1-6 GENERAL OBNITHOLOGY. 



happens in the hirks (Alaudidce) : they are rare among Linil birds, common among waders. 

 Those swimming birds with a very tliin skinny podotheca are apt to sho\i' traces of the foiir- 

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

 (dose inspection to be somewhat ovate ov drop-shaped on cross- section, — gently rounded in 

 front, more compressed laterally, and sharp-ridged behind. Tliis results from the lamimplan- 

 tation described above, and is equally wx-U exhibited by most passerine birds, whether they 

 have booted or anteriorly scuteUatc tarsi. The line of union tif anterior scuteUa with postero- 

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

 line of tiush union, or a ridge, or oftener a groove (well seen in the cr<.iws), wliich may or 

 may not be filled in with a few small narrow plates. In the C'lamatorial Pasneres, represented 

 by our flycatchers, the tarsus is enveloped in a scroU-lilie podotheca of irregularly arranged 

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

 ation of special states of the tarsal envelope, IioM'ever 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, (li(iiii : collectively, podiuw) is funr: there are 

 never mine. There arc tuv in the ostrich alone, in whicli both inner and hind toe are wanting. 



There are three in all the other struthious Idrds {Rheidcp, Cnsu- 

 (iriidtv), excepting Apterijx, which lias four. There are like- 

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

 genera Calodromas and Thmiiwtis {Dromceognatlue) ; throus;h- 

 iiut the auk family {AJcidaf) ; in the petrel genus Pelecau- 

 (iides; apparently in the albatrosses (SiomedeiiKc) ; usually in 

 tlie gull genus Rissn : in the flamingo genus PhcKnicoparra ; 

 throughout the bustard family (Otididee), and among various 

 related forms, as (Edicnemiis, Esacus, Ctirsorins : in tlie 

 plovers (Charadriido'), excepting Sqtiatarola ; and in the 

 Flo. asi. — Tridactyle foot of sand- bush-quails (Ti(rmcida'), excejrting Pedionomus. In higlier 



erliiig, i'alUlriii arcnaria; nat. size. i . i ^i .. i i i ^ " . 



birds, tliree toes are a rare anomaly, only Icnown to occur ui 

 three genera of woodpeckers (Picoidcx, iSasia, and Tiga), and in (me galbuline genus {Jiicii- 

 maralcyon), by loss of the hind toe ; in two genera of kingfishers {Ceijx and Akijone). by sup- 

 pression of the inner front toe; and in the passerine genus Choloniif!, by defect of tlie outer 

 front toe. Nortli American three-toed birds are these tmly : the woodpeckers of the genus 

 Pico'ides ; all auks (Aleidcs), and albatrosses (Diomedeince ; in these, however, there is a 

 rudiment of the hind toe) ; all plovers (Charadriidec, excepting one, Sqtiatarola) ; the oyster- 

 catchers (Hamatopus) ; the sanderling (Calidris, fig. 39) ; the stilt (Hi}iia)itopiiis). liirds 

 with two toes are said to be didacti/lc : with three, tridacti/le : with four, tetradacttjle. In the 

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

 liind toe, or the outermost front toe, is vermtde, that is, suscejrtible of being turned eitlier 

 way. Such is tlie condition of the c_>uter front toe in most owls (Striges), and in the fish-hawk 

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

 but several cases of its stationary somewhat lateral position, as in goatsuckers (Cajiriiiiiilgidfc)) 

 some of the swifts {Cyp^elida;), the loons (Coh/mhidrc), and all the totipalmate swimmers 

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

 Cijpselidir, and the African Cotiider) in which all four toes are turned forward. The arrange- 

 ment of toes in pairs, two before and two behind, is (juite coinmou, being the characteristic 

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

 Such arrangement is called sygodactijle or zygodaetglotis (Gr. fuyoV, :ugon, a yoke; baxrvKos, 

 daJctiilos, a digit) ; and birds exhibiting it are said to be gol^e-toed (fig. 45). In all yoke-toed 

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



