PKOFESSOE OWEN ON CNEMIOENIS. 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 (PI. XXXVI. fig. 11, c, 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, z') 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 heemapophyses, or 

 sternal ribs, have, for the most part, bilobed articular ends for a double joint with the 

 costal border of the sternum (PI. XXXVII. fig. 3). 



Cnemiornh 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, iu 

 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 XXXVII. 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 {b), the lateral ones 

 between these and the costal processes (<?, 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 striae for aponeurotic attachments. It loses 

 breadth and depth as it retrogrades, and subsides (at 5') 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 degi-ee 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 



