OCR Text |
Show 1902.J OSTEOLOGY OF THE FALCONIFORMES. 283 The Squamosal Prominence.-In the more primitive forms, such as Serpentarius, Polyboroides, and Pernis, the squamosal prominence is very feebly developed. As usual, its inferior surface affords a glenoid cavity for the articulation of the squamosal head of the quadrate. Mesiad of this glenoid cavity is the aperture of the superior tympanic recess. The zygomatic process is very small; in Serpentarius it is wanting. The squamosal prominence is seen at its best in the Falconidse (including Polyborus), where it projects conspicuously from the skull-wall. The zygomatic process is excessively developed in Polyborus, where it hangs downwards, eaves-fashion, over the quadrate. In addition to this, is a second and equally large process depending from the antero-lateral angle of the lateral occipital wing, at its junction with the zygomatic process. The postero-inferior angle of the squamosal, in Polyboroides and in the Falcons, develops a large, downwardly-directed and pointed spike-the jjrocessus articularis squamosi. Between this and the zygomatic process just described, the squamosal head of the quadrate is tightly grasped. In Serpentarius, the Eagles, Pernis, Pandion, Buteo, Circus, Gypaetos, and many of the true Vultures, for instance, this articular process is but feebly developed. In Cathartse it is wanting. The temporal fossce are for the most part but shallow, linguiform depressions in the parietal region of the skull, and which never extend backwards to meet the mid-dorsal line. In Serpentarius they are exceedingly shallow and scarcely rise above the level of the base of the postorbital process. They are best developed in the Falcons and Polyborus, where they extend inward to within a a short distance of the cerebellar prominence. The trigeminal foramen is completely isolated, lying far removed from the mouth of the superior tympanic recess, and considerably in front of a line drawn transversely through the skull across the squamosal head of the quadrate. The orbits are large. In Serpentarius they are protected from above by wide overhanging ledges formed by the frontal bones, behind, and by large, horizontal, backwardly-directed, flattened plates developed by the lachrymal, in front. These, one on either side, fit closely to the frontal. In the higher Accipitres the width of the interorbital region of the frontals is much less, the free edo-e forming a deep hollow. In this case the horizontal process of "the lachrymal is left as an isolated spur projecting on either side of the roof of the skull and overhanging the orbits. In the majority of such cases, the length of the spur is increased by the addition of a separate scale-shaped ossicle-the superciliary ossicle. This is attached to the lachrymal by connective tissue. In the Falcons and Vultures it fuses with the lachrymal. In the Cathartse the supra-orbital limb of the lachrymal is suppressed, the lachrymal itself fusing completely with the frontal. The orbito-sphenoid is completely ossified in all the Falconi- |