occipital foramen ; in the great pneumaticity of the cranium ; in the ratio of the upper
mandible to the cranium; in the retrogression of the ethmoidal fossæ; in the absence
of the frontal protuberance ; and of the lateral excavations of the upper mandible. Such,
then, are some of the more important and characteristic distinctions ; without entering into
superfluous details, regarding the differences in the minute configuration of similar parts, as
these may vary even in the same group.
The Cathartes resembles the Dodo, in the absence of the ossified vomer ; in the anchylosis
of the prefrontal ; in the retrogression of the ethmoidal fossæ ; in the breadth of the
interorbital region; and in the curvature of the lower jaw. It differs, however, in other
more important characters, common to it with the typical Vultures, and is peculiar in
possessing the nasal vestibule, characteristic of the Cathartine modification of the raptorial type.
From the typical Rasores, the Dodo differs, in the elongation of the external nasal
orifice; in the greater development of the maxilla; in the obliquity of the zygoma; in the
greater complexity of the palatine bone ; in the double mastoid condyle of the tympanic ;
in the absence of the posterior and internal angular processes of the basal facet of the lower
jaw ; in the anchylosis of the prefrontal, and great development of its inferior process ; in the
presence of the alæ of the ethmoid ; in the retrogression of the ethmoidal fossæ ; in the
great pneumaticity of the prefrontal, and of the sphenoidal rostrum ; and in the absence of the
mesial supra-occipital foramen.
The skull of Pterocles resembles that of the Dodo in the same degree as it approaches
the type of the Columbidæ.
From the Insessores, the Dodo is at once distinguished by the form of the palatine
bone ; by the absence of the vomer ; by the elongation of the external nasal fissure ; by the
obliquity of the zygoma ; and by the relation of the antorbital process to the prefrontal.
I t would be useless to state the essential differences between the skull of the Dodo, and
that in the different families of the Grallatorial and Natatorial orders, as 110 one is likely to
suppose that it has any affinity with either of these groups.
I now proceed to describe the skull of the Dodo in greater detail.
The posterior subelliptical facet of the cranium, is formed by the occipital bone ; its greater diameter
is transverse, and measures two inches and eight lines and a half; and its lesser, one inch and seven lings
and a half. It presents an upper crescentic segment, with a vertical plane, embracing in its concavity a
lozenge-shaped surface, which inclines obliquely downwards and forwards at an angle of 125°.
The upper convex margin corresponds to the supra-occipital ridge, continued on each side into the
convex incurving border of the paroccipital process, which projects outwards, forming the posterior wall of
the tympanic cavity. The infra-occipital ridge, forming the central moiety of the concave edge, overhangs
the recess perforated by the foramen magnum, like the dripstone of a Gothic arch; a line drawn from its
corbal-like origin outwards, on each side, to the inferior angle of the paroccipital process, indicates the
remainder of this boundary; along which the vertical supra-occipital surface is broadly rounded off into the
rhomboidal fossa, occupying the lateral angle of the lozenge. This depression is bounded externally by
the lower sharp edge of the internal wall of the tympanic cavity, arching from the paroccipital angle to
the posterior border of the basilar pyramidal protuberance, which projects vertically downwards ; a rough
prominent ridge, notched in the centre, ascends, inclining inwards and backwards along its internal edge,
and with its fellow forms the anterior boundary of the occipital facet, indicating nearly the division between
the sphenoid and occipital bones. The supra-occipital plate presents, in the centre, a triangular, broad and
depressed cerebellar elevation ; the truncated apex is on a level with the infra-occipital ridge, a line above
which it is perforated mesially by a short canal, half a line in diameter, opening internally immediately
within the upper margin of the foramen magnum : a slight crest traverses the median line, becoming more
apparent as the convexity subsides towards the base, the angles of which extend to the most concave part
of the supra-occipital ridge ; below it enters the furrow leading to the orifice just mentioned. The large
oblong surface, external to the central protuberance on each side, is divided into two subequal portions, by
a convexity directed downwards and inwards from the origin of the superior occipital ridge to that of the
inferior, it corresponds to the semicircular canals within; on the left side it is widest and most prominent
superiorly, and subsides towards the lateral venous groove ; the floor of the inner segment is slightly
elevated towards the supra-occipital ridge, but on the right side it is raised into a triangular convexity,
more prominent tfyan the canalicular elevation, to which it is parallel, separated only by a slight digital
impression. The lateral venous groove passes obliquely inwards and upwards, above the infra-occipital
ridge, and terminates at the margin of the cerebellar protuberance, in a short oval canal perforating the
cranium, two lines and a half above the foramen magnum; and opening upwards, internally, at the margin
of the cerebellar fossa ; it transmits the lateral venous sinus. The groove contracts in the centre of its
course, and is there covered by a narrow osseous bridge on the left side ; a small canal lodging a muscular
vein opens downwards into the internal segment. Externally, it curves round the origin of the infra-
occipital ridge ; a narrow tract, one line in breadth, separating its termination from the groove for the bulb
of the jugular vein, which the lateral sinus joins.
The area of the strongly pitted muscular impression, on each side, is elliptical ; its inner angle is prolonged
inwards across the base of the cerebellar protuberance ; the outer occupies the upper part of the
paroccipital process, the lower portion of which is smooth. In its centre it extends from the venous groove
to the supra-occipital ridge, and the surface is increased by the elevations already described. The cerebellar
eminence is smooth and polished. From the notch between the paroccipital process and mastoid, inwards
for half an inch, the digastric and occipital impressions are separated only by a smooth convex edge ; more
internally, a prolongation of the parietal tract intervenes, the apex extending to the canalicular elevation ;
where the supra-occipital ridge originates.
This ridge is broad and rough externally ; it ascends on each side, becoming narrow and rounded,
following the undulation of the surface to the angle of the cerebellar elevation ; from thence it descends to
near the mesial line, over which it arches-: it presents a slight notch at the upper and inner angle of the
canalicular convexity, from which a groove leads outwards and downwards to a canal perforating that
eminence, and traversing the cranial diploë to open on the lateral facet below the superior pneumatic foramen
; it transmits a vein from the integuments of the cranium. The supra-occipital ridge is defined by the
subsidence of the posterior surface, not by its elevation above the parietal tract.
The convex margin of the paroccipital process increases in breadth inferiorly, and is rough and flattened,
giving origin to the Biventer maxilla muscle ; a strong ligament passing from its lower angle,
forwards and inwards to the apex of the basilar facet of the ramus of the lower jaw, is still present.
The infra-occipital ridge is broad, rough, and prominent externally, the lateral venous groove bending
round its origin ; the roughness subsides internally, as it passes into the cerebellar eminence. The foramen