INTRODUCTION 5 



of the stout scissors between the jaws. Bring 

 this blade to the angle of the jaw, the other 

 blade over the junction of the head and trunk. 

 Cut off the skull with a single closure of the 

 scissors. Thrust the pithing wire into the cranial 

 cavity and then into the vertebral canal, destroy- 

 ing the brain and spinal cord. The frog ceases 

 to move; the muscles are relaxed. Divide the 

 body transversely behind the fore limbs. Ee- 

 move the viscera. Seize the spinal column with 

 the finger and thumb of one hand, and the 

 skin of the back with the other hand, covered 

 with a cloth to prevent slipping. Draw the 

 hind limbs out of the skin. Lay the limbs 

 down, back uppermost, upon a clean glass 

 plate, which the outside of the frog's skin has 

 not touched. The skin of the frog, like that of 

 the salamander and some other batrachians, is 

 provided with a protective secretion injurious to 

 sensitive tissues. Note on the outside of the 

 thigh the triceps femoris muscle ; on the median 

 side, the semi-membranosus ; between these, the 

 narrow biceps femoris. (Fig. 1.) Cautiously di- 

 vide the connective tissue between the semi- 

 membranosus and the biceps femoris. On 

 drawing these muscles apart, the sciatic nerve 

 and the femoral vessels will be seen. Clear the 

 nerve with scissors and forceps from the knee 



