46 CONDITIONS OF THE PODOTHECA. 
§ 76. Tae Naxkep Part of the leg is covered, like the bill, by a hard- 
ened, thickened, modified integument, which varies in texture between cor- 
neous and leathery. This is called the poporHEca (Gr. podos, of a foot, 
theke, sheath). Land birds have the most horny covering, and water birds 
the most skinny ; in general this is distinctive of these two great divisions 
of birds, and the exceptions are few. The perfectly horny envelope is 
tight and immovably fixed, or nearly so, while the skinny is looser, and may 
usually be slipped round about a little. The covering may also differ on 
different parts of the same leg; in fact, such is usually the case-to a degree. 
Unlike the covering of the bill, that of the legs is NEVER simple and contin- 
uous throughout ; it is divided and subdivided in various ways. The lower 
part of the crus, when naked, and the tarsus and toes, are variously cut up 
into scales, plates, tubercles, etc.; these have all received special names ; 
and moreover, the mode of this division becomes, especially among higher 
birds, a matter of the utmost consequence, for purposes of classification, 
since it is fixed and definite in the same groups. 
§ 77. Scurenya (pl. of L. scutellum, a little shield; figs. 10, 11, 6) are 
scales, generally of large comparative size, arranged in definite up and down 
lines, and apt to be imbricated, or fixed shingle-wise, with the lower edge of 
one overlapping the upper edge of the next below. The great majority of 
birds have them. They generally occur on the front of the tarsus (which is 
called acrotarsium, and corresponds to our “instep”), and almost inva- 
riably on the top of the toes (called acropodium) ; frequently on the back 
of the tarsus; not so often on the tibia, sides of the tarsus, sides and under 
surfaces of the toes (if ever in the latter situation). A tarsus so furnished 
is said to be scutellate, before or behind, or both, as the case may be; 
the term is equally applicable to the acropodium, but the expression is 
rarely used because the scutella are so commonly there. 
§ 78. Puares, or reticulations (L. reticulum, a little net or web; fig. 
11, a), result from the cutting up of the envelope by cross lines in various 
ways. Plates are of various shapes and sizes; but however they may be, in 
these respects, they are distinguished from scutella by not appearing imbri- 
cated; their edges simply meet, but do not overlap. They are generally 
smaller than scutella. The commonest shape is the six-sided, or hexagonal ; 
a form best adapted to close packing, as strikingly shown, and long ago 
mathematically proven, in case of the cells of bees’ honey-comb. They are 
sometimes five-sided, or even four-sided; but are more likely to have more 
sides, becoming irregularly polygonal, or even circular; when crowded in 
one direction and loosened in another, this develops into the oval, or even 
somewhat linear. A leg so furnished is called reticulate; it may be wholly 
so, but is generally partly scutellate. A particular case of reticulation is 
called 
§ 79. GranuLation (L. granum, a grain) ; when the plates become ele- 
vated into little tubercles, roughened or not. Such a leg is said to be gran- 
ulated or rugose; it is well seen in the parroquet and fish hawk. 
