to the former; it extends forwards, contracting to a groove, which leads to the posterior angle of the ramal
vacuity; behind, it extends upwards to the coronoid edge.
Having thus given a detailed account of the skull of the Dodo, it now remains to
contrast it generally with that of other Pigeons; for this purpose, and to supersede the
necessity of lengthened descriptions, it has been thought desirable to give in Plate X., figures
of some of the more remarkable and varied forms of the skull in that family, with a reduction
of the head of the Dodo for comparison.
I am indebted to that eminent ornithologist, Sir W. Jardine, for permission to examine
the bones remaining in the only specimen of the Didunculus in Europe; and thus I am
enabled to confirm the opinion expressed by Mr. Gould, regarding the columbine affinities of
that singular form, by the most certain of all tests, to wit, an examination of its osteological
characters.
The most important and apparent difference between the skull in the Dodo and that in the lesser
forms, depends on the small relative size of the brain and visual organs in the former, and the consequent
abbreviation of the cranium and elongation of the basal part of the mandible. This difference, though
readily explicable, might cause many, even, acute anatomists to overlook the family resemblances to that
of Pigeons in the skull of this extinct bird. The happy appreciation of these by Eeinhardt, entitles that
learned zoologist to a high place among Palaeontologists. In Treron, the extreme length of the cranial
cavity is nine lines, and in Goura, one inch two lines; while in the Dodo, it is only one inch nine lines,
little more than double the length of that cavity in the diminutive Treron. The outlet (foramen magnum)
is also relatively less in the Dodo than in Treron. (Plate X., Pig. 2 a, 3 a.)
I n the smaller Pigeons, the supra-occipital plate is less vertical and flattened than in the Dodo, being
more arched transversely, and inclined obliquely backwards. The occipital condyle is less prominent, and
the basilar protuberances for the insertion of the M. recti capitis laterales majores less apparent. The
mesial supra-occipital aperture exists in all; and at an early period, it is very large and not separated by
bone from the foramen magnum. Reference to t he plates will indicate other minor differences, which mayvary
in the species of the same genus.
The superior facet in t he smaller Pigeons is longer and narrower than in the Dodo, and the expansion
of the frontal diploii less abrupt; the mastoidal angles, bearing the muscular impressions, are also bent
downwards on the lateral aspects; while in the Dodo, they are thrown upwards by the great development
of pneumaticity in the upper part of the lateral walls of the cranial cavity. The supra-orbital border is
broadly concave and the intcrorbital region narrowed in ordinary Pigeons, and especially in Geophaps.
The profile is best seen in the respective figures; the dotted line in the Dodo indicates the probable
outline before the development of the frontal protuberance. In Treron and Goura, there is a foramen as
in the Dodo, perforating the cranium in the position of the coronal fontauelle; numerous venous grooves
converge towards it. The form and relative proportion of the different muscular areas vary in the different
genera; they arc most deeply impressed in Treron.
I n Goura there is a tendency to the development of the frontal protuberance opposite the apex of the
cerebral cavity, and it is distinctly bilobed, the mesial line being traversed by a deep longitudinal furrow.
The anterior portion of the coalesced frontals is elongated, as in other Pigeons, in relation to the great
extent of the intcrorbital septum: the nasals touch each other in the median line, and then- inner limbs
are in contact with, and ultimately soldered to, the turbinated aire. The hinge formed by the upper
its lower edge. A large vascular canal perforates the dentary very obliquely, running forward from the
dental space; it opens externally nearer the upper than the lower border, about nine lines behind the
symphysis, and passes into a deep groove, which, advancing towards the core, is concealed anteriorly
by the perforated and midermined, posterior crenate edge of the latter, as it ascends obliquely backwards : its
outer wall is pierced by two foramina, opening behind into a furrow, which disappears halfway to the dentary
notch. The dental canal terminates, internally, above the anterior extremity of the opercular; the orifice is
subdivided by a small process of the latter; a rough depressed triangular tract is continued forwards from
it, to the thick posterior sub-vertical border of the symphysis, which is perforated horizontally by a vascular
canal, emerging close to its lower edge, and midway between its angles; the mentary groove, already
mentioned, joins this canal at its centre; externally, a series of five large apertures open upwards from i t ;
three or four downwards, and one on t he rough concave symphysial surface.
The fissure between the angular and articular pieces, is conceded by the dentary without, and the opercular
within; that between the thin lamina of the surangular and the tumid rostrum of the articular
element, is converted by the dentary fork into an elongated elliptical foramen, six lines and a half long,
and one line and a half deep, its anterior angle corresponding to the posterior orifice of the dental space.
The posterior segment of the ramus increases in breadth as it retrogrades, and chiefly inwards in its hinder
moiety, so as to present a large pyramidal internal angle; while the external is produced backwards into a
compressed semi-lunar plate, with a thick and rough projecting edge, passing below into the smooth crest
running upwards and inwards, between the basal facet, and the anterior aspect of the inner angle, which
slopes obliquely forwards and outwards and passes into the inner surface of the ramus.
The basal or digastric facet is triangular, with the rough obtuse apex internal; the subconcave pitted
surface passes externally into the inner convex aspect of the angular plate.
The complex articular surface is transversely oblong; without, it presents a longitudinal, slightly
concave, rcniform tract, with an external convex border; which plays on the outer flattened segment of the
tympanic mandibular surface: within, it is deeply excavated for the reception of the ridge-like inner condyle;
the concavity is directed inwards and forwards, becoming wider and shallower, its anterior depressed edge
descending, while the posterior rises internally into a rough projection, rendering it concave transversely;
this edge is narrow, rounded without, but internally, it presents the large oval pneumatic aperture. Synovial
cartilage lines the inner half of its floor and its anterior surface, detaching a tract to line the rcniform concavity.
The low short coronoid process is separated by an interval of six lines and a half from the
articular surface, and corresponds to the junction of the four anterior fifths with the posterior; the upper
edge of the surangular, anterior to it, is smooth and rounded.
An elongated tubercle extends downwards and forwards from the centre of the outer projecting border of the
external segment of the articular surface, and its anterior angle is prolonged into a ridge, passing forwards to
the extremity of the lower dentary liinb. The outer surface of the posterior segment is thus divided
diagonally, into two subequal surfaces; the posterior of which is triangular, most concave, and deeply
pitted; it gives attachment to the muscles of the tongue, while the anterior furnishes insertion to the
M. temporalis.
The pitted surface on the inner aspect of the jaw, for the attachment of the M. pterygoideus
internus is defined anteriorly by an oblique irregular ridge, commencing at the upper edge a little anterior to
the articular surface, and descending obliquely forwards to a groove, directed obliquely inwards and forwards,
across the lower edge of the angular, from the extremity of the dentary to that of the opercular; it extends
backwards on the anterior aspect of the inner angle.
The deeply concave pitted tract for the insertion of the external pterygoid, is anterior and superior