X\ 1 
INTIiODUCTlOX. 
that the earliest traces of land-mammals from the Eocene of Africa include remains 
of ])rimitive Proboscidea, as well as early forms of llyracoidea, Sirenia, and perhaps 
some of the other grou[)s. 
d'he (xirliest-known Proboscidean is Mmrithermm, which occurs first in the Qasr-el- 
Sagha beds (Middle Eocene) and persisted till the Upper Eocene, its remains having 
been found in the Eluvio-marine series. 'I'liis animal was about the size of a 
Ta])ir, 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 maxillm send forward on the palate 
[)rocesses 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. r>, c. pm. ij, m. .p 
so that of the complete primitive Eutherian dentition only one lower incisor, the 
lower canine, and the first upper and lower premolars are wanting. 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 a])proaches 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 uj^per 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 up[)er jaw, but on the first and second there is a very small 
posterior ridge wliicli in the third becomes a large talon. 
In the vertebral column the most striking point is that the axis retains the ])eg-like 
form of its odontoid such as occurs in generalised Ungulates, e.(j. the Eig, 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. 
