TEJiTIARY VERTERHATA OF Till] FAYtJM. 
r, 
mentioned in the account of that bone. The ])ost-tym])amc process {pt}].) curves 
forwards and forms the posterior wall of the large external auditory meatus {e.a.m.). 
d'ho anterior wall of this o})euing is formed by an extremely long and broad 
l)ostglcnoid ])rocess {pyl--), which curves backwards so as nearly to meet the lower 
end of tlie ])ost-tympauic. The outline of the external auditory meatus is oval, 
the long axis being nearly vertical ; the meatus narrows somewhat towards its 
inner end, Avhere it opens into the large fossa occurring on either side of the 
hasis crmiii, and no doubt lodging in life the ])etrosal and tympanic, the latter 
of which may have extended into the passage between the post-tympanic and 
j»ostglenoid 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 
(PI. II. fig. 1,,^^.) 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, Avhich separates it from the upper end of the 
])tcrygoid plate, and outwardly it extends upon the base of the zygomatic process. 
'Fhis 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 the level of the anterior border of the glenoid surhice. 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 trout edge of the glenoid articulation (PL II. fig. I 
and PI. III. fig. '!). 
The frontals {/>'■) not only form the lower part of the upper surface and the 
hinder portion of the sides of the 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, 
'fhe parieto-frontal suture has already been referred to ; that between the frontals 
themselves persists for some time, and both it and the froiito-nasal suture are shown 
on PI. 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./., see text-fig. 4, p. ]3). The sujuatemporal ridge is continued on the frontals 
