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_.)