Cu. I.] OF THE DODO. 85 
The orbito-sphenoids, or lower segments of the fronto-neural arch, are rarely developed in birds, as distinct 
elements: the bones indicated as such, by Mr. Owen, having no real or separate existence; that learned 
author regards them as the neurapophyses of the fronto-neural arch, and the frontal bones as the expanded 
and divided frontal spe. As growth advanced, the diploé of the coalesced frontals would begin to expand, 
and the obliteration of the sutures connecting them to the facial bones, would enable the increased deve- 
lopment of pneumaticity to invade the frontal portions of the nasals and the median process of the pre- 
maxillary, so as to render them tumid, and tilt their anterior walls forward, producing the marked distinction 
between the cranial and mandibular segments of these elements. 
The frontal protuberance culminates at a height of eleven lines above the cranio-facial line, and seven 
lines above the highest part of the parietal tract: it slopes rapidly downwards to the supra-orbital edge ; its 
anterior border is undefined, where the frontals coalesce with the expanded cranial portions of the nasals 
and premaxillary ; its posterior boundary follows nearly the posterior margin of the frontal, passig on each 
side outwards and forwards from the mesial line to a point on the supra-orbital border, midway between the 
notch and the post-orbital process. A broad shallow furrow traverses the median line, rendering it sub- 
bilobed; at the posterior extremity of the groove, where the coronal fontanelle existed, is a small foramen 
leading into a canal capable of admitting a fine bristle ; it perforates directly the cranial parietes and opens 
internally towards the apex of the cerebellar fossa, transmitting a vein from the scalp to the posterior 
cerebellar sinus: the thickness of the cranium, here, amounts to eight lines and a half. Behind the foramen 
is a transversely oblong band, three lines and two-thirds wide, and one line long; defined posteriorly by an 
ungueal fissure-like groove, the angles of which extend outwards, curving backwards: its extremities are also 
defined by grooves. From the foramen a venous groove passes outwards, along the posterior border of the 
frontal protuberance, and externally curves slightly backwards to the aperture or notch on the supra-orbital 
plate, leading to the furrow on the roof of the orbit; about half an inch external to this edge, it is joined 
by a semi-circular groove which sweeps inwards, convex anteriorly, over the summit of the protuberance, 
and, bending backwards, reaches the median furrow ; finally diverging from it, to meet the posterior groove 
at the outer and anterior angle of the band just mentioned. Where the semi-lunar grooves diverge from 
each other behind, a triangular, slightly elevated tract is left on the floor of the median furrow, with its 
base separated from the osseous band by a slight groove. From the convexity of the semi-lunar groove, 
two others pass forwards, on the left side, to a furrow, which appears to indicate the anterior edge of the 
combined frontals ; in the centre it reaches half way up the frontal slope, its angle extends to the suture 
between the antorbital process and prefrontal on each side. 
The precise limit of the subtriangular frontal plate of the nasal, is undefined ; the external limb rises 
to a higher level than the internal, and is less abruptly bent on the body: on the left side, a-groove 
curving outwards as it retrogrades, and continuous in front with the fissure between the prefrontal and 
ecto-nasal limb, indicates the outer margin of the body; the upper would form a segment of the frontal 
furrow; the internal is denoted by an interrupted fissure-like groove, which may be traced upwards from 
the linear impression separating the premaxillary median process, and the inner lmb of the nasal, along the 
upper beam of the mandible; it passes inwards as it ascends, but appears not to have come in contact with 
its fellow behind, being separated in its whole extent by the termination of the premaxillary nasal process ; 
which ascends to touch the frontals mesially, its apex having been probably inserted into the frontal suture. 
The lateral moieties of this extremity are also separated by a median fissure-like groove, which disappears 
as it ascends; the left one is more tumid than the right, and its anterior bullose extremity overhangs the 
cranio-facial line; on the right side, the pneumatic diploé does not cease so abruptly, and has a tendency to 
invade the median mandibular stem. ‘This portion of the premaxillary measures six lines across its base, 
