24 INTRODUCTION. 



the maxillary bone, s. The lower jaw admits only of a direct 

 hinge-like motion. Both together constitute the general organ 

 of prehension in birds, and undergo great modifications of form, 

 according to the nature of the food. 



It is only necessary further to observe here that the skull 

 contains the cerebrum, cerebellum, and optic lobes, constituting 

 the central organ of the nervous system ; that in the temporal 

 bone, Fig. 1, ^, is contained the organ of hearing; while in 

 the large cavities formed between the cranium and face, at ^, 

 A, p^ named the orbits, are placed the organs of vision ; those 

 of smell being situated in the cavity at the base of the upper 

 jaw, 0, s ; and that the organs of taste and deglutition, with 

 the entrance of the respiratory apparatus, are placed in the 

 mouth and throat. 



Plate I. represents the skeleton of the Golden Eagle, Aquila 

 Chrymetus^ reduced to one fourth of its natural size. The parts 

 already spoken of may, for the most part, be readily traced in 

 the head, which has an additional small bone, appended to the 

 lachr^Tiial, and named the superciliary. It is the basis of the 

 thin-edged projection which gives a peculiar character to the 

 eyes of the birds of prey. The cranium is marked a, the upper 

 jaw 6, the lower c. 



The vertebral column, or spine, along the centre of which 

 runs the spinal cord, is divided into three regions : the cervical, 

 from ^ to ^ ,• the dorsal, from eio f ; the sacral, or united lum- 

 bar and sacral, from / backwards ; and lastly, the caudal or 

 coccygeal, g. The number of vertebrae, or pieces of which it 

 is composed, varies much in this class of animals. 



The cervical vertebrae, f?, ^, are here thirteen. The articula- 

 tion of the skull with the first takes place by a single condyle, 

 or hemispherical knob, seen in Fig. 2, and a corresponding 

 depression in the first cervical vertebra, which is of an annular 

 form. This sort of joint allows a much freer motion than in 

 the mammalia. The other vertebrae are articulated by alter- 

 nate concave and convex surfaces, but so as to permit extended 

 motion, the upper vertebrae moving more easily forwards, those 

 in the middle backwards, and the lower forwards or down- 

 wards ; in consequence of which the ordinary flexure of the 



