VERTEBRATES 127 



F. Fore Leg, or Arm : — 



1. Humerus, the single bone of the upper arm. 



2. Radius, the bone of the lower arm on the thumb 

 side ; in the frog united to the ulna. 



3. Ulna, the bone of the forearm opposite the radius. 



4. Carpals, small bones of the wrist. 



5. Metacarpals, a single series of long bones forming 

 the palm of the hand. 



6. Phalanges, the bones of the fingers and thumb (singu- 

 lar phalanx). 



G. Hind Leg : — 



1. Femur, the thigh bone, next to the body. 



2. Tibia, the larger bone of the lower leg on the inner 

 side ; in the frog united to the fibula. 



3. Fibula, the smaller bone of the lower leg. 



4. Tarsals, the small bones of the instep. 



5. Metatarsals, the long bones of the instep. 



6. Phalanges, the bones of the toes. 

 Questions. 



1. Whereabouts in the frog has nature made an attempt 

 to inclose delicate or vital structures in bony cases .' 



2. Examining the inside of the mouth, find the teeth. 

 Judging from their size and structure, of what use are 

 these teeth ? 



3. What advantages can you see in having the arms and 

 legs attached to girdles instead of having them fastened 

 directly to the vertebral column ? How has their develop- 

 ment affected the shape of the trunk, as opposed to that 

 of the fish .' 



4. Make a comparison of the two girdles as to their at- 

 tachment to the spine and their consequent rigidity or free- 

 dom of movement. 



