10. Name four mechanical devices, or machines, found in the skeleton and state the purpose served by each.
11. Name one or more of the body machines not located in the skeleton.
12. Of what advantage is the peculiar shape of the lower jaw? Of the ribs? Of the bones of the pelvic girdle?
13. State the importance of preserving the natural form of the skeleton. How are unnatural curves produced in the spinal column?
14. How may slight deformities of the skeleton be corrected?
15. What different systems are employed in the body in the production of motion? What is the special function of each?
PRACTICAL WORK
To obtain clear ideas of the form and functions of the bones, a careful examination of a prepared and mounted skeleton is necessary. Many of the bones, however, may be located and their general form made out from the living body. Bones of the lower animals may also be studied to advantage.
Experiments to show the Composition of Bone.—1. Examine a slender bone, like that in a chicken's leg. Note that it resists bending and is difficult to break. Note also that it is elastic—that, when slightly bent, it will spring back.
2. Soak such a bone over night in a mixture of one part hydrochloric acid and four parts water. Then ascertain by bending, stretching, and[pg 242] twisting what properties the bone has lost. The acid has dissolved out the mineral matter.