BONES AND JOINTS OF THE EXTREMITIES 45 



secure surface for the joint, and its form regu- 

 lates the direction in which the joint is to move. 

 A jockey, putting his hand on the knee of a colt, 

 and finding it broad and flat, augurs the perfec- 

 tion of the full-grown horse. To admit of this 



o 



enlargement and difference of form, a change 

 in the internal structure of the bone is neces- 

 sary, and the hollow of the tube is filled up with 

 cancelli 9 or lattice- work. These cancelli of the 

 bone are minute and delicate-like wires, which 

 form lattice-work, extending in all directions 

 through the interior of the bone, and which, were 

 it elastic, would be like a sponge. This more 

 uniform texture of the bone permits the outer 

 shell to be very thin, so that whilst the centre of 

 the long bones are cylinders, their extremities are 

 of a uniform cancellated structure. But it is per- 

 tinent to our purpose to notice, that this minute 

 lattice-work, or the cancelli which constitute the 

 interior structure of bone, have still reference 

 to the forces acting on the bone; if any one 

 doubts this, let him make a section of the upper 

 and lower end of the thighbone, and let him 

 inquire what is the meaning of the difference in 

 the lie of these minute bony fibres, in the two 

 extremities ? He will find that the head of the 

 thighbone stands obliquely off from the shaft, 

 and that the whole weight bears on what is termed 

 the inner trochanter ; and to that point, as to 



