154 CROSS-BEAKS. 



the water- ousel is said to haunt the mouth of the 

 Lewes river, near Newhaven ; and the Cornish 



insertion of the large pterygoid muscles. The os omoideum 

 on each side is strongly articulated to the os quadratum, 

 affording firm support to the upper mandible. The jugal 

 bone is 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, 

 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 

 downwards ; the same process in the crossbill is spherical. 

 The cavity in the lower jaw, destined to receive this 

 process, is a hollow circular cup. The union of these two 

 portions, therefore, forms an articulation possessing the 

 universal motion and flexibility of the mechanical ball-and- 

 socket joint. The lower jaw is of great strength the 

 sides or plates elevated, with prominent coronoid processes, 

 to which, as well as to the whole outer sides of the plates, 

 the temporal muscle is attached ; and in a head of this 

 bird, which had been divested of all the soft parts, I found, 

 on sliding the lower laterally upon the upper, as performed 

 by the bird, that before the coronoid process is brought 

 into contact with the pterygoid on its own side, the extreme 

 points of the mandibles were separated laterally to the 

 extent I have already mentioned of 3-8ths of an inch. 

 The temporal and pyramidal muscles on the right side 

 of the head that being the side to which the lower jaw 

 inclined were considerably larger than those of the left, 

 and indicated by their bulk the great lateral power this 

 bird is capable of exerting, to be hereafter noticed. The 

 unusually large size of the pterygoid muscles, on each side, 

 was very conspicuous, the space for them being obtained 

 by the great distance to which the articulated extremities 

 of the lower jaw were removed ; and the food of the bird 

 being small seeds, rendered a narrow pharynx sufficient 

 for the purpose of swallowing. The muscles depressing 

 the lower mandible are three in number, only one of which, 

 the greater pyramidal, is visible. This strong muscle covers 

 two other small ones, the triangular and square muscles, 



