1 64 ELEMBlfTS OF OENITHOLOGY, 



Claws are alwayss more or less concave bsneafch transversely 

 as well as in the direction of their length. They may be grooved 

 — suleate ; or ridged — carinate. The inner edge of the middle 

 claw may be dilated and its margin very strongly toothed. It 

 is then said to hepectinated, and such a " comb " is well seen in 

 the Goatsucker's foot. 



Spurs or calcars exist, as everyone knows, on the back of the 

 tarsus of the Cock ; and two spurs may exist on each foot, as in 

 the double-spurred Peacock {Polyplectron bicalcaratum), or even 

 more, as in Ithaginis. They are sexual characters — only found 

 in the males. 



Thus very different types of feet are to be found amongst 

 birds, according to their habits. The " Scratehers," as, e. g., 

 the Fowl, have the foot rather thick, the claws short, and the 

 hallux elevated — the "rasorial" type. The "Climbers," as, 

 e. jr., the "Woodpecker, have the foot zygodactyle and the claws 

 well developed and curved — the " scansorial " type. In the 

 " raptorial " type, «. g. the Hawk, we find a powerful foot, with 

 long, curved, sharp, and jiowerf ul claws. In the " grallatorial " 

 and the " cursorial " types we find a foot with a minimum 

 power of grasping, and a reduced or elevated hallux and an elon- 

 gated tarsus. In the most opposite type — that of the " perchers " 

 — the "insessorial " type — there is a long, well-developed hallux, 

 and the other digits are cleft to their bases ; while, on the con- 

 trary, in the " natatorial " type — the Swimmers — we find the 

 feet webbed more or less completely or else lobate. 



Ptebtlosis. 



As before said * the feathers of birds do not usually grow 

 all over the body, but along certain definite tracts, each of which 

 is termed a pteryla. These are separated by spaces wherein 

 feathers are not implanted, or apteria. 



A. few birds, however, have feathers implanted all over the 

 body. Amongst these are the Toucan, the Penguin, and the 

 Ostrich. The definite " pterylse " which have been defined are 

 the foUovring : — 



The dorsal or spinal pteryla, which extends from the nape 

 of the neck to the tail. Its shape varies greatly in different 



* See ante, p 141, 



