THE BOXES OF THE POSTERIOR LIMB 215 



and tarsus, like other parts of the Hmb, 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 than the cuboid and 

 articulate 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 formed by fusion of the fourth and fifth distal tarsals and 

 articulating, 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 (tuber- 

 ositas OSS. cuboidei), in front of which is a groove for the accom- 

 modation of the peculiar insertion tendon of the peronaeus primus 

 muscle. 



The Metatarsus and Phalanges 



The metatarsus (Fig. 98) comprises five elements, of which 

 four are fully developed and greatly exceed in size the corresponding 

 bones of the 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 

 distinguished 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. 



The phalanges are distributed according to the formula 0, 3, 3, 

 3, 3, the terminal, ungual phalanges being modified like those of 

 the anterior limb. 



Sesamoid Bones 



The sesamoid bones of the posterior limb occur at the knee- 

 joint and on the plantar surface of the foot. On the anterior 

 surface of the knee is the knee-pan or patella, through which, as 

 indicated above, the tendon of the quadriceps femoris muscle is 

 carried over the knee and continued as the patellar ligament to 



