Wyman on the Cancelli of Bones. 133 
series are braced by other fibres, which are arranged at right 
angles to their direction. The cancelli of the great trochanter, 
at (c) have no determinate form. 
If this description be correct, the * archwork" described by 
Mr. Ward does not exist, nor the more complex arrangement 
described by Bourgery and Jacob. In fact, an arch which 
should be made to resist force in this direction, would not be 
used in accordance with recognized architectural rules. An 
arch is usually made to resist or sustain pressure in lines per- 
pendicular to its surface; but is not adapted for opposing 
lateral traction. 
The upper series of fibres will get their points of resistance 
on the wall of bone below the trochanter, and not on the 
supposed archwork. ‘The curved fibres (b b) will resist in 
virtue of their tenacity, and the straight or radiating series 
(a a) in virtue of their rigidity. One resists and is adapted 
to resist pressure, and the other resists and is equally adapted 
to resist traction. 
We can appreciate the effect which force applied to the 
head of the femur would have upon its shell and cancelli, by 
calling to mind what takes place in a cylinder or tube when 
an attempt is made to bend it. If it be but slightly elastic, it 
will become more or less flattened or collapsed on the side 
toward which it is bent; if sufficient force be applied, when it 
yields it will bend into an angle on the concave side, but the 
convex side still retaining its curve. "The tenacity of the 
material being greater than its rigidity, it yields to pressure 
rather than tension, the concave side of the tube being com- 
pressed, while the convex stretches. "The same effect will be 
still better seen in bending the branch of a tree, when the 
bark, if it yield on the convex side, will be torn asunder, 
whereas on the concave side it is thrown into folds. The 
shell of the neck of the thigh may be regarded as a bent tube, 
and is adapted to resist pressure by its oval form, the longest 
axis being vertical; and secondly, by the greater thickness of 
the concave side of the neck, to which the weight is more 
