_ARTIODACTYLA._ Just as in the manus, the third and fourth digits are well and subequally developed; their ungual phalanges have the contiguous sides flat, and the axis of the limb passes between them, and between the cuboid and navicular. The astragalus has both the proximal and distal surfaces pulley-like, and articulates with the navicular and cuboid by two facets of nearly equal size. The calcaneum articulates with the lower end of the fibula if that bone is fully developed. In the Suina four toes are developed, and though in the Peccaries the third and fourth metatarsals are united, they are all distinct in most members of the group, as are all the tarsal bones. In the Hippopotami the four digits are of approximately equal size, and the middle ones do not have the contiguous faces of their ungual phalanges flattened. In the Tragulina the cuboid, navicular, and two outer cuneiforms are united forming a single bone; all four metatarsals are complete and the two middle ones are united. In the Tylopoda and _Anoplotherium commune_ only the third and fourth digits are developed, their metatarsals are free distally, but are elsewhere united. In the Ruminantia the cuboid and navicular are always united and so are the second and third cuneiforms, while in _Cervulus_ all four bones are united together. The third and fourth metatarsals in Ruminants are always united in the same way as are the third and fourth metacarpals, while the second and fifth are always wanting. In Deer the second and fifth digits are usually each represented by three small phalanges, but in the Giraffe and most Bovidae the bones of these digits are wanting. [Illustration FIG. 110. _A._ LEFT PES OF A TAPIR (_Tapirus americanus_). × 1/6. _B._ RIGHT PES OF A RHINOCEROS (_R. sumatrensis_). × 1/8. _C._ (CAST OF) RIGHT PES OF _Hipparion gracile_. × 1/7. _D._ RIGHT PES OF A HORSE (_Equus caballus_). × 1/10. (All Camb. Mus.) 1. calcaneum. 2. astragalus. 3. navicular. 4. cuboid. 5. external cuneiform. 6. middle cuneiform. 7. internal cuneiform.]