THE FOOT 3 



united by webs in the ducks only three being thus united, 

 and the hallux free. The coots have a form of webbing 

 which is characterised by applying the term ' lobate ' to the 

 foot. Each toe in the case of a lobate foot is bordered by a 

 flat expansion of skin, but there is no connection between 

 the borders of adjacent toes. The foot is covered to a vary- 

 ing degree with a horny integument, which is arranged as 

 larger or smaller flat scales, or as granules of various shapes 

 and sizes. This scutellation sometimes extends on to the 

 tibia ; it generally occupies the tarsus as well as the foot 

 proper ; the other extreme is shown by Syrrhaptes, where 

 feathering extends down to the last digits of the foot. The 

 form of these is sometimes useful in classification, as in the 

 Passeres (q.v.) The digits are armed with claws, which are 

 straighter in wading birds, and very curved in the birds of 

 prey. Their relative lengths vary ; in the larks, for example, 

 and in the cuckoo (Ccntropiis) that of the hind toe is enor- 

 mously long. The middle toe is often serrated, as in herons, 

 owls, and goatsuckers, &c. 



The order of the toes may be almost always settled by 

 counting the number of the phalanges. This is progressive, 

 the first toe having two phalanges, the second three, the 

 third four, and the fourth five. To this general rule there 

 are a few exceptions. I have described in the owl (Plwto- 

 dilux} only four phalanges in the last (fourth toe), a state of 

 affairs, however, which is plainly due to a fusion between 

 the two first phalanges. The goatsuckers (of genus Capri- 

 uinhiiis and allied forms) have a digital formula of 2, 3, 4, 4. 

 In many Tubinares the formula is 1, 3, 4, 5. In the swifts 

 the toes are still further reduced, for we have in that group 

 the digital formula 2, 3, 3, 3. Pterocles has a digital formula 

 agreeing with that of Caprinuth/iis. ZEHNTNER ' has lately 

 shown 'that the digital formula of the swifts is due to 

 reduction ; he has found, in fact, in Cypselus niclba, in a 

 certain stage of development, four phalanges in each of 

 digits 3 and 4, in which stage, therefore, the bird is only 

 one digit short of the normal. 



1 'Beitriige zur Entwicklung von Cypseius melba,' Arch.f. Natury. 1890. 



B 2 



