THE CANCELLI OF BONES 



117 



foot forms an arch, one end of which springs 

 from the ground in the os calcis, and the other 

 from " the ball of the foot ' or the ends of the 

 metatarsal bones. The arch is formed by the 

 metatarsal and tarsal bones, the centre of which 

 corresponds with a line passing transversely 

 through the scaphoid and cuboid bones. By re- 

 ference to the skeleton, it will be seen that the 

 surface of the astragalus, on which the tibia rests, 

 and the surfaces of the os calcis, which support 

 the astragalus, are behind this centre of the 

 arch ; consequently, the weight of the body will 

 be thrown more upon the os calcis than upon 



FIG. 33. 



the metatarsal bones. A section through this 

 bone (Fig. 33) gives two series of cancelli, one 

 radiating from the upper surface towards the two 

 surfaces on which the bone rests, and more spar- 



