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 (singular 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 development affected the shape of the trunk, as opposed to that of the fish?
  4. Make a comparison of the two girdles as to their attachment to the spine and their consequent rigidity or freedom of movement.
  5. How many vertebræ are there in the spinal column? What advantage can you see in having the column composed of many small vertebræ instead of a few large ones? Enumerate those having a special form or structure, and state the use of each.
  6. On the vertebræ notice any irregularities, prominences, or roughenings. For what are such bones better adapted than smooth bones would be?
  7. How is the frog's humping permitted? How are the urostyle and the pelvis connected, if at all? Has this any effect on motion? (See living frog.)
  8. In parallel columns, keeping corresponding parts in a line, tabulate the bones of the fore and hind limbs.
  9. State how extra length has been attained in the hind leg, and give the purpose or the result of this lengthening.
  10. In the forearm notice the fusing of the radius and ulna. How would these parts act in rotating the hand, as compared with your own, where they are free? Compare also the tibia and fibula. Where in the frog's leg is turning made possible by the use of parallel bones?
  11. Compare the frog's hand and foot as to number of fingers and toes; as to length and spread. Have any fingers or toes only two phalanges?
  12. How would an inner skeleton affect the growth and the size of an animal, as compared with an outer skeleton, like the clam's?
  13. How would the lack of an outer skeleton influence sensitiveness, activity, and intelligence?
Suggested drawings.
  1. The skull and trunk, with appendages of one side.
  2. Each set of bones separately, as the skull, the column, etc.