THE FROG. 95 



examine first with a low, and then with a high power, to 

 see the cross-markings of its finest fibres. This kind of 

 muscle is called striped or striated. 



THE ACTION OF A FBOG's MUSCLE. 



Entirely remove the skin from one of the frog's hind 

 limbs ; sever the limb from the body at the hip-joint ; clear 

 away all the muscles of the thigh, carefully preserving the 

 sciatic nerve, still connected with the leg below; sever 

 the heel-cord below the heel, and separate the calf-muscle 

 from the other muscles of the leg, leaving undisturbed its 

 attachment above ; just below the knee, cut away the 

 shin-bone, with all the muscles of the leg, except the calf- 

 muscle ; there should now remain the thigh-bone, with the 

 lower part of the sciatic nerve running to the calf-muscle 

 suspended below ; tie a string around the thigh-bone, and 

 suspend the whole ; hang a slight weight, such as a door- 

 key or a pair of scissors, to the tendon at the lower end of 

 the muscle ; now pinch the upper end of the sciatic nerve, 

 meanwhile closely watching the muscle. 



THE FROG'S SKELETON. 



Clean the skeleton of the frog after dissection. This 

 is easier after soaking it in water for a few days. 



1. Note how open and light the skull is, and how easily 

 the bones are cut. 



2. Count the parts of the spinal column ; these are the 

 vertebrae. The long bone terminating the spinal 

 column is the urostyle. 



3. Observe the long bones of the pelvis, parallel with 

 the urostyle. What makes the frog hump-backed ? 



