242 PEOFESSOE OWEN ON THE GENUS DINOKNIS. 



The curve of the anterior border (ib. fig. 3) is limited to the slight concavity upward 

 or dorsad (a) as it extends from one ' costal angle ' (d) to the other ; in relation to a 

 longitudinal axis the border is straight (figs. 1, 2, a), as it is in the preceding 

 species. The coracoid fossse (fig. 3, c, c) show the usual small and shallow proportions ; 

 they are relatively smaller even than in Apteryx, and thus are indicative of a still 

 greater reduction of the scapular arch. 



The costal border presents, as usual, three articular depressions. The anterior one 

 (fig. 4, 1 ) is smooth and shallow, to which the short and straight anterior sternal rib 

 (fig. 1, si) appears to have been connected by ligament. The second costal pit (fig. 4, 

 02) is better defined, is chiefiy extended transversely, and receives the correspondingly 

 extended sternal end of the second sternal rib (fig. 1, S2) by a distinct synovio-carti- 

 laginous articulation. The third costal pit (fig. 4, o3) has a similar shape, but is of 

 smaller size; it ofi'ers the same articulation to the third sternal rib (fig. 1, ss). The 

 foregoing articular surfaces are limited to the anterior fourth part of the lateral length 

 of the sternum. 



The inferior or haemal convexity of the sternum (ib. fig. 1) is slight, but is rather 

 more pronounced along the mid fourth of the surface than in I), maximus, or I), rheides. 



On the concave or neural surface (fig. 2) the pair of deeper hollows [p, n) at the base 

 of each costal process {d) are less marked than in D. rheides, and the foraminal indica- 

 tions of extensions into the substance of the bone, of either vessels or air-cells, are 

 much fewer and smaller. 



The lateral borders of the sternum continued from the costal tracts (o, o) are obtuse, 

 and in the side processes (A) narrow to an edge mesiad. The side borders of the mid 

 process {g) are similarly trenchant. 



The retention of the dinornithic type of sternum under all its minor modifications puts 

 the generic distinction of the wingless genus Apteryx, still existing in New Zealand, in 

 a strong light. Yet the sternum of that bird difi'ers in a much more marked degree 

 from the keelless breastbone of the larger known existing Ratitse of Nitzsch than do 

 these from one another'. 



Nevertheless the differences whicli the sternum of the Ostrich (Trans. Zool. Soc. 

 vol. iii. pi. Ivii. fig. 4) presents, in the manubrial prominence from the fore border and 

 the side processes from the hind border, from that bone in Rhea (loc. cit. fig. 3), and 

 the greater difiierence exemplified by the median notch in the fore border of the sternum 

 of Casuarius (loc. cit. fig. C) with the limitation of the coracoid grooves, which almost 

 meet in Strut/no, to the outer third parts of that border in Hhea and Casuarius, together 

 with the more marked modifications in the hind limbs of these flightless birds, and 

 the modifications of the syrinx^ testify to the artificiality of Nitzsch's order — a condition 



' Trans. Zool. Soc. toI. iii. pi. xliii. 



' Compare this structure in Bhea (Forbes, Proc. Zool. Soc. Juno 1881) with that of Struthio (prep. no. 1159), 

 p. 103, ' Descriptive and Illustrated Catalogue of the Physiological Series of Comparative Anatomy, contained 

 in the Museum of the Royal College of Surgeons in London,' 4to, vol. iii. part 1, 183G), and with that in 

 Apteryx australis (Trans. Zool. Soc. vol. ii. p. 279, pi. xlix. figs. 4, 5). 



