124 



GENEBAL OBNITHOLOOY. 



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 homy to leathery. This sheath is called the podotheca 

 (Gr. jroCs, noSos, pons, podos, foot, and Btjkij] theke, sheath). It is more corneous in land birds, 

 and in water birds more leathery ; this general distinction has but few exceptions. The perfectly 

 homy 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 

 received 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. 



tr^. — . 



StcLL 



Fig. 36. — Booted laminiplantai 

 tarsus 43f a robin. Nat. size. 



Pig. 37. - Scutellate 

 lamlniplantar tarsus of a 

 cat-bird. Nat. size. 



Fig. 38. — a. Reticulate tarsus 

 of a plover. Nat. size. ■ b. Scutel- 

 late and reticulate tarsus of a 

 pigeon. Nat. size. 



The commonest division of the podotheca is into scales or smtella (Lat. scutellum, a little 

 shield; pi. scutella, not scutellce as often written) ; figs. 37, and 38, 6. 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 cuyrotarsium, corresponding to our " instep"), and 

 almost invariably on the tops of the toes (collectively called acropodium) ; frequeriHy 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 podotheca is said to be 

 scutellate, — scutellate before (fig. 37), or behind, or both, as the case may be. The term is 

 equally applicable to the acropodium, but is not so often used because scutellation 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 Oscime podotheca (figs. 36, 37), characterizing 

 that great group of birds, is given beyond (next paragraph). 



Plates, or retimdaUons (Lat. retimlum, a web ; fig. 38, a) result from the cutting up of 



