TIBIO-FIBULAR ARTICULATION — THE HOCK JOINT 



199 



ridge. During flexion, whicli is accompanied by slight inward rotation of the leg, the condyles 

 of the femur and the s(>milunar cartilages glide backward on the tibia; the movement of the ex- 

 ternal condyle and cartilage is greater than that of the inner one. In extreme fi(>xion the patellar 

 and posterior crucial ligaments are tense; the other ligaments are relax(>d. Tlie mo\'ement of tiu^ 

 patella is gliding with coaptation, i. c, different parts of the opjiosing articular surfaces come into 

 contact successively. Only a narrow transverse strip (ca. l.o to 2 cm. wide) of the patella is in 

 contact with the trochlea at a time. 



TIBIO-FIBULAR ARTICULATION 



The head of the fibula articulates with a crescentic facet just below the outer 

 margin of the external condyle of the tibia. The joint capsule is strong and close. 

 The shaft of the fibula is attached to the external border of the tibia by the inter- 

 osseous membrane of the leg (Membrana interossea cruris) ; this is perforated 

 about an ineii from its proximal end by an opening which transmits the anterior 

 tibial vessels to the front of the tibia. A fibrous cord usually extends from the 

 distal end of the shaft of the fibula to the external malleolus. The latter is the 

 distal end of the fibula which has fused with the tibia. No appreciable movement 

 occtu's in this joint. 



Exterudl 



later (d 



(short) ,^-^ 



lignnwnt ,.-- 



Trochlea of 



tibial tarsal 



Dorsal liga 



mcnt 



Plantar 

 liga mcnt 



Plantar 

 ligament 



Internal 

 lateral 

 -:-:--■-. (short) 

 ligament 

 Trochlea of 

 tibial tarsal 

 Dorsal 

 ligament 



Fig. 102. — Left Hock .Joint op Horse, Externai> Fk;. 16.3. — Left Hock Joint of Horse, Internal, 



View. View. 



^i, Tibia; ;?4, tuber calcis; ;2.5, large metatarsal bone; .4'', long external lateral ligament; oi, long internal lateral 

 ligament. (After Ellenberger-Bauin, Anat. fur Kiinstler.) 



THE HOCK JOINT 



This is a composite joint made up of a number of articulations (Articulationes 

 tarsi). These are: (1) The til)io-tarsal articulation; (2) the intertarsal articula- 

 tions; (3) the tarso-metatarsal articulation. 



Tlu^ tibio-tarsal articulation (Articulatio talo-cruralis) is a typical ginglymus 

 formed by the trochlea of the tibial tarsal bone (astragalus or talus) and the cor- 

 responding surface of the distal end of the tibia. The ridges and grooves of these 

 surfaces are directed ol)liquely forward and outward at an angle of al)Out 12° to 15°, 

 with a sagittal plane. The trochlear surface is about twice as extensive as that 

 on the tibia, and its ridges have a spiral curvature. The other articulations are 



