198 THE ARTICULATIONS OF THE LOWER LIMB. 



supporting foot leaves the ground, the outer side of the foot is raised, the weight is thrown 

 onto the second, and then the first metatarsal bone, and the propulsion is completed by the 

 flexion of the phalanges of the great toe. The longitudinal arch is supported by the strong 

 plantar ligaments, especially the calcaneo-navicular and calcaneo-cuboid, assisted by the 

 plantar fascia and the muscles of the sole. The transverse arching of the foot is most 

 marked in the line of the tarso-metatarsal articulations, and is maintained by the plantar 

 and interosseous ligaments. The weight of the body in standing, especially when the 

 heel is raised from the ground, tends to spread out the metatarsal bones at their distal 

 extremities, and to flatten the transverse arch, which recovers its position when the pressure 

 is removed. 



The chief movements taking place between the tarsal bones are those of inversion and 

 emersion of the foot, which have their seat mainly in the astragalo-caloanean and transverse 

 tarsal articulations. In inversion the fore part of the foot is depressed and carried inwards, 

 the longitudinal arch is increased, and the outer part of the foot descends more than the 

 inner, so that the sole is turned to some extent inwards. In eversion these actions are 

 reversed, and the foot resumes its normal position. The movement between the astragalus 

 and calcaneum is a rotation about an axis which is directed obliquely from the upper and 

 inner part of the neck of the astragalus, backwards, downwards, and outwards, to the lower 

 and outer part of the tuberosity of the os calcis, so that in inversion the posterior articular 

 surface of the os calcis glides forwards and downwards beneath the astragalus, the susten- 

 taculum tali moves backwards and upwards, and the anterior extremity of the bone is carried 

 slightly inwards. The navicular and cuboid bones are moved at the same time downwards 

 and inwards over the fore part of the astragalus and calcaneum respectively. The move- 

 ment is assisted by a slight amount of gliding between the anterior tarsal bones, and between 

 these and the metatarsal bones. Inversion of the foot is commonly associated with extension, 

 and eversion with flexion of the ankle-joint. The metatarsal bones are capable of only a 

 limited amount of movement, by which they are carried downwards and brought together 

 (opposition), or raised and separated. This movement is necessarily freest in the first and 

 fifth metatarsal bones, while the third moves hardly at all. It is, however, to be remarked 

 that the movement of the first and second metatarsal bones does not wholly take place 

 between them and the corresponding cuneiform bones, 'but to a considerable extent also in the 

 naviculo-cuneiform articulations. The movements of the metatarso-phalangeal and inter- 

 phalangeal articulations are similar to those of the corresponding joints of the fingers, but 

 are more restricted in their extent. In the condition of rest the metatarso-phalangeal 

 articulations of the smaller toes are slightly over-extended, while the interphalangeal joints 

 are somewhat flexed. (GL H. v. Meyer. " Statik und Mechanik des menschlichen Fusses," 

 1886.) 



