76 



HITCH COCK'S ANATOMY 



little material as possible. For example, were the human 

 femur a solid rod, instead of a hollow cylinder, as it now is, 

 it would require a bone twice the diameter of the present one 

 to be sufficiently strong for the purposes required of it. 

 Hence were the whole skeleton constructed on this principle, 

 it would be so cumbersome and heavy that it would require a 

 larger amount of muscle, making the body unwieldy, and 

 thus deprive it of its rapid and easy motion. 



168. Protection given to the Brain. Use of the Diploe. 

 Reason for several Bones in the Skull. — The bones af- 

 ford much protection to all the enclosed and adjacent or- 

 gans. In the bones of the head, for example, how perfect 

 the guard over the nervous center. Here are three means 

 for protection, two plates of bone, and an intervening cel- 

 lular space. The outer table being very tough presents 

 a substance somewhat yielding to blows inflicted by pointed 

 substances, and even if the blow be so severe as to cause 

 fracture, this can not extend so far as in a hard and 

 brittle material. And the intervening space or diploe very 

 materially deadens the force of any shock given to the 

 outside of the head, precisely as the springs of a carriage 

 prevent the unevenness of the road from giving the same 

 sudden jolt to the body that is communicated to the wheels. 

 The inner table is necessarily brittle, since the brain de- 

 mands the firmest possible support. But why is the skull 

 made up of several bones instead of one ? In the first place a 

 more symmetrical growth can be effected, provided the points 

 of increase are numerous, and especially so since in early life, 

 while the growth is going on, there is a thin layer of cartilage 

 between the edges of each bone, thus allowing all necessary 

 motion; secondly, because a fracture can not extend furthei 

 than a suture, as all the vibrations are overcome by the inter- 

 position of any soft substance like cartilage. And for this 



168. How do the bones afford a protection to the softer parts? What is tho 

 use of the diploe in the bones of the skull ? State the reason of several bones in 

 the skull. 



