8 
thereto contributed by the mastoid: the fore part of the base forms the posterior tym- 
panic cup. The mastoid (PI. I. fig. 3, 8) is short, obtuse, inclined downward and forward. 
The inner and back part of its base is excavated by a deep transverse oval fossa for the 
anterior condyle of the tympanic element (ib. 28), 
The occipital surface of the cranium is vertical, subsemicircular ; its upper and lateral 
border forms a deep and sharp ridge, dividing it from the temporal fossee. Each fossa 
is divided into an anterior (ib. fig. 1, 11) and posterior (ib. 4) compartment ; the latter 
divisions meet above and define a short low “‘ parietal”’ ridge (ib. fig. 2,7). 
The fore or postorbital part of the temporal fossa is divided from the deeper back 
part by a low ridge descending from the hind angle of the smooth convex frontal tract 
to the fore part of the mastoid. The interorbital supracranial space is occupied by the 
deep oblong fosse (ib. so) of the superorbital glands, between which fossw is a sharp 
median ridge. A lateral ridge defines each fossa from the superorbital ridge itself, which 
is very narrow. There is an oval vacuity for the duct of the gland at the outer and fore 
part of each superorbital fossa, 4 lines, by 2 lines in diameter; and there are two or three 
foramina at the back part of each fossa, leading to the orbit. The postorbital process (12) 
is depressed and triangular, impressed above by the fore part of the temporal fossa, which 
is there divided by a short longitudinal ridge from the superorbital glandular fossa. 
The prefrontals (ib. fig. 1, 14) send outward a triangular antorbital plate, which inclines 
a little forward to join the lacrymal, but leaving an intermediate lacrymal vacuity about 
the same size as that for the duct of the superorbital gland. 
The basisphenoid rapidly narrows as it advances forward, and does not send out pro- 
cesses (pterapophyses) for the tympanic or pterygoid bones ; its presphenoid prolongation 
(ib. fig, 3,9) diminishes in transverse but increases in vertical extent, developing upward 
the lower part of the interorbital ridge, which is continuous with the ossified anterior 
part of the interorbital septum, and, by means of its backward extension, with the orbito- 
sphenoids (ib. 10). The lower border of the presphenoid is convex, and rests upon the 
groove formed by the approximated palatines (20) and intervening vomer (13). 
The very thin fore part of the cranial wall shows four large vacuities, one medial 
and superior, triangular, and giving exit to the crura of the olfactory lobes, which 
slightly groove the under surface of the interorbital part of the frontals on their way to 
the prefrontals. On each side and a little below the olfactory aperture is an irregular 
oblong vacuity. An ossified tract of the interorbital septum extends from the confluent 
orbitosphenoids, between the above vacuities and below the olfactory one, forward to 
the anterior ossified part of the septum: a narrow unossified tract lies above, and a 
broader unossified oblong space is beneath this upper ossified part of the septum. The 
inferior vacuity gives exit to the optic and orbital nerves. 
The palatines (ib. fig. 3, 20) are broadest behind, and present each towards the palate a 
long triangular surface sloping from within outward and downward, and defined mesially 
by a low vertical plate bounding an angular cavity thus formed on that surface. The 
