COMMON CROSSBILL. 27 



nor is there the slightest indication to which side either 

 mandible would hereafter be inclined. I may here add, 

 that an opinion prevails that the sexes in the Crossbill may 

 be known by the direction of the curves of the mandibles, 

 those of the males turning outward in the contrary direction 

 to those of the females ; but the examination of a great many 

 specimens, in reference to this point, has convinced me that 

 this is not a rule to be depended upon, the upper mandible 

 in both sexes turning sometimes to the right and sometimes 

 to the left. I observe a record in the Essex Literary Jour- 

 nal for January 1839, that the Crossbill bred in Orwell Park, 

 near Ipswich, in the year 1822. 



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 exercised, 

 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 object of investigation, it may be 

 necessary to premise that our three species of Crossbills are 

 the only British Birds that exhibit, or seem to require, any 

 lateral motion of the mandibles, and it is my object here to 

 describe the bony structure and muscles by which this pecu- 

 liar 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 



