EXTEBNAL PARTS OF BIBBS.— THE FEET. 125 



the envelope iu various vpays by cross lines. Plates are of various shapes and sizes, and 

 grade usually into true scutella, from which however they are generally distinguished by being 

 smaller, or of irregular contour, or not in definite rows, or lacking the appearance of imbrica- 

 tion ; but there is no positive distinction. They are oftenest hexagonal (six-sided), a form best 

 adapted to close packing, a.s shown very perfectly in the cells of the honey-bee's comb ; but 

 they may have fewer sides, or be polygonal (many-sided), or even circular ; when crowded in 

 one direction and loosened in another the shape tends to be oval or even linear. A leg so' fur- 

 nished is said to be reticulate : the reticulation may be entire, or he iissociated with scutellation, 

 as often happens (fig. 38, 6). A particular case of reticulation is called granulation (Lat. 

 granum, a grain) : when the plates become elevated into little tubercles, roughened or not. 

 Such a leg is said to be granular, granulated, or rugose : it is well shown by parrots, and the 

 fish -hawk (Pandion). When the harder sorts of scales or plates are roughened without 

 obvious elevation, the leg is said to be scabrous or sca/rious (Lat. scabrum, a scab). But 

 scabrous is also said of the under surfaces of the toes, when these develop special pads, or 

 wart-like bulbs (called tylari) : as is well shown in the sharp-shinned and many other hawks. 

 The softer sorts of legs, and especially the webs of swimming birds, are often marked cross'wise 

 or cancellated with a lattice work of lines, these however not being strong enough to produce 

 plates ; it is more like the lines seen on our palms and finger-tips. The plates of a part of the 

 leg occasionally develop into actual serrations; as witnessed along the hinder edge of a 

 grebe's tarsus. When an unfeathered tarsus shows no divisions of the podotheca in front 

 (along the acrotarsium), or only two or three scales close by the toes, it is said to be booted or 

 greaved; and such a podotheca is holothecal (Gr. o\os, holos, whole, entire, and SijKri; fig. 36). 

 The generic opposite is schizothecal (Gr. axi-Ca, I cleave), whether by scutellation or reticula- 

 tion or in any other way the integument may be cut up. A booted or holothecal tarsus chiefly 

 occurs in the higher Osdnes, and is supposed by many, particularly German oriiithologists, to 

 indicate the highest type of bird structure. It is, however, found in a few water birds, as 

 Wilson's stormy petrel and other species of Oceanites. It is not a common modification. 

 Exceptions aside, it only occurs in connection with an equally particular condition of the 

 sides and back of the tarsus, or planta. In almost all Oscime Passeres (Alaudidm are an 

 exception), which constitute the great bulk of the large order Passeres, the planta is covered 

 vrith one pair of plates or lamina, one on each side, meeting behind in a sharp ridge ; a condi- 

 tion called laminiploMtar, in distinction from the opposite, scutelliplantar, state of the parts. 

 A holothecal podotheca only occurs in connection with the laminiplantar condition, the combi- 

 nation resulting in the perfect "boot." Among North American birds, the genus Oceamites 

 aside, it is exhibited by the following genera, and by these only : Turdus, Cinclus, Saxieola, 

 Sialia, Begulus, Cyanectela, Phylloscopus, Chamcea, Myiadestes ; and even birds of these 

 genera, when young, show scutella which disappear with age by progressive fusion of the 

 aorotarsial podotheca. ("Compare figs. 36, 37.) 



The Cms, when bare of feathers below, may, like the tarsus, be seutellate or reticulate 

 before or behind, or both ; such divisions of the crural integument being commonly seen in 

 long-legged wading birds. Or, again, this integument may be loose, softish, and movable, not 

 obviously divided, and passing directly into ordinary skin. 



The Tarsus, in general, may be called subcylindrical : it is often quite circular in cross- 

 section ; generally thicker from before backward, and only rarely vidder fi-om one side to the 

 other than in the opposite direction; but such a shape as this last is exhibited by the penguins. 

 When the transverse thinness is noticeable, the tarsus is said to be compressed; and such 

 compression is very great in a loon, in which the tarsus is almost like a knife blade. Quite 

 cylindrical tarsi occur chiefly when there are similar scales or plates before and behind, as 



