Wyman on the Cancelli of Bones. 131 
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 
reference 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 the metatarsal bones. A. 
section through this bone (Fig. 5.) gives two series of cancelli, 
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one radiating from the upper surface towards the two surfaces 
on which the bone rests,and more sparingly to the intervening 
portions ; a second series at right angles to the last and which, 
as the former radiate from a common centre, will necessarily 
assume a curved direction. By far the largest portion of the 
first, are directed towards the tuberosity of the heel, which 
serves the double purpose of a base and lever. In that por- 
tion which is just beneath the articulating surface, and which 
does not come within the range of either of the surfaces of 
support, may be regarded as forming an inverted arch. 
The os calcis of man contrasts with that of other animals, 
not only in its size and relation to the rest of the foot, but in 
its minute and internal arrangement, so that the assertion 
JOURNAL B. S. N. H. 18 
