How To Study Living Animals


The Endoskeleton of the Frog
Materials.

Prepared frog skeletons mounted in glass-covered boxes or in other cases suitable for individual study; other vertebrate skeletons for reference.

Observations.

The pupil should examine his specimen and identify the following structures:—

A. Skull:—

1. Cranium, or brain case, the central and hinder portion.

2. Nasal bone, a triangular bone lying in front of each large opening, or eye orbit, and attached to the anterior end of the cranium herunterladen.

3. Premaxillaries, a pair of small bones which form the tip of the nose.

4. Maxillary, a slender bone forming the side of the upper jaw.

5. Dentary, the bone of the lower jaw, corresponding to the maxillary.

6. Occipital foramen, the posterior opening or entrance into the cranium, normally covered dorsally by cartilage and most easily seen in a separate skull.

B. Vertebral Column:—

1. Cervical vertebra, the first vertebra, supporting the skull.

2. Dorso-lumbar vertebræ, vertebræ with small lateral processes herunterladen.

3. Sacrum, the ninth vertebra, bearing extra long lateral processes or “arms.”

4. Urostyle, the last vertebra, lying in the median line, a long, slender, blade-like bone, really formed by the fusion of several vertebræ.

C. Vertebra:—

1. Centrum, the solid, nearly circular portion.

2. Lateral process, one of the paired projections, extending outward on either side.

3. Neural spine, the single projection, extending toward the dorsal side.

4. Neural arch, formed largely by a connection between the lateral process and the neural spine microsoft office kostenlos downloaden vollversion deutsch chip. The arch above and the centrum below inclose the neural canal.

D. Pectoral, or Shoulder, Girdle:—

1. Sternum, the “breastbone,” extending along the median ventral line.

2. Coracoid, a heavy bone extending from the sternum sidewise to support the arm.

3. Clavicle, the “collar bone,” a light bone in front of the coracoid.

4. Scapula, the “shoulder blade,” a broad, thin bone which arches around to the dorsal side.

E. Pelvic, or Hip, Girdle:—

1. Ilium, a long, slender, curved bone, with its mate uniting to form an inverted “wishbone”; it is joined to the sacrum.

2. Pelvis, the region of the socket at the junction of the ilia.

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.

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

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