1Q6 ZOOLOGY. 



forms lenticular, iungii'onii. and conical. The tongue itst-lt' 

 is niiiMMilar, and receives branches of motor and sentient 

 nerves. A branch of the fifth pair is the gustatory; it is 

 sometimes called lingual. 



215. If this nerve be cut in the living animal, the sense 

 of taste is destroyed, but the movements of the tongue 

 remain ; if divided within the cranium, the sense of taste is 

 destroyed all over the interior of the mouth. 



The section of the hypoglossal nerves destroys the motion 

 of the tongue and of all other parts to which these nerves pro- 

 ceed. The sense of taste remains unaffected. The glosso- 

 pharyngeal, distributed chiefly to the pharynx, and which are 

 sensitive nerves, have also some gustatory powers. 



216. The tongue has nearly the same structure in all 

 animals ; but in birds it is generally cartilaginous, and without 

 nervous papillae; accordingly, their sense of taste is con- 

 sidered as obscure. It is much the same in fishes ; and in 

 the lower animals, the faculty seems to be exercised by all 

 the interior of the mouth. 



OF THE SENSE OF SMELL. 



217. Odours are produced by particles of extreme 

 tenuity, which escape from odorous bodies, and spread 

 through the air like vapours. The quantity requisite of 

 some of these odorous matters powerfully to affect the smell, 

 is extremely small ; a morsel of musk, for example, will per- 

 fume the air of a room for a considerable time without losing 

 its weight. Some bodies imbibe vapours and become odorous 

 in their turn, such as clothes and water ; but others resist 

 their passage altogether, such as glass. Odours may be per- 

 ceived at a great distance, but the odorous particles must 

 always come in contact with the organs. For this, the me- 

 chanism of smell is analogous to that' of taste and touch, 

 whilst in sight and hearing it is quite other 



218. As the air is the ordinary vehicle of odours, the 

 organ perceiving them is placed at the entrance of the respi- 

 ratory tubes. In man, as well as in mammals, birds, and 

 reptiles, the nasal fossa} are the seat of the sense of smell. 



219. These fossae communicate with the exterior by the 

 nostrils, and open behind into the pharynx. They are separated 

 from each other by a vertical partition; their walls are 

 formed by various bones of the face, and by the cartilages of 



