 

 posterior part of the thigh, then amputating the leg just above 

 the knee-joint, leaving the nerve connected with the leg, c. 



If the nerve of c be laid upon the muscles of either leg of 

 Galvani's frog, a or b, and if these muscles are excited to contrac- 

 tion, by pricking the myelon in S, the muscles of the galvanoscopic 

 leg, C, will be simultaneously contracted. If a second galvano- 

 scopic leg be prepared, and the nerve be laid upon the muscles of 

 the first, and a third be placed in the same relation with the 

 second, contractions will take place in all three legs, when the 

 thigh-muscles of the Galvani's frog, a & b, are excited to contract. 

 This ' induced contraction ' cannot be extended to a fourth gal- 

 vanoscopic leg. 



If the nerve of the galvanoscopic leg be left in connection with 

 the rest of the frog's body, and the nerve be laid across the thighs 

 of a ' Galvani's frog,' as in fig. 208 ; these being excited to con- 

 tract, not only the galvanoscopic leg, C, but the opposite leg, F, 

 contract; the one by direct stimulus of the sciatic nerve, the 

 other by stimulus of the myelon from the inferent or ' sensitive ' 



Galvani's frog, and the galvanoscopic leg. ccv. 



