' 



NATUKALTSTS CABINET. 



Auditory passage Nictitating membrane. 



though concealed from his sight at a consider- 

 able distance. 



Birds have no external ears, but merely a tuft 

 of fine feathers covering the auditory passage; 

 which readily allows the rays of sound, and at 

 the same time precludes the entrance of dust or 

 insects. 



As many of these creatures are frequently pas- 

 sing through hedges and thickets, their eyes are 

 secured from external injuries, as well as from 

 too much light, by a nictitating or winking mem- 

 brane, which can at pleasure be drawn over the 

 whole eye, like a curtain. This covering is nei- 

 ther opaque nor wholly pellucid, but is somewhat 

 transparent ; and it is by means of this, that the 

 eagle is said to gaze at the sun. The sight in 

 birds is evidently more piercing, extensive, and 

 accurate than in the other orders of animals. 

 The eye is much larger in proportion to the bulk 

 of the head, than in any of these. This is a su- 

 periority not only necessary but even indispen- 

 sable to their safety and subsistence. Were this 

 organ in birds dull, or in the least degree opaque, 

 they would be in perpetual danger of striking 

 against various objects in their flight. In this 

 case their celerity, instead of being an advan- 

 tage, would become an evil, and their flight must 

 be restrained by the danger resulting from it. 



The respiration of volatiles is performed by 

 means of air-vessels, extended through the whole 

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