THE VISCERAL EFFERENT DIVISION. 



201 



to the gill arches and slits. The motor fibers of the trigeminus 

 supply the muscles which move the mandibular arch, i.e. the 

 chief muscles of mastication. In all gnathostome vertebrates 

 the muscles of mastication are supplied in this way; with the 

 exception of the posterior belly of the digastric, which is supplied 

 by the corresponding component in the VII nerve. In higher 

 vertebrates the motor component of the facial nerve also controls 

 highly specialized muscles which move the skin of the face, of the 



N.hom.Cl. so i t NXdors. 



IXXXI 



N.amb. 



XII"' 



FIG. 107. Diagram to show the central relations of the IX, X and XI nerves in 

 mammals. From Onuf and Collins. N.X.dors., dorsal vagus or vago-glos- 

 sopharyngeal nucleus, nucleus for the visceral or vegetative (sympathetic) efferent 

 fibers; N.amb., nucleus ambiguus, nucleus for the striped muscle innervated by 

 the IX, X and XI nerves; sol., fasciculus solitarius; N.homol.CL, nucleus homolo- 

 gous with Clarke's column; N.XTI, nucleus of hypoglossus; spin.V.R., spinal V 

 tract. 



scalp and ears, the muscles of expression. This mode of inner- 

 vation indicates that these muscles are derivatives of the branchial 

 muscles of the hyoid segment which have spread forward to their 

 present position, whither the motor branches of the facial nerve 

 have followed them. This- is one example of the way in which 



