01 apteryx australis - University of Texas Libraries

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convex behind and concave in front, where they form the back part of the wide meatus
auditorius externus. Allthe parts of the occipital bone were anchylosed together, and
also to the surrounding bones.
The angle between the posterior and superior regions of the cranium is scarcely
produced into a ridge. The superior region is smooth and regularly convex ; it is
separated from the temporal depressions by a narrow ridge, a little more marked than
the occipital one. The sagittal suture runs across a littlebehind the middle of the upper
part of the cranium :the left half of this suture, with the frontal suture, was persistent
in one cranium of the Apteryx, whichIextracted from a dried skin inMr.Gould's Museum
;but all the sutures were obliterated in the skull ofMr.Bennett's male specimen.
The persistent sutures were more denticulated than those in the skullof a young Ostrich
with whichIhave compared them.
The superior is continued into the lateral regions of the cranium by a continuous curvature,
so that the upper part of the small orbital cavity is convex, and its limits undefinable,
there being no trace of supraorbital ridge or antorbital or postorbital processes :
this structure is quite peculiar to the Apteryx among birds, but produces a very interesting
resemblance between it and the monotrematous Echidna. The temporal bone
sends forwards a short and slender zygomatic process, which inits small relative development
resembles most that of the Rhea among the larger Struthionidæ.
The frontal bones gradually contract to their junction with the nasal bones, between
which there is the trace of a small part of the ethmoid bone. The narrow frontal region
of the skull is traversed by a mesial longitudinal depression.
The ethmoid bone is remarkably expanded in the Apteryx, and its cells, instead of
being restricted to a narrow vertical septum of the orbits, as in the diurnal Struthionidæ,
occupy not only the ordinary orbital space, but extend outwards for more than two lines
beyond the lateral boundaries of the anterior part of the frontals. A small process extends
from the frontal to the side of the expanded ethmoid, anterior to the orbital foramina,
which are distinct, and remarkably wide apart, and the expanded ethmoid is also
supported anteriorly by a similar anchylosed conjunction with the lacrymal bone.
The entire breadth of the ethmoid is 9 lines. The nearest approach to this peculiar
structure of the Apteryx is made by the Ostrich, in which the interorbital septum,
though much thinner than in the Apteryx, is also occupied by ethmoidal cells, and is
thicker than in any of the other large Struthionidæ. The Ibis (Numenius arcuatus, Cuv.,
Pl. VII.figg. 3 &4.) offers a striking contrast with the Apteryx in this respect, the
interorbital osseous septum being almost entirely absent. In all the other parts of the
cranium already noticed it also differs widely from the Apteryx. In the posterior region
of the skull of the Ibis the bony covering of the cerebellum is in great part defective :
in the superior part the cranial parietes above the cerebral hemispheres form two convexities,
separated by a middle longitudinal depression, and the narrow space between
the supraorbital ridges is occupied by the impressions corresponding to the nasal or
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