386 Mr. R. F. Tomes on White's Thrush. 



coincidence ends ; these species do not any further represent the 

 former ones : the sternum of the Fieldfare docs indeed represent 

 pretty accurately that of the Redwing ; but that of the Blackbird 

 will not satisfactorily take the place of the Song-Thrush. The 

 sternum of the Blackbird has its hinder margin much more 

 deeply incised on either side than that of the Fieldfare or Song- 

 thrush, or Redwing, — the notches entering into the body of the 

 bone for half its length, whereas in the latter species they do not 

 divide the bone for more than one-third of its length. Again, 

 instead of the transverse and nearly straight outline which this 

 margin of the bone assumes in the species just referred to, we 

 have in the Blackbird a distinctly rounded outline — the two 

 lateral processes which are separated by the notch being a 

 quarter of an inch shorter than the centi-e where the keel merges 

 into that margin. 



On comparing the sternum of Oreocincla aurea with those of 

 the foregoing species, I meet with characters which are common 

 to several of them. The keel is deep, as in the migratory species ; 

 and its depth, as in them, is proportional to the length of wing. 

 In accordance with this indication of its powers of flight, are the 

 strength of all the bones therewith connected. Thus the ribs 

 are rather broad, and have their hind processes considerably 

 developed, well united to the rib from which they spring, and 

 lying firmly upon the one over which they pass. The scapular 

 and clavicular bones also are strong, and firmly set, and well 

 marked with seams and ridges for the attachment of muscles ; 

 and the sternum itself has similar impressions. The costal 

 process is divided from the body of the bone by a more promi- 

 nent ridge than is usual in the Turdida, which first assists in 

 forming a support for the foot of the coracoid bone, and then, 

 extending in a backward direction, divides w^here it meets the 

 the notch in the hinder margin of the sternum, and, proceeding 

 backward on each side of that notch, assists at the same time in 

 giving strength to that part of the bone, and supplying a suit- 

 able surface for the attachment of the muscles used in flight. 



Notwithstanding the strength of these parts of the skeleton, 

 the hinder part of the sternum itself exhibits a low degree of 

 development. As in the Blackbird, that margin is rounded, and 



