168 THE ABTICVLATI0N8. 



diminishes from above to below, like that of the space it fills (Fig. 92, 13) ; 

 3, Below, by a ligamentous cord (Fig. 92, 14) which prolongs the fibula to 

 the external tuberosity of the inferior extremity of the tibia, where this cord 

 bifurcates, and is united to the two external lateral ligaments of the tibio- 

 tarsal articulation." — Bigot. 



In the Or, Sheep, and Goaf, the fibula being replaced by a ligament, there is no 

 proper tiblo-fibnlar articulation. 



In tlie Dog and Cat, the two principal bones of the leg are united at their extremities 

 and middle part : 



1. At their superior extremity, by means of a small arthrodial articulation, analogous 

 to that of the Horse, and, like it, provided -with a particular synovial bursa ; 



2. At their inferior extremity, by means of a second arthrodial articulation, whose 

 action is facilitated by a prolongation of tlje tibio-tarsal synovial membrane ; 



3. By their middle part, through the interposition, between the two bones, of an 

 interosseous ligament, which is wide and membranous in its upper two-thirds, and formed 

 of extremely short and strong fibres at its lower third. 



In the Pig, the arrangement is somewhat the same as in Carnivora. It may be noted, 

 however, that the facet of the ujjper extremity of the fibula is joined to the tibia by a 

 small interosseous ligament, and that the articulation which results should be looked 

 upon as a small amphiarthrosis. 



In Man, as in the Dog there are iwo peroneo-tibial arfhrodix : a superior and inferior. 



5. Articulations of the Tarsus or Hock. 



[Preparation. — ^Eemove the tendons from around the articulation, and incise, layer 

 after layer, the superficial fibres of the lateral ligaments.) 



These comprise: 1, The tibio-tarsal articulation; 2, The articulation of 

 the first row of bones — the astragalus and calcis ; 8, Those which unite the 

 bones of the lower row; 4, The articulation of the two rows with each 

 other ; 5, The tarso-metatarsal articulation. The first is a perfect gingly- 

 moid, and the only joint really movable ; all the others are arthrodial, and 

 their action is so restricted that they appear to be condemned to almost 

 absolute immobility. This intimate union of the tarsal and metatarsal 

 bones is evidently chiefly intended to guarantee precision in the movements 

 of the tibio-tarsal articulation. 



TiBio-TAKSAii Aetioulation. — Two bones alone concur in the formation 

 of this angular ginglymoid joint : these are the tibia and astragalus. 



Articular surfaces. — For the tibia : 1, The two deep grooves, oblique 

 forwards and outwards, channeled in the inferior extremity of the bone ; 2, 

 The salient tenon which separates these grooves, and on which there is often 

 a small synovial fossette. — For the astragalus, the pulley occupying its 

 anterior face (see page 103). 



Mode of union. — Seven ligaments bind these articulations : two external 

 lateral, three internal lateral, an anterior and a posterior. 



a. External lateral ligaments. — These are distinguished, according to their 

 relative position, into superficial and deep. 



The external superficial ligament (Figs. 93, 2 ; 94, 2), is a thick 

 funicular cord, flattened in its inferior half. It commences above on the 

 external tuberosity of the tibia, behind the groove which divides this tube- 

 rosity into two parts ; from thence it descends almost vertically, fixing itself 

 successively to the astragalus, calcaneus, cuboides, middle metatarsal bone, 

 and the external rudimentary metatarsal bone. Passing in front with and 

 partly covered by, the lateral extensor of the phalanges, to which it 

 supplies a retaining band (Fig. 94, 2), this ligament is confounded behind, 

 and nsar its inferior extremity, with the calcaneo-metatarsal ligament. It 



