708 



MISS B. LINDSAY ON THE AVIAN STERNUM. [Juiie 16, 



sternum, plain in outline, is produced ; in birds that hop and run 

 more than they fly, long, thin processes are seen for the attachment 

 of certain abdominal muscle?, Init the rest of the sternum is not filled 

 up, so that we have a very short sternum with complicated processes. 

 In proof of this, contrast the sternum of the Gull, in which the two 

 pairs of lateral processes, which afford attachment to the end of the 



Fig. III. 



1, 2, 3, posterior outline of the sternum in TroccUaria f/iganfca, Biomcdca exu- 

 lam, and Crux alhcrfi ; tlie shaded part is very thin, and the presence of 

 a similar thin margin ou the flattened ribs of the last-named conclusively 

 shows that this margin results li-om a process of addition. 4, sternum 

 of Didv.nnilvs, b, of Hespcrornis (cast), showing posterior Literal process ; 

 the last shows, like Casvarkis, Ehca, and fig. 9, Plate XLII., an incom- 

 plete fusion, probably due to the same causes that have operated in 

 widening the sternum during the establishment of the Avian type. (All 

 CO., reduced.) 



«, h, e, Eterna of 8 and 9 c'ays' Chicks : a, shows abnoi mal persistence on the 

 right side of rudimentary Stli rib attached to the Tth ; h and c, dorsal 

 and ventral aspects of sternum, showing incomplete keel and absence of 

 median furcular apophysis. 



large pectoralis major, are scarcely seen to project from the sternum, 

 with the sternum of the Fowl or Tinamus, in which the long 

 processes afford attachment merely to a few thin fibres of that 

 muscle. Sterna of the Common Duck show much variation, with a 

 tendency to fill up the sternum. The sternum of the Gull {cf. 

 Plate XLIII. figs. 9 and 10) shows how the process of filling up 

 takes place. In all the specimens examined except the one figured, 

 the two processes were distinct, even in the earliest stages examined ; 



