28 FRINGILLIDE. 



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 Avith 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 su- 

 perior 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 

 also peculiar to this bird. 



The pterygoid processes of the palatal bones are consi- 

 derably elongated downwards, as shown at figure 8, letter a, 

 to afford space for the insertion of large pterygoid muscles. 

 The OS omoideum on each side, figure 3, letter h, is strongly 

 articulated to the os quadratum, figure 3, letter c, affording 

 firm support to the moveable portion of the upper mandible. 

 Letters c/, </, 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 for- 

 wards by its own peculiar muscles, to be hereafter mentioned, 

 the jugal bone on each side by its pressure forwards elevates 

 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 de- 

 stined to receive this process is a hollow circular cup, figure 

 5, letter a ; the union of these two portions, therefore, forms 

 an articulation possessing much of the universal motion and 

 flexibility of the mechanical ball and socket joint. 



