network of fibers to enter the taste bud. Here they 

 branch a number of times to entwine about and 

 make contact with the surface of both the taste and 

 supporting cells. Two to three nerve fibers may enter 

 each bud and each fiber may connect with one or 

 more sense cells. Extrageminal nerve fibers with fine 

 terminations also arise from the same network of 

 fibers to innervate the surrounding epithelium (124). 



NEURO.^NATOMY 



The lingual nerve to the anterior two thirds of the 

 tongue subserves touch, temperature, pain and taste. 

 The taste aflferent fibers leave this nerve in a small 

 strand, the chorda tympani nerve, which passes 

 through the middle ear cavity close to the tympanum 

 to enter the brain stem as part of the seventh cranial 

 nerve. In some instances an alternative pathway via 

 the greater superficial petrosal nerve seems indicated 

 (63, 145, 188). The chorda tympani nerve also con- 

 tains the efTerent fibers for salivation, and tempera- 

 ture and tactile sensory fibers. The taste fibers are 

 moderately small myelinated fibers less than 4 /i in 

 diameter (70, 205). In the chorda tympani nerve of 

 the cat, 18 per cent of the afferent fibers are unmye- 

 linated (less than 1.5 /i) and the remaining are 

 myelinated, ranging from 1.5 to 6.0 // in diameter 

 (77). Taste fibers from the posterior tongue travel in 

 the glossopharyngeal and those from the larynx and 

 pharynx in the vagus (see fig. 3). 



The gustatory fibers of the seventh, ninth and 

 tenth nerves run into the tractus solitarius together 

 with its nucleus in the medulla. This tract extends 

 from the posterior two thirds of the fourth ventricle 

 caudally to the closed part of the medulla where it 

 lies dorsal to the central canal, but the fibers of the 

 seventh and ninth nerves terminate in the rostral 

 portion of the nucleus (172). Insulated wire elec- 

 trodes inserted into the medulla at this locus yield 

 potentials when chemical stimuli are applied to the 

 anterior tongue region (95). A response to the tactile 

 stimulation occurs when the solution flow Ijegins, 

 but the response is brief compared with the con- 

 tinued discharge to taste solutions. Responses from 

 the anterior tongue tactile stimulation and anterior 

 tongue taste stimulation can be recorded from the 

 same electrode loci using a 40 /z insulated wire elec- 

 trode. Taste and the somatosensory pathways are 

 closely related at this level. 



Lesions in the anterior nucleus solitarius produce 

 degeneration in fibers of the opposite ascending 



Greater superficial 

 petrosal n. 



VII n. 



Otic ganglion 



Petrous ganglion 



Chorda tympani n. 



THE SENSE OF TASTE 509 



.Gasserian ganglion 



V2 



Sphenopalatine 

 ganglion 



•Tongue 



FIG. 3. The nerve supply to the tongue. The solid tines indi- 

 cate the most common pathways for the taste impulses. The 

 broken tine indicates an alternative path from the chorda tym- 

 pani believed to exist in a limited number of cases. [Modified 

 from Gushing, 1903 and Schwartz & Weddell, 1938; from 

 Pfaflrmann(i6i).] 



medial lemniscus close to the fibers of the ventral 

 trigeminothalamic pathways (7, 81). Lesions in the 

 region of the medial lemniscus produced by a stereo- 

 taxic instrument were associated with elevated thresh- 

 olds in a two-bottle preference test with quinine 

 solutions (155). 



Patton & Ruch following BSrnstein (30) have 

 emphasized that the central pathways for taste are 

 closely associated with the somatosensory systems for 

 the face which at the level of the thalamus synapse 

 medially in the arcuate nucleus (182). Degenerating 

 fibers following lesions in the region of the nucleus 

 .solitarius were found in the arcuate nucleus (81), and 

 retrograde degeneration was noted in the medial 

 part after ablation of the cortical taste area (82). 

 Destruction of a large portion of the arcuate nucleus 

 in the monkey was followed by an elevation in the 

 quinine preference threshold (157). Unilateral im- 

 pairment of gustatory and cutaneous sensitivity has 

 been reported following unilateral tumor of the 

 medial part of the arcuate nucleus opposite to the 

 sensory disturbance (3). The failure to find tactile 

 representation in the ventromedial nucleus in spite 

 of the fact that it adjoins the tactile representation of 

 the inner mouth and tongue of the medial part of 

 the ventrobasal complex led to the suggestion that 

 taste as well as interoceptive fibers may terminate in 

 the ventromedial complex (146, 182). Monkeys with 

 ageusia resulting from cortical ablation showed lesions 

 in the \'entromedial complex (13). Taste-sparing 

 cortical lesions of the inferior Rolandic cortex are 



