OCR Text |
Show 172 MR. *W. K. PARKER ON STEATORNIS CARIPENSIS. [Apr. 2, basitemporal plate below ; this conical cavity is the " anterior tympanic 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 convexities, concavities, sinuosities, and directions ; the result of all this careful adaptive specialization would seem to be a perfect combination 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 (Strix 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 (c.hy.) converge and unite in front; they remain unossified ; their length is 12 millim. The basal bar (b.h.br.) is of the same length; it is moderately dilated where the posterior cornua (cornua majora, br1.) |