The Afferent and Efferent Neurons 



63 



stimulus on to the dendritic branches in contact with them. The auditory 

 hair cells are arranged in a single or double row on the ' inner ' side of the 

 organ of Corti ; and a triple or quadruple row on the ' outer ' side. There 

 are possibly from 20,000 to 25,000 of these hair cells in an ear in the 

 human being. In the vestibule and semicircular canals of the ear are 

 small hair cells, not serially arranged, in contact with which are the 

 branches of nerve fibers from the vestibular branch of the cochlear nerve. 



A somewhat similar form of end cell is in contact with the terminations 

 of the gustatory nerve fibres in the tongue (fibers of the 9th or glosso- 

 pharyngeal nerve and of the lingual branch of the 5th or trigeminal 

 nerve). This is the gustatory cell, found in the taste bud [Fig. 49]. 

 Taste buds are irregular ellipsoid or conical bodies 70-80 /j. in diameter, 

 lying in the epithelium of the mucous membrane, most numerously in the 



Fig. 48. Vertical cross-section of a 

 papilla circumvallata, showing taste- 

 buds in the side. Magnified probably 

 IOO diameters. (Merkel-Henle, Ana- 

 tomic.) 



Fig. 49. Taste-bud, schematic. Mag- 

 nified probably 500 diameters. (Mer- 

 kel-Henle, Anatomic) 



sides of the annular groove in the circumvallate papillae [Fig. 48] (prob- 

 ably 100 to 150 for a single papilla). They are found in smaller numbers 

 in the ' foliate papillae ', and on the edges and tip of the tongue. Some- 

 times buds are found in the ' fungiform papillae ', the soft palate, the 

 posterior surface of the epiglottis, and occasionally in the lining of the 

 cheek. 



Taste buds are composed of two kinds of cells : gustatory and sup- 

 porting cells. The supporting cells form the enclosing walls of the bud, 

 and are also found inside it between the gustatory cells. These latter are 

 in general elongated and spindle-shaped, although found in various wedge 

 and other shapes. At the outer edge of the bud is a small opening; the 



