PROFESSOR OWEN ON CNEMIORNIS. 263 
height, the forward curvature of both upper and lower spines, and, above all, the ab- 
sence of the osseous splints which connect together the summits of the neural spines 
and the diapophyses of a greater or less proportion of the dorsal series in all living and 
volant Lamellirostrals. The vigorous actions of flight need corresponding fixedness in 
the complex congeries of bones forming the centre whence the muscular forces converge 
to work the wings. 
In Lamellirostrals, as in most other birds’, the vertical convexity and transverse con- 
cavity of the anterior articular end of the centrum (Pl. XXXVI. fig. 11, ¢, c) closely 
clasps the posterior surface with reverse curvatures of the next centrum before it; and 
this double interlocking runs throughout the series of movable dorsals. The zyga- 
pophysial surfaces (ib. z, 2’) are large, and strongly connect together the neural arches 
of the dorsals. The pleurapophyses have two cup-and-ball joints with their vertebra, 
widely separate upon the bifurcate ends of the ribs) The bony hemapophyses, or 
sternal ribs, have, for the most part, bilobed articular ends for a double joint with the 
costal border of the sternum (Pl. XX XVII. fig. 3). 
Cnemiornis retains all these modifications, but has not the superadded strength gained 
by the bony beams passing from parts of one dorsal vertebra to the next; to which, in 
birds of strongest and swiftest flight, is superadded continuous anchylosis of certain 
neural spines of the segments of the thorax. Cereopsis shows the splint-like ossifications 
of the tendons of muscles inserted into the diapophyses and neural spines of the free 
dorsals; and this retardation of the ordinary Lamellirostral structure coexists with a 
development of wing, endowing the Australian Goose with the power of flight. 
§ 4. Sternum. 
The sternum of Cnemiornis (Pl. XX XVII. figs. 1, 2,3) is of an oblong-quadrate form, 
7 inches long by 4 inches broad at the middle of the bone, expanding to 4 inches 
9 lines in the present specimen across the anterior border. 
This border shows three wide and shallow emarginations, the median one between the 
advanced angles (a, a) of the inner wall of the coracoid groove (), the lateral ones 
between these and the costal processes (d, d), near which the emargination deepens. 
From the median end of the outer wall of each coracoid groove the anterior ridged 
origins (c, c) of the keel converge backward to form the low, rather broad and flat 
beginning (s) of this instructive process. Its extreme depth or projection from the plane 
of the sternum does not exceed 3 lines; the breadth of its free border is 4 lines; and 
this is flat and roughened by transverse strie for aponeurotic attachments. It loses 
breadth and depth as it retrogrades, and subsides (at s’) about 3 inches from the origins. 
Beyond the keel the body of the sternum retains somewhat of the convexity, transversely 
and lengthwise, which characterizes in a greater degree the carinate part of the sternum; 
but the terminal third of the bone becomes almost flat. It is truncate posteriorly, with 
* The exception, in Aptenodytes, is figured in ‘ Phil. Trans.’ 1851. 
2N2 
