THE VISCERAL AND GUSTATORY APPARATUS 243 



may also be true of the bladder. The free nerve-endings (see 

 Fig. 33, p. 90) known to be present in these mucous membranes, 

 particularly in the bladder, may, however, share in exciting these 

 sensations, for these membranes may well be sensitive to stretch- 

 ing, even though quite insensitive to simple pressure. The only 

 immediate cause of true visceral pain is tension, and it is stated 

 by Hertz that, so far as the alimentary canal is concerned, this 

 tension is exerted on the muscular coat, not on the mucous 

 lining. See the further discussion of visceral pain, p. 250. 



The vomiting reflex may be caused by excitations of sensory 

 termini of the vagus nerve in the stomach, which are transmitted 

 to the nucleus of the fasciculus solitarius in the medulla oblon- 

 gata, whence the nervous impulses are distributed as shown in 

 Fig. 1 13 to the appropriate motor centers. 



The Gustatory Apparatus. Taste, like smell, is a chemical 

 sense (see pp. 75, 91, 218). Physiologically, it is classed by 

 Sherrington as an interoceptive or visceral sense, and its primary 

 cerebral center is intimately joined to the general visceral 

 sensory center in the-nucleus of the fasciculus solitarius. Unlike 

 the general visceral sensory system, however, its peripheral 

 fibers have no connection with the sympathetic nervous system 

 and the reactions may be vividly conscious. The end-organs, 

 or taste-buds (Fig. 35, p. 91), are present in the mucous mem- 

 brane of the tongue, soft palate, and pharynx and are innervated 

 by the VII and IX cranial nerves; there are a few taste-buds also 

 on the larynx and epiglottis which are probably supplied by the 

 vagus (J. G. Wilson). All of these peripheral gustatory fibers, 

 upon entering the medulla oblongata, terminate in the nucleus 

 of the fasciculus solitarius (Figs. 71, 72, 73, 114) along with 

 those of general visceral sensibility, those of the gustatory sys- 

 tem probably ending farther forward (toward the mouth) in this 

 nucleus than those of the general visceral systems. 



There has been considerable controversy as to the exact course 

 taken by the peripheral nerves of taste on their way to the brain, 

 many clinical neurologists believing that all of these fibers enter 

 the medulla oblongata through the root of the V cranial nerve. 

 It has now been clearly shown by the studies of Gushing and 

 others that the V nerve takes no part in the innervation of 

 taste-buds. Figure 115 shows in continuous lines the true 



