EXTEBNAL PARTS OF BIRDS. ^ THE FEET. 
125 
the envelope in various ways by cross lines. Plates are of various shapes and sizes, and 
grade usually into true scutella, from which however they are generally distinguished by being 
smaller, or of irregular contour, or not in definite rows, or lacking the appearance of imbrica- 
tion ; but there is no positive distinction. They are oftenest hexagonal (six-sided), a form best 
adapted to close packing, as shown very perfectly in the cells of the honey-bee's comb ; but 
they may have fewer sides, or be polygonal (many-sided), or even circular; when crowded in 
one direction and loosened in another the shape tends to be oval or even linear. A leg so fur- 
nished is said to be reticulate : the reticulation may be entire, or be associated with scutellation, 
as often happens (fig. 38, h). A particular case of reticulation is called granulation (Lat. 
granum, a grain) : when the plates become elevated into little tubercles, roughened or not. 
Such a leg is said to be granular, granulated, or rugose : it is well shown by parrots, and the 
fish-hawk (Pandion). When the harder sorts of scales or plates are roughened without 
obvious elevation, the leg is said to be scabrous or searious (Lat. scahrum, a scab). But 
scabrous is also said of the under surfaces of the toes, when these develop special pads, or 
wart-like bulbs (called tylari) : as is well shown in the sharp-shinned and many other hawks. 
The softer sorts of legs, and especially the webs of swimming birds, are often marked crosswise 
or cancellated with a lattice work of lines, these however not being strong enough to produce 
plates ; it is more like the lines seen on our palms and finger-tips. The plates of a part of the 
leg occasionally develop into actual serrations; as witnessed along the hinder edge of a 
grebe's tarsus. When an unfeathered tarsus shows no divisions of the podotheca in front 
(along the acrotarsium), or only two or three scales close by the toes, it is said to be booted or 
greaved ; and such a podotheca is holothecal (Gr. o\os, holos, whole, entire, and STjKrj; fig. 36). 
The generic opposite is scliizothecal (Gr. o-x^C^j I cleave), whether by scutellation or reticula- 
tion or in any other way the integument may be cut up. A booted or holothecal tarsus chiefiy 
occurs in the higher Oscines, and is supposed by many, particularly German ornithologists, to 
Indicate the highest type of bird structure. It is, however, found in a few water birds, as 
Wilson's stormy petrel and other species of Oceanites. It is not a common modification. 
Exceptions aside, it only occurs in connection with an equally particular condition of the 
sides and back of the tarsus, or planta. In almost all Oscine Passeres {AlaudidcE are an 
exception), which constitute the great bulk of the large order Passeres, the planta is covered 
with one pair of plates or lamince, one on each side, meeting behind in a sharp ridge ; a condi- 
tion called laminiplantar, in distinction from the opposite, scutelliplantar, state of the parts. 
A holothecal podotheca only occurs in connection with the laminiplantar condition, the combi- 
nation resulting in the perfect ''boot." Among North American birds, the genus Oceanites 
aside, it is exhibited by the following genera, and by these only : Turdus, Cinclus, Saxicola, 
Sialia, Regulus, Cyanecula, Phylloscopus, Chamcea, Myiadestes ; and even birds of these 
genera, when young, show scutella which disappear with age by progressive fusion of the 
acrotarsial podotheca. (Compare figs. 36, 37.) 
The Cms, when bare of feathers below, may, like the tarsus, be scutellate or reticulate 
before or behind, or both ; such divisions of the crural integument being commonly seen in 
long-legged wading birds. Or, again, this integument may be loose, softish, and movable, not 
obviously divided, and passing directly into ordinary skin. 
The Tarsus, in general, may be called subcylindrical : it is often quite circular in cross- 
section ; generally thicker from before backward, and only rarely wider from one side to the 
other than in the opposite direction ; but such a shape as this last is exhibited by the penguins. 
When the transverse thinness is noticeable, the tarsus is said to be compressed; and such 
compression is very great in a loon, in which the tarsus is almost like a knife blade. Quite 
cylindrical tarsi occur chiefly when there are similar scales or plates before and behind, as 
