216 MEHTJLID^. 



four inches and five-eighths : the first feather very short ; 

 the second rather longer than the fifth; the third and 

 fourth nearly equal in length, longer than the second ; the 

 third the longest in the wing. 



The female is smaller than the male ; the head and upper 

 part of the neck are lighter ; the white of the breast not 

 so pure, with less of the yellow colour ; the breast spots 

 larger, and not so well defined. 



The back and scapulary feathers in young birds have 

 each a pale yellowish spot in the centre, and the smaller 

 wing-coverts streaked with pale brown. 



Varieties in colour among Thrushes are not uncommon. 



The sternum, or breastbone, in Birds may be considered 

 the most characteristic, as it is also one of the most import- 

 ant, of the bones in their skeleton. It has already been 

 observed, that the extent of surface furnished by the sides 

 and keel of this bone indicate the size and strength of 

 the muscles which move the wings, and therefore afford 

 a criterion by which to judge of the comparative power 

 of flight possessed by the species. The breastbone also 

 supports and protects all the most important soft parts of 

 the body. A figure of the sternum of one species in each 

 genus, as far as practicable, will therefore be introduced 

 among the vignettes, for the purpose of illustrating generic 

 form in bone, and the general accordance in figure, in con- 

 junction with external characters and habits, may be ac- 

 cepted in proof of systematic arrangement. 



