﻿EXTERNAL ANATOMY. NOSTRILS. 59 



by the narrow membranaceous skin which conceals the 

 linear aperture, that the nostrils would never be disco- 

 vered by a student unacquainted with this curious form- 

 ation : upon raising this lappet, the aperture appears as 

 an elongated slit ; but which, in the suribirds (Cinnyridce) 

 is of a semicircular form. The most tumid nostrils are 

 those of the pigeons; but in what respect this structure is 

 connected with their economy, we know not. There is an 

 obvious analogy, however, even between this shape and 

 that which is seen in the plovers. In rasorial types the 

 aperture is almost lateral-^- that is, placed on that side of 

 the membrane which is nearest to the margin of the bill ; 

 the membrane itself being unusually thick and strong, 

 almost corneous, and often very convex. It is obvious 

 that all these are different modes for protecting an organ 

 so delicate: but Nature is ever inexhaustible in her vari- 

 ations ; and thus we find that in numberless instances she 

 accomplishes the same object by the means of bristles, 

 or feathers, variously disposed, according to the particu- 

 lar habits of the birds. The great majority of insectivo- 

 rous birds have setaceous feathers or bristles incurved 

 over the nostrils, sufficient to ward off injury, yet leaving 

 the orifice, in other respects, exposed to the free action 

 of the air. In birds, however, whose habits lead them 

 to plunge their bill into substances which might enter 

 the apertures, the nostrils are completely covered by 

 thick- set feathers, or rigid bristles, reposing flat upon the 



bill. We have already 

 adverted to this structure 

 in the whole of the wood- 

 peckers ; and it is almost 

 as general among the 

 crows (fig. 26.), which 

 have not only their nostrils, 

 but a great part of the base of the bill, protected and even 

 covered by stiff bristles. Hence they are enabled, with 

 impunity, to perforate the earth and pick holes in the 

 ground, during their search for insects, without the least 

 particle of dirt getting into their nostrils. The genus 



