INTRODUCTION. XV 



which vary in number and size. When they are very 

 small and numerous the covering of the foot is said to be 

 " reticulated " or netted. The scales down the front of 

 the shank may be fused into a single plate, as in the 

 Thrush. In some birds, as in Owls and Grouse, the 

 shanks, and often the toes, may be covered with small 

 soft feathers, but no wild bird produces the large stiff 

 quills which grow on the sides of the feet of some tame 

 fowls and Pigeons. As a general rule all the toes are 

 provided with claws, usually curved and pointed, and 

 there is never more than one toe without a claw. 



The tail quills vary very much in length and propor- 

 tions. When the outer ones are longest, as in Swallows, 

 the tail is said to be forked, and this formation usually 

 occurs in birds of powerful and graceful flight. When 

 the centre ones are longest, and those outside of them 

 diminish progressively in length, as in the Pheasant, 

 the tail is said to be wedge-shaped or graduated. Birds 

 with this form of tail are very seldom very powerful 

 fliers, but taking the class all round, it is not easy to 

 establish the relation of length and form of tail and 

 powers of flight. In some birds the tail feathers are not 

 quills at all, but soft, ordinary short feathers, as in 

 Quails and Tinamous, or, in Grebes, a mere wisp of 

 hairy-looking down. 



The number of the tail feathers is normally twelve, 

 or some number near it, as ten or fourteen. When 

 more than the latter number exists, it is only in the 

 case of birds where the tail is of no great importance in 

 flight, as in the Swan and many of the Pheasants. 



On the root of the tail is situated the oil-gland, almost 

 the only skin-gland which birds possess, and with the 

 creamy secretion of which they dress their plumage. 

 It is not infrequently, however, ill-developed or absent ; 

 the surface of the nipple-like top of the gland is also 

 sometimes naked and sometimes furnished Hvith a greasy 

 tuft of feathers. 



