THE BIRDS. 



201 



There are three general types of feet in birds, viz. , the run- 

 ning, walking, or wading; the swimming, and the perching; 



FIG. 206. Tarso-meta- 

 tarsus of the Penguin. 



FIG. 208. Lobate foot of the Coot. (One- 

 half natural size. 



and under these heads are many varieties (Figs. 207, 208). 



In the toes of the perching birds 

 the muscles and their tendons are 

 so arranged that they automatically 

 maintain while the bird is asleep a 

 grasping position on the perch by 

 means of the bird's own weight. 



The most striking external feature 

 of birds is the presence of feathers; 

 no reptile, on the one hand, or mam- 

 mal, on the other, is clothed with 

 feathers. The ordinary feathers are 

 called peniup, or contour feathers, as 

 they determine by their arrangement 

 the outline of the body. They are, 

 like hairs, developed in sacs in the 

 skin ; the quill is hollow, partly im- 

 bedded in the skin ; this merges into 

 the shaft, leaving the outgrowths on 

 each side called barbs, which send 

 off secondary processes called bar- 

 bides. The barbules and booklets 

 (barbicels, Fig. 209) are commonly ^ 



J FIG. 209. -Feather, sh, shaft; 



serrated, and end in little hooks by \ vanes: 4, barbuie, with (&cj 



i i j.i 111 11 /-FT the barbicels. 



which the barbules interlock (Fig. 



209). Down is formed of feathers with soft, free barbs 



called plumules. 



