404 ORGANS OF THE SENSES. 



bitter substances, for when their innervation lias been de- 

 stroyed, the animal will swallow bitter substances without any 

 apparent repugnance. The sensations of nausea, which give 



Fig. 104. Tongue, with its papillse and nerves. (L. Hirschfeld and Leveille).* 



rise to the antiperistaltic movement of deglutition, of vomit- 

 ing, also take place chiefly in this part ; but these are phe- 

 nomena of ordinary sensibility, for if the finger be placed at 

 the back of the mouth, this reflex action will be produced, and 

 still better if the uvula be touched instead of the base of the 

 tongue. 



Snpid bodies must be dissolved in order to be tasted : the 

 secretion of the saliva is, therefore, necessary to gustation, 

 and if the mouth be dry, the substance received will make 

 little impression. The impressions made by sapid substances 

 are, therefore, peculiarly fitted to produce the reflex phenom- 

 enon of the salivary secretion, especially the sub-maxillary 

 secretion, as we know that the sight or remembrance of a 

 favorite dish will sometimes make the mouth water ; thus, 

 if a piece of meat be shown to a dog, the saliva is seen to 

 flow freely from a tube inserted in the duct of the sub-rnaxil- 



* 1, Hypoglossal nerve. 2, Lingual branch of the tri-geniinus. 3. Lingual 

 branch of* the glosso-pharyngeal nerve. 4, Chorda tympani. 8, Sub-maxil- 

 lary ganglion. 11, Anastomoses of the lingual with the hypoglossal nerve. 12, 

 Facial nerve. 13, Mucous membrane detached and thrown upwards : the circum- 

 vallate papilla; are seen behind. 



