IS4 



GENERAL ORNITHOLOGY 



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 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. 



rt . - ; w^ Flo. 37. — Scutel- Fig. 38. — a, Reticulate tarsus of a 



<J '''"'- - — late laminiplantar plover. Nat. size. 6, Soutcllate and 



Pia. 3ti. — Booted laminiplantar tarsus of a cat - reticulate tarsus of a pigeon. Nat. 



tarsus of a robin (TurdMsmiffratoriwi). bird (ilfiwiws caro- size. 



Nat. size. UiktwS). Nat. size. 



The commonest division of the podotheca is into scales or scutella 

 (Lat. scutellum, a little shield ; pi. scutella, not scutellm as often 

 written); Figs. 37 and 38, h. These are generally of large com- 

 parative 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, corre- 

 sponding to our " instep "), and almost invariably on the tops of the 

 toes (collectively called acropodivm) ; frequently also on the sides 

 and back (planta) of the tarsus ; 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 



