OF THE TARSUS. 289 



elasticity to the arch and spring to the foot; hence it is sometimes called the "spring" 

 figament. It is supported, on its under surface, by the tendon of the Tibialis posticus ; which 

 spreads out at its insertion into a number of fasciculi which are attached to most of the tarsal 

 and metatarsal bones ; this prevents undue stretching of the ligament and is a protection against 

 the occurrence of flat-foot. 



4. ARTICULATION OF THE ASTRAGALUS WITH THE NAVICULAR BONE. 



The articulation between the astragalus and navicular is an artlirodial joint : 

 the rounded head of the astragalus being received into the concavity formed by 

 the posterior surface of the navicular, the anterior articulating surface of the 

 calcaneum, and the upper surface of the inferior calcaneo-navicular ligament, 

 which fills up the triangular interval between these bones. The only ligament of 

 this joint is the superior astragalo-navicular. It is a broad band, which, passes 

 obliquely forward from the neck of the astragalus to the superior surface of the 

 navicular bone. It is thin, and weak in texture, and covered by the Extensor ten- 

 dons. The inferior calcaneo-navicular supplies the place of an inferior ligament. 



The Synovial Membrane which lines the joint is continued forward from the 

 anterior calcaneo-astragaloid articulation. 



Actions. 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 medio-tarsal joint is formed by the articulation of the 

 os calcis with the cuboid, and by the articulation of the astragalus with the nav- 

 icular. 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 NAVICULAR WITH THE CUNEIFORM BONES. 

 The navicular is connected to the three cuneiform bones by 

 Dorsal and Plantar ligaments. 



The Dorsal Ligaments are small, longitudinal bands of fibrous tissue arranged 

 as three bundles, one to each of the cuneiform bones. That bundle of fibres 

 which connects the navicular with the internal cuneiform is continued round the 

 inner side of the articulation to be continuous with the plantar ligament which 

 connects these two bones. 



The Plantar Ligaments have a similar arrangement to those on the dorsum. 

 They are strengthened by processes given off from the tendon of the Tibialis posticus. 



Actions. The movements permitted between the navicular and cuneiform 

 bones are limited to a slight gliding upon each other. 



The Synovial Membrane of these joints is part of the great tarsal synovial 

 membrane. 



6. THE ARTICULATION OF THE NAVICULAR WITH THE CUBOID. 



The navicular bone is connected with the cuboid by 



Dorsal, Plantar, and Interosseous ligaments. 



The Dorsal Ligament consists of a band of fibrous tissue which passes obliquely 

 forward and outward from the navicular to the cuboid bone. 



The Plantar Ligament consists of a band of fibrous tissue which passes nearly 

 transversely between these two bones. 



The Interosseous Ligament consists of strong transverse fibres which pass 

 between the rough non-articular portions of the lateral surfaces of these two 

 bones. 



Actions. The movements permitted between the navicular and cuboid bones 

 are limited to a slight gliding upon each other. 



The Synovial Membrane of this joint is part of the great tarsal synovial 

 membrane. 



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