246 
MR. W. K. PARKER ON THE STRUCTURE AND 
thinner than it is above. Above (fig. 4) the inflated olfactory chambers turn round 
behind, and clasp the fore part of the orbitosphenoid (o.s.); there they are sharp or 
angular, but below (fig. 5), they end as rounded pouches, clasped by the base of the 
orbitosphenoids, and separated by the base of the perpendicular ethmoid ( p.e .), where 
it is floored by the two large postero-lateral vomers ( v".). These huge olfactory pouches 
reach nearly as far outwards as the equally large auditory capsules (c hi.), although these 
latter are separated by the mass of the hind brain. Where the palatine processes of the 
premaxillaries are given off, and in the space between them and the alveolar margin of 
those bones (figs. 2 and 5), there the floor of the snout is emarginate and soon 
ceases; its hind selvedge being elegantly bracket-shaped. In that emargination lies 
the openings of Jacobson’s organs ( j.o .), seen in the anterior palatine foramina. For 
the rest there is a large ovato-oblong open space divided at the middle by the 
great septum and its splints. In front, the recurrent cartilages ( rc.c.), are seen out¬ 
side the antero-lateral vomers (y '.); for some distance, then, the inferior turbinals (i.th.) 
are also seen; but the nasal turbinals are out of sight, and the upper and middle are 
well within the great pouches. All these parts are cartilaginous at present; their 
detailed structure is quite like what I have already described in the Hedgehog and the 
Mole—by dissections and sections. 
But the axial part of the nasal labyrinth (Plate 24, fig. 7) deserves special notice ; 
it is mainly formed by the huge intertrabecula ( i.tr .), which is as large relatively as in 
the embryo Bird, or in an average Selachian Fish. When we come to the long-faced 
Cetacea we shall see this element playing an important part—as in the embryo Bird— 
in the formation of the face, serving as a model on which the huge facial splints are laid ; 
in them, however, the olfactory organs and their outer openings are drawn backwards, 
and this bar runs forwards independently of them; here, as is normal for a Mammal, 
the nasal roof is continued along its whole extent, and the alinasal part, runs round 
its front end. 
In the rounded front of the snout the internarial septum is fenestrate ( i.n.f, !), a 
common thing in low Eutheria; and at that part the septum itself is largely formed of 
the alinasal cartilages, that, placed back to back, have coalesced with each other as well 
as with the median intertrabecular bar. Now, here, for the whole length of the aliseptal 
region, this is the case, so that up to the true olfactory territory the intertrabecula 
itself, is only slightly crested, the top of the low septum is, in reality, merely the con¬ 
fluent alee, or roof cartilages. Hence, in this low wall, the first three-fifths is septum 
nasi, part of it roofed by the alinasal and part by the aliseptal tracts ; these tracts are, of 
course, continuous, but they are true morphological regions. Of the hinder two-fifths, 
the first half is twice as high as the septum in front of it; it is now the perpendicular 
ethmoid (p.e.), then it lowers again, at first suddenly, and becomes a mere rounded bar, 
which passes insensibly into the presphenoid ( p.s .), most of which is already ossified. 
The roof has several regions, well marked out; beginning at the front of the snout, we 
see the alse nasi turned round and formed into the coiled nostril-valves, then comes a 
