BIRDS 143 



Twenty-three quills (remiges) are attached to the hinder margin 

 of each wing, eleven of them being primaries fixed to the hand, 

 while the twelve others are secondaries borne by the fore-arm. 

 The bases of these quills are covered above and below by other 

 feathers known respectively as upper and lower wing-coverts. 

 There is also a tuft of feathers, the bastard wing (ala spuria), 

 upon the thumb. 



Twelve tail-quills (rectrices) are attached in the form of a 

 fan to the stumpy tail, and the bases of these are covered by 

 upper and lower tail-coverts. 



The contour feathers, including the coverts and the bastard 

 wing, resemble quill - feathers on a small scale, but when they 

 are plucked away a number oi filoplumes are found among them, 

 each consisting of a stalk bearing a loose tuft of barbules at 

 its end. The down-feathers with which the nestling is covered 

 closely resemble these. 



Endoskeleton (fig. loi). — The same regions and parts can be 

 recognized as in a mammal, but there are very considerable 

 differences in detail, most, if not all, of which are related to the 

 mode of life. The bones are particularly light and spongy, while 

 many of them contain air instead of marrow, one of the arrange- 

 ments whereby the specific gravity of the body is reduced as 

 an adaptation to flight. 



A number of features distinguish the skull from that of a 

 mammal, one being that in the adult the bones are fused together 

 so as to obliterate the junctions between them. This feature, 

 however, is also seen in the lowest mammals, i.e. the Spiny Ant- 

 Eater and Duck-billed Platypus, and is not the only point in which 

 these creatures show a resemblance to birds. We have seen that 

 at the back of a mammal's skull (p. 28) there are two rounded 

 occipital condyles which fit into corresponding cups in the first 

 joint of the backbone, but in the pigeon only one such condyle 

 is to be seen, and as a result of this the head can be turned 

 very freely about from side to side. There is also a remarkable 

 peculiarity in the attachment of the lower jaw to the skull, as 

 this takes place by the intervention of a special bone, the quadrate, 

 there being thus a double jaw joint, permitting the mouth to 

 be opened very widely, a capacity which must have struck anyone 

 who has ever examined a nest of young pigeons, sparrows, or 

 canaries. It may also be noted in a young skull that each half 



