FOSSIL VERTEBRATES. 



429 



lost its power of flight only when the bird attained its full size 

 and weight. In Tachyeres the young are said to be able to fly *. 

 In the large extinct Cnemiornis calcitrans it is not only this 

 bone which had Ijeen enormously reduced but likewise the other 

 bones of tlie wing, while the keel of the sternum had almost 

 completely disappeared ; whereas in Tachyeres, although there is 

 already some reduction in the size of the ulna and radius, the 

 sternum appears to be normal. 



Text-fifi^ure 2. 



A. Proximal portion of left humerus of Cygnus equittim. 



B. Right coracoid of C. equitum. 



Both natural size. 



Compared with that of C. olor, the metacarpus from Malta is 

 a-elatively a very much shorter and stouter bone ; also the third 

 metacarpal is separated from the second for a comparatively 

 much shorter distance, causing the articular ends to be more 

 massive. Tlie first metacarpal is in keeping with the rest of 

 the bone, being large and stout. The proximal articular surface 

 is mvich flatter than in either C. olor or C. inusicus owing to the 

 pre-axial border being less raised. The comparative proportions 

 ■of this bone perhaps appi-oach, on the whole, more nearly to 

 those of C. musicus, which, judging from the skeletons which 



* Owen, "On Cnemiornis," Trans. Zool. Soc. vol. ix. 1875, p. 266. 



