300 RECENTLY DISCOVERED TERTIARY VERTEBRATA OF EGYPT. 



forms have still to be found, but the predictions of the above writers 

 have already been fulfilled in the case of the Proboscidea, the Sirenia, 

 and the Hyracoidea, so that there is good reason to hope that ances- 

 tral forms of some of the other groups will yet be discovered in 

 northern Africa. 



The earliest Proboscidean yet known is Mwritherium^ remains of 

 which are found in the Middle and Upper Eocene. This animal was 

 about the size of a tapir, which, moreover, it must have much resem- 

 bled in general appearance. The skull presents none of the striking 

 peculiarities of the later Proboscidean skull, though traces of the 

 beginnings of some of these characters can be seen. Thus, the nares 

 are already a little removed from the front of the snout, and the 

 nasal bones are small ; again, the bones of the occipital region are 

 somewhat swollen by the development of cellular tissue in their inte- 

 rior, a development that reaches enormous dimensions in the modern 

 elephants. In the upper jaw" all the teeth of the full Eutherian 

 dentition are present, with the exception of the front j)remolars. 

 The second incisors are much larger than the others and form down- 

 wardly directed tusks, the begimiing of the great tusks of the later 

 types. The premolars are all simpler than the molars, the low 

 crowns of which Ijear two transverse ridges, each ridge being formed 

 by the fusion of two tubercles, so that in fact the teeth may almost 

 be said to be quadrituberculate — a very primitive condition. The 

 anterior portion of the mandible is spout-like and bears two pairs of 

 incisors, which project forward. Of these the inner pair are small, 

 while the outer are enlarged, and become the lower tusks of later 

 forms. The canine is lost. The description of the upper-cheek teeth 

 given above applies equally well to the lower, except that, as usual, 

 the last lower molar has a third lobe or heel. The skeleton is imper- 

 fectly known, but it is certain that the neck was relatively long, so 

 that the animal could reach the ground with its mouth in the usual 

 way. The limb bones, so far as known, are practically those of a 

 diminutive elephant. In this animal, therefore, we have a compara- 

 tively generalized type, but at the same time some of the characters 

 which developed to such an extraordinary extent in later forms are 

 already recognizable. Such are the transverse ridging of the teeth, 

 the enlargement of one pair of incisors to form tusks, the beginning 

 of the shifting back of the narial opening, owing to the development 

 of a short proboscis and the commencement of the inflation of the 

 bones at the back of the skull. 



Although remains of Mcerithei^rum are first found in the Middle 

 Eocene beds, it persisted till the Upper Eocene period ; but there it 

 is accompanied by an animal, Palwoimastodon^ which shows a con- 

 siderable advance tow^ard the later proboscidean type. Probably 

 Mmritherium still continued to inhabit the swamps, while Palceomas- 



