| OCR Text |
Show 708 MISS B. LINDSAY ON THE AVIAN STERNUM. [J sternum, plain in outline, is produced ; in birds that hop and run more than they fly, long, thin processes are seen for the attachment of certain abdominal muscles, but the rest of the sternum is not filled up, so that we have a very short sternum with complicated processes. In proof of this, contrast the sternum of the Gull, in which the two pairs of lateral processes, which afford attachment to the end of the Fig. III. a /) c 4 1, 2, 3, posterior outline of the sternum in Trocellaria yiyantca, Tiomedea exu-lans, and Crax alberti ; the shaded part is very thin, and the presence of a similar thin margin on the flattened ribs of the last-named conclusively shows that this margin results from a process of addition. 4, sternum of Didunculus, 5, of Hesperornis (cast), showing posterior lateral process ; the last shows, like Casuarius, Bhea, and fig. 9, Plate XLIL, an incomplete fusion, probably due to the same causes that have operated in widening the sternum during the establishment of the Avian type. (All CO., reduced.) a, b, c, sterna of 8 and 9 clays' Chicks: a, shows abnormal persistence on the right side of rudimentary 8th rib attached to the 7th; b and c, dorsal and ventral aspects of sternum, showing incomplete keel and absence of median furcular apophysis. large pectoralis major, are scarcely seen to project from the sternum, with the sternum of the Fowl or Tinamus, in which the long processes afford attachment merely to a few thin fibres of that muscle. Sterna of the Common Duck show much variation, with a tendency to fill up the sternum. The sternum of the Gull (cf. Plate XLIII. figs. 9 and 10) shows how the process of filling up takes place. In all the specimens examined except the one figured, the two processes were distinct, even in the earliest stages examined |
