182 
MR. W. K. PARKER ON THE STRUCTURE AND 
The tilting of the canal-region of the capsule is well shown in the side view ; the 
fore part of the large anterior canal ( a.s.c.) leans backwards, under the prootic bone 
(pr.o.), at a right angle to the squamosal bone ; its hinder half, below the sinus-canal 
is parallel with the outer edge of the occipital roof. The posterior canal ( p.s.c .), 
which joins the anterior, is parallel with the general direction of the occipital condyle, 
and the horizontal canal ( h.s.c .) runs downwards and backwards, from the end of the 
squamosal to the exit of the facial nerve (YII.). 
But for the ossifications of the hind skull, and the continuation of the nasal roof 
cartilages to the end of the intertrabecular beam—a peculiarly valuable Mammalian 
diagnostic—the upper view of the skull (fig. 4) might have seemed to belong to 
a Skate. There is a large membranous fontanelle (fo.), but it is well surrounded 
by solid hyaline cartilage, and in several places the “ tegmen cranii,” or cartilaginous 
roof is well developed. 
The large and long nasal labyrinth is practically divisible into three regions, 
namely, the snout, or alinasal (al.n .); the middle region with the nasal and inferior 
turbinals, and, like the snout, supplied from the 5th nerve only ( al.sp .); and the true 
olfactory region, containing the upper and middle turbinals—the aliethmoidal region 
( al.e .). The fluted roof becomes concave near the end, and then terminates abruptly, 
in an almost transverse line, at the middle of which there is a small projection—the 
crista galli ( cr.g .). The wide, lateral, olfactory regions, with their hill-and-valley 
markings, reach backwards, right and left, beyond the end of the roof; the oblique 
postero-internal margin is confluent with the front of the tegmen tympani, a part which 
is continuous with the orbitosphenoid (o.s.). Its tegminal lobe has a sinuous inner 
margin, it ends behind, in the narrowish posterior band that runs from the posterior 
angle of the orbitosphenoid to the supra-auditory tract ( o.s'.,s.a.c .); this band is convex 
on its outer, and concave on its inner, side. From the end of this band the cartilaginous 
tegmen is almost complete, but the supra-auditory tracts ( s.a.c.) do not meet, they are 
separated at the middle by a large round notch, at the back of which there is already 
a smallish crescentic interparietal scale (i.p.). These tracts, however, send forward a 
thinner bilobate lamina, sharply marked off from the hinder main part by a crescentic 
line, whose convexity is behind; this line, and the thinning-out of the tegmen, is 
caused by the parietal bone. Behind the lateral band (o.s'.) the supra-auditory 
cartilage is ossified, beyond the turning over of the roof, by the prootic (pr.o.). 
Answering to the great size of the occipital arch, the supraoccipital ( s.o.) is already 
more than a third the width of the widest part of the hind skull, its sides are bilobate, 
its extent, lengthwise, is from the fontanelle to the foramen magnum. 
An upper view of the cranial floor (Plate 26, fig. 6), after the membranous 
fontanelle has been removed and the orbitosphenoids (o.s.), lateral bands (o.s'.), and 
the tegmen (s.a.c., pr.o'., s.o.) have been cut down to the top of the wall, shows some 
things very instructively. The top of the great internasal septum (p.e.) projects 
backwards, as a small triangular crista galli (cr.g.), and below that ends as an oblique, 
