8 6 O S T E O L O G Y [PART II.
and appears to ascend ten lines and a half to its apex. The cranio-facial line is notched on each side, by
the termination of the nasal fissure; the distinction between the mandibular and cranial segments of the
nasal is least marked on the right side: the part of the latter, immediately behind the broad outer liinb,
is more inflated than the upper and inner angle; the expanded portion behig defined by a semi-lunar
groove. The triangular frontal aspect of the prefrontal, from the compression of the anterior part of the
cranium, is directed very obliquely outwards; the anterior edge being much in advance of the posterior,
which is anchylosed to the antorbital process; a deep fissure separates the anterior or inner margin from
the ecto-nasal limb; the base forms the upper rounded border of the lacrymal groove, and terminates
anteriorly hi an obtuse projecting angle. This surface is perforated by numerous vascular apertures.
The sub-erescentic supra-orbital tract is rough, and perforated by periosteal vascular foramina; a
series of larger size extend from the notch on the antorbital process to the supra-orbital foramen or notch,
and indicate its inner boundary; hence the supra-orbital plate appears formed, as it were, by a separate
ossification of the periosteum extending outwards to protect the eyeball. The space in front of the semicircular
venous grooves is also minutely punctate, the apertures becoming larger anteriorly. The tabula
externa of the pneumatic diploe, on the frontal slope, is thinned and inflated opposite the individual cells;
and some of these have opened out; these appearances indicate that the skull in question belonged to a
domesticated individual.
The parieto-mastoid tract is gently arched transversely, but ascends rapidly in the anteroposterior
diameter. It is narrow mesially, but extends laterally so as to occupy two-thirds of the convex external
edge of the cranium, behind the supra-orbital notch. The rhomboidal digastric impression occupies the
posterior angle of this tract, its transverse diameter is less than one-fourth of the breadth of the cranium;
its posterior external angle corresponds to a slight groove on the mastoid process leading to the mastoid
notch ; its broadly rounded inner and posterior angle is separated from the supra-occipital ridge by the
hinder horn of the parietal surface; a smooth narrow tract intervenes between its anterior margin and the
temporal notch, and is continued into the smooth external surface of the mastoid process; the superior
and anterior angle touches the pyriform muscular area which surrounds the crotophytc impression in
front; the posterior border, as already mentioned, is separated from the occipital muscular surface by
the smooth convex edge extending from the canalicular elevation to the mastoid notch. The crescentic
crotophyte impression, forms a shelving entrance internally and anteriorly to the temporal notch; on the
left side, a sharp ridge separates from the anterior limb of this surface, a triangular segment impressing the
post-orbital process, with its base external. Surrounding the crotophyte impression in front and within,
is a subpyriform excavation; its apex is truncated on a level with the posterior margin of the temporal notch,
whilst its rounded extremity is separated by a narrow scabrous tract, four lines in breadth, from the orbital
margin, and is so abruptly sunk beneath the level of the frontal protuberance, as to lodge the point of the
finger. This impression doubtless gave origin to a cutaneous muscle, dermo-madoidens, which is inserted
into the integument of the posterior surface of the neck; it would erect the feathers on the head of the
Dodo, and push forward the hood-like cutaneous ridge.
The anterior horn of the parietal tract sweeps round the dermo-mastoid impression to be continued
into the rough supra-orbital space, bounding it externally. The parietal surface is variously marked by
small vascular impressions, but is destitute of the foramina so abundant on the frontal slope.
The anterior and lesser aspect of the cranium presents the deep olfactory fossa;, separated mesially by
the thin anterior prolongation of the interorbital septum, which rests below on the sphenoidal rostrum. The
single small olfactory foramen, on each side, opens directly, with an inclination outwards, into the base of
CH. I.] OF THE DODO. 8 7
its respective fossa; at their exit from the apex of the cerebral cavity, they diverge slightly from each
other, and arc separated by an interval of about four lines, corresponding to the breadth of the interorbital
septum.
Before describing more minutely the formation of the olfactory fossa; in the Dodo, it will be necessary
to consider them first in other Pigeons, by which we shall alone gain a correct conception of several peculiarities
in the cranium of this extinct form. In all Pigeons, as in many other birds, the anterior extremity
of the vertical osseous plate, forming the interorbital septum, advances beyond the junction of the nasal
with the frontal bones; and is completely covered by the former, which meet in the median line posteriorly,
but arc separated anteriorly by the extremity of the nasal process of the prcmaxillary; hence no part of it
appears mesially, behind the prcmaxillary and between the nasals, as in the Emeu and other Slruthionida. From
each side of the expanded upper border of this advanced portion of the septum, a thin lamina passes horizontally
outwards; contracting rapidly from before in the antero-posterior diameter, it bends downwards
and inwards, arching over the foramen for the transmission of the olfactory and ophthalmic nerves and accompanying
vessels, to meet and be continued for a greater or less extent along the outer border of a
vertically transverse, subtriangular plate, projecting outwards from the interorbital septum; this last commences
beneath the common aperture, and increases in breadth as it descends; by its anchylosis with the
inferior extremity of the prefrontal, it forms the anterior wall of the orbit, separating it from the open
olfactory cavity in front.
For reasons which cannot be discussed here, I regard the interorbital septum as the
compressed body of the third and last, or most anterior of the cranial vertebra;; and the
processes just mentioned, as ossified portions of the ethmoid or olfactory capside; the superior
I have hitherto denominated the turbinated, and the lower, the inferior ala of the ethmoid,
and I shall continue to use these terms in the remainder of this description. By the
sphenoidal rostrum, or rostrum simply, I understand the anterior prolongation of the sphenoid
which supports the interorbital septum; it has been incorrectly considered as homologous with
the anterior sphenoid in mammals, and hence has received the special appellation of presphenoid
in Professor Owen's late paper on the Vertebrate skeleton;1 whereas the interorbital
septum in birds is the homologue of the mammalian presphenoid. The bone which lias
heretofore been denominated the lachrymal in birds, is undoubtedly the homologue of the
prefrontal in the cranium of fishes and reptiles ; the true lachrymal bone, which is external to
the lachrymal duct, exists in certain Saurians, and in the Crocodilidte; it does not occur in
the higher Vertebrata, Avea and Mammalia, while the prefrontal only disappears in certain
exceptional instances among mammals; in birds and mammals it has erroneously been regarded
as the true lachrymal, and is so named even by the learned Hunterian Professor;
this false homology masks one of the most beautiful instances of the unity of organization.
Having thus explained the meaning of the terms employed, we may return to our
subject:—
The fissure remaining between the turbinated ala and the prefrontal, which in many birds transmits
the upper diverticulum of the suborbital sinus, in several Pigeons, is diminished by the extension upwards of
1 Reports of British Association, 1S46.
2 A