INTRODUCTION. 



shape, and of great importance in the classification of different 

 races. 



The Tarsus, by which name we shall designate the shank, is 

 zMhcv feathered, as in many of the birds of prey (Fig. 7), or naked, 

 as in the generality of birds. 



A Naked tarsus is protected by Scales {scutellatcd) ; and next 

 to the relative length of the tarsus, the form and disposition of 

 these scales supply us with the best discriminative characters taken 

 from this part of the bird. The generality of naked-footed birds 

 have the tarsus protected by three series of scales, each of which 

 is frequently of a peculiar form. The first series is in front, the 

 second occupy the two sides, and the third is at the back of the 

 leg. 



The front scales, called also the anterior, are either composed 

 of one or several pieces. When the anterior scale is simple, or 

 composed of one piece, it extends from the front of the knee as 

 far as the hinder toe, and its external surface is quite smooth. 

 Generally, however, this front plate is marked by transverse di- 

 visions, or composed of pieces, which sometimes overlap each 

 other. In many birds, both the front and sides of the tarsus are 

 covered with numerous small scales that do not touch each other, 

 but are so disposed that the interstices, or spaces between them, 

 resemble the lines of a net : such a tarsus is said to be retieidatcd. 



The lateral scales of the tarsus are not always present ; fre- 

 quently their office is supplied by the anterior scales, which are 

 then extended round the leg, so as nearly to envelope it. 



The posterior scales are very frequently wanting, and when pre- 

 sent seldom extend much below the upper part of the tarsus. 



The Toes of birds, by their leading variations, furnish the pri- 

 mary characters whereby the whole Class is divided into Orders, 

 and the subordinate modifications of their structure indicate for 

 the most part natural groups. 



The great majority have four toes on each foot, three of vdiich 

 are usually placed before, and one (the hallux) behind. The 

 exceptions to this number of toes and to their disposition are 

 comparatively few. They will be noticed when speaking of 

 the particular races in which they exist. 



