132 VETERINARY PHYSIOLOGY 



A. Receptors. — The most important receptors consist of 

 groups of spindle-shaped cells with which the dendritic ter- 

 minations of the nerves from the mouth are connected. 

 Each group of cells is surrounded by a series of flat epithelial 

 cells like the staves of a barrel to form a taste bulb. These 

 taste bulbs are most abundant on the sides of the large 

 circumvallate papillse which form the prominent V-shaped 

 line on the posterior part of the dorsum of the 

 tongue. 



B. Connection with the Central Nervous System. — The 

 posterior third of the tongue is supplied by the glosso- 

 pharyngeal nerve. The anterior two-thirds are supplied by 

 the lingual of the fifth and the chorda tympani of the 

 seventh. It has been maintained that all the taste 

 fibres enter the medulla by way of the Gasserian ganglion 

 and the root of the fifth nerve ; but the study of cases in man 

 in which the ganglion has been removed does not support this 

 view, and the evidence seems to indicate that the fibres 

 enter the medulla bv the roots of the nerve in which they 

 run. 



The first synapses are in the medulla and pons, and from 

 this the lemniscus quinti — the fillet of the V. — passes up, 

 crosses, and forms synapses in a special nucleus of the 

 thalamus (fig. 50), from which fibres must pass to the 

 cortex, but to what part is not clearly determined. 



The close association of taste and smell, and the results 

 of Ferrier's experiments (p. 136), make it possible that the 

 cortical representation is in the hippocampal region. On 

 this point evidence is by no means conclusive. 



C. Physiology. — As to the way in which this mechanism 

 is stinmlated our knowledge is very imperfect. In order to 

 act, the substance must be in solution. The strength of the 

 sensation depends (i.) on the concentration of the solution, 

 (ii.) upon the extent of the surface of the tongue acted upon, 

 (iii.) upon the duration of the action, (iv.) and upon the 

 temperature of the solution. If the temperature is very 

 high or very low, the taste sensation is impaired by the 

 sensations of heat or cold. 



It is most difficult to classify the many various taste 



