VERTEBRATA 175 



1 6. Passeres. This order is the most numerous and 

 varied in the whole class. It comprehends all those 



FIG. 160. White-throated sparrow (Zonotrichia albicollis). United States. 



tribes which live habitually among trees, excepting the 

 rapacious and climbing birds, whose toes three in 



FIG. 161. Redstart (Setophaga ruticitta). United States. 



front, and one behind are eminently fitted for perch- 

 ing only. The legs are slender, and seldom used for 

 locomotion. 



They are divisible into two sections : a. Clamatores, 

 having the tarsus usually enveloped in a row of plates 

 meeting behind in a groove, and the bill broad, and bent 



