148 THE BONES. 



which is in contact with another on the small cuneiform. Its anterior border is 

 roughened throughout its extent (Figs. 99, 100). 



Small Cuneiform bom (Figs. 99, 101). — Situated at the inner side of the tarsus, 

 this bone — the smallest of any yet examined — is elongated from before to 

 behind, flattened on both sides, and wedged in between the os scaphoides, the large 

 cuneiform bone, and the large and internal small rudimentary metatarsal bones, 

 with which it corresponds by four articular facets : a superior, two inferior, and 

 one internal. When this bone is in two portions, there are then three cuneiforms, 

 which may be distinguished, as in Man, by naming them first, second, and third 

 (Fig. 99). 



It is not very rare to find the scaphoid {cuneiform magnum) fused with the 

 great cuneiform {cuneiform medium), and sometimes even the cuboid is joined to 

 the cunean bones. 



Development. — All the bones of the tarsus, with the exception of the calcis, 

 are developed from a single nucleus of ossification. 



The astragalus in the Ass is distinguished from that of the Horse by the 

 external lip of the trochlea, which is abruptly deviated outwards at its inferior 

 extremity ; and by the disposition of the inferior articular surface, which is 

 regularly convex from side to side, behind the groove for insertion ; in the 

 Horse this part of the articular surface is formed by the union of two facets 

 inclined towards each other. In the same animal, the scaphoid {cuneiform 

 magnum) is recognized by the shape of the superior diarthrodial surface, which 

 is a hollowed reproduction of the inferior face of the astragalus ; and the great 

 cuneiform {cuneiform medium) by the larger concavity of its scaphoid face. 



Differential Characters in the Tarsal Bones of the other Animals. 



In the domestic animals, the tarsus difl'ers in the number and shape of the bones entering 

 into its formation. 



A. Ox, Sheep, Groat. — The tarsus of these animals is slender, and has only five bones, 

 the cuboid and scaphoid being fused into one. The astragalus is elongated from above to 

 below, and is united to the scaphoid by an antero-posterior groove, and to the calcis by a 

 vertical groove ; so that it has three trochleas. The principal trochlea has its external border 

 thicker than the internal, and decreases from below to above. The posterior trochlea is not 

 so deep as the others. The calcis is long and tljin ; tlie posterior gliding surface on the 

 summit is excavated into a channel. The small cuneiform is pisiform, and but slightly developed. 



B. Camel. — In the Camel, there are six tarsal bones, two of which are cuneiform. The 

 astragalus articulates, by means of a double groove, with the si-aphoid and cuboid. The 

 calcis is relatively short, and about equally excavated on its two faces. The cuboid is 

 voluminous. 



C. Pig. — The tarsus of this animal much resembles that of Ruminants in its general 

 disposition, and in the astragalus ami calcis; but it has seven bones, because the cuboid aud 

 scaphoid are separate, and there are constantly three cuneiform bones. 



D. Dog, Cat. — There are seven bones in the tarsus of these animals. The astragalus 

 articulates with the scaphoid — almost as in Man — by means of a true ht ad, separated from the 

 rest of the bone by a constriction named the neck of the astragalus. The cuboid and the three 

 cuneiform bones articulate with the five metatarsal bones. 



2. Bones of the Metatarsus (Figs. 98, 102). 



These bones are three in number — a median and two lateral — and offer the 

 greatest analogy to the metacarpal bones. This enables us to dispense with a 

 general description of them, and to confine ourselves only to indicating the 

 differential characters which distinguish them from the corresponding bones in 

 the anterior limb. 



