DEVELOPMENT OF PERIPHERAL NERVOUS SYSTEM 831 



components is motor, innervating the musculature derived from the embryonic 

 third visceral arch, while the other component is sensory. The sensory com- 

 ponents are derived from neuron bodies within the superior and petrosal 

 ganglia (fig. 356B). Aside from receiving general sense impulses from the 

 pharyngeal area, many of these sensory components are associated with the 

 taste buds on the caudal portion of the tongue. The latter components thus 

 are special sensory components. 



The visceral motor (efferent) components to the musculature derived from 

 the third visceral arch arise from neuroblasts located in the ventro-lateral 

 floor of the anterior part of the myelencephalon (fig. 356A). The sensory 

 components take origin from neural crest cells located in the region of the 

 third visceral arch. Fibers from these neuroblasts grow mediad into the nerve 

 tube, and latero-ventrad toward the third visceral arch region. 



Summary of functional components: (1) General visceral afferent fibers 

 with cell bodies in petrosal ganglion whose peripheral fibers terminate in the 

 posterior tongue region and in the pharyngeal area, (2) special visceral afferent 

 fibers with cell bodies in petrosal ganglion whose peripheral fibers contact 

 the taste buds in the posterior third of the tongue, (3) special visceral efferent 

 fibers to musculature derived from the third visceral arch. In mammals, this 

 musculature is the stylopharyngeus muscle, (4) in mammals: general visceral 

 efferent fibers, composed of preganglionic fibers from neurons in inferior 

 salivatory nucleus located probably in the region between the pons and medulla 

 pass to the otic ganglion. Postganglionic fibers from otic ganglion innervate 

 the parotid gland. (5) In fishes: lateral-line components are present and dis- 

 tributed to posterior head region. In mammals, some general somatic afferent 

 fibers from cell bodies in the superior ganglion appear to innervate cutaneous 

 areas in the ear region. 



X. Vagus 



The tenth cranial or vagus nerve is composed of several functional com- 

 ponents. It is a prominent nerve associated with the autonomic nervous system 

 as indicated below. In addition to these autonomic components, the functional 

 components of the tenth cranial nerve are related to the visceral arches caudal 

 to the third visceral arch. The tenth cranial nerve thus supplies several vis- 

 ceral arches. In consequence, it must be regarded as a composite nerve, 

 arising from extensive motor nuclei, the dorsal motor nucleus and the 

 nucleus ambiguus in the ventro-lateral area of the myelencephalon (fig. 356A). 

 The tenth nerve has two main ganglia, the jugular and nodose ganglia. The 

 motor fibers arise from neuroblasts in the nuclei mentioned above and grow 

 out laterally to the visceral arch area, and the sensory components take 

 origin from neuroblasts of neural crest origin which become aggregated in 

 the jugular and nodose ganglia. 



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



