360 THE PERIPHERAL NERVOUS SYSTEM 



supply the premuscle masses which later form the muscles of mastication. From 

 the chief motor nucleus a line of cells extending cranially into the mesencephalon 

 constitutes a second source of origin for motor fibers. In the adult, the motor 

 fibers form a part of the mandibular division of the nerve. 



The facial, glossopharyngeal and vagus nerves are essentially visceral in func- 

 tion. Their sensory fibers, chiefly of the visceral type, supply the sense organs 

 of the visceral arches and viscera. These fibers originate in the ganglia of their 

 respective nerves and, entering the alar plate of the myelencephalon, course 

 caudally as the solitary tract (Fig. 345). A few somatic sensory fibers having 



us root gang, (jugular). 



Accessory root gang. 



Gang. 

 Froriep. 



Gang, nodos 

 N. laryng. sup. 



Inter- gang, 

 bridge. 



FIG. 344. Reconstruction of the cerebrospinal nerves of an embryo of 10.2 mm. (Streeter). X 16.7. 



the same origin and course in the myelencephalon supply the adjacent integu- 

 ment. 



7. The Facial Nerve is largely composed of efferent motor fibers which supply 

 the facial muscles of expression (Fig. 341). In 10 mm. embryos these fibers arise 

 from a cluster of neuroblasts in the basal plate of the myelencephalon located 

 beneath the third rhombic groove or neuromere (Fig. 345). The fibers from these 

 cells course laterally, and emerge just mesial to the acoustic ganglion. The motor 

 trunk then courses caudally and is lost in the tissue of the hyoid visceral arch, 

 tissue which later gives rise to the muscles of expression. The sensory fibers of 



