640 PEOF. H. G. SEELEY ON THE SKULL OF 



part meets the supraquadrate (sq). The upper border of the post- 

 orbital unites by transverse slightly irregular suture with the post- 

 frontal bone. 



The ■prefrontal hone (pf) is relatively small as compared with that 

 of some other species. It is an irregularly oblong bone, somewhat 

 compressed behind, with its orbital border necessarily concave, joining 

 the lachrymal in front by a nearly vertical, but slightly oblique suture. 

 It joins the nasal by a straight suture above in its front part, and 

 the postfrontal behind and above by an oblique irregular suture. 

 Its length is about 3 inches, and its depth in front, where greatest, 

 is about 2i inches. 



The postfrontal bone (pt) is broad transversely on the roof of the 

 skull, and becomes compressed from side to side in its posterior 

 part, which is bent backward at a considerable angle to form the 

 upper border of the orbit (fig. 1). The outline of this bone is concave 

 posteriorly where it enters into the temporal foss, as well as in- 

 feriorly where it enters into the orbit (fig. 2). Its superior surface is 

 flattened and elevated in front of the temporal foss ; but anterior to 

 this elevated transverse ridge, which becomes narrower as it extends 

 outward from the parietal bone, the bone is depressed anteriorly 

 towards its union with the inner part of the nasal. Its inner trun- 

 cated end is received between divergent processes of the parietal 

 bone ; and owing to the middle of its anterior part being overlapped, 

 as already remarked, by a claw-like posterior process from the nasal 

 bone, it is divided into two angular portions. The inner of these ex- 

 tends forward in a Y shape into a corresponding notch in the nasal 

 bone ; and the outer extends rather further forward in a more irre- 

 gular way between this claw-like process of the nasal and the com- 

 pressed posterior part of the prefrontal bone. The extreme length 

 of the bone appears to be about 8 inches ; its extreme transverse 

 width is under 5 inches ; but the outer part of the bone being bent 

 so as to descend at the back of the orbit, the measurement taken 

 in the two planes is greater. The extreme extension forward of 

 the bone from the interior margin of the temporal foss is less than 

 3| inches, and its anterior width is somewhat greater. Its posterior 

 end joins the squamosal bone at about the hinder third of the outer 

 margin of the temporal foss, while its inferior border rests upon 

 the postorbital bone in front and the supraquadrate bone behind. 



The region of the skull which is posterior to the orbit and 

 below the temporal foss is flattened, comparatively smooth, and 

 obliquely inclined, so that it looks outward and upward. It is 

 convex in length, rounding towards the posterior end of the skull, 

 and is slightly concave from above downward. It is formed by the 

 squamosal and postfrontal bones above, below which are the post- 

 orbital and supraquadrate bones, with the triangular mass of the 

 quadrato-jugal forming the base and posterior prolongation of the 

 alveolar border, and dividing the lower parts of these bones from 

 each other by extending upward between them. 



The squamosal hone (sqm) is a curved sickle-shaped element, which 

 joins th e outer posterior angle of the parietal bone somewhat low down 



