14 INTRODUCTORY CHAPTER. 



neously. The method which Nature has provided for the preser- 

 vation of this curious texture of feathers with which the volatile 

 part of the creation is clothed, will merit our attention. 



Lest they should be damaged by their violent attrition against 

 the air, or by imbibing the moisture of the atmosphere, birds are 

 fuinished with a gland situated on the rump, containing an oil 

 winch they can press out with their bill, and with which they 

 anoint their feathers. In water-fowls this oil is so plentiful, that 

 by it their plumage is rendered completely water-proof. 



In all birds the eye is peculiarly calculated for distant vision, 

 and the ear for accurate and quick perception ; and their sense 

 of smelling is exceedingly acute. Their legs and feet are ad- 

 mirably adapted to the different purposes for which they are de- 

 signed, being light, compact, and long. In water-fowl the toes 

 aie joined by a ligament of tough skin, to facilitate their swim- 

 ming, and render them fit for the element in which Nature has 

 destined them chiefly to live, while in others they are constructed 

 for their security in perching upon trees. 



The internal structure of birds is, not less than their external 

 conformation, wisely adapted to the peculiar circumstances of 

 their existence ; all their bones being light and thin, as well as 

 all the muscles, except those which are appropriated to the pur- 

 pose of moving the wings. The lungs are extended over almost 

 the whole cavity of the body, and peculiarly calculated for the 

 reception and retention of air ; a great quantity of which enter- 

 ing in by the windpipe, is conveyed into a number of mem- 

 branous cells, which are placed upon the sides of the pericardium, 

 i.nd communicate with those of the sternum. In some of the 

 volatile tribes these cells are continued down the wings, and 

 extend even to the pinions and thigh bones, which the bird can, 

 by the inhalation of the lungs, fill and distend with air at its 

 pleasure. 



One of the most remarkable circumstances discoverable in the 

 formation of birds, is this general and copious diffusion of air, 

 calculated most probably, as Mr. Hunter supposes, for the pur- 

 pose of rendering their body more buoyant ; for as that ingenious 

 gentleman observes, this circumstance appertains in a more em- 

 inent degree to eagles and other birds of the lightest and longest 

 flight. In regard to the ostrich, although it does not fly, the 

 extreme velocity with which it runs, renders a similar supply of 

 air equally necessary. Were it possible that a man should move 

 with the velocity of a swallow or several other birds, the resist- 

 ance of the air would soon produce suffocation, for want of those 

 internal reservoirs which in birds are of incalculable use, in pre 

 venting the stoppage of respiration, by the rapidity of their mo- 



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