ARTICULATIOSS OF THE POSTEHIOR LIMBS. 221 



In the Dog and Cat, the two principal boues of the leg are united ut their extremities 

 and midflle part : 



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

 that of tlie Hor.se, and, like it, proviiled witii a particular synovial bursa; 



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

 fiicilitat«Ml by a jirolongatiou of tiie tibio-tarsal syiioviiil 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 atrong fibres at its lower third. 



T). Articulations of the Tarsus or Hock (Figs. Ul, 144). 



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

 of tlie tibin-tarsal diathrosis. Then tlie proceiiure 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. Tlie tibio-tarsal articulation. 2. The articulation of the 

 first row of bones — the astragaluj and calcaneuin or calcis. 8. Those which unite 

 the bones of tlie 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 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 tlie 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 xurf((res. — 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 Ugampntx. — ^These are distinguished, according to their 

 relative position, into supei-ficial 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 tiience it descends almost vertically, fixing itself 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. 

 14o, 2), this ligament is confounded behind, and near its inferior extremity, 

 with the calcaneo-metatai'sal 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 smaU 

 cuboido-cunean (cuneiform) ligament. 



The external deep ligammf (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 do«Tiwards, 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. 

 17 



