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 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 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. 
