CHAP, v.] TASTE AND SMELL. 265 



. development of taste sensations, including bitter sensations, at the 

 tip of the tongue, from which taste-buds are said to be absent, 

 presents a difficulty. Unless we suppose that taste-buds, though 

 often absent from the tip of the tongue are present in those cases 

 in which sensations are developed, we must conclude that gus- 

 tatory sensations may originate by the help of some kind of nerve 

 ending other than that of taste-buds. It might be suggested that 

 bitter and sweet tastes are developed by means of taste-buds and 

 acid and salt tastes by means of other endings ; but there is no 

 satisfactory evidence of this. 



868. The question which nerve or nerves subserve taste and 

 what is the course of the gustatory fibres is one which presents 

 great difficulties. The front surface of the tongue is supplied by 

 the lingual or gustatory branch of the fifth nerve, the hind surface 

 by the glossopharyngeal nerve, which nerve also supplies the soft 

 palate, though a branch (palatine) of the fifth nerve goes there 

 also. The nerves traced to the taste-buds in the papillae foliatae 

 and circumvallatae belong to the glossopharyngeal nerve, and it 

 can hardly be doubted that gustatory fibres run in the branches of 

 that nerve which go to the back of the tongue. On the -other hand 

 in the cases in which sensations are distinctly developed in the 

 tip of the tongue we must infer that gustatory fibres run in the 

 lingual branch of the fifth, since no glossopharyngeal fibres are 

 distributed to this part of the tongue. 



But it by no means follows from this that gustatory fibres 

 pass straight both up the trunk of the glossopharyngeal nerve, 

 and up the trunk of the fifth nerve to their respective nuclei in 

 the bulb. 



On the one hand there is a good deal of evidence to shew a 

 connection between sensations of taste and the chorda tympani 

 nerve. Cases have occurred in which disease of the ear, involving 

 destruction of the chorda tympani within, the tympanum, has been 

 followed by loss of taste in the tongue on the same side ; and 

 stimulation of the chorda tympani within the tympanum has been 

 known to give rise to sensations of taste. Neither of these results 

 is conclusive. The chorda tympani contains afferent fibres which 

 have a remarkable effect on the nutritive processes of the tongue, 

 and the loss of taste due to destruction of the chorda might be due 

 to disordered nutrition of the tongue, and so be analogous to the 

 loss of smell which may follow injury of the fifth nerve. Again, 

 where stimulation of the chorda within the tympanum produces 

 sensations of taste these may be due to efferent impulses pro- 

 ducing changes in the tongue, which in turn give rise to sensations 

 of taste reaching the brain by other channels than the chorda 

 itself ; we have no satisfactory evidence that direct stimulation of 

 the central stump of a divided chorda will give rise to sensations 

 of taste. The connection between the chorda and taste, however, 

 may be of a more real kind. 



