114 ON THE CLASSIFICATION OF BIRDS. 
to the relative length of the tarsus, it is the form and 
disposition of these scales which supply us with the best 
discriminative characters taken from this part of the 
foot. As no writer has yet given this subject tlie attention 
it deserves, we shall here endeavour to elucidate it. The 
generality of naked footed birds have the tarsus protected 
by three series of scales, each of which is frequently of 
a peculiar form. The first series is in front ; the second 
occupy the two sides, and the third is at the back of the 
leg. The front scales are called the anterior, and are 
either composed of one or of several pieces. When the an- 
terior scale is simple, or in one piece, it extends from the 
front of the knee to the articulation of the hinder toe; and 
its external surface, consequently, is very smooth. The 
next deviation from this is seen in the sparrow-hawks, 
where the tarsus is still very smooth, but there are slight 
transverse divisions, which, upon a close inspection, seem 
to be rather beneath than upon the surface; for they 
are imperceptible to the touch. The next modification 
is seen in these transverse divisions being, in some de- 
gree, imbricate; that is, the edge of one lying over the 
edge of the next: this is the general appearance of the 
anterior scales in most birds, the number being variable 
in the groups, though not in the individuals ; in most 
of the small [lerchers the anterior scales are five or six, 
the longest being in the middle of the tarsus, and the 
smallest at its two extremities. Wailing and aquatic 
birds have the anterior transverse scales very narrrow, and 
numerous. Tracing this modification onward, we find 
that in some of the falcons the transverse scales begin to 
be of unequal sizes, — next a few of them are divided, 
as if to break the regular series, until, in the Falco 
sparveriim, and its sillies, the whole of the anterior scales, 
which would otherwise be transverse, are divided by a 
suture down the middle of the front into two sets : this 
prepares us for a new pattern of scales, which we term 
angulated or hexagonal, because the sutures of these 
scales, or the lines by which tliey are connected, often 
appear irregularly angulated. This latter form is more 
especially found in the llasorial birds, and the different 
