BONES OF THE HEAD IN BIKDS. 181 



moulded upon the osseous part of the jaws. The form and 

 texture of the bill vary with the habits and food of the 

 animal. In rapacious birds the bill is hard and hooked at the 

 end for seizing and tearing the prey. In birds that bruise 

 very hard seeds it is also of firm texture. The bill is of a 

 more delicate structure in birds which use a softer food. 

 Finally, it is found to be soft and remarkably sensitive in birds 

 of the duck kind, which seek their food in water or in mud. 

 In poultry, as well as in the hawk tribe, a soft skin covers the 

 base of the bill. It is named cire, but the use of it is not 

 ascertained. 



Bones of the Head. The bones of the head in birds have 

 created much discussion among comparative anatomists. The 

 plan of this work does not admit of any attempt to exhibit 

 the several views insisted on. It will be sufficient to state a 

 few particulars hardly admitting of doubt. There are no 

 sutures in the skull of adult birds. The false sutures in young 

 birds soon become obliterated. The bones of the cranium, 

 like the rest of the skeleton in birds, admit air to give addi- 

 tional lightness. The crest or horn peculiar to some birds is 

 united with the frontal bone, and may be regarded as an 

 enlargement of its orbitar portions. The interior of the 

 cranium is divided into two principal compartments, the one 

 for the cerebrum, the other for the optic thalami, the cere- 

 bellum and medulla oblongata. There are nearly as many 

 bones in the skull of the bird as in the human skull. The 

 orbital cavities are of great extent. In some birds there is 

 only a membrane between the two orbits ; in others the par- 

 tition is more or less osseous. The temporal bones are destitute 

 of a zygomatic process. In the whole order of birds, the head 

 is supported on the neck by a single hemispherical condyle 

 situated at the fore part of the foramen magnum. 



Jaws. The proportion between the cranium and the jaws 



