NATURAL SCIENCES OP PHILADELPHIA. 309 



orifice of the meatus auditorius a simple circular opening in the 

 bullous mass. 



Viewed from below, the general contour is substantially the 

 same as that already noted from above; but many special parts 

 claim attention. So great is the backward obliquity of the inci- 

 sors that their faces show in this view with comparatively little 

 foreshortening. The incisive foramina are a pair of contracted 

 slits midway between the incisors and molars. The palatal surface 

 in advance of the molars is much compressed ; that between these 

 teeth is broader and quite flat ; its width posteriorly is little less 

 than its length : it contracts somewhat anteriorly, where it is marked 

 by a median ridge continuous with the septum between the incisive 

 foramina. That part of the palate constituted by the palatal 

 bones is marked with several minute foramina. The palate ends 

 behind with a sharp median spur ; on either side of this is an 

 emargination, and external to this a large fossa perforated with two 

 foramina anteriorly, and a third and much larger one behind. 

 Beyond the palatals themselves, the walls of the posterior nares 

 are continued by the pterygoids, which are small and hamulate, 

 the hook abutting against the petrosals. Between the ends of the 

 pterygoids, and right across the middle line of the skull, the apices 

 of the petrosals meet each other, forming a bridge beneath the 

 basisphenoid. The posterior parts of the skull, behind those 

 already considered, are almost entirely occupied by the inflated 

 elements of the temporal bone, between which lies the reduced 

 basioccipital ; this bone is narrowly acuminate, and is sepai-ated 

 from the petrosals for its whole length by a continuous fissure, 

 like that which, on the other side of the petrosals, separates these 

 bones from the alisphenoid and squamosal. The foramen mag- 

 num appears partly in this view, flanked by the slight condyles, 

 outside of which are seen the small distinct flange-like paroccipi- 

 tals. 



The posterior view of the skull shows little but the inflated 

 mastoids, with a cleft between, mostly occupied by the large 

 foramen magnum, around which the contracted occipital bone 

 appears as little more than the rim of this foramen. 



All the bones of the skull, as well as those of the top already 

 so described, are thin and light; and the base of the cranium is 

 remarkable for its extensive vacuities. Not only are the petrosals 

 separated from their surrounding by great fissures on either side, 



