46 CONDITIONS OF THE PODOTHECA. 



§ 76. The Naked 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 podotheca (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 ijerfectly- 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 cms, 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. ScuTELLA (pi. of L. scutellum, a little shield; figs. 10, 11, i) ai'e 

 scales, generally of large comparative size, arranged in definite wg 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 gi-eat 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 acropodiuni) ; 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. Peates, or reticulations (L. reticulum, a little net or Aveb ; fig. 

 11, a), result from the cutting up of the envelope by cross lines in various 

 waj's. 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. Thcj^ are 

 sometimes five-sided, or even four-sided ; but are more likely to have more 

 sides, becoming irregularly polj'gonal, 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 Avholly 

 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. 



