CRANIAL NERVES 1 89 



unites with the mandibular branch of the fifth nerve and then its 

 fibres enter the lingual branch of the fifth and go to the taste organs 

 of the tip of the tongue. The rest of the facial is largely motor, its 

 fibres controlling the muscles of the neck and those which open the 

 mouth. In the mammals, with a greater development of the facial 

 musculature (p. 139), the facial gains a greater distribution in the 

 facial region, extending to almost all parts of the face. 



The lateraUs element of the seventh has its own ganglion, beyond 

 which the nerve divides into three branches. Of these the super- 

 ficial ophthalmic of VII usually unites with the similarly named nerve 

 of the fifth and supplies the lateral line organs and related structures 

 of the top of the head, dorsal to the eyes. The second branch, the 

 buccal nerve, supplies the organs below the eye and along the line of 

 the upper jaw. The last, the external mandibular nerve, is con- 

 nected with the lateral-line organs of the operculum (where present) 

 and the lower jaw. The buccalis usually is closely associated with 

 the maxillary nerve and the external mandibular is similarly related 

 to the mandibular ramus of the fifth. 



In the higher vertebrates, where the lateral-line organs never 

 appear, the corresponding nerves are not even outHned in the em- 

 bryo, and in the anura and the salamandrine amphibia, where both 

 organs and nerves are present in the larva, they are lost at the time of 

 metamorphosis. 



VIII. The auditory nerve (N. acusticus) is always closely related 

 to the facial, their ganglia being fused, although the roots are distinct. 

 This nerve is wholly sensory, its two branches (the cochlear and the 

 vestibular nerves) being distributed to the sensory structures of the 

 inner ear. Both the central relations of the nerve and the pecuUari- 

 ties of the ear proclaim that the acustic nerve belongs with those of 

 the lateral line. In the higher vertebrates this is all that is left of 

 that system. 



IX. The glossopharyngeal nerve (figs. 190, 193) is the first of the 

 postotic nerves and is more like a spinal nerve than those in front of 

 the ear. It arises from the medulla oblongata close to the tenth 

 nerve and in the amphibia its roots and its gangUon (the petrosal) 

 fuse with those of the vagus. In the branchiate vertebrates the 

 nerve goes to the first gill cleft, dividing above it into pre- and post- 

 trematic rami, the pretrematic going to the region of the hyoid arch, 

 the oral cavity and in teleosts to the pseudobranch. The posttrematic 

 branch is larger, supplying the muscles of the first cleft and sending a 



