406 THE ORGANS OF SPECIAL SENSE 



This diaphragm-like action of the iris is produced 

 by the contraction and relaxation of the muscle fibers 

 contained therein sphincter pupillse and dilator pupillae 

 muscles. The contraction of the sphincter pupilhr is 

 reflex and is spoken of as the iris reflex. 



THE ANATOMY AND PHYSIOLOGY OF THE 



STRUCTURES CONCERNED IN THE 



SENSE OF TASTE 



The structures concerned in the sense of taste 

 include the tongue and its taste-buds, and the nerves 

 conveying the sensations to the taste centre situated 

 in the fourth temporal convolution of the temporal 

 lobe of the cerebrum, where the nerve impulses give 

 rise to the sensations of taste. The stimuli to create 

 these nerve impulses is matter, organic and inorganic, 

 in a state of solution, as brought about by the actions 

 of mastication and insalivation. 



The End-organs or Taste-buds. They are ovoid 

 bodies embedded in the epithelial cells covering the 

 mucous membrane of the tongue, soft palate, and 

 posterior surface of the epiglottis. Their broadest 

 portion or base rests on the basement membrane and 

 the apex reaches the surface of the epithelial cells, 

 when it opens by means of a narrow funnel-shaped 

 opening called the taste-pore. The wall of the taste- 

 buds consists of long, slender, epithelial cells, within 

 which are narrow spindle-shaped neuro-epithelial cells, 

 which give off hair-like processes which project into 

 the taste-pore; these neuro-epithelial cells connect 

 with the filaments of the glossopharyngeal and chorda 

 tympani nerves (gustatory nerves), and are considered 

 as the peripheral end-organs of the nerves of taste, 

 called taste-buds or taste-beakers. 



Sensations of Taste. It must be remembered the 



