XIV 
INTRODUCTION. 
by some resemblances of the structure of the skull and by the flict that both groups 
originated in the Ethiopian region. In the skeleton the chief characteristic is the 
massiveness of all the bones, a jieculiarity that no doubt has had much to do with 
f heir ])rescrvation in such large numbers, while the much more lightly constructed 
limb-bones of Palceomastodon are extremely rare. The neck was very short and thick, 
ihe posterior cervical vertebrae being much like those of Elephas. The limbs are 
extraordinarily massive ; the fore limb is a little the shorter and was probably bowed 
slightly outwards. The feet are pentadactyl ; the fore foot is very similar to that of 
the Proboscidca, the rdna taking an even greater share in the formation of the carpal 
joint, so that the bones of the proximal row tend to overlap those of the distal row 
])reaxially. In the hind foot the astragalus articulates distall y with both the navicular 
and cuboid as in the Amblypoda, not with the navicular alone as in the Proboscidca. 
The relationships of ArshioUherium are very doubtful, and it so far differs from all 
other Ungulates that a new suborder, the Barypoda has been founded for its 
reception. It is a highly specialised form, of which the ancestors are quite unknown; 
possibly, as suggested above, it may have originated from the same group which gave 
rise to the Hyracoidea, and through this primitive stock may be related to some of 
the early, perhaps pre-Tertiary, South-American types : this possibility will be referred 
to again below. 
The Hyracoidea are an extremely isolated and in some ways very primitive group : 
previous to the discovery of these Egyptian members of the suborder, no fossil 
representatives were known, at least in the Old World, except Pliohjrax from the Lower 
Pliocene of Samos and Pikermi. The genera Sagliatherium and 3Iegaluhgrax now 
described from the Upper Eocene of the Eayum throw little or no light on the history 
of the group : they are more primitive only in having the incisors and canines all 
present in the adult, and the premolars all simpler than the molars ; otherwise, as 
in the peculiar modiffcation of the anterior incisors, they are much like the recent 
forms. The considerable number of species together with the large size of some of 
them show that in the Upper Eocene ])eriod they were an important factor in the 
fauna of the Ethiopian region, to which the group seems to bo endemic. Of 
their relationshi])s little is knowm : Ameghino has described as Ilyracoids a 
considerable number of animals from different horizons in Patagonia, and while 
* It has been pointtfl out that this name was used by Haeckel (Denerelle IMorphologie, vol. iii. p. clvii) 
to include certain genera of extinct Marsupials, and the alternative name Einbrithopoda has boon suggosteil 
(Nature, vol. Ixxiii. (1900) p. 221). 
