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Show 1 9 O 2 0 OSTEOLOGY OF THE FALCONIFORMES. 285 aliethmoidal extensions of this plate extend backwards so as to form a complete olfactory chamber leading backwards directly, tunnel-wise, into the brain-cavity, through the apertures for the olfactory nerve. In the Tubinares we have a very similar olfactory chamber, but of far greater size. This is due to the fact that the prefrontal, which is enormous, arises so far back that the interorbital septum is reduced to a small ring of bone surrounding the interorbital fenestra. Furthermore, the backward position of the prefrontal has involved it in the formation of the lower lateral segment of the aperture for the olfactory nerve, which may also be legitimately described as enormous. The upper lateral segment of this circular aperture is formed by the downturned edge of the horizontal aliethmoidal plate. Normally, in Neognathse, the olfactory nerve leaves by a small foramen pierced through the free edge of the orbital plate of the frontal and the perpendicular plate of the mesethmoid, runs in a groove along the dorsal border of the plate, and thence gains the olfactory chamber. In the instance we have just examined, the olfactory aperture opens directly into the chamber. It is possible that the conditions which obtain in the Tubinares may represent a primitive stage, the olfactory chamber having been pushed forwards by the great development of the orbits, demanded by the increasing size of the eye. In Apteryx, where the eyes are very small, the olfactory cavity is in close juxtaposition with the brain-case. The fact that the chamber is of still greater relative size, and very complicated internally, only indicates a further specialization of the primitive condition. In the Palaao-gnathse we may trace several stages in the forward shifting of the olfactory chamber correlated with increased size of the eyes and orbits; as a study of the skulls of Dinornis, Struthio, Dromceus, Rhea, and Tinamus will show. The development of the olfactory cavity is a point which will evidently repay further investigation. The nasal septum is divided by a considerable gap, or cleft, from the mesethmoid. This cleft, the cranio-facial fissure, is widest ventrally ; the mesethmoid and nasal septum being in contact immediately below the nasal processes of the premaxilla. In the Cathartse alone among the Falconiformes, the external nares are pervious, only the proximal portion of the nasal septum being present. This, in Pseudogryphus californianus, extends forwards for a short distance to encroach upon the external narial aperture, and is pierced by a round fenestra. This posterior portion of the nasal septum, in Cathartse, expands to form a broad base which, extending outwards on either side, joins the widely separated maxillo-palatine processes, and so converts a schizo- into an indirectly desmognathous palate. In many of the true Vultures, e. g. Gyps, by the ossification of the alinasal ectoethmoidal wall, the nostril, in the dried skull, is of the same shape as in life. The olfactory region of the nasal labyrinth, in Gyps, is provided |