436 HUMAN ANATOMY. 



PRACTICAL CONSIDERATIONS. 



The union of the foot with the leg at a right angle, while necessitated by the 

 erect attitude of man, makes it essential that the bones of the foot shall be so shaped 

 and united that they may afford a basis for both support and propulsion, all pre- 

 hensile function being sacrificed to those ends. Accordingly, we find the tarsus 

 proportionately much larger, both it and the metatarsus stronger, and the pha- 

 langes much smaller and less mobile than the corresponding parts of the hand. 

 The strength of the foot and its comparative freedom from injury, in spite of its con- 

 stant exposure to traumatisms of various grades of severity, are due to the arrange- 

 ment of its component bones into the form of an arch, which is well adapted not only to 

 sustain weight and to provide leverage for motion, but also to resist and distribute 

 excessive force received, as in falls upon the feet. The posterior pillar of the arch, 

 composed of the os calcis and the hinder portion of the astragalus, has but one joint 

 — the calcaneo-astragaloid — with a very limited range of motion. The action of the 

 calf muscles upon the heel is thus applied to the elevation of the hinder pillar with 

 the least possible expenditure of force, as there are no unnecessary movements 

 between their point of insertion and the ankle-joint. 



The anterior pillar beginning at the top of the astragalus — the summit of the 

 arch — may be said to include practically most of the foot anterior to the ankle and to 

 separate naturally into ( i ) a larger and stronger inner division consisting of the neck 

 and head of the astragalus, the scaphoid, the three cuneiforms, and the three inner 

 metatarsals ; and (2) a weaker and smaller outer division composed of the cuboid 

 and the remaining metatarsals. 



The anterior pillar thus secures in the wide surface of the distal extremities of 

 the metatarsal bones a broad basis of support ; its inner division carries most of the 

 weight, and is enabled to do this by the thickness and strength of the metatarsal bone 

 of the great toe and by the parallelism of the latter with the great toe ; its outer 

 division bears less weight, but supports the inner division laterally and broadens the 

 surface in contact with the ground. The normal foot thus rests directly upon the os 

 calcis and the anterior extremities of the metatarsals, the outer side of the foot aiding 

 more in preserving balance than in carrying weight. 



An imperfect transverse arch — including the scaphoid, cuboid, and cuneiforms — 

 adds to the elasticity of the foot and aids the main arch in affording a pressure-free 

 area for the plantar vessels and nerves. Both arches depend for their integrity not 

 only upon the shape of the bones, but also upon the fasciae, ligaments and tendons, 

 and to some extent upon the small plantar muscles. Still another transverse arch is 

 formed by the bases of the metatarsal bones, and a third, but less distinct one, by 

 their heads. 



Perhaps the most accurate conception of the foot mechanically is as a semi-dome 

 (Ellis), the whole dome being completed in well-shaped feet when the inner borders 

 are approximated. 



The epiphysis of the os calcis occupies the posterior rounded extremity of the 

 bone, and has inserted into it the tendo Achillis. No positive clinical evidence of 

 separation exists, but it is probable that the X-rays will show that in young persons 

 lesions heretofore supposed to be fractures of the os calcis from muscular action are 

 actually epiphyseal disjunctions. 



The epiphyses of the remaining bones of the foot have but little surgical interest. 

 The first metatarsal, like that of the thumb, has its epiphysis at the proximal end, 

 and to that extent resembles a phalanx. The other four metatarsals have their epiph- 

 yses at the distal ends. All the phalangeal epiphyses are at the proximal ends. 

 In the metatarso-phalangeal joints the synovial membrane is in close relation to the 

 epiphyseal lines ; in the phalangeal joints it is not. A knowledge of these facts may 

 occasionally be useful in cases of disease or injury limited to a particular bone. 



Fracture of the bones of the tarsus is rare, except as a result of crushing injuries 

 or of falls from considerable heights. If the bones of the anterior pillar are broken, 

 it is usually by direct violence, as the numerous joints and ligaments of this region 

 render it so elastic, and so diffuse forces applied, as in jumps or falls, as effectually to 



