102 
TERTIAKY VEllTEBRATA OF THE FATtlM. 
Palceomasiodon and the later Proboscidea. The supraoccipital, together with that 
portion of tlie exocci])itals above the joramen magnum, forms a sort of escutcheon- 
shaped area, which ])rojects a little behind the rest of the occipital surface formed by 
the exoccipital-squamosal plate above referred to. One peculiar feature is, that 
between the lower end of the lambdoidal border of the su])raoccipital and the occipital 
ri'gion of the s(piamosal, a small triangular })rocess of the ])arietal is interposed, this 
l)one thus assisting in the formation of the occipital surface (PI. VIII. fig. 1 b, and 
PI. X. fig. 4 A, pa.). 
The sqiunnosal [.sq.) is a very large and massively constructed bone, in which it 
appears tliat the development of the diploe, carried to such a higli pitch in later types, 
has already begun ; and on the upper surface of the bone above the auditory opening 
there are several foramina (PI. VIII. fig. I, /or.) communicating with the interior, just 
as in Pahvomastodon : this inflation of the squamosal is especially well shown in the 
type skull of M. gracile (PI. XVII. fig. 2). The posterior portion of the bone forms 
the outer part of the occipital surface : internally it unites with the exoccipital, but it 
is excluded from contact with the supraoccipital by the process of the parietal above 
referred to. This post-tympanic region of the squamosal forms the posterior wall of 
the external auditory meatus (Pis. VIII., IX. fig. 1, e.a.m.), and closes it ventrally by 
uniting with the posteiior edge of the glenoid surhice, just as in Palccomastodon and 
the later Proboscidea. The lower border of the post-t\ mpanic process {ptg.) extends 
considerably below the glenoid surface and forms a sort of spurious postglenoid 
process ; internally it is wedged between the glenoid surface and the paroccipital 
process of the exoccipital. Superiorly the squamosal unites with the parietal, the 
suture with which runs down to about the middle of the temporal fossa, but, owing 
to the condition of that part of the skull, cannot be traced further. The zygomatic 
process is large and projects strongly on the side of the skull. It is triangular in 
section : the upper edge is continued upwards on to the side of the skull, forming the 
lower portion of the lambdoidal ridge ; the outer edge turns inwards and forms the 
posterior border of the glenoid surface. This surface is very large, extending from 
the outer edge of the zygomatic process inwards almost to the level of the pterygoid 
processes. It is concave from side to side and strongly convex from before backwards, 
particularly anteriorly. A portion of its antero-external border is formed by the binder 
end of the jugal. The posterior portion of the glenoid surface is borne upon the shelf- 
like projection, of which the upper surface forms the floor of the auditory opening. 
The tympanic is so much crushed and obscured by matrix that neither it nor the 
foramina in its neighbourhood can be described. 
The gtariedah {pa-), as already described, send back a short process on to the 
occipital surface on either side. Above they unite with the supraoccipital, wdiich 
sends a process between them for some distance. In front of this they meet one 
another in the middle line and form a not very prominent sagittal crest for some 
