THE CANCELLI OF BONES 103 



weight ; they form, by their union, a canal for 

 the lodgment and protection of the spinal mar- 

 row ; and constitute a series of levers for the 

 application of muscular force. The first of these 

 functions is performed by the "body," whose 

 special use in a given region is to support the 

 weight of the head, arms, and of all that portion 

 of the trunk which is above it ; which weight ac- 

 quires its maximum in the lumbar region, where 

 the vertebraB acquire their greatest size. The 

 pressure on all the vertebra is vertical. 



If a section be made through a lumbar ver- 

 tebra, the areola3 between the cancelli will be 

 found to have generally a quadrangular form, 

 and the direction of the cancelli either vertical 

 or transverse (Fig. 29 J ). The vertical ones ex- 

 tending from the upper to the lower face of the 

 vertebra receive the weight which they sustain 

 on their ends ; and this they will sustain in virtue 

 of their rigidity. If they have a tendency to 

 yield, it is either by being crushed, or by bending 

 in a lateral direction. This last is prevented by 

 the transverse cancelli which are placed at right 

 angles to the vertical ones, and serve the purpose 



1 This and the following diagrams are intended merely as 

 plans of the cancelli, the different lines representing their general 

 directions. For accurate figures of the bones described, except 

 the neck of the thigh, the vertebra, and astragalus, see the plates 

 of Bourgery and Jacob. 



