102 TEETIAEY VEETEBEATA OF THE PATtM. 



Palceomastodon and the later Proboscidea. The supraoccipital, together with that 

 portion of the exoccipitals above the foramen magnum, forms a sort of escutcheon- 

 shaped area, which projects 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 supraoccipital and the occipital 

 region of the squamosal, a small triangular process of the parietal is interposed, this 

 bone thus assisting in the formation of the occipital surface (PL VIII. fig. 1b, ^«., and 

 PL X. fig. Ak,pa.). 



The squamosal (sq.) is a very large and massively constructed bone, in which it 

 appears that the development of the diploe, carried to such a high pitch in later types, 

 has already begun ; and on the upper surface of the bone above the auditory opening 

 there are several foramina (PL VIII. fig. \,for.) communicating with the interior, just 

 as in Palceomastodon : this inflation of the squamosal is especially well shown in the 

 type skull of M. gracile (PL 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 posterior edge of the glenoid surface, just as in Palceomastodon and 

 the later Proboscidea. The lower border of the post-tympanic process (pty.) 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 hinder 

 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 parietals {pa.), as already described, send back a short process on to the 

 occipital surface on either side. Above they unite with the supraoccipital, which 

 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 



