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Show 284 MR. W. P. PYCRAFT ON TnE [Apr. 15, The interorbital septum is pierced only in the lower members of the various groups of Falconiformes. For instance, in Serpentarius and Cathartes, in Pandion and Pernis, Polyborides, Gypohierax, and the lower Vultures and Eagles. The Ethmoidal Region.-The mesethmoid, as in Neognathse generally, is, as it were, obliquely truncated at its anterior end, so that its free edge slopes upwards and forwards. This is due probably to the shortening of the parasphenoidal rostrum. This shortening process is very conspicuous in the Accipitres. It rarely, if ever, extends forwards beyond the level of the lachrymals in any Neognathse. In the Palseognathse this rostrum extends forwards for a considerable distance in front of a line drawn transversely through the skull across the lachrymals. The mesethmoid extends backwards, as in all other birds, to fuse with the orbital plate of the frontal, and the orbito- and presphenoid, and the parasphenoidal rostrum below; thus forming the interorbital septum referred to above. From the neighbourhood of its truncated anterior border springs, on either side, a more or less extensive wing-like process-the prefrontal or antorbital plate. The prefrontal is somewhat feebly developed in Serpentarius, Polyboroides, and Pernis, for instance. In Cathartse and in the Falcons it is much larger; in the latter it extends outwards to afford a more or less extensive lateral support for the lachrymal. In the former, the lachrymal and prefrontal relations become still more intimate, since they fuse one with another. The preorbital region of the mesethmoid expands dorsad into a broad horizontal plate underlying the anterior ends of the frontals, the nasals and the nasal processes of the premaxillary. In the Vultures, Eagles, and Cathartse markedly, and in the majority of the Accipitres to a less extent, the free edges of the horizontal aliethmoidal plate turn downwards and inwards, and finally backwards, to join the prefrontal; thus forming an ossified olfactory chamber. This is most perfectly developed in the Cathartse, where the chamber is of very considerable extent, recalling that of the Tubinares. In Serpentarius, the Falconidse, and Buteonidse, this ossified olfactory chamber is extremely reduced. In the two latter forms perhaps the great development of the prefrontal may be regarded as filling the place of the ossifications of the horizontal plate. The olfactory nerve, in leaving the skull, generally travels along a groove in the dorsal border of that portion of the mesethmoid which forms the interorbital septum ; sometimes this groove is covered in by the ossification of connective tissue, e. g. Cathartse. I would revert once again to the comparison between the olfactory chamber of Cathartse and that of the Tubinares. In the former the free edge of the horizontal aliethmoidal plate turns downwards on either side mesiad of the lachrymal, so as to leave a considerable space between itself and the lachrymal, to form the Harderian fossa. Furthermore, it would seem that the |