240 VERTEBRATA. 



the changeable metallic or iridescent gloss of this part 

 of the feather, are not the least worthy of admiration. 



The hinder extremities are by no means so much 

 developed as the wings : their general structure is 

 much the same as in the Mammalia. Being used for 

 various purposes, such as seizing prey, holding food 

 to the mouth, climbing, perching, swimming, walk- 

 ing, &c., they of course vary in the form and rela- 

 tive proportions of their parts. The thigh is usually 

 concealed within the body, what is commonly called 

 the thigh, the " drum-stick," being the leg, whilst 

 this last name is as often misapplied to the long 

 shank-like foot which rises perpendicularly from the 

 toes. The general number of toes is four ; three 

 are usually directed forwards and one backwards ; 

 some, as the Swallows, have all four pointed for- 

 wards, and others, as the Parrots and Wood-peckers, 

 have two in front and two behind. Some running 

 birds, the Bustards and the Cassowaries, have but 

 three, and the Ostrich has but two, placed forwards. 



The jaws are much altered, being lengthened 

 into two horny projecting mandibles, forming a bill 

 or beak. While this organ retains its general cha- 

 racter in all birds, it is susceptible of great variation 

 in form and size. It is now a pair of sharp and 

 formidable pincers for tearing flesh ; then a wedge- 

 shaped chisel to bore living wood ; or a slender probe 

 to insert into minute crevices ; now it becomes a 

 long and pointed spear for transfixing fishes; now 

 a pair of oval plates for dabbling in the slushy ooze ; 

 and again it is transformed into a hollow scoop for 



