ARTICULATIONS OF THE POSTERIOR LIMBS. 223 



and inwards, because it is only sustained at that place by the anterior capsular 

 ligament. But the effusion may also elevate the posterior- ligament, and produce 

 hernia in the hollow of the hock, behind the lateral ligaments. It is not, there- 

 fore, absolutely correct to attribute all the synovial tumours in the hollow of the 

 hock to dilatation of the tarsal tendinous sheath. (See the figure of the tendons 

 and synovial capsules of the posterior limb, in the description of the perforans 

 muscle.) 



Movements. — Nothing can be less complicated than the mechanism of the 

 tibio-tarsal articulation, this joint only permitting two opposite movements — 

 those oi flexion and extension — which are so simple and precise that we may dispense 

 with a description of the manner in which they are executed. It may only be 

 remarked that, in order to prevent contact between the leg and foot during flexion, 

 the latter fraction of the limb deviates a little outwards, owing to the marked 

 obliquity of the articular grooves. 



Articulation of the Bones of the First Row, or Calcaneo-astraga- 

 LOiD Articulation. — This is a compound arthrodial joint, resulting from the 

 coaptation of the three or four articular facets of the posterior face of the astragalus 

 with the analogous facets of the calcis. 



This joint is maintained by the lateral ligaments of the tibio-tarsal articulation, 

 and by four cakaneo-astragaloid ligaments — a superior, external, internal, and the 

 last interosseous. 



The superior calcaneo-astragaloid ligament is formed of short parallel fibres 

 thrown across from one bone to the other, and is situated towards the superior 

 extremity of the pulley of the astragalus ; it is lined superiorly by the synovial 

 membrane of the tibio-tarsal articulation. 



The lateral ligaments are two very thin fasciculi concealed by the ligaments 

 which bind, laterally, the tibia to the tarsal bone. 



The interosseous ligament is very strong, and occupies a great portion of the 

 rugged excavation which separates the articular facets. 



This articulation does not usually possess proper synovial capsules. Two 

 prolongations of the synovial membrane of the two rows, in ascending between 

 the calcis and astragalus, facilitate the gliding of the two inferior facets. An 

 analogous prolongation of. the tibio-tarsal synovial membrane is effected for the 

 superior facets, and it is not rare to find this prolongation form a distinct 

 capsule. 



Movements nearly null. 



Articulation of the Bones of the Second Row with each other. — 

 These bones, four in number, are brought into contact in the following manner : 

 The cuboides responds to the scaphoid by two facets — one anterior, the other 

 posterior ; it articulates with the great cuneiform by two similar facets, the 

 posterior of which is not always present. The scaphoid is united to the two cunei- 

 forms by the large convex facet occupying its entire lower face. The two cunei- 

 forms are joined by means of a small articular surface. 



The fibrous fasciculi which maintain the diarthrodial surfaces in contact are 

 somewhat numerous. They are as follows : — 



1. The astragalo-metatarsal ligament and tarso-metatarsal apparatus, which 

 will be described hereafter ; these two bands do not properly; belong to the articu- 

 lations of the second row of bones. 



2. Two anterior ligaments, named cuhoido-scaphoid and cuboido-cunean (Figs. 

 143, 8 ; 144, 5), which are carried from the cuboid to the scaphoid and to the 



