THE FOOT. 



563 



the external portion is balance. They suggest that from a functional standpoint the 

 foot may be divided into an internal portion composed of all the tarsal bones and 

 the first metatarsal bone with its phalanges, and an external portion consisting of 

 the outer four metatarsal bones and 

 phalanges. They show that in dis- Astragalus 



. o . J 1,. ^ ~-s. s External, middle, and internal 



location of the metatarsus the line /$a^a S cuneiform bones 



of division passes between the first 

 and second metatarsal bones; the 

 first metatarsal is usually displaced 

 inwardly, while the second, third, 

 fourth, and fifth metatarsal bones 

 practically always displaced 



are 



Os calcis 



Inferior calcaneo- 

 scaphoid ligament 



Scaphoid (tubercle) 

 Flo. 579. The inner arch of the foot. 



Fourth Fifth Cuboid 

 metatarsal metatarsal 



FIG. 580. The outer arch of the foot. 



Highest point of arch 



outwardly, there being a consid- 

 erable separation between the met- 

 atarsal bone of the big toe and the 

 second metatarsal bone adjacent. 



When there is congenital absence of the tibia the foot bones related to it are 

 also lacking, and when the fibula is lacking there are no bones of the external set. 

 In man both sets contribute to support, but the tibial or inner set is the more impor- 

 tant, the fibular or outer 

 Os calcis set being in a condition 

 of regression. 



As has been stated 

 above, the foot is dome- 

 shaped, being arched 

 anteroposteriorly and 

 laterally. The antero- 

 posterior arching has 

 been divided into an 

 inner and outer arch. 

 The inner arch is com- 

 posed of the os calcis, 

 astragalus, scaphoid, 

 three cuneiform and inner three metatarsal bones. The highest point of this arch is the 

 midtarsal joint between the astragalus and scaphoid (Fig. 579). The outer arch is 

 composed of the os calcis, cuboid, and outer two metatarsal bones. It is much lower 

 than the inner arch. The highest point 

 is between the cuboid and os calcis, and 

 when weight is borne on the foot this outer 

 arch becomes obliterated and comes in con- 

 tact with the ground. 



The lateral arch has its outer end sup- 

 ported by the outer edge of the foot, which 

 through the medium of the soft parts is in 

 contact with the ground. Its inner end is 

 supported by the inner edge of the foot 

 which is some distance above the ground. 

 Thus it is seen that the weight of the 

 body is transmitted from the body of the 

 astragalus in three directions, viz. , back- 

 ward to the tuberosities of the os calcis, for- 

 ward to the heads of the metatarsal bones, 

 and laterally toward the base of the fifth 

 metatarsal bone. The posterior pillar of the anteroposterior arch is short, thick, and 

 composed of only two bones, the astragalus and os calcis. It is stiff and strong, but 

 having only two parts is comparatively immovable. The anterior pillar of the arch 

 is longer and has more bones and, while it is not so strong against static pressure as 

 the posterior pillar, is, on account of its elasticity and mobility, far more effective 

 against dynamic (active) pressure. Thus it is that when a person jumps from a 



FIG. 581. Lateral or transverse arch of foot. 



