.}21 TIIK ANATOMY OF THE HORSE 



.superior tihi.-il .surfai-os, tiaiisfdniiiiiL; tlioin into glciiuid cavities, move upon 

 the citiulylos of the foiuur, from bi-ftire backwards, or from behind forwards, 

 according to the movement executed. But at the same time they glide, 

 in a very appreciable manner, upon tlio superior extremity of the tibia. 

 Thus, at the time of ilexion, they move from behind forwards upon thia 

 extrcnnty, and are brought backwards during extension. Rotation takes 

 place from within to without, or vice versa, and is produced not only by 

 the first movement of the cond^-les in their glenoid cavities, but by the 

 displacing of the semilunar cartilages on the superior extremity of the 

 tibia. 



TIBIO-FIBULAR ARTICULATION 



Tins ARTICULATION' is formed by the union of the little arthrodial spot, 

 found at the internal sui'face of the head of the fibula, with a corre- 

 sponding surface upon the external and superior tuberosity of the tibia. 

 Short and strong fibres envelop these surfaces on the sides, and keep them 

 firmly in contact. The fibula is again attached to the tibia — 1st, above, by 

 little ligamentous bundles, ci'osscd in the shape of an X, which form the 

 superior part of the arcade, or bridge, formed between the tibia and fibula ; 

 2nd, in tlic middle, by a .sort of aponeurotic membrane, of which the breadth 

 diminishes from above downwards, like that of the interval which it fills ; 

 3rd, below, by a ligamentous band, which joins the fibula to the external 

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

 and unites with the two external lateral ligaments of the tibio-tarsal 

 arti 'ulation. 



The movements of this articulation are very limited. 



THE HOCK JOINT 



Two BONES only concur to form the ginglymu.s, or true hinge, constituting 

 the hock joint : these arc the tibia and astragalus. Tico artkniatory surfaces 

 are situated on the sides of the inferior extremity of the tibia, presenting 

 two cavities, separated by an eminence, upon which a little spot often 

 exists, uncovered by cartilage of incrustation. The astragalus presents, on 

 its antero-superior border, two semicircular prominences, separated by a 

 deep cavity which exactly corresponds to the inferior tibial eminence just 

 mentionecl, all being covered by cartilage. 



The tihia and astrar/abts are united by seven ligaments : two external 

 lateral, three internal lateral, one anterior, and a posterioi*. 



The external lateral ligaments are two, distinguished according to their 

 relative position. The superjicial external ligament is a large cord, flattened 

 in its inferior lialf. It descends from the external tuberosity of the tibia, 

 behind the groove which separates this into two parts : taking a vertical 

 course, it attaches itself succes.sfully to the astragalus, the os calcis, os 

 cuboidcs the large metatarsal bone, and to the head of the small external 

 metatarsal bones. This ligament gives off fibres, anti'riorly to the tendon 

 of the extensor pedis, and behind it mixes with the oalcaneo-metatai-sal 



