6 TEETIAET VEETEBEATA OP THE EAYtTM. 



mentioned in the account of that bone. The post-tympanic process {pty.) curves 

 forwards and forms the posterior wall of the large external auditory meatus {e.a.m.). 

 The anterior wall of this opening is formed by an extremely long and broad 

 postglenoid process {pgl-}, which curves backwards so as nearly to meet the lower 

 end of the post-tympanic. The outline of the external auditory meatus is oval, 

 the long axis being nearly vertical ; the meatus narrows somewhat towards its 

 inner end, where it opens into the large fossa occurring on either side of the 

 basis cranii, and no doubt lodging in life the petrosal and tympanic, the latter 

 of which may have extended into the passage between the post-tympanic and 

 postglenoid processes just described. In one skull (M. 8463) a portion of the inner 

 surface of the petrosal is preserved, but in all other cases both that bone and the 

 tympanic are wanting, leaving the large vacuity just referred to. The glenoid surface 

 (PL II. fig. 1, gl.) is much wider from side to side than from before backwards ; it 

 is slightly concave in the former direction, and rather more so in the latter. Internally 

 it is bounded by a deep groove, which separates it from the upper end of the 

 pterygoid plate, and outwardly it extends upon the base of the zygomatic process. 

 This latter is stout and is laterally compressed anteriorly, where it terminates in 

 a sharp point. Ventrally it unites in suture with the jugal, which extends back 

 beneath it to tlie level of the anterior border of the glenoid surface. The sharp 

 upper edge of the zygomatic process is continued backwards and upwards as a ridge 

 forming the posterior and outer boundary of the temporal fossa. The upper surface 

 of the squamosal between this ridge and the parieto-squamosal suture forms a sort 

 of concave floor to the posterior portion of the temporal fossa ; the anterior boundary 

 of this surface is the sharp front edge of the glenoid articulation (PL II. fig. 1 

 and PL III. fig. 2). 



The frontals {fr.) not only form the lower part of the upper surface and the 

 hinder portion of the sides of th6 base of the great anterior horns, but each of 

 them also bears a small horn, which is situated near their junction with the 

 parietals and on the outer edge of the skull-roof. These small horns are hollow 

 and their cavity is continuous with the extensive sinus occupying the great anterior 

 horns and the roof of the skull generally. This sinus will be described below. 

 The parieto-frontal suture has already been referred to; that between the frontals 

 themselves persists for some time, and both it and the fronto-nasal suture are shown 

 on PL III. figs. 2, 2 A. It will be seen that the fronto-nasal suture first runs nearly 

 vertically downwards, then downwards and forwards, and finally directly downwards, 

 meeting the fronto-maxillary suture nearly at right angles. This latter suture 

 runs directly backwards until just outside the border of the orbit, where the two 

 bones are separated by the small square lachrymal ; within the orbit they again 

 unite, the suture between them running downwards to a large orbito-nasal foramen 

 {on.f., see text-fig. 4, p. 13). The supratemporal ridge is continued on the frontals 



