CHAP. XIX.] OKGANS OF SPECIAL SENSE. 221 



cesses are exceedingly delicate, and seem to be specially con- 

 nected with the sense of touch, which on the tip of the tongue 

 is highly developed, and which serves to guide the tongue in its 

 variable and complicated movements. 



In the circumvallate, some of the fungiform papillae, and 

 scattered also over the mucous membrane of the tongue and 

 soft- palate, are little clusters of cells lying in cavities of the 

 epithelium, called taste-buds. The bases of these cell-clusters, 

 or taste-buds, are supplied with nerve-fibres, and it is surmised 

 that they are more specially connected with the sense of taste 

 than the other portions of the mucous membrane covering the 

 tongue. 



The special nerves of the sense of taste distributed to the 

 tongue are the glosso-pharyngeal, or ninth nerve, and the lin- 

 gual or gustatory, a branch of the fifth nerve. The former 

 supplies the back of the tongue, and section of it destroys taste 

 in that region ; the latter is distributed to the front of ' the 

 tongue, and section of it, similarly, deprives the tip of the 

 tongue of taste. 



We often confound taste with smell. Substances which have 

 a strong odor, such as onions, are smelled as we hold them in our 

 mouths ; and if our sense of smell is temporarily suspended, as 

 it sometimes is by a bad cold in the head, we may eat garlic 

 and onions and not taste them. Hence the philosophy of hold- 

 ing the nose when we wish to swallow a nauseous dose. 



The sense of smell. The nose is the special organ of the 

 sense of smell. It consists of two parts, the external feat- 

 ure, the nose, and the internal cavities, the nasal fossse. The 

 external nose is composed of a triangular framework of bone 

 and cartilage, covered by skin and lined by mucous membrane. 

 On its under surface are two oval-shaped openings the nos- 

 trils separated by a partition. The margins of the nostrils 

 are provided with a number of stiff hairs which arrest the pas- 

 sage of dust and other foreign substances carried in with the 

 inspired air. 



The nasal fossae are two irregularly wedge-shaped cavities, 

 separated from one another by a partition or septum, and com- 

 municating with the air in front by the anterior nares or nostrils, 

 while behind they open into the back of the pharynx by the 

 two posterior nares. Fourteen bones enter into the formation 



