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 obhque 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 appeiirance 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, tlie 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 milhm. 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 (Sirix alma), 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 kyoid arch (Plate XVIII. fig. 2) is normal, but rather feeble. 

 The tongue is short and sagittiform, and in it the cerato-hyals {c.hy.) 

 converge and unite in front ; they remain unossified ; their length is 

 12 milHm. The basal bar {b.h.br.) is of the same length ; it is 

 moderately dilated where the posterior cornua {cornua major a, br^.) 



