THE SKELETON IN BIRDS. THE EXOSKELETON. 329 



Herons and most birds of prey. It is absent or extremely 

 small in the Ostrich, Apteryx, Rhea, Pigeons, Owls, Anseres, 

 and others. 



The quill feathers include two groups, the remiges or 

 wing quills, and the rectrices or tail quills. In most birds 

 the primary remiges, or those which are attached to the bones 

 of the manus, are ten or eleven in number, and are set in 

 grooves in the bones, being firmly attached to them. In the 

 Ostrich however the primaries are little specialised in character 

 and are as many as sixteen in number. They are also less 

 definitely attached to the bones ; as their ends do not lie in 

 grooves in the bones, but project beyond them. 



The secondary quills or those attached to the ulna vary 

 much in number according to the length of the bone. The 

 large dark quills in the wings of Cassowaries are the second- 

 aries. 



The wing of Penguins is very little differentiated. It 

 is covered at the margin by overlapping scales which gradually 

 merge into scale-like feathers at the proximal end. The wing 

 of the Penguin has nothing comparable to the remiges of other 

 birds. 



In some birds, such as Herons (Ardea), there occur in 

 places plumulae of a peculiar kind, which grow persistently 

 and whose summits break off into fine powder as fast as they 

 are formed. These feathers are known as powder -down 

 feathers. They occur also in some Parrots and are then 

 scattered indiscriminately all over the body. 



Other exoskeletal structures besides feathers are commonly 

 well developed. Thus the extremities of the jaws are sheathed 

 in horny beaks whose form varies enormously according to 

 the special mode of life. 



In ducks and geese the beak with the exception of the 

 anterior end is soft, and its edges are raised into lamellae, 

 while in the Mergansers these lamellae become pointed pro- 

 cesses supported by bony outgrowths. These lamellae act as 



