674 SCIENCE PROGRESS 



have much resembled in general appearance. The skull pre- 

 sents 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 interior, 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 premolars. The 

 second incisors are much larger than the others, and form 

 downwardly directed tusks, the beginning of the great tusks of 

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

 the low crowns of which bear 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 

 forwards. 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 imperfectly 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 comparatively generalised type, but at 

 the same time some of the characters which developed to such an 

 extraordinary extent in later forms are already recognisable. 

 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 Mceritherium are first found in the 

 Middle Eocene beds, it persisted till the Upper Eocene period ; 

 but there it is accompanied by an animal, Palceomastodon, which 

 shows a considerable advance towards the later proboscidean 

 type. Probably Mceritherium still continued to inhabit the 

 swamps, while Palceomastodon represents a form becoming 



