276 THE ARTICULATIONS 



the rounded eminence (anterior tubercle) at the anterior end of the under surface 

 of the calcaneuni, and to the bone in front of it, and then takes an obHque course 

 forwards and inwards, and is attached to the whole of the depressed inferior surface 

 of the cuboid behind the oblique ridge, except its outer angle. It is strongest near 

 its outer edge, and is formed by dense strong fibres. 



The synovial membrane is distinct from that of any other tarsal joint. 



The arterial supply i>f the medio-tarsal joints is from the anterior tibial, from 

 the tarsal and metatarsal branches of the dorsalis pedis, and from the plantar 

 arteries. 



The nerve-supply of the medio-tarsal joints is from the external division of 

 the anterior tibial, and occasionalh' from the musculo-cutaneous or external 

 plantar. 



The movements which take place at the medio-tarsal joints are mainly flexion 

 and extension, witli superadded lateral and rotatory movements. Flexion at these 

 joints is simultaneous with extension of the ankle, and rice verm. Flexion and 

 extension do not take place upon a transverse, but round an oblique axis which 

 passes from within outwards, and somewdiat backw^ards and downwards through 

 the astragalus and calcaneum. 



Combined with flexion and extension is also some rotatory motion round an 

 antero-posterior axis which turns the inner or outer border of the foot upwards. 

 There is also a fair amount of lateral motion whereby the foot can be inclined 

 inwards (i.e. adducted) or outw'ards (i.e. abducted). 



These movements of the medio-tarsal joint occur in conjunction with those of 

 the ankle and calcaneo-astragaloid joints. Rotation at the calcaneo-astragaloid 

 joint is, however, round a. vertical axis in a horizontal plane, and so turns the 

 toes inwards or outwards; whereas at the medio-tarsal union, the axis is antero- 

 posterior and the inner or outer edge of the foot is turned upwards. Gliding at the 

 calcaneo-astragaloid joint elevates or depresses the edge of the foot, while at the 

 medio-tarsal it adducts or abducts the toes without altering the relative position of 

 the calcaneum to the astragalus. 



Thus flexion at the medio-tarsal joint is associated with adduction and inward 

 rotation of the foot, occurring simultaneously wdth extension of the ankle; and 

 extension at the medio-tarsal joint is associated with abduction and outward 

 rotation, occurring simultaneously Avith flexion of the ankle. 



Flexion and adduction are far more free than extension and aViduction, which 

 latter movements are arrested by the ligaments of the sole as soon as the foot is 

 brought into the position in which it rests on the ground. 



Although the astragalo-scaphoid is a ball-and-socket joint, yet, owing to the 

 union of the scaphoid wdth the cuboid, its movements are limited by the shape of 

 the calcaneo-cuboid joint; this latter being concavo-convex from above downwards, 

 prevents rotation round a vertical axis, and also any side-to-side motion except 

 in a direction obliquely downwards and inwards, and upwards and outwards. This 

 is also the direction of freest movement at the astragalo-scaphoid joint. Movement 

 is also limited l)y the ligamentous union of the calcaneum with the scaphoid. The 

 tw'isting movement of the foot, such as turning it upon its inner or outer edge, and 

 the increase or diminution of the arch, take place at the tarsal joints, especially the 

 medio-tarsal and calcaneo-astragaloid articulations. Here too those changes occur 

 which, owing to paralysis of some muscles or contraction of others, result in talipes 

 equino-varus, or valgus. 



6. THE TARS0-METATAR8AL ARTICULATIONS 



There may be said to l)e three articulations between the tarsus and metatarsus,, 

 viz: — 



(a) Tlie Internal, between the inner cuneiform and first metatarsal bones. 



(h) The Middle, between the three cuneiform and second and tliird metatarsal 

 bones. 



(c) The Outer, or cnbo-metatarsal, between the cuboid and fourth and fifth 

 metatarsal bones. 



