108 



Anatomy of the; Rabbit. 



M 



THE TARSUS. 



The tarsus (Fig. 43) comprises six elements, the tarsal, or ankle-bones 

 (ossa tarsi), which, like the corresponding bones of the carpus, are 

 arranged in proximal and distal rows. An exception is to be made, how- 

 ever, for one element, the navicular, which occupies an intermediate 

 position. The proximal row contains two elements, the talus and cal- 

 caneus. The talus is medial and also slightly dorsal in position. Its 

 proximal end, described as the body (corpus 

 tali), bears an extensive pulley-like surface, 

 the trochlea tali, for articulation with the tibia, 

 these two surfaces together forming the chief 

 portion of the ankle-joint. Its distal end, 

 termed the head of the talus (caput tali), pro- 

 vides a convex articular surface for the navi- 

 cular bone, and is separated from the larger 

 trochlear portion by a slightly constricted 

 intermediate portion or neck (collum tali). 

 Its ventrolateral border is extensively arti- 

 culated with the calcaneus. The latter is a 

 cvlindrical element, fully twice as long as the 

 talus, since it is extended backward behind 

 the ankle-joint, as the tuber calcanei, or bone 

 of the heel. Its dorsal surface bears a prom- 

 inent elevation for articulation with the 

 fibular side of the tibiofibula. Its medial 

 surface bears a flat, shelf-like process, the 

 sustentaculum tali, which forms a ventral 

 support for the talus. The distal extremity 

 of the bone articulates with the cuboid and 

 also with the navicular. 



The intermediate element, the navicular 

 bone, is a somewhat cubical bone, lying on 

 the medial side of the tarsus between the 

 talus, on the one hand, and the proximal end 

 of the second metatarsal bone and the second 

 and third cuneiform bones, on the other. 

 Its position is more nearly that of a central 

 element than is the case with the bone called 

 by this name in the rabbit's carpus. In this 

 connection it will be remembered that the 

 carpus and tarsus, like other parts of the limbs, 

 are primarily constructed on the same plan. 



The distal row of the tarsus contains 

 three elements, namely, the second and 



third cuneiform bones and the cuboid bone. The two former and 

 especially the first, are smaller bones, articulated respectively with 

 the second (first developed) and third metatarsals. In the rabbit the 

 first cuneiform bone — the first element of the distal row in the usual con- 



P 



Fig. 4,3. The bones of the left foot, 

 viewed from the dorsal surface: 

 T, tarsus; M, metatarsus; P, 

 phalanges. II-V, the four me- 

 tatarsal bones: cb., cuboid; cl., 

 calcaneus; c.s., second cuneiform; 

 c.t., third cuneiform: f.a., 



articular svirface for fibular side of 

 the tibofibula: n navicular; t, 

 talus; t.c, tuber calcanei; t.t., 

 trochlea tali. 



