LOCOMOTION ON SOLIDS. THE ERECT POSTURE. 



169 



toes, and the parallel arrangement of the metatarsal bones, Figs. 51, 

 52, is admirably adapted for the support of 

 weight. The foot, moreover, forms a strong 

 double arch. The chief arch, Fig. 52, from 

 before backwards, passes from the broad os 

 calcis, or heel bone, 2, through the astragalus, 

 1, and other bones of the tarsus, 4, 6, 7, and 

 metatarsus, 8, as far forward as the balls of 

 the toes, the chief support in front, however, 

 being in the ball of the great toe *. The ex- 

 tension of the phalanges of the toes, 9, 10, 11, 

 forwards, from this arch, serves to increase the 

 length of the foot, for the purposes of holding 

 on to uneven surfaces, and of more effectually 

 raising the body over the foot and propelling 

 it forwards in the act of walking or running; 

 besides this, they impart elasticity to the step. 

 The lateral arching of the foot occurs in 

 the middle and anterior parts of the tarsus 

 and in the posterior and middle portions of 

 the metatarsus; it contributes greatly to the 

 strength of this part of the frame, which has 

 at every step to bear the whole weight of the 

 body. The marked projection of the heel, 2, 

 gives a great advantage in leverage to the 

 large muscles of the calf. The arching of the 

 foot likewise assists in protecting the important 

 soft parts, namely, the muscles, bloodvessels, 

 and nerves, which are situated beneath it. 

 The bones of the foot are not merely so shaped 

 as to fit together in the form of an arch, like 

 the keystones in masonry, but they are main- 

 tained in that position by strong ligamentous 

 bands, passing either between or across the 

 under sufaces of the bones; the short muscles of the foot also con- 



Fig. 51. Dorsal or upper view 

 of the bones of the left foot, 

 showing its great strength, 

 breadth, the parallel arrange- 

 ment of all the toes, and the 

 great size of the innermost toe. 

 1 to 7, the tarsal bones, or tar- 

 sus; 1, astragalus; 2. os calcis, 

 calcaneum or heel bone: 3, cu- 

 boid bone; 4, scaphoid bone; 5, 

 6, 7, the three cuneiform bones; 

 8. the five metatarsal bones; 9, 

 10, 11, the first, second, and 

 third rows of phalanges. 



Fig. 52. 



Fig. 52. Internal lateral view of the bones of the foot, showing the strength of the tarsal bones, and of 

 the metatarsal bone of the great toe, the projection of the heel bone, and the antero-lateral arch of the 

 foot. 1 to 7. the tarsus; 1. astragalus; 2, os calcis; 4, scaphoid bone; 6, 7, two of the cuneiform bones; 

 8, the metatarsal bones; 9, 10, 11, the three rows of phalanges of the toes; * sesamoid bones at the ball of 

 the great toe. 



tribute to maintain its arch-like form (see Fig. 4), and even the 

 strong plantar fascia, with its great thickness of fibres, serves not 



