S^S A MANUAL OF ANATOMV 



jected to pressure is the astragalo-navicular joint. This joint, 

 however, is powerfully braced inferiody by (i) the elastic inferior 

 calcaneo-navicular or spring ligament, which blends internally with 

 the anterior part of the internal lateral, or deltoid, ligament of the 

 ankle-joint; and {2) the strong tendon of the tibialis posticus 

 muscle, which hes on the inferior or plantar aspect of the spring 

 ligament, and acts as a strong auxiliary to it. 



The external pillar of the longitudinal arch is constructed by the 

 OS calcis, cuboid, and outer two metatarsal bones. Its calcaneal 

 pier is formed by the internal and external tubercles on the plantar 

 aspect of the tuber calcis, and its metatarsal pier is formed by the 

 heads of the outer tivo metatarsal bones. The summit of the ex- 

 ternal pillar corresponds to the highest part of the postero-external 

 facet on the superior surface of the os calcis. Through the medium 

 of the OS calcis the external pillar receives from the astragalus a 

 small part of the superincumbent weight. This pillar is only 

 slightly arched, and is characterized by its stability. The part of 

 it most subjected to pressure is the calcaneo-cuboid joint. This joint, 

 however, is powerfully braced inferiorly by the inferior calcaneo- 

 cuboid ligaments — namely, the long and short plantar ligaments. 



The two pillars of the longitudinal arch receive material strength 

 from the plantar fascia. 



The transverse arch of the foot is most conspicuous at the tarso- 

 metatarsal joints. In this situation it is due to (i) the broad 

 aspects of the middle and external cuneiform bones being dorsally 

 placed, and (2) the broad aspects of the wedge-shaped bases of the 

 second, third, and fourth metatarsal bones being also dorsally 

 placed. The arch is braced inferiojly by plantar and interosseous 

 ligaments, and by the tendon of the peroneus longus muscle. 



The arches of the foot serve the following purposes: (i) They 

 impart strength and elasticity to the foot; (2) they protect the 

 important structures which occupy the sole or plantar region; and 

 (3) they allow of the heel-to-toe movement in walking. 



THE ARTICULATIONS OF THE FOOT. 



The articulations of the foot are divided into tarsal, tarso-meta- 

 tarsal, intermetatarsal, metatarso-phalangeal, and interphalangeal. 



The Tarsal Articulations. 



I. Astragalo-calcaneal Joints. — The astragalus is connected with 

 the OS calcis by two synovial joints, anterior and posterior, both 

 of which belong to the class diarthrosis, and to the subdivision 

 arthrodia. 



Posterior Astragalo-calcaneal Joint. —The ligaments are inter- 

 osseous, ])osterior, internal, and external. 



The interosseous ligament passes between the oblique grooves 

 separating the two articular surfaces of each bone, and forming 



