3. Show by a drawing the general plan of the heart, locating and naming
the essential parts. Show also the connection of the large blood vessels
with the cavities of the heart.

4. Compare the purpose served by the chordæ tendineæ to that served by
doorstops (the strips against which the door strikes in closing).

5. Explain how the heart propels the blood. To what class of pumps does it
belong? What special work is performed by each of its divisions?

6. Define a valve. Of what use are the valves in the heart? In the veins?

7. By what means is pressure from contracting muscles in different parts
of the body made to assist in the circulation?

8. Of what advantage is the elasticity of the arteries?

9. How is blood forced from the capillaries back to the heart?

10. Why should there be a difference in structure between the two sides of
the heart?

11. Following Fig. 23, trace the blood through a complete circulation,
naming all the divisions of the system in the order of the flow of the
blood.

12. If the period of rest following the period of contraction of the heart
be as long as the period of contraction, how many hours is the heart able
to rest out of every twenty-four?