172 COMPARATIVE MORPHOLOGY OF VERTEBRATES. 



to the fifth being a compound nerve, this branch being the remnant of a somite 

 otherwise lost. Others would view the ophthalmic as the representative of the 

 dorsal ramus of a spinal nerve. 



VII. The Facial Nerve, the hindmost of the preotic nerves, differs 

 greatly in the branchiate and the pulmonate vertebrates. In all there 

 is a close association with the eighth nerve, and in the anura, some 

 teleosts and ganoids, and in the holocephals the fifth and the seventh 

 are so closely related that their ganglia are fused. 



FIG. 171. Dagram of seventh (facial) nerve; for components see fig. 170. b, buc- 

 calis nerve; ct, chorda tympani; gg, geniculate ganglion; h, hyoid nerve; hm, hyomandib- 

 ular nerve; Ig, lateralis ganglion; mxe, maxillaris externus nerve; os, ophthalmicus 

 superficialis nerve; pal, palatine nerve; sp, spiracle. 



In the aquatic ichthyopsida the several roots by which the seventh 

 nerve leaves the medulla unite in a compound ganglion, the upper 

 element being the ganglion of the lateralis component, the lower the 

 geniculate, the true ganglion of the seventh nerve. Beyond the 

 ganglion the nerve divides into five trunks, as follows: 



A. The ophthalmicus superficialis, which runs forward near 

 the dorsal surface of the head; B. the buccalis, which courses nearly 

 parallel to the maxillaris of the trigeminal and is often bound up with it; 

 C. the mandibularis externus, which usually divides into two branches, 

 usually follows much the same course as the mandibularis trigemini, 

 and supplies the lower jaw and the spiracular and hyoid region; D. 

 the palatinus which goes to the mucous membrane of the oral cavity, 

 E. the hyoideus (usually united with the mandibularis for some distance 

 as a hyomandibular nerve), which goes ventrally and supplies the 

 mucosa of the mouth and the muscles of the hyoid region. In cases, 

 like many elasmobranchs, where a spiracle is present, the hyomandib- 



