DEVELOPMENT OF PERIPHERAL NERVOUS SYSTEM 833 



whose cell bodies lie in nodose ganglion with peripheral terminations in taste 

 buds of pharyngeal area, (2) general visceral afferent fibers whose cell bodies 

 lie in nodose ganglion, with peripheral distribution to pharynx, esophagus, 

 trachea, thoracic and abdominal viscera, (3) general somatic afferent fibers 

 with cell bodies in jugular ganglion and peripheral distribution to external 

 ear region, (4) special visceral efferent fibers to striated musculature of 

 pharyngeal area; cell bodies lie in nucleus ambiguus, (5) general visceral 

 efferent fibers. Preganglionic cell bodies in dorsal motor nucleus; terminate 

 in sympathetic ganglia associated with thoracic and abdominal viscera, (6) in 

 fishes: a prominent lateral line component is present which is distributed 

 along the lateral body wall. 



The special visceral motor fibers of the vagus are associated with muscula- 

 ture arising from the caudal visceral arches. 



XI. Spinal Accessory 



The spinal accessory nerve arises in close association with the vagus. It is 

 composed mainly of motor fibers and distributed to musculature derived from 

 premuscle masses in the caudal branchial area (fig. 356A). They may be 

 regarded as special visceral motor fibers. 



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

 whose cell bodies lie in nucleus ambiguus and in anterior part of spinal cord 

 and distributed to trapezius, and sternocleidomastoid, muscles and striated 

 muscles of pharynx and larynx, (2) general visceral efferent fibers associated 

 with vagus nerve, with cell bodies in dorsal motor nucleus of vagus. 



XII. Hypoglossal Nerve 



The twelfth cranial nerve is a somatic motor nerve composed mainly of 

 efferent fibers distributed to the hypobranchial or tongue region. These fibers 

 arise from neuroblasts in an extensive nuclear region from the anterior cervical 

 area along the floor of the myelencephalon near the midventral line (fig. 

 356A). In lower vertebrates these fibers innervate certain of the anterior 

 trunk myotomes whose muscle fibers travel ventrad into the hypobranchial 

 area. In higher vertebrates the hypoglossal nerve fibers innervate the tongue 

 and associated muscles. 



Fig. 357 — Continued 



views, respectively, of the adult form of the brain in the frog, Rana cateshiana. Like the 

 developing brain in Sqiialus, the brain of the developing frog loses its pronounced cephalic 

 flexure as development proceeds. (L and M) Ventral and dorsal views, respectively, of 

 the adult form of brain in the chick shortly before hatching. The cervical, pontine, and 

 cephalic flexures are partly retained in developing brain of chick, and in this respect it 

 resembles the developing mammalian brain. Compare these diagrams with Figs. 354E. 

 259. (N and O) Ventral and dorsal views, respectively, of the adult brain of the dog. 

 (Redrawn from models.) 



