Fig. 107. Left manus of
A. Coryphodon hamatus. (After Marsh.) × 1/5.
B. Phenacodus primaevus. (After Cope.) × 1/3.
C. Procavia (Dendrohyrax) arboreus. (After von Zittel.) × 6/7.
| 1. scaphoid. | 7. unciform. |
| 2. lunar. | 8. centrale. |
| 3. cuneiform. | 9. pisiform. |
| 4. trapezium. | I, II, III, IV, V. first, second, |
| 5. trapezoid. | third, fourth and fifth |
| 6. magnum. | digits respectively. |
In the Hyracoidea (fig. 107, C) the manus is very similar to that in Phenacodus, but a centrale is present and the pollex is much reduced.
The manus of the Amblypoda, such as Coryphodon (fig. 107, A) and Uintatherium, is short and broad, with five well developed digits and large carpal bones. The carpals however interlock to a slight extent, and the corner of the magnum reaches the scaphoid.
In the Proboscidea the manus is very short and broad, with large somewhat cubical carpals which articulate by very flat surfaces and do not interlock at all. All five digits are present, and none of them are much reduced in size. The manus in Proboscidea and in Coryphodon is subplantigrade.
In the Tillodontia the manus is plantigrade and has pointed ungual phalanges, in this respect approaching the Carnivora. It differs however from that of all living Carnivora in having the scaphoid and lunar distinct.
In Rodentia the manus nearly always has five digits with the normal number of phalanges: the pollex may however be very small as in the Rabbit, or absent as sometimes in the Capybara. The scaphoid and lunar are generally united, and a centrale may be present or absent. In Pedetes caffer the radial sesamoid is double and the distal bone bears a nail-like horny covering. In Bathyergus the pisiform is double. It is upon these facts that the contention for the former existence of prehallux and post-minimus digits has partly been based.