mandibular beam which here is chiefly constituted by the ento-nasal limbs, exists at the anterior edge of
•these plates, and in front of the posterior extremity of the nasal fissure. In the Dodo, on the contrary,
this hinge is in the same transverse line as the hinder angle of the fissure, and the mesial beam is, as it were
started off the flat arch, formed by the turbinated alas, which projects free under the mesial beam, separated
from it by a space permitting the downward flexion of the mandible; the flexibility of ifft tipper beam
being increased by the thinning away of the part which conceals the free portion of‘the turbinated aim.
The bifid posterior extremity of the mesial process of the premaxillary is much smaller than in the Dodo, ifc
passes beneath the coalesced nasals, resting on the upper edge of the inter-olfactory septum, and reaching
about half-way to the frontal border of the nasal; in the Dodo, this extremity is much broader, and forms
the principal part of the mesial beam, at the hinge; and it reaches further back, separating the nasals
mesially; its apex corresponding to the anterior extremity of the coronal suture. (See Plate X., Kg. 4, i).
In Treron, the diploe of the anterior portion of the coalesced frontals, is, more expanded than
in Gama, and the frontal aspect is convex transversely, and in the antero-posterior diameter; while in
Gmtra it is concave transversely, and depressed longitudinally; the increased pneumaticity invades the
nasals and overflows the extremity of the mesial beam, forming a tumid and abrupt cranio-faeial line. The
compact elastic extremity of the premaxillary process is wedged between this expansion and the
inter-olfactory septum. The frontal aspect is depressed for a crescentic space, on each side, internal to the
superciliary margin, and raised in the centre. (Id. Pig. 3 b.)
In Didunculus, the forehead is flatter longitudinally than in Treron, but the broad extremity of the
mesial mandibular beam is, in like manner, overhung by the tumid convex segment of the expanded and
coalesced nasals; the central elevation of the frontal region is broader. (16. Kg. 1 3 ).
In all the lesser Pigeons, the arrangement of. the mandibular hinge is essentially as in Gama - in
Gowa, Geophaps, and other slender-billed Pigeons, the imto-nasal limbs are very narrow posteriorly, hence
the hinder angles of the nasal Assures are widened out, and expose to view the turbinated aim. In Calamus,
the mesial beam is broader at the hinge, owing chiefly to the greater width of the nasal process of the
premaxillary; and the posterior angles of the nasal Assures are reduced to narrow chinks, as in the Dodo • in
Treron and Didnmmlm, these angles are also obliterated; but in all, the extremity of the nasal process of
the premaxillary is concealed mesially by the junction of the. nasals, and does not ascend: on the frontal
region to separate tlie nasal bones from each other, as in the Dodo.
The lateral aspect of the cranium in the lesser Pigeons differs from that in the Dodo, in the large
relative size of the orbit, and in the great ratio which it bears to the temporal segment of the orbito-tem-
poral fossa; the latter being diminished by the bending down of the mastoid element. The interorbital
septum intervenes between the cerebral and olfactory fossae: its junction with the coalesced frontals is
traversed by the olfactory groove, which terminates in the antorbital foramen; the septum is thick and
complete in Treron, in most other Pigeons it is thinner, and perforate in front of the common anterior
boundary of the optic outlets: the floor of the cerebral cavity also- is frequently membranous behind the
olfactory foramen. In Geophaps, the post-orbital process is elongated, and nearly meets the post-temporal
process of the mastoid; in Didnmculus, the strong post-temporal .plate is extended forwards and joins a
slender bar from the post-orbital process, which completes externally the circular temporal outlet.
Inferiorly, the rostrum of the sphenoid in the lesser Pigeons is necessarily more elongated than in the
Dodo; the pterygoid articular surfaces do not exist in the Didmiculus; even in Gowa, they are much
reduced in size; in Geophaps and Gowa, the groove on the rostrum leading from the common outlet of the
Eustachian tubes is well marked, and the lateral venous depressions are also perceptible in Gowa', the
existence of these markings depending on the pneumatic expansion of the rostrum. The sphenoid and
prefrontals are much inflated in Treron and Geophaps.
The ratio in length of the upper mandible to the cranium, in various forms of Columbidce, is seen
by reference to Plate X .; in the ordinary Pigeon they are subequal, but in the stronger-billed fruit-eating
genera, the beak is shorter than the cranium, and in Did/mculus, only half its length, while in the Dodo, it
is twice as long. In the slender-billed species, the core is small, feebly hooked, and broadly rounded off
apically; it is relatively large, broad, and depressed in Geophaps-, in Treron it is stronger and wedge-shaped;
but attains its maximum of development in Didunculus, where it is much compressed and more sharply
uncinate than in the Dodo, assuming a pseudo-raptorial character, which, however, is negatived by the
feeble osseous apex, and by the soft and foliated texture of the gnathotheca. The mesial beam is also
much shortened in Didunculus, but its great breadth gives the necessary strength to the resilient hinge,
required for the movements of this powerful beak; it is covered by a vestige of the cere, which is much
extended in certain Trerons, but arrives at its greatest extension in the Dodo. The peculiar characters
of the mfl.yil1ft and the obliquity of the zygoma in Pigeons, have already been described; in Didv/nculus, the
horizontal portion of the maxilla almost, disappears, but the very strong basal segment ascends obliquely
to join the broad ecto-nasai limb, and from their junction the zygoma descends to gain the tympanic. The
palatine tuberosity or plane in other Pigeons, is, in Didunculus, replaced by the greatly developed funicular
tendon of the internal pterygoid muscle, which arises from a strong tubercle at the base of the under surface
of the core; as it passes backwards external to the palatine bone, it is covered within by the membrane
of the subocular sinus, and below by that of the palate, forming a surface on which the convexity of the
lower jaw glides. The short lunate nasal fissure in Didmiculus, forms a striking contrast to its elongation
in other Pigeons.
The shape of the palatine bone in the typical Pigeons, is well seen in Treron, (Plate X, Pig. 3 c,) and
the deviations from it, in that of the Dodo, are readily accounted for, by the shortening of the sphenoid and
the contraction of the mandible; the chief differences consisting, in the absence of the inflected portion of
the palatine process, which in Treron diminishes the wide posterior nasal fissure; in the shortness of the
sphenoidal plate, in relation to the abbreviated sphenoid; and in the less curvature of the nasal process,
depending perhaps on the compression of the mandible.
In the Diduncukis, the palate bone is much elongated, being attached anteriorly to the union between
the very short lateral stem and the oblique ascending base of the maxilla, opposite the lower angle of the
nasal fissure; the middle segment corresponding to the nasal process is drawn out, forming the extended
base of the lachrymal vacuity; and from the great pneumaticity of the bone, the crest is expanded, narrowed,
and subsides before reaching the sphenoidal plate. The nasal process is also but little apparent, the fossa
between it and the crest being obliterated by the expansion of the diploe: the palatine process is a small
curved triangular larafnaj prolonging downwards the nasal concavity; it subsides behind at the anterior and
inferior angle of the sphenoidal plate, and in front towards the termination of the crest; the large pneumatic
aperture perforates the lower part of the sphenoidal plate. The small area afforded by the palatine, for the
origin of the powerful internal pterygoid, is amply compensated by the great development of the tendon of
that muscle.
The pterygoid bone is relatively longest in Didmiculus, but has nearly the same form as in the Dodo,
being destitute of pneumaticity, and of the sphenoidal articular surface; in Geophaps it has a similar shape/
but articulates, as in most other Pigeons, with the sphenoid; it is much inflated in Gowa &c., the pneumatic
aperture being at the posterior extremity. The form of the inferior articular surface of the tympanic
varies in the different genera of Pigeons; this surface in the Dodo closely resembles that in Treron and
Calmas; in Geophaps, the articular surface on the outer segment is much reduced in size, though that angle
of the bone is much expanded, and chiefly backwards. In Didunculus, we observe the greatest deviation
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