A Guide for the Study of Animals Part 40

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 vertebrae are there in the spinal column? What advantage can you see in having the column composed of many small vertebrae instead of a few large ones? Enumerate those having a special form or structure, and state the use of each.

6. On the vertebrae 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._

a. The skull and trunk, with appendages of one side.

b. Each set of bones separately, as the skull, the column, etc.

Comparative Study of Amphibia

_Materials._

Various amphibia, either dead or alive, such as newts, mud puppies (_necturus_), salamanders, and several species of frogs and toads, especially tree toads.

_Observations._

Answer the following questions with respect to each animal:--

1. What regions of the body are present? What is the general shape and size of the body?

2. For what kind of locomotion are the limbs fitted? How?

3. Have the hands and feet any special adaptations? If so, what are they and for what purpose?

4. With what organs does the animal breathe? If with gills, are they external or internal?

5. Judging from the specimen, what do you think is the habitat? Give reason for your answer.

Summary from the Comparative Study of Amphibia

1. Which of the amphibia in this study are fish-like in character?

What are the fish-like characters? Do you think these fish-like amphibia are of a lower or higher type than the others? Give reasons for your answer.

2. Show how the variation in (a) the form of the body, (b) color patterns, and (c) the structure of the legs and arms of the amphibia are related to habitat and mode of life.

Amphibia: A General Review and Library Exercise

1. The usefulness of the American toad.

2. The breeding habits of the common frog; of the Surinam toad; of the obstetrical toad; of the "smith."

3. The development of the axolotl.

4. The habits of the tree frogs and their variable coloration.

5. The croaking of frogs and of toads.