igo GENERAL ORNITHOLOGY part ii 



position varies insensibly, so that the foregoing distinctions are not 

 readily perceived, it is practically best to recognise only two of these 

 three conditions, . saying simply " hind toe elevated," when it is 

 inserted fairly above the rest, and " hind toe not elevated," when 

 its insertion is flush with that of the other toes. In round terms : 

 it is characteristic of all insessorial (Lat. insedo, I sit upon) or perch- 

 ing birds to have the hind toe DOWN ; of all other birds to have it 

 UP (when present). The exceptions to the first of these statements 

 are extremely rare. 



The Hallux has other Notable Characters. — It is free and 

 simple, in the vast majority of birds : in all insessorial birds, 

 nearly all cursorial (Lat. cursor, a courser), and most natatorial 

 (Lat. natator, a swimmer) forms. Its length, claw included, may 

 equal or surpass that of the longest anterior toe ; and generally 

 exceeds that of one or two of these. It is always longest when 

 incumbent; when thus down on a level with the rest it also 

 acquires its greatest mobility and functional efficiency. In most 

 Passeres it has a special muscle for independent movement, so that 

 it may be perfectly apposable to the other toes collectively, just as 

 our thumb may be brought against the tip of any finger. In 

 general, it shortens as it rises on the metatarsus ; and probably in 

 no bird in which it is truly elevated is it as long as the shortest 

 anterior toe. It is short, barely touching the ground, in most 

 wading birds ; shorter still in some swimmers, as the gulls, where it 

 is probably functionless ; it is incomplete in one genus of gulls 

 (Bissa), where it bears no perfect claw ; it has only one phalanx and 

 is represented only by a short immovable claw in the petrels (Pro- 

 cellariidm) ; it disappears in the birds named in the last paragraph 

 but two above, and in some others. It is never actually soldered 

 with any other toe for any noticeable distance ; but it is webbed to 

 the base of the inner toe in the loons (Colyrribus), and to the whole 

 length of that toe in all the Steganopodes (Fig. 52). It may also be 

 independently webbed ; that is, be provided with a separate flap or 

 lobe of free membrane. This lobation of the hallux is seen in all 

 our sea-ducks and mergansers (FuliguUnce and Merginm), and in all 

 the truly lobe-footed birds, as coots (Fulica), grebes (Podicipedidm), 

 and phalaropes (Phalaropodidce). The modes of union of the 

 anterior toes with one another may be finally considered under the 

 head of the 



Three leading Modifleations of the Avian Foot. — Birds' feet 

 are modelled, on the whole, upon one or another of three plans, 

 furnishing as many types of structure ; which types, though they run 

 into one another, and each is variously modified, may readily be 

 appreciated. These plans are the perching or insessorial; the 

 walking or wading, cursorial or grallatorial ; and the swimming or 



