iS6 GENERAL ORNITHOLOGY part ii 



Exceptions aside, it only occurs in connection with an equally 

 particular condition of the sides and hack of the tarsus, or 2)lanta. 

 In almost all Oscine Passeres {Alaudidce are an exception), Avhich 

 constitute the great bulk of the large order Passeres, the planta is 

 covered with one pair of plates or kuiiina-, one on each side, meeting 

 behind in a sharp ridge ; a condition called laminiplantar, in dis- 

 tinction from the opposite, scuteUiplantar, state of the parts. A 

 holothecal podotheca only occurs in connection with the lamini- 

 plantar condition, the combination resulting in the perfect " boot." 

 Among British birds it is exhibited by the following genera : 

 Turdus, Cinclus, Saxicola, Begulus, Cyanemla, Phylloscopus ; and even 

 birds of these genera, when young, show scutella which disappear 

 with age by progressive fusion of the acrotarsial podotheca. (Com- 

 pare Figs. 36, 37.) 



The CPUS, when bare of feathers below, may, like the tarsus, be 

 scutellate 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 back- 

 ward, and only rarely wider from 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 happens in the larks (Alaudidce) ; they are rare among 

 land birds, common among waders. Those swimming birds which 

 have a very thin skinny podotheca are apt to show traces of the 

 four-sidedness of the metatarsal bone. The tarsus in the vast 

 majority of land birds is seen on close inspection to be somewhat 

 oval or drop-shaped on cross-section, — gently rounded in front, 

 more compressed laterally, and sharp-ridged behind. This results 

 from the laminiplantation described above, and is equally well ex- 

 hibited by most passerine birds, whether they have booted or 

 anteriorly scutellate tarsi. The line of union of anterior scutella 

 with posterolateral plates on the sides of the tarsus is generally in a 

 straight vertical line, — either a mere line of flush union, or a ridge, 

 or oftener a groove (well seen in the crows), which may or may not 

 be filled in with a few small narrow plates. In Clamatorial Passeres 

 the tarsus is enveloped in a scroll-like podotheca of irregularly 

 arranged plates, the edges of the scroll meeting along the inner side 

 of the tarsus. — But the full consideration of special states of the 



