OF THE SOUTHERN APTERYX. 283 
convex behind and concave in front, where they form the back part of the wide meatus 
auditorius externus. All the 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 little behind 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 Apterya, which I extracted from a dried skin in Mr. Gould’s Mu- 
seum ; but all the sutures were obliterated in the skull of Mr. Bennett’s male specimen. 
The persistent sutures were more denticulated than those in the skull of a young Ostrich 
with which I have compared them. 
The superior is continued into the lateral regions of the cranium by a continuous cur- 
vature, so that the upper part of the small orbital cavity is convex, and its limits unde- 
finable, 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 inter- 
esting resemblance between it and the monotrematous Echidna. The temporal bone 
sends forwards a short and slender zygomatic process, which in its small relative deve- 
lopment resembles most that of the Rhea among the larger Struthionide. 
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 Apteryz, and its cells, instead of 
being restricted to a narrow vertical septum of the orbits, asin the diurnal Struthionide, 
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 ex- 
tends from the frontal to the side of the expanded ethmoid, anterior to the orbital fora- 
mina which are distinct, and remarkably wide apart, and the expanded ethmoid is also 
supported anteriorly by a similar anchylosed conjunction with the lachrymal 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 Apteryz, is also occupied by ethmoidal cells, and is 
thicker than in any of the other large Struthionide. The Ibis (Numenius arcuatus, Cuv., 
Pl. LILI. figg. 3 & 4.) offers a striking contrast with the Apteryzx 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 Jbis the bony covering of the cerebellum is in great part defective : 
in the superior part the cranial parietes above the cerebral hemispheres form two con- 
vexities, separated by a middle longitudinal depression, and the narrow space between 
the supraorbital ridges is occupied by the impressions corresponding to the nasal or 
2P2 
