ARTICULATIONS 339 



possible. It is here that the movements of inversion and eversion of the 

 foot chiefly take place. 



The first and the fifth metatarsal bones enjoy a considerable degree of 

 mobility. The second metatarsal is so tightly grasped by the medial and 

 lateral cuneiform bones, and so firmly bound to the tarsus by its basal 

 ligaments, that only a slight degree of movement is possible. 



At the metatarso-phalangeal joints, flexion, extension, abduction, and 

 adduction are allowed ; whilst the digital joints only permit of flexion 

 and extension. 



In the erect posture the parts of the foot which are chiefly concerned in 

 transmitting the weight of the body to the ground are the heel, the head of 

 the first metatarsal bone, and the shaft of the fifth metatarsal bone. Rather 

 more than the middle third of the medial border of the foot is raised above 

 the ground. The lateral border of the foot is more or less in contact with 

 the ground in its entire extent, whilst the tips of the toes rest lightly on the 

 ground. In walking (i) the heel is brought down ; (2) the sole and toes 

 follow ; (3) the heel is raised, and the weight of the body is transferred to 

 the heads of the metatarsal bones and the toes. In the second and third 

 parts of this operation the arches of the foot are flattened to a certain extent, 

 but more especially in the third part of the process is the transverse arch 

 spread out. Great elasticity is thus given to the step. 



The muscles which are chiefly concerned in producing eversion of the 

 foot are the three peroneal muscles ; those which operate as inverters of the 

 foot are the tibialis anterior and the tibialis posterior. 



The extensors of the toes are the extensor hallucis longus, the extensor 

 digitorum brevis, and the extensor digitorum longus. The lumbrical 

 muscles, and the interosseous muscles, through their insertions into the 

 extensor tendons of the four outer toes, operate as extensors of the second 

 and third phalanges. 



The flexors of the proximal phalanges are the lumbricales, interossei, 

 flexor hallucis brevis, and flexor digiti quinti brevis. The flexor of the 

 second phalanges is the flexor digitorum brevis ; whilst the flexors of the 

 distal phalanges are the flexor digitorum longus, the quadratus plantse and 

 the flexor hallucis longus. 



Abduction and adduction of the toes at the metatarso-phalangeal joints 

 are produced by the interosseous muscles, the abductor hallucis, the 

 adductor hallucis obliquus, the transverse head of the adductor hallucis, 

 and the abductor digiti quinti. The movements of abduction and adduc- 

 tion take place with reference to a line drawn through the second toe. 



