930. Why are the bones of the skull arched?
Because in that form they acquire greater strength, and hence the utmost degree of safety is combined with extreme lightness of material.
Fig. 54.—VIEW OF THE BONES OF THE THORAX, OR CHEST, SHOWING THE PROTECTION AFFORDED TO THE ORGANS OF CIRCULATION AND RESPIRATION.
A. The sternum, or breast-bone.
B B. The ribs, which rise a little from behind, and fall as they come forward, by which they acquire a greater flexibility.
C C. The cartilaginous points of the short ribs, by which their expansive and compressive powers are much increased.
D E. Part of the vertebral column, or back-bone.