386 
Mr. R. F. Tomes on Whitens Thrush, 
coincidence ends ; these species do not any further represent the 
former ones : the sternum of the Fieldfare does 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 centre 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 Twrdida , which first assists in 
forming a support for the foot of the coracoid bone, and then, 
extending in a backward direction, divides where 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 
