164 ELEMENTS OF ORNITHOLOGY. 
Claws are always more or less concave beneath transversely 
as wellas 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 be pectinated, 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 biealcaratum), or even 
more, as in /thaginis, 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 ‘‘ Scratchers,” as, ¢.4., 
the Fowl, have the foot rather thick, the claws short, and the 
hallux elevated—the ‘“rasorial” type. The ‘“ Climbers,” as, 
e.g., the Woodpecker, have the foot zygodactyle and the claws 
well developed and curved—the “scansorial” type. In the 
“‘raptorial ” type, e.g. the Hawk, we find a powerful foot, with 
long, curved, sharp, and powerful claws. In the “ grallatorial ” 
and the ‘‘cursorial” types we find a foot with a minimum 
power of grasping, and a reduced or elevated ballux 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. 

PrERYLOSIS. 
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 “ pteryle” which have been defined are 
the following :— 
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, 
