THE TARSAL JOINTS 273 



masses of ligamentous tissue which connect the middle cuneiform with the internal 

 and external cuneiform ]iones, and the external cuneiform with the cuboid; occu- 

 pying all the non-articular portions of the apposed surfaces of the bones. The 

 ligaments extend the whole vertical depth between the middle cuneiform and the 

 external, and the external cuneiform and the cuboid, and blend with the dorsal 

 and plantar ligaments; they are situated in front of the articular facets, and com- 

 pletely shut off the synovial cavity behind from that in front. The ligament 

 between the internal and middle cuneiform l)ones occupies the inferior and anterior 

 two-thirds of the apposed surfaces, and does not generally extend high enough to 

 separate the synovial cavity of the anterior tarsal joint from that of the second and 

 third metatarsal and cuneiform bones. If it does extend to the dorsal surface, it 

 divides the facets completely from one another, making a seventh synovial sac in 

 the foot. 



The synovial cavity will be described later on. 



The arterial supply is from the metatarsal and plantar arteries. 



The nerves are derived from the anterior tibial, and internal and external 

 plantar. 



The movement permitted 'in these joints is very limited, and exists only for 

 the purpose of adding to the general pliancy and elasticity of the tarsus without 

 allowing any sensible alteration in the position of the different parts of the foot, as 

 the meclio-tarsal and calcaneo-astragaloid joints do. It is simply a gliding motion, 

 and either deepens or widens the transverse arch. The external cuneiform being 

 wedged in between the others is less movable, and so forms a pivot upon which 

 the rest can move. The movement is more produced by the weight of the body 

 than by direct muscular action; and of the muscles attached to this part of the 

 tarsus, all deepen the arch save the tibialis anticus, which pulls the internal cunei- 

 form up, and so tends to widen it. 



(c) The Medio-tarsal or Transverse Tarsal Joints 



The articulations of the anterior and posterior portions of the tarsus, although 

 in the same transverse line, consist of two separate joints, viz. (i) an inner, the 

 astragalo-scaphoid, which communicates with the anterior calcaneo-astragaloid 

 articulation; and (ii) an outer, the calcaneo-cuboid, Avhich is complete in itself. 

 The movements of the anterior upon the posterior portions of the foot take place 

 at these joints simultaneously. It will be most convenient to deal Avith the 

 joints separately as regards the ligaments; while the arteries, nerves, and move- 

 ments will be considered together. 



(i) The Astragalo-8caphoid Articulation 

 Class . — Diarthrosis. Subdivision . — Enarthrodia. 



This is the only ball-and-socket joint in the tarsus. It communicates with the 

 anterior calcaneo-astragaloid articulation, and tw^o of the ligaments which close it 

 in do not touch the astragalus, but pass from the calcaneum to the scaphoid. The 

 uniting ligaments are: — 



External calcaneo-scaphoid. Inferior calcaneo-scaphoid. 



Astragalo-scaphoid. 



The external calcaneo-scaphoid has been already described (page 283). 



The inferior calcaneo-scaphoid ligament (figs. 2oG and 257) is an exceed- 

 ingly dense tliick plate of fi])ro-(,'lastic tissue. It extends from the sustentaculum 

 tali and the under surface of the calcaneum in front of a ridge curving outwards to 

 the anterior tubercle of that bone, to the whole width of the under surface of the 

 scaphoid, and also to the inner surface of the scaphoid behind the tubercle. 

 Internally it is blended with the anterior portion of the internal lateral ligament of 

 the ankle, and externally with the lower border of the external calcaneo-scaphoid 

 ligament. It is thickest along the inner border. Its upper surface loses the well- 

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