1 86 



Anatomy of Skeleton 



The oblique direction of the first phalanx in the great toe does not appear to be 

 the result of wearing boots : possibly it may be correlated with the outward turn of the 

 foot as an adaptation to such acts as running or even walking, in which the body is 

 lifted forward on the ball of the great toe, and such a direction of the phalanx keeps it 

 out of the way and avoids over-extension of the joint. This does not, however, seem 

 a very satisfactory explanation of the condition. 



The account already given of the phalanges of the hand can be applied, mutatis 

 mutandis, to those of the foot, but a few points must be noticed first. The middle 

 phalanges get quickly smaller from within outwards, the fifth being usually an irregular 

 nodule of bone ; the same in a less marked degree may be said of the last phalanges, 

 and there is frequently a fusion between the middle and last bones in the little toe, 

 and even occasionally in the other toes. 



The bones of the tarsus are composed of cancellous tissue enclosed in very thin 



FIG. 157. A., scheme to show the relations between the skeletons of hand, foot, and a general 

 hypothetical type. The last has a preaxial bone, K.T., radius or tibia, and a postaxial, U. F., 

 ulna or fibula ; these carry corresponding carpal or tarsal units which are separated by an 

 " intermedium " (stippled). The distal row are the carpalia or tarsalia (numbered from 

 preaxial side). Between the two rows an " os centrale " (shaded). This becomes the 

 scaphoid in the foot but is fused with the os magnum or scaphoid in the hand. Os inter- 

 medium becomes semilunar in hand and os trigonum in foot. Pisiform (p) is represented 

 by calcaneal epiphysis ; it has no place in the type form, and may stand for a rudimentary 

 digit. B., scheme of transmission of weight and consequent direction of main lamellae in 

 cancellous tarsal bones ; supporting lamellae run at right angles to the main ones. 



shells of compact bone. The cancellous lamellae are mainly directed in the lines of 

 pressure transmitted from the tibia through the astragalus to the other bones : the 

 arrangement is shown schematically in Fig. 157. 



The correspondence of the foot with the generalised type of carpus and tarsus 

 (p. 116) is seen in Fig. 157. In the same figure the hand and foot are compared to show 

 the different components that " correspond " with each other. 



Development of Bones of Foot. 



The bones are preformed in cartilage, which at birth shows centres for the shafts 

 of the metatarsals and nearly all the phalanges, and for two or three of the tarsal 

 bones. 



The cartilage is first apparent in the sixth week, and the form of the various bones 

 is distinct by the middle of the third month. The metatarsals are at first rather 

 spread out and resemble the skeleton of the hand, but by the latter part of the third 

 month they have come to lie closer together, and the foot exhibits a definite tarsal 

 arch. 



