XVI INTEODUCTIOX. 



that the earliest traces of land-mammals from the Eocene of Africa include remains 

 of primitive Proboscidea, as well as early forms of Hyracoidea, Sirenia, and perhaps 

 some of the other groups. 



The earliest-known Proboscidean is Moeritherium, which occurs first in the Qasr-el- 

 Sagha beds (Middle Eocene) and persisted till the Upper Eocene, its remains having 

 been found in the Fluvio-marine series. This animal was about the size of a 

 Tapir, which it must have greatly resembled in general appearance. The skull 

 (see fig. 40, p. 100) presents no very striking peculiarities, the chief points of 

 interest being that (1) the nasals are short and the nasal opening is not quite at 

 the end of the Snout ; (2) the bones of the back of the skull tend to become 

 swollen by the presence of air-cells ; (3) the maxillae send forward on the palate 

 processes which help to support the enlarged second incisors. The mandible is 

 short and stout, its ascending ramus being inclined a little forwards ; the symphysis is 

 spout-like and the upper surface is continuous with that of the sloping lower incisors. 

 The teeth are of greater interest. The dental formula is i. 5, c. q, pm. 3, m. o' 

 so that of the complete primitive Eutherian dentition only one lower incisor, the 

 lower canine, and the first upper and lower premolars are Avanting. Of the upper 

 incisors, the second pair are greatly enlarged, forming trihedral downwardly directed 

 tusks ; the others as well as the canine are quite small. The three premolars 

 are all simpler than the molars, but the fourth approaches them most nearly. 

 The premolars replace milk-teeth in vertical succession in the ordinary way. The 

 molars consist essentially of four low blunt tubercles, arranged so as to form two 

 transverse ridges ; the last upper molar has a very small posterior lobe in addition 

 to the main ridges. In the lower jaw only the first and second pairs of incisors 

 remain : of these the median ones are small, the second enlarged and tusk-like ; 

 both slope strongly forwards and their upper surface is continuous with that of 

 the spout-like symphysis. The canines and first premolar are entirely lost, and, 

 as in the upper jaw, all the . remaining premolars are simpler than the molars, 

 although the last approaches them in complexity. The molars are on the whole 

 like those of the upper jaw, but on the first and second there is a very small 

 posterior ridge which in the third becomes a large talon. 



In the vertebral column the most striking point is that the axis retains the peg-like 

 form of its odontoid such as occurs in generalised Ungulates, e. g. the Pig, and at the 

 same time the centra of the cervicals are not shortened to any great extent, so that 

 no doubt the animal could reach the ground with its mouth in the ordinary way. 



