PAIi^OMASTODON, 133 



resulting from the great development of the diploe. These cavities communicate with 

 the exterior by perforations of the outer table of the bone {for.). One of the largest 

 of the openings is in the parietal, close to its junction v^ith the squamosal and in the 

 same vertical plane as the auditory meatus : the occurrence of similar openings in 

 the skull of Moeritherium has beea referred to. 



The squamosal (sq.) is a very large bone and forms the whole of the latei'al 

 prominence at the posterior part of the skull. Posteriorly it unites with the exoccipital 

 and above with the supraoccipital and parietal. In the specimen upon which this 

 description is founded the upper portion is broken away, but it can be seen that it 

 helped to form the lower part of the massive lambdoidal crest which runs down from 

 the top of the skull to just above the auditory meatus, and that it is greatly thickened 

 by the development of extensive air-sinuses. The posterior part of the bone which 

 unites with the exoccipital behind forms a broad and deep post-tympanic flange {pty.), 

 which, by meeting the posterior border of the glenoid surface, closes the external 

 auditory meatus [e.a.m.) below. Externally the inferior edge of this post-tympanic 

 process projects a little below the glenoid surface, forming a sort of false postglenoid 

 process, but internally the border of the articular surface is more prominent and projects 

 below it. In this inner portion it is possible that a narrow wedge of the tympanic bone 

 may, be interposed between the post-tympanic flange and the glenoid surface. This 

 latter is very large and extends very high up in front ; it is gently concave from side 

 to side and broadly convex from before backwards. This region differs considerably 

 from that found in the later Elephants, in that the convexity of the glenoid surface 

 continues up to the post-tympanic process, so that there is not, as in Elephas, a deeply 

 concave area beneath the auditory meatus and behind the glenoid convexity (see text- 

 fig. 49). The inner end of the articular surface forms a large prominence, to the inner 

 side of which there is a deep fossa mainly excavated in the tympanic and referred to 

 more fully in the account of that element. The outer side of the lateral prominence 

 was prolonged forwards into a stout zygomatic process articulating with the jugal, 

 which apparently extended beneath it nearly as far back as the hinder edge of the 

 articular surface, of which it probably formed the outer part. In the later Elephants, 

 owing to the great development of air-cells both in the squamosal itself and more 

 especially in the surrounding bones, the zygomatic prominence is much less marked, 

 and, in fact, the whole zygomatic arch is of much less importance. From the inner 

 end of the glenoid surface the suture between the squamosal and the alisphenoid runs 

 forwards for some distance, the squamosal having a somewhat greater extension on the 

 side of the skull than in the recent Elephants. Anteriorly the squamosal joins the 

 frontal for a short distance, and superiorly it meets the parietal in a nearly straight 

 suture running downwards and forwards. 



The tympanic (text-fig. 49, ty.) is much less swollen than in Elephas and is a 

 compressed mass of bone bounded posteriorly by t]\Q foramen lacerum posterius (f.l.p.) 



