the apex of the inferior ala, to join the interorbital septum, so as to form a bridge over the olfactory groove,
behind that produced by the turbinated ala; the interval left between them, transmits a branch of the
ophthalmic nerve with the accompanying vessels, which groove the outer surface of the turbinated ala, and
escaping from between the nasal limbs are distributed to the nostrils. The outward expansion or development
of the produced apex obliterates the fissure; the anterior wall of the orbit presenting only the olfactory
outlet.
There is thus left a space between the turbinated ala and the prfefrontal, which is closed behind by the
outward extension of the former; it lodges a part of the subocular pneumatic sinus, from which the pre-
frontal receives air directly, by a large aperture on its inner surface. The compressed cavity internal to the
turbinated ala is wider above and below, narrowest in the centre, where the olfactory orifice opens into it;
the apposition of the pituitary membrane with that of the pneumatic sinus beneath the lachrymal duct
bounds it externally, and below it is continued over the groove on the inferior ala to open into the posterior
nares by the concavity of the nasal process of the palatine bone.
In Gowra, the prefronto-ethmoidal fissure is not obliterated. In Treron, Geophaps, and Goldinas, it is
completely closed; in Carpophaga, Ptilinopus, and Lidimculus, only partially so. *
In Treron, Lidimculus, and Caloenas, &c., the turbinated ala is so curved, outwards or evasated, as to
come into contact with the apex of an inwardly inclined, subtriangular projection from the anterior margin
of the prefrontal, supporting the termination of the lachrymal duct; and thus the pneumatic space is divided
into two compartments; in Treron, from the great expansion of the diploe, it is much reduced in size.
In the Dodo, the prolongation of the interorbital septum, and the turbinated ake, project about five
lines beyond the junction of the cranium and mandibular apparatus; completely concealed from above by
the latter, but not in contact with it, as in other Pigeons. The resilient hinge having retrograded to the
cranio-facial line, space is left to permit of the downward flexion of the mandible; the remainder of this
mechanism we shall see hereafter. The curved plate is much widened out to lodge the olfactory apparatus,
and the convexity comes in contact with the prefrontal, in its whole length, at that part of the surface
of the latter, which corresponds to the lachrymal groove externally; so that the subocular space is completely
obliterated in the centre. The inferior ala is much compressed transversely and extended forward, so as to
leave between it and the rostrum, a deep narrow groove; and the subocular space is reduced to a small
irregular depression between its thin anterior edge and the prefrontal, with which it coalesces inferiorly.
The prefronto-ethmoidal fissure is obliterated by the expansion of the posterior border of the turbinated
ala, arching over the foramen that transmits the ophthalmic branch of the fifth nerve, which grooves
the roof of the olfactory fossa. This aperture is diminished by an extension forwards of an osseous- plate,
from the interorbital septum outside of the foramen olfactorium • it forms the outer part of the floor of the
olfactory fossa, and is, as it were, an ossification of the external wall of the periosteal tube, which conducts
the olfactory peduncle to its exit at the antorbital foramen in most other birds; here, the tube in relation to
the extremely short olfactory peduncle is much abbreviated, and its base widened out, serving to obliterate
the space intervening between the antorbital and olfactory foramina. The olfactory fossa has a subhemi-
spherical base, perforated by the single aperture for the transmission of the olfactory nerve; its floor presents
the deep narrow groove just mentioned; the outer wall is perforated by the antorbital foramen about three
lines anterior to the olfactory outlet. Each fossa is one inch two lines deep, and five lines wide at its
anterior orifice; the height exclusive of the groove is six lines. The extremity of the high compressed
rostrum is removed, exposing to view the very loose diploe enclosed by thin and elastic parietes; it probably
terminated in a subacute apex. The anterior thickened margin of the inter-olfactory septum is
concave anteriorly, and its lower portion ascends obliquely backwards, to a deep notch immediately below its
upper end; it is sharp in the centre. The septum is translucent centrally, and its thinness gives increased
space for the lodgement of the olfactory apparatus.
The relatively small cerebral cavity has its axis placed more horizontally, than in other Pigeons; so
that the brain is, as it were, rotated on its transverse axis, and this rotation gives rise, or is related, to the
verticality of the occipital facet.
The apex of the cerebral case is so depressed as to be nearly equidistant between the upper and
under surfaces of the cranium, and to correspond externally to a point a little behind the centre of the
groove on the interorbital septum. The frontals attain a median thickness of one inch and two or three
lines, above the truncated apex, formed by a broad septum separating the olfactory foramina; which open
directly into the bases of their respective fossae. This septum is not homologous with the crista galU of
the ethmoid, but is a prolongation upwards of the thick interorbital septum, or body of the olfactory vertebra,
to coalesce with the frontals mesially, and thus to divide the anterior orifice of the cerebral tube into, two
foramina for the transmission of the olfactory peduncles, and so far to close i t : the non-existence of any
vertebral segment anterior to the frontal, permits the olfactory capsules to converge towards the median
line and to be separated only by a thin septum, the prolongation of the anterior centrum; they are thus
most exposed to the inspiratory currents of air loaded with odorous particles; the optic and auditory
capsules, on the contrary, are situated between two adjacent vertebras and project laterally. The thickness
of the interorbital septum, beneath the olfactory foramina, is one inch two lines, and diminishes one
half at the optic outlets. The length of the cerebral cavity, measured from the upper or lower margin
,of the foramen magnum to the olfactory septum, is one inch nine lines and a half; its breadth between the
foramina for the transmission of the ophthalmic branch of the fifth is one inch; the extreme width of the
cerebral fossae is perhaps one inch nine lines, and its greatest height from the floor of the optic groove,
probably about ten lines.
The basilar fossa for the lodgement of the medulla oblongata is slightly concave transversely, and rises
towards the posterior clinoid plate, which projects with a subconvex border over the pit containing the
orifices of the carotic canals, at the' posterior part of the shallow and broad sella turcica; this plate is
traversed at its base by the canal for the abducens nerve. The extreme length of the basilar fossa, from
its posterior angle on the upper surface of the occipital condyle to the clinoid process, is one inch and a
third of a line; its transverse diameter is equal to that of the lower segment of the foramen magnum: it
presents, posteriorly and laterally, the condyloid foramen; and in front of it, the large infundibular pneumo-
gastric orifice overhung by the vestibular prominence, which projects into the area of the foramen magnum
at the centre of its lateral margin; a narrow convex ridge separates this aperture from the meatus auditorius
internus, which has’ a subacute anterior edge running backwards on the vestibular convexity, between it and
the petrosal fossa. The cerebellar fossa is relatively narrow, its length from the upper margin of the
foramen magnum to its apex, dividing the cerebral fossa posteriorly, is one inch; its surface is considerably
depressed beneath the level of the cerebral fossae; it neither presents the longitudinal venous groove, nor
transverse furrows corresponding to the laminae of the cerebellum; along its margin posteriorly is seen the
lateral venous groove terminating in the lateral occipital foramen; its lower angle, immediately above the
foramen magnum, is perforated by the mesial occipital aperture. The fossa for the optic lobe is relatively
very shallow internally, and its edges undefined; at its apex, beneath the lateral venous groove, there is a
tumid pneumatic projection about the size of a large pea, overhanging the petrosal excavation. The thin
floor of the optic fossa is pierced by the foramen giving passage to the ophthalmic branch of the fifth pair;
internal to which it is grooved by the fourth nerve, which perforates the thin plate forming the posterior