220 STRUCTURE OF THE FOOT. 



process on the inside of the os calcis, which supports the 

 astragalus, increases the breadth of the arch ; and the os 

 naviculare completes it. The arch, thus constructed, does not 

 appear very firm, and this apparent want of strength seems 

 increased by the position of the anterior portion of the astra- 

 galus, a part of which is between the os calcis and os naviculare, 

 and not supported by either. These bones, however, are 

 firmly connected by ligaments, and one which passes from the 

 os calcis to the os naviculare, under the forepart of the astra- 

 galus, gives effectual support to that bone. 



The outside of the foot, formed by the os calcis, os cuboides, 

 and the lesser metatarsal bone, does not partake much of the 

 nature of an arch ; for it is almost flat. As the internal side 

 forms a considerable arch, the foot is to be considered as 

 possessing a double convexity, viz. transversely, as well as 

 longitudinally. 2f 



The great toe, from its internal situation, is the principal 

 anterior abutment of the arch on the internal side of the foot ; 

 hence its great importance. 



The astragalus, which is the basis of the tibia, and of course 

 pressed by half of the weight of the body when we stand, 

 appears to be in a situation which is very oblique, and imper- 

 fectly supported ; and accordingly it has been completely 

 forced from its position, by accidents in which the leg has 

 been twisted or turned inward, and the foot prevented from 

 turning with it. It is probable that this misfortune would 

 often take place if the fibula did not previously yield, as in 

 some of the cases of fracture of that bone near the external 

 ankle. 



One great object of this peculiar structure is, that the foot 

 may yield in cases of violent and sudden pressure, as when we 

 jump or fall upon the feet. The safety of the foot, and the 

 facility of its ordinary movement, are not the only objects of 

 its peculiar structure, but concussion of the whole body, and 

 particularly of the brain, is thereby avoided to a certain de- 

 gree. 



^his may be inferred from the fact that many persons suffer 

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