OCR Text |
Show 1903.] OSTEOLOGY OF THE CUCULIFORMES. 277 appears to have been thrust forward by a considerable increase in the length of the posterior sternal ribs. As a consequence, the shaft of the coracoid and the long axis of the sternum form nearly a right angle with the vertebral column, and the shaft of the scapula lies parallel with the vertebral axis, instead of forming an oblique angle therewith. This forward movement of the sternum, furthermore, has brought the acrocoracoid upwards to the level of the neural crests of the vertebrae, whilst the distance between the acetabulum and the free edge of the metasternum has been enormously increased. In fact, the thorax of this bird approaches very closely, in the relative position of the sternum, that of the Text-fig. 43.- Left side view of sternum and shoulder-girdle of Cuculus canorus, to show the great size of the carina sterni and the form of the posterior border of the sternum. Text-fig. 4 i.- Left side view of sternum and shoulder-girdle of Coua reynaudi, to show the degenerate carina sterni, which is actually more reduced than the figure indicates. Note also the long hypocleideum and the doubly notched corpus sterni. Shortening of the sternum is most marked in Piaya, Zanclo-stomus, and Taccocoua. The sternum of the Musophagi is relatively longer and more Coraciiform than that of the Cuculi, but is at the same time thoroughly Cuculine in character. In both Turacus and Schizorhis, the only genera represented in the National Collection, the hinder border of the sternum is doubly notched, and the notches are of considerable extent, the outermost being the deepest. The posterior lateral process is slender, and directed straight backwards. The intermediate process lies midway between the posterior lateral process and the metasternum. The outermost notch is about twice the depth of the inner. The corpus sterni of Turacus is relatively much shorter antero- Text-fig. 43. Text-fig. 44. |