206 MERULID&. 
The whole length rather less than nine inches. The 
wings from the carpal joint to the end of the longest 
primary, 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, page 112, 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 sup- 
ports 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. 
