348 THE TISSUES. 



and density, and others incidental to these. Upon these proper- 

 ties their uses depend. 



The cohesive force of bone is truly astonishing; it being twice as 

 great as that of oak, though its specific gravity is to that of oak as 

 92:65.' 



The vertical strength of bone, or its power as a column of sup- 

 port, and to resist pressure, is still more wonderful. Prof. Robin- 

 son found that a disk of bone one inch square, supported a weight 

 of 5000 2 Ibs. He does not, however, specify the thickness of the 

 disk. 



The power of the bones to resist flexion and fracture, or as mere 

 levers, must also be mentioned here. Prof. Robinson found bone re- 

 lated, in this respect, to freestone, lead, and several of the strongest 

 kinds of wood, as follows : 



Fine freestone 1. 



Lead . .6.5 



Elm and ash 8'.5 



Box, yew, and oak . . . .11. 

 Bone 22. 



In other terms, bone is 22 times as strong in this respect as fine 

 freestone; about 3 J times as strong as lead; nearly 2} times as 

 strong as elm and ash, and twice as strong as box, yew, and oak. 



Uses of the Bones. 



The bones in their aggregate constitute the osseous skeleton of 

 the vertebrate animals. 3 



1. The skeleton gives firmness to the body and preserves its sym- 

 metry. The spinal column and the cranium at the same time also 

 protect the spinal cord and the encephalon; and the bony walls of 

 the thorax and pelvis, the contents of these cavities respectively. 

 All the bones, moreover, afford fixed points for the attachment of 

 the muscles. 



2. The long bones are acted upon by the muscles as levers, and 

 hence are the passive organs of the motions; those of the lower 

 extremities being subservient to locomotion, and those of the upper, 



1 London Lancet, April, 1846, p. 346. 2 Ibid., p. 240. 



3 At the age of 21 years, the weight of the skeleton is to that of the whole body 

 (the latter being 125 to 130 Ibs.) as 10.5 : 100 in man, and as 8.5 : 100 in woman. 



