From the shape of the premaxillaries and maxillaries, and the form and position of the teeth the camelline affinities have been indicated. Future research must be relied on to throw light upon the structure of the limbs and the axial skeleton; as it is from these that the conclusive proof must be deduced that Ithygrammodon is the ancestor of the camels, and that Poëbrotherium is the second link in the chain, instead of the progenitor.
Measurements of Ithygrammodon cameloides with Protolabis.
| Ithygrammodon c. | Protolabis. | |
| Length of alveolar border of premaxillaries | ·035 | ·049 |
| Greatest height of premaxillaries | ·017 | ·022 |
| Greatest width of premaxillaries at last incisor | ·013 | ·01155 |
| Thickness of premaxillary process | ·010 | ·017 |
| Length of diastema between first and second incisors | ·0035 | |
| Length of diastema between second and third incisors | ·003 | |
| Length of diastema between third incisors and canine | ·004 | |
| Teeth. | ||
| Fore-and-aft diameter of first incisor | ·007 | |
| Fore-and-aft diameter of second incisor | ·0075 | |
| Fore-and-aft diameter of third incisor | ·008 | ·011 |
| Fore-and-aft diameter of canine | ·012 | ·012 |
| Fore-and-aft diameter of first premolar | ·011 | ·011 |
| Transverse diameter of first incisor | ·007 | |
| Transverse diameter of second incisor | ·0073 | |
| Transverse diameter of third incisor | ·0085 | |
| Transverse diameter of canine | ·0113 | ·009 |
| Transverse diameter of first premolar | ·005 | ·007 |
[AMBLYPODA.]
(Cope. Wheeler's Survey, vol. iv., pp. 178 et ss.)
"Mammalia, with small cerebral hemispheres which leave the olfactory lobes and cerebellum exposed. The feet short and plantigrade, with numerous (in the known genera, five) digits, terminating in flat, hoof-bearing, ungual phalanges. The seven bones of the carpus distinct, the unciform articulating with both lunar and cuneiform. The astragalus flat, without trochlear surface, and attached to the tibia with very little freedom of movement; its distal extremity divided into two facets, one for the navicular, and the other more or less for the cuboid. Molars inserted with enamel, with wide crowns and transverse crests. A post-glenoid process."