COMMON CROSSBILL. 17 



turned upwards, and to the right, as the figures 1 and 2, 

 in the vignette at the end of this subject, will demonstrate. 

 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 distance 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 well as the magnitude 

 of the processes of the bones of the head are likewise pecu- 

 liar to this bird. 



The pterygoid processes of the palatal bones are consi- 

 derably elongated downwards, as shown at figure 3, letter a, 

 to afford space for the insertion of large pterygoid muscles. 

 The os omoideum on each side, figure 3, letter b, is strongly 

 articulated to the os quadratum, figure 3, letter c, afford- 

 ing firm support to the movable portion of the upper 

 mandible. Letters d, d, refer to the jugal bone, which, 

 united to the superior maxillary bone in front, is firmly 

 attached by its posterior extremity to the outer side of the 

 os quadratum ; when, therefore, the os quadratum is pulled 

 upwards and forwards by its own peculiar muscles, to be 

 hereafter mentioned, the jugal bone on each side by its 

 pressure forwards raises the upper mandible. 



The inferior projecting process of the os quadratum, to 

 which the lower jaw is articulated, in most other birds is 

 somewhat linear from before backwards, and compressed at 

 the sides, admitting vertical motion only upwards and down- 

 wards ; the same processes in the Crossbill are spherical, as 

 shown at figure 3, letter c ; the cavity in the lower jaw 

 destined to receive this process is a hollow circular cup, 

 figure 5, letter a ; the union of these two portions, there- 



VOL. II. c 



