242 PROFESSOR OWEN ON THE GENUS DINORNIS. 
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 toa 
longitudinal axis the border is straight (figs. 1, 2, a), as it is in the preceding 
species. The coracoid fosse (fig. 3, ¢, ¢) 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, 01) is smooth and shallow, to which the short and straight anterior sternal rib 
(fig. 1, s1) appears to have been connected by ligament. The second costal pit (fig. 4, 
02) is better defined, is chiefly 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, 03) has a similar shape, but is of 
smaller size; it offers the same articulation to the third sternal rib (fig. 1,s3). The 
foregoing articular surfaces are limited to the anterior fourth part of the lateral length 
of the sternum. 
The inferior or hemal convexity of the sternum (ib. fig. 1) is slight, but is rather 
more pronounced along the mid fourth of the surface than in D. maximus, or D. rheides. 
On the concave or neural surface (fig. 2) the pair of deeper hollows (p, 7) 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 (0, 0) are obtuse, 
and in the side processes (i) narrow to an edge mesiad. ‘The side borders of the mid 
process (7) are similarly trenchant. 
The retention of the dinornithic type of sternum under all its minor modifications puts 
the generic distinction of the wingless genus Apteryz, still existing in New Zealand, in 
a strong light. Yet the sternum of that bird differs in a much more marked degree 
from the keelless breastbone of the larger known existing Ratite of Nitzsch than do 
these from one another’. 
Nevertheless the differences which the sternum of the Ostrich (Trans. Zool. Soc. 
vol. iii. pl. lvii. 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 difference exemplified by the median notch in the fore border of the sternum 
of Casuarius (loc. cit. fig. 6) with the limitation of the coracoid grooves, which almost 
meet in Struthio, to the outer third parts of that border in Rhea 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. Soe. vol. iii. pl. xliii. 
? Compare this structure in Rhea (Forbes, Proc. Zool. Soc. June 1881) with that of Struthio (prep. no. 1159), 
p- 103, ‘ Descriptive and lustrated 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, 1836), and with that in 
Apteryx australis (Trans. Zool. Soe. vol. ii. p. 279, pl. xlix. figs. 4, 5). 
