124 i oS GENERAL ORNITHOLOGY. 
minimum lengths of tarsus are nearly thirty and under three per cent. of a bird’s whole 
length. 
The Horny Integument of the Foot requires particular attention. That part of the 
limb which is devoid of feathers is covered, like the bill, by a hardened, thickened, modified 
integument, varying in texture from horny to leathery. This sheath is called the podotheca 
(Gr. mois, odds, pous, podos, foot, and Onn, theke, sheath). It is more corneous in land birds, 
and in water birds more leathery ; this general distinction has but few exceptions. The perfectly 
horny envelope is tight, and immovably fixed or nearly so, while the skinny styles of sheath 
are looser, and may usually be slipped about a little. The integument may differ on different 
parts of the same leg, and in fact generally does so to some extent. Unlike the sheath of the 
bill, the podotheca is never simple and continuous, being divided and subdivided in various 
ways. The lower part of the crus, when naked, and the tarsus and toes, always have their 
integument cut up into scales, plates, tubercles, and other special formations, which have 
reteived particular names. The manner and character of such divisions are often of the 
utmost consequence in classification, especially among the higher birds, since they are quite 
significant of genera, families, and even some larger groups. 
Fie. 38. — a. Reticulate tarsus 
Fig. 37. — Scutellate ofa plover. Nat. size. 6. Scutel- 
Fie. 36.— Booted laminiplantar laminiplantar tarsus of a late and reticulate tarsus of a 
tarsus of arobin. Nat. size. cat-bird. Nat. size. pigeon. Nat. size. 
The commonest division of the podotheca is into scales or scutella (Lat. scutellwm, a little 
shield; pl. scutella, not scutelle as often written) ; figs. 37, and 38, b. These are generally of 
large comparative size, arranged in definite vertical series up and down the tarsus and along 
the toes, and apt to be somewhat imbricated, or fixed shingle-wise, the lower edge of one 
overlapping the upper edge of the next. The great majority of birds have such scutella. They 
oftenest occur on the front of the tarsus (or acrotarsium, corresponding to our “ instep”), and 
almost invariably on the tops of the toes (collectively called acropodium) ; frequently also on 
the sides and back of the tarsus or planta ; not so often on the crus, and rarely if ever on the 
sides and under surfaces of the toes. A tarsus so disposed as to its podotheea is said to be 
scutellate, — scutellate hefore (fig. 37), or behind, or both, as the ease may he. The term is 
equally applicable to the acropodium, but is not so often used because seutellation of the upper 
sides of the toes is so universal as to be taken for granted unless the contrary condition is 
expressly said. The most notorious case of the Oscine podotheca (figs. 36, 37), characterizing 
that great group of birds, is given beyond (next paragraph). 
Plates, or reticulations (Lat. reticilum, a web; tig. 38, a) result from the cutting up of 
