52 MAEGINAL MEMBKANE THE CLAWS. 



or cut out at the joints, as in the coot, or plain, that is, straight-edged. 

 (Fig. 162.) True lobation, occurring, among North American birds, only 

 iu the grebes, coots, and phalaropes, must be carefully distinguished from 

 various 



§ 90. Marginal Fringes, or processes, that birds of the lower orders 

 often exhibit. Thus, if a galliuule be examined in a fresh state, it will be 

 found to have a margin of membrane running along the sides of the toes, 

 and the same is the case, if less evident, in a great many waders. Palmate 

 birds also show it, on the free borders of 2t and U; it is very conspicuous 

 in the albatrosses, and plain enough in geese, &c. In the grouse family 

 there is a remarkable development of horny substance, resembling a real . 

 fringe, being cut into a series of sharp teeth, or pectinations. 



§ 91. The Claws. With certain anomalous exceptions, as in case of a 

 rudimentary hind toe, every toe bears a claw. The general shape of the 

 claw is remarkably constant throughout birds : variations are in degree only, 

 rather than in kind. A cat's claw represents nearly the usual shape, viz : 

 compressed, arched, acute. The great talons of a bird of prey are only the 

 extreme of this typical shape. Besides this general shape, the claws are 

 usually dug out underneath, so that the transverse section, as well as length- 

 wise outline below, is concave, and the under surface is bounded on either 

 side by a sharp edge. One of these edges, and particularly the inner edge 

 of the middle claw, is somewhat dilated or expanded in a great many birds ; 

 and iu some it becomes changed into a perfect cornb, by having a regular 

 series of teeth. This pectination occurs only on the inner edge of 

 the middle claw ; it is beautifully^ shown by all the true herons (Ardeidm) ; 

 by the whippoorwills and nighthawks, by the frigate pelican, and, to 

 a less degree, by the barn owl. It is supposed to be used for cleaning 

 out lice from parts that cannot be reached by the bill ; but this is open 

 to question, seeing that outside the herons, it chieily occiu's among very 

 short-legged birds, that cannot possibly reach many parts of the plumage 

 with the toes. Besides Raptores, most perching birds are very sharp- 

 clawed ; the claws are more obtuse among the pigeons and Gallince 

 (scratchers) and still more so among most swimming birds. Obtuseness is 

 generally associated with flatness, or depression; this is seen in Wilson's 

 petrel, as distinguished from all our others, and carried to the extreme iu 

 the grebes, where the claws resemble human nails. The deviations from 

 curvature occur principally^ in the hind claw ; this is straight or nearly so, in 

 the shore lark, and some terrestrial sparrows, as the genus Plecfrophanes 

 (63). All the claws are straight, and prodigiously long, in some exotic 

 birds of the rail tribe — the jacanas (Parra) ; this enables the birds to 

 run lightly over the floating leaves of aquatic plants, by so much increase of 

 breadth of support that they do not slump in. Claws are also variously 

 carinate, sulcate, etc. Tiiey are always horny. They take name from and 

 are reckoned by the digits they belong to : thus, Id. = claw of It : 2cl. 

 = claw of 2t, etc. 



