SENSE OF TASTE. 893 



auditory nerve, must be conducted to the brain to be recognized as 

 sounds, and that the analysis of sounds take place not in the ear, 

 although, perhaps, we may have there a special organ set aside for the 

 observation of certain sounds, but in the brain. 



D. THE SENSE OF TASTE. 



The sense of taste is generally described as the facultj^ by which 

 the flavors of different sapid substances is distinguished. It will be 

 shown direct^ that the sense of taste is much more limited than this, as 

 many substances which are said to be appreciated through the sense of 

 taste are only effective through exciting the sense of smell. The sense 

 of taste even in this restricted sense is more highly developed in man 

 than in other animals, for it is not the sense of taste but the sense of 

 smell which guides animals in their choice of food, for that choice 

 precedes the prehension of food. 



Even in man and the higher mammals there is a considerable 

 difference of opinion as to what regions of the mouth are endowed with 

 the sense of taste, and this difficulty of location becomes even more 

 marked as we descend the animal series. In animals where a tongue is 

 present it is probable that that organ partakes, with the upper part of 

 the digestive tract, in the property of presiding over the sensation of 

 taste, but in many animals the tongue is absent or is so horny as to pre- 

 clude this possibility. In invertebrates, where no analogue of a tongue 

 exists, if the sense of taste is present, as it would seem without doubt 

 to be, as in insects, its seat must be in the parts about the mouth, such 

 as the proboscis, suckers, etc. In fishes the tongue is rudimentary and 

 in many it is covered with horny scales or even rudimentary teeth, and if 

 the sense of taste is present in this group of animals it is either 

 confined to the upper part of the digestive passages or perhaps to the 

 olfactory cavities. 



In reptiles a thick, fleshy tongue is often present, but it is more fre- 

 quently slender, sometimes bifid and protractile, and is to be regarded, 

 as already indicated, as an organ for the prehension of food. 



In birds the sense of taste must be very obtuse, since they swallow 

 their food without comminution, and the tongue is usually hard or semi- 

 cartilaginous, especially at the point. This particularly obtains in her- 

 bivorous birds, while in birds of prey, where the tongue is fleshy, it may 

 perhaps be supposed that the sense of taste is present. 



In mammals the sense of taste may, to a certain extent, be definitely 

 localized in the tongue, and special sense organs have been detected 

 which apparently preside over this function. The so-called taste bulbs 

 are found on the lateral surface of the circumvallate papillae and upon 

 the external side of the depression which surrounds the central eminence 



