108 



THAT S IT; 



in the rays of the unclouded sun, 

 and serves to modify the light. 

 The eagle is said to use this^when 

 it " looks at the sun." The owl, 

 goatsucker, and a few others, 

 have the power of using the 

 upper eyelid when closing the 

 eye, but generally they raise the 

 lower lid, which action may be 

 observed in domestic poultry, and 

 in parrots .* 



Their power of smelling is 

 only moderately developed : the 

 nasal chambers are placed upon 

 the upper mandible, 9, the latter 

 being generally enveloped with 

 a tough skin, called the cere. 



The ears of birds are well de- 

 veloped, their sense of soun$ 

 acute ; but there is no external 

 organ, the auditory apparatus 

 being placed internally, and 

 covered by a tuft of fine feathers. 



But oicls 

 have, sur- 

 rounding 

 the open- 

 ing to their 

 ears, m m- 

 branes, by 

 which 

 they throw 

 back the 

 feathers, and enlarge or contract 

 the orifice, 10. 



Their mandibles, 11, are of 

 various forms and sizes ; some- 

 times forming a simple pointed 

 beak as in the partridge, 12 ; 

 curved and unequal as in the 

 parrot, 13 ; extended to a long 

 slender bill, as in the woodcock, 

 14 ; or enlarged to enormous 

 proportions, as in the toucan, 15. 



* This curious provision may be clearly noticed in 

 the eagle tribes in the Zoological Gardens. 



These various forms of mandibles 

 have their distinct uses, accord- 

 ing to the habits of the birds, as 



392. 



will hereafter be shown. The 

 upper mandible of the parrot is 

 moveable. 



Birds have an imperfect sense 

 of taste, though _ provided with 

 tongues. Some have soft, thick, 

 pulpy tongues, covered with pa- 

 pilla? (small projections contain- 

 ing nerves), and through these 

 they derive a low degree of grati- 

 fication from the sense of taste. 

 But they generally swallow their 

 food without any signs of such 

 gratification. 



They are either carnivorous 

 (flesh eaters), insectivorous (in- 

 sect eaters), granivorous (grain 

 eaters), or omnivorous (eating 

 various substances indiscrimi- 

 nately). Their digestive organs 

 are modified in accordance with 

 their habits. A remarkable fea- 

 ture in the digestion of birds is 

 that, teeth, being absent, they are 

 provided with powerful muscles 

 by which the food is ground. after 

 being swallowed. These muscles 

 are highly developed in grani- 



