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Show 692 PROF. OWEN ON THE STERNUM OF NOTORNIS. [Nov. 28, the process so called1, but is slightly concave : its extent equals that of the coracoid margin, b, the pair of which margins, with themanu-brial one, divide the fore border of the sternum into three equal parts. The degree of transverse concavity is the same in each; but the coracoid ones have also a moderate excavation in the opposite direction for their articular relations with the scapular arch. The outer end of each of these joint-surfaces is slightly produced (ib. d). Articular cavities for the sternal ends of six haemal ribs mark the costal division, c, c, of the outer border, which is thence continued backward, with a very slight sigmoid curve, to the hind end of that border, one third of which bounds tbe part of the sternum converted by the deep notch,/, into a " postmarginal " process, g. The intermediate end of the sternum, x, representing, though hardly homologous with, the " xiphoid appendix," in " Anthropotomy," is terminally truncate, not extending so far back as the " postmarginal " processes: these resemble the same parts in Tribonyx in being un-expanded at the end, as is slightly the case in Ocydromus and Porphyrio. The sternal keel in Notornis (figs. 1 and 2, s *') shows the same shallowness as in Tribonyx, with a further reduction of the anterior angle (fig. 2, s'), in which Notornis resembles Ocydromus. The transverse convexity of the sternum, reduced as it is in that genus, is relatively less in Notornis : it subsides almost to flatness in Apteryx2. Other comparisons with the smaller existing Rallines of N e w Zealand, notable either for loss or much reduced powers of flight, are carried out and well illustrated in the reduced figures (plates xx. and xxi.) of Prof. Jeffery Parker's memoir3. These have led m e to believe that the accompanying figures, front and side, of the sternum of Notornis, natural size (pp. 690, 691), may not be unacceptable, as tending to complement the illustrations of the osteology of the extinct Ralline which have previously appeared in the Society's publications4. In its sternal modifications the larger form, Aptornis, though strictly ralline in the sum of its osteology, has departed further from the existing forms. Not only have the " postmarginal processes " disappeared, with great reduction of breadth of sternum, but the place of a keel is indicated by a mere low obtuse ridge. Now, on the supposition that, with further atrophy of the pectoral muscles, the keel should disappear from the sternum and leave no trace, as it has done in several genera of birds otherwise structurally distinct, as, for example, in Struthio5, Rhea6, Dromaius7, Casuarius8, Apteryx9, and Dinornis10, are Aptornis and therewith Notornis to be 1 ' Anatomy of Vertebrates,' vol. ii. p. 24, fig. 15, e. 2 Trans. Zool. Soc. vol. ii. pl. 55. figs. 2 & 3. 3 Loc. cit. p. 245. 4 Trans. Zool. Soc. vol. iii. pl. 56. figs. 7-13; and vol. iv. pl. 4. figs. 5-8. 6 Trans. Zool. Soc. vol. iii. (1848), plate 57. fig. 4. 6 Ib. ib. fig. 5. ' Ib. ib. fig. 7. s Ib. ib. fig. 6. 9 Trans. Zool. Soc. vol. ii. (1838), plate 55. figs. 1-3. 10 Trans. Zool. Soc. vol. viii. plates 7-9. |