ANATOMY OF BIRDS 



197 



terrestrial Passeres, as in the whole family Alaudidce (larks), and 

 some of the finches (Fringillidm), as the species of "long-spur" 

 (Cenkophanes). But all the claws are straight, sharp, and pro- 

 digiously long, in birds of the genus Parra l(Fig. 53 ter) ; these 

 ia(jands being enabled to run lightly over the floating leaves of 

 aquatic plants by such increase in the spread of their toes. Claws 

 are also variously carinate or ridged, sulcate or grooved. In a few- 

 cases they are rounded underneath, so as to be nearly circular in 

 cross-section, as is the case with those of the osprey (Pandion). 

 They are always horny (corneous). They take name from, and are 

 reckoned by, their respective digits: thus, 1 d. = claw oi It / 2 d. 

 = claw of 2t, etc. 



Spurs (Lat. calcar, a spur) are developed on the metatarsal 

 bones of a few birds. They are of the nature of claws, being hard, 

 horny modifications of the epiderm : but they have nothing to do 

 with the digits. They possess a bony core upon which they are 

 supported, like the horns of cattle. Such growths chiefly occur in 

 gallinaceous birds : the spurs of the domestic fowl are a familiar 

 case. Sometimes there are a pair of such weapons on each foot, as 

 in the Pavo bicalearatus, and there may be several more, as in the 

 genus Ithagenis. Another instance of their occurrence is off'ered 

 by the wild turkey (Meleagris gallipmo). Metatarsal spurs are 

 characteristic of the male sex ; they are offensive weapons, and 

 belong to the class of " secondary sexual characters " (p. 133). (For 

 wing-spurs, as shown in Fig. 53 ter, see p. 168.) 



§ 4.— AN INTRODUCTION TO THE ANATOMY OF BIRDS 



Anatomical Structure now affords ornithologists many and the 

 most important of the characters used in classification. In fact, few 

 if any of the'groups above genera can be securely established without 

 consideration of internal parts and organs, as well as of exterior modi- 

 fications of structure. Therefore, the student who really "means 

 business '' must be on speaking terms at least with avian anatomy. 

 For example, none could in the least intelligently understand a 

 wing or a leg without knowing the bony framework of those 

 members. Yet to adequately set this matter forth would be to 

 occupy a very much larger volume with anatomy ; whereas, I can 

 only devote a few pages to the entire subject. In such embarrass- 

 ment, which attends any attempt to treat a great theme in a short 

 way that shall not also be a small way, attention must be mainly 

 confined to those points which bear most directly upon systematic 

 ornithology as distinguished from pure anatomy, in order to bring 



