Til K ARTICULATIONS OF THE TARSUS 



349 



continued from the anterior calcaneo-astragaloid articulation, upon which a portion 

 of the head of the astragalus rests. Its under surface is in contact with the tendon 

 of the Tibialis posticus muscle, its inner Border is blended with the fore part of 

 the deltoid ligament, thus completing the socket for the head of the astragalus. 



Applied Anatomy. The inferior calcaneoscaphoid ligament, by supporting the head of the 

 astragalus, is principally concerned in maintaining the arch of the foot, and when it yields the 

 head of the astragalus is pressed downward, inward, and forward by the weight of the body, and 

 the foot become flattened, expanded, and turned 

 outward, constituting the condition known as flat- 

 foot. This ligament contains a considerable amount 

 of elastic tissue, so as to give elasticity to the arch 

 and spring to the foot; hence, it is sometimes called 

 the "spring" ligament. It is supported, on its under 

 surface, by the tendon of the Tibialis posticus, which 

 spreads out at its insertion into a number of fascic- 

 uli which are attached to most of the tarsal and 

 metatarsal bones; this prevents undue stretching of 

 the ligament, and is a protection against the occur- 

 rence of flat-foot. 



4. THE ARTICULATION OF THE ASTRAGALUS 



WITH THE SCAPHOID BONE (ARTICULATIO 



TALONAVICULARIS) (Fig. 276). 



This is an arthrodial joint, the rounded 

 head of the astragalus being received into 

 the concavity formed by the posterior sur- 

 face of the scaphoid, the anterior articulating 

 surface of the calcaneum, and the upper sur- 

 face of the inferior calcaneoscaphoid liga- 

 ment, which fills up the triangular interval 

 between these bones. The only ligament of 

 this joint is the superior astragaloscaphoid 

 (Fig. 274). It is a broad band, which passes 

 obliquely forward from the neck of the 

 astragalus to the superior surface of the 

 scaphoid bone. It is thin, and weak in 

 texture, and covered by the Extensor ten- 

 dons. The inferior calcaneoscaphoid liga- 

 ment supplies the place of an inferior 

 astragaloscaphoid ligament. 



Synovial Membrane (Fig. 280). The synovial membrane which lines the joint is continued 

 forward from the anterior calcaneo-astragaloid articulation. 



Movements. This articulation permits of considerable mobility, but its feebleness is such 

 as to allow occasionally of dislocation of the other bones of the tarsus from the astragalus. 



The transverse tarsal or mediotarsal joint (articulatio tarsi transversa [Choparti]) (Figs. 276 

 and 281) is formed by the articulation of the os calcis with the cuboid, and by the articulation 

 of the astragalus with the scaphoid. The movement which takes place in this joint is more 

 extensive than that in the other tarsal joints, and consists of a sort of rotation by means of 

 which the sole of the foot may be slightly flexed and extended or carried inward (inverted') and 

 outward (everted). 



5. THE ARTICULATION OF THE SCAPHOID WITH THE CUNEIFORM BONES 

 (ARTICULATIO CUNEONAVICULARIS) (Fig. 276). 



The scaphoid is connected to the three cuneiform bones by 

 Dorsal and Plantar Ligaments. 



FIG. 279. Ligaments of the plantar surface 

 of the foot. 



