608 AVES BIRDS. 



in the construction of the organs of their senses many circumstances 

 of considerable interest to the physiological reader ; and, conse- 

 quently, these will require a more extended description. 



(676.) The sense of touch must obviously be extremely imperfect 

 in these animals : their body, enveloped in feathers, can be little 

 sensible to impressions produced by the contact of external objects ; 

 and their limbs, covered as they are with plumes, or cased in horny 

 scales, are but little adapted to exercise the sense in question. The 

 beak alone offers itself as calculated to be a tactile instrument ; but 

 even this, enclosed as it is in the generality of birds by a dense 

 corneous case, must be very inefficient in investigating the outward 

 surfaces of substances : nevertheless, in some tribes the beak is un- 

 doubtedly extremely sensible, and is used to search for food in 

 marshy soils, or to find it in the mud at the bottom of shallow 

 waters ; this is the case, for instance, in many of the long-billed 

 Wading Birds, and also in the flat-billed aquatic families, such as 

 the Goose and Swan ; in these, in fact, the covering of the beak is 

 comparatively soft, and the nerves that supply it, derived from the 

 fifth pair, are of very considerable size. 



(677-) Taste is evidently one of the last indulgences granted, as 

 we advance from the lower to the more highly gifted races of the 

 animal creation ; and even in birds it is only necessary to inspect 

 the structure of the tongue in order to be convinced that they can 

 derive but small enjoyment from this source. The skin of the 

 tongue in these creatures is totally devoid of gustatory papillae, and 

 frequently, indeed, enveloped in a horny sheath; so that, if the sense 

 of taste exists at all, it must be, to the last degree, limited and 

 obtuse. 



(678.) In return, however, for the imperfection of the above 

 senses, the olfactory apparatus in this class of animals begins to 

 assume far greater importance than in the cold-blooded Vertebrata ; 



Fig. 277. ." : -- ;; 



