SONG THRUSH. 



197 



part of tlie neck are lighter ; tlie white of tlie 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 important, 

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

 page 105, that the extent of surfice 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 crite- 

 rion 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 practica- 

 ble, will therefore be introduced among the vignettes, for the 

 purpose of illustrating generic form in bone, and the general 

 accordance in figure, in conjunction with external characters and 

 habits, may be accepted in proof of systematic arrangement. 



The outlines below represent the forms of the sterna in 

 the genera Lani'us and Muscicapa, or the Shrikes and the 

 Flycatchers. The figure on the left hand is from the Great 

 Grey Shrike : the other is from the Spotted Flycatcher. 



