BONES AND JOINTS OF THE EXTREMITIES 41 



much farther to show the form of strength in the 

 bone. If the part of the cylinder which bears 

 the pressure be made more dense, the power of 

 resistance will be much increased ; whereas, if a 

 ligamentous covering be added on the other side, 

 it will strengthen the part which resists extension : 

 and we observe a provision of this kind in the 

 tough ligaments which run along the vertebrae of 

 the back. 



When we see the bone cut across, we are 

 forced to acknowledge that it 

 is formed on the principle of 

 the cylinder ; that is, that the 

 material is removed from the 

 centre, and accumulated on the 

 circumference (Fig. 8). We 

 find a spine, or ridge running 

 along the bone, which, when FlG 8 



divided by the saw in a trans- 

 verse direction, exhibits an irregularity, as at A. 



The section of this spine shows a surface as 

 dense as ivory, which is, therefore, much more 

 capable of resisting compression than the other 

 part of the cylinder, which is common bone. This 

 declares what the spine is, and the anatomists 

 must be wrong who imagine that the bone is 

 moulded by the action of the muscle, and that the 

 spine is a mere ridge, arising by accident among 

 the muscles. It is, on the contrary, a strength- 



