168 



ON THE EXTERNAL SENSES 



very visibly in the tail ; and M. Cuvier suspects that it has a similar existence 

 in all the prehensile-tailed mammals. 



Blumenbach supposes the same sense to have a place in the same organ in 

 the platypus, or ornithorhynchus, as he calls it, that most extraordinary duck- 

 billed quadruped which has lately been discovered in Australia, and, by its 

 intermixture of organs, confounds the different classes of animals, and sets 

 all natural arrangement at defiance. 



The local organ of touch or feeling in ducks and geese, and some other 

 genera of birds, appears to be situated in the integument which covers the 

 extremity of the mandibles, and especially the upper mandible, with which 

 apparatus they are well known to feel for their food in the midst of mud in 

 which they can neither see nor perhaps smell it. 



We do not know that amphibials, fishes, or worms possess any thing like 

 a local sense of touch : it has been suspected in some of these, and especially 

 in the arms of the cuttle-fish, and in the tentacles of worms that possess this 

 organ ; but at present it is suspicion, and nothing more. 



In the insect tribes, we have much reason for believing such a sense to 

 reside in the antennas, or in the tentacles ; whence the former of these are de- 

 nominated by the German naturalists fiihlhorner or feeling-horns. This be- 

 lief has not been fully established, but it is highly plausible, from the general 

 possession of the one or the other of these organs by the insect tribes, the 

 general purpose to which they apply them, and the necessity which there seems 

 for some such organ from the crustaceous or horny texture of their external 

 coat. 



The senses of taste and smell in animals bear a very near affinity to the 

 local sense of touch ; and it is difficult to determine whether the upper man- 

 dible of the duck-tribe, with which they distinguish food in the mud, may not 

 be an organ of taste or smell as well as of touch; and there are some natu- 

 ralists that in like manner regard the cirrous filaments or antennules attached 

 to the mouths of insects as organs of taste and touch equally. Taste in the 

 more perfect animals resides jointly in the papillae of the tongue and the 

 palate ; but I have already had occasion to observe that it may exist, and in 

 full perfection, in the palate alone, since it has been found so in persons who 

 have completely lost the tongue from external force or disease. 



In animals that possess the organ of nostrils this is always the seat of 

 smell ; and in many quadrupeds, most birds, and perhaps most fishes, it is 

 a sense far more acute than in man, and that which is chiefly confided in. 

 For the most part it resides in the nerves distributed over a mucous mem- 

 brane that lines the interior of the bones of the nostrils, and which is called 

 the Schneiderian membrane, in honour of M. Schneider, a celebrated anato- 

 mist, who first accurately described it. Generally speaking, it will be found 

 that the acuteness of smell bears a proportion in all animals to the extent 

 of surface which this membrane displays; and hence, in the dog and cattle 

 tribes, as well as in several others, it possesses a vaikty of folds or convolu- 

 tions, and in birds is continued to the utmost points of the nostrils, which in 

 different kinds open in very different parts of the mandible. 



The frontal sinuses, which are lined with this delicate membrane, are 

 larger in the elephant than in any other quadruped, and in this animal the 

 sense is also continued through the flexible organ of its proboscis. In the 

 pig the smelling organ is likewise very extensive ; and in most of the mam- 

 mals possessing proper horns it ascends as high as the processes of the fron 

 tal bone from which the horns issue. 



It is not known that the cetaceous tribes possess any organ of smell ; their 

 blowing holes are generally regarded as such ; but the point has been by no 

 means fully established. We are in the same uncertainty with respect to 

 amphibials and worms ; the sense is suspected to exist in all the former, and 

 in several of the latter, especially in the cuttle-fish, but no distinct organ has 

 hitherto been traced out satisfactorily. 



In fishes there is no doubt; the olfactory nerves are very obviously distri- 

 buted on an olfactory membrane, and in several instances the snouts are 



