125 
The following are the dimensions of this mutilated but instructive bone :— 
In. Lin, 
Breadth across the articulation of the last rib . <9 & ie Bectiocw Ss 
Breadth between ends of posterior angular processes 4 4 =. .4 9. 7 Si 
Length, or antero-posterior diameter at middle of posterior emarginations . 
Thickness at articular margin for ribs Pie & aE 
Length of posterior angular process from middle of emargination 
Extent of costal articular surface . 
Extent of coracoid articular surface 
* *. 
aSooTeco 6 
* 
6 
1 
t 
2 
fA ; % Wit ele 
This, the largest sternum which has hitherto been discovered in the class of Birds, 
is relatively the smallest in proportion to the body, if it belong to the Dinornis giganteus. 
That it belongs to the genus there is no room for doubt, since it was found associated 
exclusively with the abundant remains of different species of Dinornis, and especially 
with those of Din. giganteus. In its small relative size, its shortness as compared with 
its breadth, its shield-shape and the total absence of a keel, it demonstrates the want of 
a power of flight in the genus Dinornis, and its closer relationship to the Cursorial or 
Struthious order. The following are comparisons of the present sternum with the mo- 
difications of form which that bone presents in the different genera of that strictly ter- 
restrial order. 
The sternum of the Ostrich (Struthio, Pl. XXXV. fig. 4) is larger in proportion to its 
breadth ; the hind-part is narrower, instead of being, as in Dinornis, broader than the 
fore-part : the sternum of the Ostrich is more convex, and is a much thicker bone, 
especially at the middle prominent part of the body of the bone which transmits the 
weight of the trunk upon the sternal cushion or callosity, upon which the Ostrich rests 
when prone on the ground. The coracoid grooves (ib. c, c) are considerably larger in 
the Ostrich, extending from the outer angle, close to the middle of the anterior border, 
which is thin and sharp: the costal articulations (ib. r) are broader, much deeper, and 
occupy a much greater proportion of the lateral borders of the sternum. The posterior 
angles (ib. p) are prolonged backwards, but not so far as in the Dinornis, and there are 
two emarginations (éb. e, e) on each side between the angles and the middle line, to which 
a cartilaginous, and, in old Ostriches, a semi-osseous xiphoid appendage () is attached, 
In the Rhea the sternum (PI. XXXV. fig. 5) deviates more than in the Ostrich by its 
ereater length, median convexity and posterior contraction, from that of the Dinornis : it 
further differs in the absence of posterior angular prolongations and the presence ih a pos- 
terior median marginal notch (e) ; but the coracoid cavities (c, ¢), though considerably 
larger than in the Dinornis, are more confined to the anterior angles than in the Ostrich: 
The coracoid cavities have a similar position, but rather smaller relative size, in the 
sternum of the Cassowary (ib. fig. 6), which however differs as much as that of the Rhea 
from the sternum of the Dinornis in its greater length as compared with its breadth, and 
especially in its contraction to the posterior margin, where the angles are rounded off 
and the middle part slightly produced. 
R 2 
