692 PROF. OWEN ON THE STERNUM OF NOTORNIS. [NoV. 28, 



the process so called^ but is slightly concave : its extent equals that 

 of the coiacoid margin, 5, the pair of which margins, with themami- 

 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 direc- 

 tion 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 the part of the sternum converted 

 by the deep notch,/, into a " postmarginal " process, g. The in- 

 termediate end of the sternum, x, representing, though hardly homo- 

 logous with, the " xiphoid appendix," in " Anthropotomy," is ter- 

 minally 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, 5 «') shows 

 the same shallowness as in Iribonyx, 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 

 Aptery,v^. 



Other comparisons with the smaller existing Rallines of New Zea- 

 land, 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 memoir ^, 



Tliese have led me 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 Ratline which have previously ap- 

 peared in the Society's publications^. 



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 Struthio^, Rhea^, Dromaius', Casuarius^, 

 Apteryx^, and Ditiornis^", are Aptornis and therewith Notornis to be 



' ' Anatomy of Vertebrates,' vol. ii. p. 24, fig. 15, e. 



- Trans. Zool. See. vol. ii. pi. 55. figs. 2 & 3. 



'•' hoc. cif. p. 245. 



" Trans. Zool. Soe. vol. iii. pi. 56. figs. 7-13 ; and vol. iv. pi. 4. figs. 5-8. 



5 Trans. Zool. Soc. vol. iii. (1848), plate 57. fig. 4. 



6 3. ih. fig. 5. ' Ih. ib. fig. 7. ** lb. ib. flg. 6. 

 9 Trans. Zool. Soc. vol. ii. (1838), plate 55. figs. 1-3. 



i" Trans. Zool. Soc. vol. viii. plates 7-9. 



