THE ANATOMY OF BIEDS.— OSTEOLOGY. 



139 



also variinisly carinate or ridged, sulcate or grooved. In a few cases they are rounded under- 

 neath, so as to be nearly circular in cross-section, as is the case with those of the tish-hawl 

 (Pandion). They are always horny (comeoMs). They take name from and are reckoned by 

 their respective digits : thus, 1 d. = claw oi I t ; 2 cl = claw of 2 1, etc. 



Fio. 53 ter. — Foot of Jacana (Asarcin) spinosa, nat. size, showing the 

 Mus. The spurred wing of the same bird is also shown. See p. 120.) 



straight claws. (From Pr. U. S. Nat. 



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 Favo bicalcaratus. The only instance of their occurrence among indigenous birds of 

 North America is offered by the wild turkey (Meleagris gallopavo). Metatarsal spurs are 

 characteristic of the male sex : they are oflFensive weapons, and belong to the class of "second- 

 ary sexual characters" (p. 9.5). (For wing-spurs, as shown in fig. 53 ter, see p. 120.) 



4.— AN INTRODUCTION TO THE ANATOMY OF BIRDS. 



Anatomical Structure now aff'ords 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 of exterior 

 modifications 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 intelli- 

 gently understand a wing or a leg without knowing the bony framework of those members. 

 Yet, for me to adequately set this matter forth would be to occupy this whole volume with 

 anatomy ; whereas, I can only devote a few pages to the entire subject. In such embarrass- 

 ment, wliich 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 uptm 

 systematic ornithology as distinguished from pure anatomy, in order to bring forward the 

 structures which are more particularly concerned in the classification of birds. I wish to 

 give a fair account of the skeleton, as osteological characters are of the utmost importance for 

 the determination of natural affinities ; and to continue with some notice of prominent features 

 of the muscular, vascular, respiratory, digestive, urogenital, and nervous systems, and 

 organs of the special senses, as the eye and ear. The tegumentary system has already been 

 treated at some length fpp. 81-9G) ; so has the osseous system, so far as the bones of the limbs 

 are concerned (pp. 111-115. 12I-128, 133). What further I shall have to say is designed 

 merely as an introduction to the rudiments of avian anatomy, and is supposed to be addressed 

 to beginners only. 



