OCR Text |
Show 1889.] MR. W. K. PARKER ON STEATORNIS CARIPENSIS. 169 weak in Steatornis; in this respect also it resembles the Owls. But it is evident that they can exert a considerable amount of force in tearing to pieces the fruits on which they feed; about equal, perhaps, to that of which an Owl is capable, whose food, however, is not ripe fruit, but small living vertebrates. Before finishing m y description of the oral apparatus, there are several things to be mentioned in the upper and hinder parts of the skull proper; besides the " remnants" of the larval palatines, or ossa uncinata. These latter structures (Plate XVII. figs. 1-3, o.u.) are attached to-grow directly out of-the hind wall of the nasal capsule (pars plana, or ectoethmoid, p.p.). The whole of this wall is an oblique tract of bone 9 millim. deep and 5 millim. wide ; it is notched deeply in its fore edge, at the middle ; the part above the notch is the ali-ethmoid " (al.e.), the back part of the region of the upper turbinals; and the lower part, or pars plana, is the back of the middle turbinal region. There are no special turbinal coils to increase the surface for the distribution of the 1 st, or olfactory nerve ; the aliethmoid merely forms a semicylindrical fold, which runs inwards and forwards from the notch between the upper and lower regions. The aliethmoid is confluent above with the frontal roof, and behind it there is a trilobate fenestra, 6 millim. long and 3 millim. deep. This latter space is the membranous representative of the outer wall of the cribriform plate of a Mammal; the olfactory crus (I.) runs along through it to the simple nasal labyrinth. In all these things this bird is normally ornithic. The olfacto^ crura are separated by the thick top of the mesethmoidal partition wall (p.e.), the fore edge of which forms the hinder boundary of the great notch, which gives rise t o - makes possible-the fronto-nasal hinge. The aliethmoid, at its ankylosis with the frontal roof, is grooved by the ophthalmic, or orbitonasal nerve, which runs, outside the olfactory crus, into the nasal labyrinth, to supply its antero-inferior region, to which the nerve of smell does not come. On the right side one, on the left two, small perforations are seen at the root of the pars plana. Now this ectoethmoid (pars plana) is continuous with the anterior crus of the cartilaginous palato-quadrate arch in the Tadpole, and also in the adult Frog: in the Salmon and other Teleostei, and also in the Urodeles, this crus articulates with the ectoethmoid. The fore part of that arch is naturally divisible into three regions, namely-the ethmo-palatine, pre-palatine, and post-palatine. Here in Steatornis, and also in Todus, the part called the " os uncinatum " -so well known in Musophagidae-is triradiate; thus it has all the three regions seen in its homologue in the Ichthyopsida. Of course it is small, and degenerates into membrane at the end of its rays ; but it is an extremely archaic,-a truly primitive structure, and is built up amongst the newer, functional parts of the palate. In passing, I may state my experience of the presence of this almost functionless remnant. It is well developed in Steatornis, Todus, the Musophagidae generally, in Scythrops, where it is very large and perfect, and in Piaya cayana, where it is a simple vertical needle of bone ; is |