MCERITIlEIirUM. 
103 
distance ; but towards their anterior end they again diverge, and tlie sagittal crest also 
divides into the feebly marked snpratemporal ridges, which are continued forwards on 
the frontals, terminating in the neighbourhood of tlic orbits. Ventrally the parictals 
unite behind with tlie scpiamosals and probably witii the alisphenoid; farther forwards 
with the frontals, which they overlap anteriorly to, a considerable extent in a sort of 
squamous suture. 
The frontals f/r.) are large bones which meet in the middle line, forming the flat 
roof of the skull between the obscure snpratemporal ridges, which terminate over 
the small orbits, though there are no distinct postorbital processes. Anteriorly the 
frontals are separated by the nasals, which run back for some distance between them ; 
they end in front in a rounded point about on a level with the anterior border of the 
orbits, and are separated from the premaxillae by a short interval, owing to the fact 
that the nasal sends down a process which joins the maxilla. The lachrymal cannot 
be made out in any specimen examined, this region being usually very badly preserved. 
In one case there is on the edge of the orbit a small tubercle presumably borne on 
the lachrymal, but there is no evidence of a lachrymal foramen. 
The nasals [na.) are fairly large bones, which run back some distance between the 
frontals. As they pass forwards they widen out, till at their widest point they form 
a short suture with the maxillae. In front of this they again narrow between the 
upper ends of the premaxillae. Anteriorly they terminate in bluntly rounded ends, 
which slightly (about 7 mm.) overhang the anterior narial opening. The difference 
between this region of the skull in Palceomastodon and Mceritheriiiin seems to be due 
to the shifting back of the nares (consequent on the development of the proboscis) in 
the former, which leads to the reduction of the nasals and the carrying back of the 
facial processes of the premaxillae till their upper ends meet the frontals and exclude 
the nasals from contact with the maxillae. 
The premaxilloe (pmx.), which together form the broad blunt snout, are chiefly 
remarkable for the depth and solidity of their alveolar region, resulting from the 
great enlargement of the tusk-like second incisors. The chief consequence of this 
modification is, that the floor of the narial cavity is raised much higher above the level 
of the alveolar border than usual, and the distance between it and the palate is 
greater. In the skull figured in PI. VIII., a portion of the anterior region of these 
bones overlying the median pair of incisors is broken away, but in another specimen 
the upper surface of this anterior region is seen to be deeply grooved in the middle 
line, the depth of the groove being increased by the presence of prominent ridges on 
either side of it ; outside these again, and separated from them by slight depressions, 
are the prominences formed by the large alveoli of ^. 2. The upper surface of the 
bones forms the floor of the nasal cavity, which, owing to the shortness of the nasals, 
is exposed for some distance. The presence of the ridges and grooves on the front of 
the snout may indicate that there was a mobile upper lip or short proboscis requiring 
