| OCR Text |
Show 296 MR. W. T. Pi CRAFT ON THE [Apr. 15, normally related, yet the latter fails to reach the sternum. In some cases the last pair of sternal ribs may be represented only by vestiges fused with the last fractional pair. The uncinates vary considerably in their development. In the Polyborhue and the Falcons the uncinates are long and slender ; but in the remaining Accipitres the base of attachment to the rib has increased enormously, extending often nearly as far- down as the articulation with the sternal segment. In the Cathartse, and in some species of Aquila, the inferior angle of this base is produced into a short spine. Generally the uncinates do not extend backwards beyond the level of the rib next behind. This is exceeded in Elanoides, and in Pandion (in P. carolinensis) they extend each to the third rib. In Serpentarius the uncinates are very degenerate, losing themselves in the rib, forming thereon nothing but a broad irregular plate. The uncinate of the first thoracic rib, however, is less degenerate, projecting distinctly backwards. The preacetabular ilium overlaps from two to three pairs of ribs. v. T H E S T E R N U M A N D PECTORAL GIRDLE. Perhaps the most striking features of the sternum of Falconiformes are the great size of the corpus sterni and the relatively slight development of the carina. Amongst the different members of the group, however, much variation occurs, in the relative proportions in the length and breadth of the sternal plate, the development of the keel, the position of the coracoid grooves and articular surfaces for the sternal ribs, and the development of notches or fenestrae on the metasternum. In Serpentarius (text-fig. 33, p. 297) the sternum is distinctly Ciconiine in character, not only on account of the great size and shape of the carina, but also in the fact that the latter affords a broad articular surface for the furcula. There is one peculiarity about the keel of Serpentarius, however, and this lies in the fact that the carina, swollen by pneumatic tissue, passes gradually into the corpus sterni. This last, it should be mentioned, is pointed posteriorly, instead of notched as in the Storks. The sternum of the Cathartse is peculiar in that the greatest curvature of the free margin of the carina is near its middle, and in that the keel extends backwards to the extreme posterior end of the sternal plate. The corpus sterni is notched posteriorly, and in Cathartes the posterior lateral processes are fenestrated. The coracoid grooves are shallow and broad, curving abruptly upwards and inwards to the middle line, not overlapping. The spina externa and interna are both wanting. The linea aspera for the origin of the subclavius extends backwards to within a short distance of the posterior end of the sternal plate: thus extending further back than in any other Falconiformes. In the Falcons only is there a distinct spina interna ; in Herpe-totheres it is very broad and deeply hollowed ; the spina externa |
