598 GEOLOGICAL SURVEY OF THE TERRITORIES. 
panic end of the infraorbital bar is on a lower level than the maxillary 
extremity; it is received into the cup-like articulating cavity on that 
bone. The two oblique sutures, persistent in many birds, and denoting 
the original division of this bony style into three separate bones, the 
maxillary, malar, and squamosal, are here entirely effaced. Asa whole, 
it is compressed from side to side, and of ample size in comparison with 
other bones of the head. At about the locality of the malo-zymotic 
suture the bone throws upwards a thin expansion that meets the de- 
scending postfrontal, thus completing the orbital circumference at that 
point. Its anterior and fixed extremity is made up by the maxillary. 
Here it forms externally a portion of the posterior surface of the bill, 
while internally it assists in forming the roof of the mouth and floor of 
the nasal cavities, and otherwise behaves as already described. The 
lacrymals are extremely spongy in texture, covered by an outside delicate, 
compact bony casing. They articulate above by a ginglymoid joint with 
the posterior border of the nasals, resting below on the spongy bones de- 
veloped from the superior surfaces of the maxillaries. They are limited 
toa slight movement inwards and outwards, and aid in separating the or- 
bital cavities from the rhinal chamber. Externally they present for ex- 
amination a shallow groove traversing the bone obliquely downwards and 
forwards and a little inwards for the lacrymal duct. The orbital cavities 
are very large, and remarkable for the completeness of their bony walls 
and the near approach their peripheries make to the circle, any diam- 
eter of which measures the merest trifle above or below two centimetres. 
The septum in the adult bird has rarely more than one small deficiency 
of bone in it. This usually occurs in about the position shown in Pl. I. 
The sutures among the various bones have entirely disappeared, nothing 
being left to define the exact outlineof the vomer especially. The groove 
for the passage of the olfactory nerves forward is well marked, the era- 
nial foramina for them being distinct, one in each orbital cavity. This 
also applies to the openings for the optic nerves. The extentot the roof 
is increased on either side by a superorbital process (shown in PI. II, 
Fig. 1) that points downwards, backwards, and outwards, and serves for 
membranous attachment. The posterior walls are marked by ramifying 
grooves for vessels. They have a direct forward aspect, which is en- 
hanced by the low descent of the broad and thin postfrontals. Ante- 
riorly, the aperture between these and the rhinal vacuities is diminished 
by the lacrymals externally and by a wing-like plate thrown off from 
the prefrontal internally. This latter bone here terminates in a sharp 
concave border, with a descending ridge on either side just within it. 
The floors of the orbits are more complete than is usually seen in the class, 
due to the flatness and position held by the pterygoids and palatines, 
the wing-like process of the ethmoid just referred to, and the pterapo- 
physial processes of the basi-sphenoid. The selerotals number from 
fifteen to sixteen, all of them being about the same length, but varying 
as to their width; in figure they are trapezoidal and universally oblong, 
with the short parallel side in the circumference of the cornea and the 
opposite one resting in the periphery of the posterior hemisphere. We 
have never observed one that was wide enough to appear square. They 
are rather thin, concave outwards, very slightly movable at their op- 
posed edges, and carry out their usual function of maintaining the form 
of the optical apparatus. The wpper mandible of this bird is made the 
more conspicuous and distinct from the remainder of the skull by the 
abrupt way in which it is attached and the much firmer texture of the 
bone. The mandibular culmen is perfectly convex from the tip of the 
sharp-pointed extremity to where it suddenly terminates under the 
