The Skeleton of the Posterior Limb. 173 



bears a prominent 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 meta- 

 tarsal bone and the second and third ctmeiform 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 condition — ^is fused with the proximal end 

 of the second metatarsal. The cuboid is a larger element articulat- 

 ing, like the hamate bone of the carpus, with two distal elements, 

 the fourth and fifth metatarsals. Its ventral surface bears a 

 transverse elevation, the tuberosity of the cuboid (tuberositas oss. 

 cuboidei) , in front of which is a groove for the accommodation ' 

 of the peculiar insertion tendon of the peronaeus primus muscle. 



THE METATARSUS AND PHALANGES. 



The metatarsus (Fig. 72) comprises five elements, of which 

 four are fully developed and greatly exceed in size the corresponding 

 bones of metacarpus, while one, the first metatarsal, is vestigial. 

 The vestigial element lies on the plantar surface of the foot, for the 

 most part ventral to the navicular and at the base of the second 

 metatarsal. In each developed metatarsal there may be distin- 

 guished a main portion or body, a proximal extremity or base, 

 and a distal extremity or head, the last-named portion articulating 

 with the proximal phalanx of the digit. The base of the fifth 

 metatarsal bears a tuberosity for the insertion of the peronaeus 

 secundus muscle. 



