| OCR Text |
Show 298 MR. w, r. TYCRAFT ON THE [Apr. 15, long spine, as in Falco. The sternum varies much both in its relative length and the form of its posterior border. Thus, this last may be either notched or fenestrated, or both, or it may be entire. As these are points which may vary in members of the same genus, they are of comparative little value save as specific characters. The sternum with the relatively largest carina of this group is that of Pandion. The carina generally has its anterior border sloped backwards, but in Accipiter this border turns forwards and upwards, thus greatly increasing the length of the keel. The carina varies much in its development, generally passing insensibly into a sternal plate before reaching its hinder border, but in Accipiter and Pernis, for instance, the carina is carried back almost to the extreme free border of the sternal plate. The sternum of the Accipitres resembles that of the Striges. In many cases this resemblance is rather close. The following characters will be found useful in determining between sterna belonging to these two very different groups. The posterior border of the sternum in the Striges is never entire and never fenestrated, but always notched. With the exception of the sterna belonging to the Strigidse, and the sternum of Huhua orientalis of the Buboniclae, there are two pairs of notches. The single pair of notches of H. orientalis are of great size. They lie on either side of the metasternum, and extending forwards to beyond the level of the middle of the posterior lateral process, cause the sternum of this bird to closely resemble that of Microhierax. The great difference in size, however, renders any possibility of confusion on account of this resemblance impossible. The single pair of notches of the Strigidse resemble those of some Accipitres, e. g. Elanoides, in that they are very shallow, so that the posterior lateral processes pass almost insensibly into the metasternum, being divided therefrom only by a sinuous line. But the processes are relatively much longer in the Strigidse than in the Accipitres, and the sternum is narrower. Furthermore, the sternum of the Owls of this group may be distinguished by the fact that the spina externa is obsolete. The anterior lateral processes in all the Owls are small. The articular surfaces for the sternal ribs never extend beyond the middle of the sternal plate, rarely so far as this. There is no spina interna. The coracoid presents two forms :•-(1) That which obtains in the Falconidse only, wherein there is a distinct hook-like pro-coracoid process curving downwards till it touches the furcula ; and (2) that in which this process is wanting. In the Falconidse we can distinguish the coracoid of the Falcones from that of the Polybori; inasmuch as in the former there is no trace of the foramen supracoracoideum in the dried skeleton, this being bounded internally by membrane only. In the Polybori this foramen is present. Whether the foramen in the coracoid of the remaining Accipitres is really the foramen supracoracoideum,, or a foramen pierced |
