830 THE NERVOUS SYSTEM 



general visceral sensory fibers providing deep sensibility to the general area 

 of distribution of the facial nerve. The special visceral afferent fibers to the 

 taste bud system are prominent elements in the seventh cranial nerve of many 

 fishes (fig. 356C). In fishes also, the seventh cranial nerve contains lateral- 

 line components distributed to the lateral-line organs of the head (fig. 356D). 



The special motor fibers of the facial nerve arise from neuroblasts located 

 in the pons as indicated in figure 356A, and the general visceral motor fibers 

 take origin from cell bodies in the nucleus salvatorius superior. 



Summary of components: ( 1 ) Special visceral efferent (motor) fibers to 

 musculature arising in area of hyoid arch, (2) in mammals, preganglionic 

 general visceral efferent fibers by way of chorda tympani nerve to submaxil- 

 lary ganglion; and from thence, postganglionic fibers to submaxillary and 

 sublingual salivary glands. (3) Special visceral afferent fibers to taste buds 

 on anterior portion of tongue by way of chorda tympani nerve; in fishes, spe- 

 cial visceral afferent fibers are extensive. (4) General visceral afferent fibers. 

 (5) In fishes, lateral-line components to head region are present. 



VIII. Acoustic 

 The acoustic nerve contains special somatic sensory components which 

 receive sensations from the special sense organs derived from the otic vesicle. 



The otic vesicle differentiates into two major structures, viz.: (1) one related 

 to balance or equilibration, and (2) the other concerned with hearing or the 

 detection of wave motions aroused in the external medium. This differentia- 

 tion is obscure in fishes. However, in those vertebrates which dwell in water 

 other hearing devices may be used aside from those which may involve the 

 developing ear vesicle. One aspect of the mechanism which enables water- 

 dwelling vertebrates to detect pressure or wave motions of low frequency in 

 the surrounding watery medium is the lateral line system associated with the 

 fifth, seventh, ninth and tenth cranial nerves. 



In accordance with the differentiation of the otic vesicle into two sense- 

 perceiving organs, the sensory neurons of the acoustic ganglion of the eighth 

 cranial nerve become segregated into two ganglia, namely, ( 1 ) the vestibular 

 ganglion containing bipolar neurons which transmit proprioceptive stimuli 

 through the vestibular nerve from the organ of equilibration composed of 

 the utricle, saccule and semicircular canals, and (2) the spiral ganglion con- 

 taining bipolar neurons which transmit somatic sensations from the spiral 

 or hearing organ (fig. 361H). 



Summary of functional components: (1) Special somatic afferent fibers 

 of proprioceptive variety associated with equilibration, (2) special somatic 

 afferent fibers of exteroceptive variety, associated with hearing. 



IX. Glossopharyngeal 

 The glossopharyngeal nerve is associated with the third visceral arch and 

 nearby areas of the pharynx. It has two major components; one of these 



