CHAPTER X 



THE SPECIAL SENSES 



We have already seen that the recognition of pain, 

 pressure, heat, and cold and muscular sensibility are 

 conducted by nerve paths as much specialized for their 

 purposes as is the nerve of vision; but long habit has 

 applied the term special senses to the organs of taste, 

 smell, vision, and hearing. 



TASTE AND SMELL 



These special senses are so intimately associated that 

 it is difficult to make a clear distinction between them, 

 except that the four qualities, sweet, salt, sour and bit- 

 ter or combinations of the four are appreciated without 

 assistance from the olfactory sense. Except these four, 

 all our so-called taste sensations, are really olfactory 

 sensations, the nerves of smell being stimulated by the 

 substance eaten either before it is placed in the mouth 

 or after it has been swallowed, the odoriferous particles, 

 in the latter case, entering the back of the nose in the 

 current of expired air which follows the act of swal- 

 lowing. 



The nerves which carry sensations of taste to the 

 brain are the glossopharyngeal for the posterior one- 

 third of the tongue, fauces and palate, and the lingual, 

 or gustatory, branch of the fifth for the anterior two- 

 thirds of the tongue. The taste fibers- in the gustatory, 

 however, are derived from the clwrda tympani of the 

 seventh. The lingual really carries fibers of cutaneous 



