COMMON CROSSBILL. 17 



The peculiar formation and direction of the parts of the 

 beak in the Crossbill, its anomalous appearance, as well 

 as the particular and powerful manner in which it is ex- 

 ercised, had long excited in me a desire to examine the 

 structure of an organ so curious, and the kindness of a 

 friend supplied me with the means. To those who have 

 not made the habits and economy of birds an ohject of 

 investigation, it may be necessary to premise that our three 

 species of Crossbills are the only British Birds that ex- 

 hibit, or seem to require, any lateral motion of the mandi- 

 bles, and it is my object here to describe the bony struc- 

 ture and muscles by which this peculiar and powerful 

 action is obtained. 



The beak of the Crossbills is altogether unique in its 

 form ; the mandibles do not lie upon each other with their 

 lateral edges in opposition, as in other birds, but curve to 

 the right and left, and always in opposite directions to 

 each other. In some specimens the upper mandible is 

 turned to the right, the lower mandible curved to the 

 left ; in others the position of the mandibles is reversed as 

 to their direction. In the specimen I examined, the upper 

 mandible curved downwards, and to the left ; the under 

 portion turned upwards, and to the right, as the figures 1 

 and 2, in the vignette at the end of this subject, will de- 

 monstrate. When holding the head of this bird in my 

 fingers, I found that I could bring the point of the under 

 mandible in a line underneath, and touching the point 

 of the upper, but not beyond it, towards the left side ; 

 while on its own side the point passed with ease to the dis- 

 tance of three-eighths of an inch. The upper mandible 

 has a limited degree of vertical motion on the cranium, the 

 superior maxillary and nasal bones being united to the 

 frontal bones by flexible bony laminae. The form, also, as 



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