XIV INTEODUCTION. 



by some resemblances of the structure of the skull and by the fact that both groups 

 originated in the Ethiopian region. In the skeleton the chief characteristic is the 

 massiveness of all the bones, a peculiarity that no doubt has had much to do with 

 their preservation in such large numbers, while the much more lightly constructed 

 limb-bones of Paloeomastodon are extremely rare. The neck was very short and thick, 

 the 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' Proboscidea, the ulna 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 

 preaxially. In the hind foot the astragalus articulates distally with both the navicular 

 and cuboid as in the Amblypoda, not with the navicular alone as in the Proboscidea. 



The relationships of Arsinoitherium are very doubtful, and it so far differs fiom 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 Pliohyrax from the Lower 

 Pliocene of Samos and Pikermi. The genera Sagliatherium and Megaluhyrax now 

 described from the Upper Eocene of the Fayum 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 modification 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 period they were an important factor in the 

 fauna of the Ethiopian region, to which the group seems to be endemic. Of 

 their relationships little is known : Ameghino has described as Hyracoids a 

 considerable number of animals from different horizons in Patagonia, and while 



* It has been pointed out that this name was used by Haeckel (Generelle Morphologie, vol. iii. p. clvii) 

 to include certain genera of extinct Marsupials, and the alternative name Embrithopoda has been suggested 

 (Nature, vol. Ixxiii. (1906) p. 224). 



