126 GENEBAL ORNITHOLOGY. 



happens in the larks {Alaudidm) ; they are rare among land birds, common among waders. 

 Those swimming birds with a very thin skinny podotheea. are apt to show traces of the fqiir- 

 sidedness of the metatarsal bone. The tarsus in the vast majority of land birds is seen on 

 close inspection to be somewhat ovate or drop-shaped on cross-section, — gently rounded in 

 front, more compressed laterally, and sharp-ridged behind. This results from the laminiplam,- 

 tation described above, and is equally well exhibited by most passerine birds, whether they 

 have booted or anteriorly scuteUate tarsi. The line of union of anterior scutella with postero- 

 lateral plates on the sides of the tarsus is generally in a straight vertical line, — either a mere 

 line of flush union, or a ridge, or oftener a groove (well seen in the crows), which may or 

 may not be filled in with a few small narrow plates. In the Clamatorial Passeres, represented 

 by our flycatchers, the tarsus is enveloped in a scroU-like podotheea of irregularly arranged 

 plates, the edges of the scroll meeting along the inner side of the tarsus. But the full consider- 

 ation of special states of the tarsal envelope, however important and interesting, would be part 

 of a systematic treatise on ornithology, rather than of an outline sketch like this. 



The Number of Toes (individually, digiU; collectively, podiuni) is fowr: there are 

 never more. There are two in the ostrich alone, in which both inner and hind toe are wanting. 



There are three in all the other struthious birds (Mheidm, Casu- 

 ariidee), excepting Apteryx, which has four. There are like- 

 wise three, the hind toe being suppressed, in the tinamine 

 genera Calodromas and Tinamotis {Bromteognathce) ; through- 

 out the auk family (Alcida) ; in the petrel genus Pelecan- 

 mdes; apparently in the albatrosses {IHomedewuB) ; usually in 

 the gull genus Bissa; in the flamingo genus Phgsnicoparra ; 

 throughout the bustard family (OUdidie), and among various 

 related forms, as (Edicnemus, Msacus, Cursorius; in the 

 plovers (Charad/i-iidtB), excepting Squatarola; and in the 

 Fig. .39. — Tridaotylefoot of eand- bush-quails (Tiirnieidce) , excepting Pedionomm. In higher 

 erling, Calidri, m-enarm: nat. size. ^^^^^^ ^^^^^ ^^^^ ^^^ ^ ^^^^ anomaly, only known to occur in 



three genera of woodpeckers (Piecfides, Sasia, and Tiga), and in one galbuline genus (Jaca- 

 maralcyon), by loss of the hind toe ; in two genera of kingfishers {Ceyx and Alcyone), by sup- 

 pression of the inner front toe ; and in the passerine genus Cholornis, by defect of the outer 

 front toe. North American three-toed birds are these only : the woodpeckers of the genus 

 Piecfides; all auks (Aldda), and albatrosses (Diomedemcs ; in these, however, there is a 

 rudiment of the hind toe) ; all plovers (Charadriides, excepting one, Squatarola) ; the oyster- 

 catchers (Heematopus) ; the sanderliug {Calidris, fig. 39) ; the stilt (Himantopus). Birds 

 with two toes are said to be didactyle ; with three, tridactyle ; with four, tet)-adactyle. In the 

 vast mBjjority of cases, birds have three toes in front and one behind. Occasionally, either the 

 hind toe, or the outermost front toe, is versatile, that is, susceptible of being turned either 

 way. Such is the condition of the outer front toe in most owls {Striges), and in the fish-hawk 

 (Pamdion). We have no case of true versatiUty of the hind toe among North American birds; 

 but several eases of its stationary somewhat lateral position, as in goatsuckers {CaprimulgidcB)f 

 some of the swifts (Cypselidm), the loons {Col/ymhidae) , and all the totipalmate swimmers 

 (Stegamopodes). Nor have we any example of that rarest of all conditions (seen in some 

 Cypselidce, and the African CoUidce) in which all foim toes are turned forward. The arrange- 

 ment of toes m paws, two before and two behind, is quite common, being the characteristic 

 of scansorial birds and some others, as all the parrots and woodpeckers, cuckoos, trogons, etc. 

 Such arrangement is called zygodaciyle or eygodactyhus (Gr. fuyrfv, zugon, a yoke ; SaKTvXos, 

 daktulos, a digit) ; and birds exhibiting it are said to be yoke-toed (fig. 46). In all yoke-toed 

 birds, excepting the trogons, it is the outer anterior toe which is reversed ; in trogons, the 



