172 MR. W. K. PARKER ON STEATORNIS CARIPENSIS. [Apr. 2, 
basitemporal plate below; this conical cavity is the “anterior tym- 
panic recess.” 
All these parts of the ornithic auditory labyrinth are well seen 
in Steatornis. 
The mandibles (Plate XVII. figs. 1 and 4) form a remarkable 
structure, being narrow and pointed in front, and extremely wide and 
bowed out at their hinder third. Behind, they curve inwards again, 
so that their “ internal angular processes” are only 15 millim. apart, 
whilst the width across the broad part is 33 millim., the rami being 
57 millim. long, and their ankylosed symphysis 5 millim. in extent, 
and their oblique hind edge 5 millim. high. Behind, in the coronoid 
region, near the hinder part of the dentary, and again at the fork of 
that bone, where there is a snag for muscular attachment, the bone 
is 7 millim. high. Under the first of these high tracts the outer face 
is hollow, but the hind part of each ramus is swollen and pneumatic, 
and there is a large foramen for the ‘‘siphonium,” on the top of the 
‘internal angular process.” The sutures are nearly filled in; 
there is a large oblique dentary canal under the coronoid process. 
The hinder or articular part is wide and triangular; there is a deep 
sinuous hollow between the cartilaginous condyloid tracts, the outer 
of which is pyriform and convexo-angular, and looks forwards and 
inwards, 5 millim. long; whilst the inner condyloid face is a semi- 
cylindrical trough, with sharp sides; it looks more inwards than the 
outer condyloid facet; this scooped space is 2 millim. wide, 2°5 
millim. long, and 1°5 millim. deep. The perforated internal angular 
process is blunt, turns upwards, and extends 2 millim. inwards from 
the condyloid trough. The motions of a jaw so hinged must have 
some peculiarity—there is so great an appearance of art in its con- 
vexities, concavities, sinuosities, and directions; the result of all this 
careful adaptive specialization would seem to be a perfect combi- 
nation of elasticity and mobility with strength,—strength sufficient 
for the purposes of this frugivorous bird. Notwithstanding the 
large size of the socket, the eyeball, like that of Opisthocomus, is 
small ; its largest diameter is 16 millim., and that of the sclerotal 
ring is 12 millim.; the largest plates are only 2 millim. wide, and there 
are 14 of them, as in Gecinus viridis ; but in that bird they are much 
more elegantly formed, and 3:5 millim. wide; and they are neatly 
turned outwards at the inner edge of the rim; in Steatornis they are 
almost flat, just a little concave externally, and are very similar to 
those of a Monitor Lizard (Psammosaurus griseus). In another 
evening bird not much larger than Steatornis, namely, the Hooting 
Owl (Striv aluco), the eyeball is 25 millim. across, and the 15 
sclerotals vary from 8 to 12 millim. in width outwards, and are 
about 6 millim. in extent at the cuter rim, although much of this is 
overlapped in most of them. 
The hyoid arch (Plate XVIII. fig. 2) is normal, but rather feeble. 
The tongue is short. and sagittiform, and in it the cerato-hyals (¢.Ay.) 
converge and unite in front; they remain unossified ; their length is 
12 millim. The basal bar (0.A.6r.) is of the same length; it is 
moderately dilated where the posterior cornua (cornua majora, br’.) 
