182 Mr. Yarrell on the Anatomy of Birds of Prey. 



entirely at your service. They are the result of observations 

 founded, and notes taken, during an examination of the bodies of 

 most of the British Birds of prey, including some of very rare 

 occurrence. 



In commencing these observations, however, I confess, without 

 reserve, my want of anatomical knowledge to do justice to so in- 

 teresting a subject, and therefore the more readily consign them to 

 your better judgment, to be altered or curtailed as their various 

 imperfections may require. 



The skeletons of birds exhibit considerable resemblance to the 

 bony structure of the Mammalia. The principal differences are — -. 

 A cranium that has no real sutures. 

 An upper jaw that does move. 

 Two pairs of extra bones in the head. 

 A single occipital condyle. 

 More than seven cervical vertebrae. 

 Motionless dorsal vertebrae. 



Clavicles constant, and an os furcatorius or furcula in all those 

 birds exercising the power of flight. 



The power of flight is one of the decided marks of the distinct 

 organization of this class, and as one division of the first genus 

 Falco appears to possess this power in the highest degree of per- 

 fection of which it is susceptible, I shall briefly consider the con- 

 ditions necessary to produce this power in its fullest extent. These 

 are, large and powerful pectoral muscles ; great extent of sur- 

 face, as well as peculiarity of form in the wing; and feathers 

 of firm texture, strong in the shaft, with the filaments of the plume 

 arranged and connected to resist pressure from below. 



A certain degree of specific gravity is necessarily imparted by 

 large pectoral muscles, and the power of these muscles may be 

 estimated by the breadth of the sternum and the depth of its keel, 

 as affording extent of surface for the attachment of the large 

 muscle by which the wing is depressed. As an illustration of 

 this form the breast bone of the Peregrine Falcon (Falco Peregrz- 

 nus) is represented Plate VI. No. 1 , of the natural size, which ex- 

 hibits the breadth of the sternum, the depth of the keel, as well as 

 the strength of the clavicles; and the power of flight peculiar io 



