MECHANISM OP THE INFERIOR EXTREMITIES. 237 



weight of the trunk is transmitted to the foot exclusively through 

 the tibia, owing to^the fibula not entering into the composition of 

 the knee joint, and not being sustained by any bony basement at 

 its inferior part. The fibula is principally intended for the origin 

 of muscles, and for the lateral security of the ankle joint ; and 

 may be broken without the'accident suspending either erection 

 or locomotion. 



The position and shape of the foot concur largely in the gene- 

 ral object of maintaining the human being in the erect attitude. 

 Fixed at right angles to the leg, and articulated by a surface in 

 the centre of its most solid structure, the tarsus, it receives the 

 weight of the body perpendicularly upon the astragalus. The 

 latter being the key-stone .to the arch, diffuses the pressure 

 through the remainder of the structure, so that the whole foot is 

 planted against the ground, an attitude more fully executed by 

 man than by any other animal. The tendency of the body to 

 fall forwards, requires a very considerable elongation of the foot 

 in front of the tarsus, in order to increase the extent of the base 

 of support in that direction, We accordingly find the metatarsal 

 bones not only forming bases for the flexion of the phalanges; but 

 also by their great length, by the flatness of the articular faces 

 which they present to the tarsus, and by their consequent im- 

 mobility at these points, extending and securing the base of the 

 body in that direction to which its gravitation most inclines 

 it. The first metatarsal bone, though corresponding in place 

 with the first metacarpal, is very unlike it in other respects. 

 Of predominating magnitude, but parallel with the other bones 

 and immoveable at its base, it is obviously intended for sustain- 

 ing the body, and least of all for prehension and for antago- 

 nizing the other bones, as is the case with the thumb. 



The points on which the foot is particularly pressed when we 

 stand, are the tuberosity of the os calcis, the tuber of the base 

 of the last metatarsal bone, with the under surface of the cuboi- 

 des, and the anterior extremity of the first metatarsal bone. 

 The arch of the foot, upon which this depends, may be considered 

 in two ways: one is in the longitudinal direction, and has its abut- 

 ments in the os calcis behind, and in the ends of the metatarsal 

 bones in front, the other is transverse, is but slightly elevated 



