140 



VERTEBRATA: AVES OR BIRDS. 



of feathers. All the so-called naked portions of the legs, 

 however, are covered with a more or less hard integu- 

 ment, varying from somewhat skinny, as in the Water 

 Birds, to horny, as in the Land Birds. This covering is 

 variously modified, divided, and subdivided, forming 

 scales or scutella, plates or reticulations, and tubercles 

 or granulations. In some cases, however, as in the 

 Thrushes, etc., the tarsus shows few or no divisions except 

 near the toes ; and such a tarsus is said to be " booted." 



Seutella are arranged in more or less regular series or up and down 

 rows, and in most cases they are imbricated, or arranged like tiles on 

 a roof ; as in the Mocking-bird and Cat-bird (Fig. 158). 



Plates or reticulations are not in regular series, and they are not im- 

 bricated, but meet edge to edge ; as in the Plover (Fig. 159). 



Granulations are elevated plates ; as in the Osprey. 



FIG. 158. 



FIG. 159. 



FIG. 160. 



Booted tarsus Scutellate tarsus Reticulate tarsus Scutellate tarsus- 



Robin. Cat-bird. Plover. Pigeon. 



U Zt St and 41 indicate 1st, 2d, 3d, and 4th toes. 



The horny covering upon the mandibles performs the 

 functions of teeth. The stomach may be regarded as com- 



* Figures 157-160, and 238, are from Cones' 

 Birds." 



Key to North American 



