ARTICULATIONS OF THE POSTERIOR LIMBS. 221 



In the 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 witli a particular synovial bursa; 



2. At their inferior extremity, by means of a second artiirodial articulation, whose action is 

 facilitated by a prolongation of the tibio-tarsal synovial membrane; 



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

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

 extremely short and strong fibres at its lower third. 



5. Aeticulations of TttE Tarsus or Hock (Figs. 141, 144). 



Preparntion. — Commence by cutting off the tendons, and so exposing the lateral ligaments 

 of the tibio-tarsal diathrosis. Tlien the procedure should be as for the carpus — dissect suc- 

 cessively the ligaments proper to each row, those uniting the two rows, and those binding the 

 lower row to the metatarsus. 



These comprise : 1. The tibio-tarsal articulation. 2. The articulation of the 

 first row of bones — the astragalu3 and calcaneum or calcis. 3. 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 ginglymoid, and the 

 only joint really movable ; all the others are aythrodial, 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-tarsal Articulation. — 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 p. 145). 



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. 143, 2 ; 144, 2) is a thick funicular 

 cord, flattened in its inferior half. It commences above on the external tube- 

 rosity of the tibia, behind the groove which divides this tuberosity into two 

 parts ; from thence it descends almost vertically, fixing itseU" successively to the 

 astragalus, calcaneum, cuboides, middle metatarsal bone, and the external rudi- 

 mentary metatarsal bone. Passing in front with, and partly covered by, the 

 lateral extensor of the phalanges, to which it supplies a retaining band (Fig. 

 143, 2), this ligament is confounded behind, and near its inferior extremity, 

 with the calcaneo-metatarsal ligament. It covers the external and deep ligament, 

 the short band which constitutes the external calcaneo-astragaloid ligament, the 

 insertion of one of the branches of the flexor of the metatarsus, and the small 

 cuboido-cunean (cuneiform) ligament. 



The external deep ligament (Figs. 143, 1 ; 144, 1), much shorter than the pre- 

 ceding, is attached, superiorly, to the anterior part of the external tuberosity of 

 the tibia, and is directed obliquely backwards and downwards, to be fixed by two 

 fasciculi at the external side of the astragalus and calcis. This ligament, covered 

 by the preceding, which crosses it like an X, is lined on its inner face by a 

 synovial membrane of the articulation. 

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