DEVELOPMENT OF THE SKULL IN THE MAMMALIA. 
139 
The parietals (p.) are nearly twice as large as the frontals, and, behind them, the 
interparietals (i.p. ) are not much larger than the nasals (n.). 
Besides the supraorbitals, the lateral and infero-lateral bones seen in this view are 
the premaxillaries, maxillaries, lachrymals, jugals, and squamosals (px., mx. ; see also 
tig. 3, l., j., sq.), these are better seen in the other views (figs. 3, 5, 6). 
In the side vieiv (fig. 5) the premaxillaries [px.) are seen to be of normal size, 
mounting upwards obliquely, and wedged in between the nasals and maxillaries above. 
The outer or facial part of the maxillary is large, with its very large infraorbital 
foramen (V 2 .) and its long concave preorbital and suborbital edge. Over the former 
part the fore end of the supra-orbital ( s.ob .) fits, and inside, below this, the smallish 
perforated lachrymal scale (l., l.c). The jugal (j.) is a small thickisli style, and is over¬ 
lapped both by the jugal process of the maxillary and of the squamosal (vix., sq.). 
Where the uncinate supraorbital (s.ob.) and the swollen parietal (p.) meet in the post¬ 
orbital region there the squamosal is seen, the fore part of its temporal plate, which 
walls in the temporal fossa, it begins there, and the bone, dilating gently backwards, is 
trifid behind, in its postglenoid end, where it just hides the ampullae of the anterior 
and horizontal canals ( ct.s.c., h.s.c.) The parietals and interparietals (p., ip.) meet over 
the arched junction of the anterior and posterior canals (a.s.c., p.s.c.). 
But the peculiarly normal Mammalian state of the superficial bones is best seen in 
the lower view (Plate 17, fig. 3). 
Here the increasingly perfect desmognathism of the skull and the great develop¬ 
ment of tooth-pulps, asking for large sockets, are the factors that make the normal 
Mammalian palatofacial structures so different from their counterparts in the Ovipara, 
generally. Add to these the metamorphosis of the mandible, giving the last finish to 
a face with limited motion, and we get the reasons for much that is novel in this type 
of skull. 
The premaxillaries (px.) are largely hollowed out for the teeth, and their palatine 
processes are, at present, short and small. The maxillaries (mx.) send inwards a large 
flange from their inner alveolar plate ; beyond this, to the mid-line, another equally 
large tract has been developed, the palatine plate ; it is joined to the outer plate by a 
broadish isthmus, and is never quite distinct from it. The palatine plate of the 
palatine (pa.) is three-fifths the size of that of the maxillaries, and is perforated behind 
its middle. The two bones wedge in between the maxillaries at the mid-line, and at 
their hind part are deficient there. Outside they are thick, where they ascend to the 
basis cranii. 
The pterygoids (pfj.) are merely small ectosteal tracts fastening upon and transforming 
the thick, short, rounded pterygoid cartilages (pg.c.), and spreading above them to 
plaster the basisphenoid ( b.s.) with a thin bony tract. 
The lower edge of the jugals and squamosals (j., sq.) are seen in this aspect, the 
latter is largely hidden by the wide three-lobed glenoid facet ( gl.c .), which is placed 
transversely to the axis of the skull. 
t 2 
