THE BXTEENAL STEUCTTTEE OE BIEDS. l6l 



Length of Digits. — Of the three external digits the median 

 one is almost always the longest ; the toes on either side of this 

 are generally of equal length, but if unequal, then,, save in rare 

 instances, the outer of the two is the longer. 



The connection between the digits may be confined to the imme- 

 diate proximity of their origin, when they are separate and dis- 

 tinct, as in the Thrush. The third and fourth toes may cohere 

 for almost their whole length, being invested by skin as if they 

 were but one toe. This condition is termed syndaetyle or aniso- 

 dactyle or syngenesious. Examples of this structure are to be 

 found in Kingfishers and Hornbills. The two outer digits 

 may be exceptionally connected in some Powls and Pigeons *. 

 The digits are often much connected together by folds of 

 skin, or are palmate. Such Birds are said to be web-footed, as 

 in the Duck. The webs ordinarily connect together only 

 the 2nd, 3rd, and 4th toes, but they may, in addition, con- 

 nect the first toe with the second — as in the Pelican and 

 Cormorant. Such a foot is called totipalmate. If the webs 

 are short, only reaching about halfway down tlie toes or less, 

 the foot is semipalmate. The webs may have their margins 

 sharply concave or cut in ; such are said to be incised. The 

 incision may extend to the roots of the toes, so that each digit 

 is fringed with membrane, which forms festoons on either side 

 of it. A foot of this kind is said to be lohate, and we find such 

 in the Coot and Grebe. 



The skin of the pelvic limb is always more or less invested 

 with feathers, but also almost always partly bare. The skin of 

 the bare portion is peculiarly conditioned and needs separate 

 description ; but the plumage had better first be noticed. 



The feathers of the pelvic limb are very different from those 

 of the pectoral one. Only by very rare exception, and as a sort 

 of monstrosity, are long pennaeeous feathers developed, com- 

 parable with the remiges of the wing. The thigh is always 

 feathered as part of the body-plumage. The feathers of the 

 crus are almost always inconspicuous, but they may be con- 

 spicuous from their length, as in the Hawks and some Cuckoos. 



The crus is always feathered at its upper part, and may be 

 feathered its whole length, as in the Diver. 



The tarsus is generally naked, but it may be closely invested 



* In some of those which have ahnormally developed feathers, technically 

 called " boots." See below, p. 168. 



