THE NERVOUS SYSTEM 451 



inal branch of the Trigeminus gains in importance and the 

 two become secondarily associated. 



With the reduction in bulk of the hyo-branchial musculature 

 the motor element of the hyo-mandibular, the only portion 

 now remaining, tends to decrease in size, but this is more than 

 compensated for in mammals by the development of the mi- 

 metic muscles. These have been shown to originate from the 

 integumental muscular layer of the neck region, innerved by 

 the branch under consideration, and, as this layer spreads up 

 over the neck and differentiates into specialized slips, the in- 

 nervation increases also and spreads eventually over the entire 

 face, thus gaining its right to the name " Facialis," a right 

 which, curiously enough, it possessed originally, in connection 

 with the lateral line organs, but which it afterward lost until 

 it regained through its motor elements what it had lost in 

 its sensory. The branch to the stapedius muscle of the middle .< 

 ear, N. stapedialis, proceeds also from the hyo-mandibular, 

 and comes originally from the branch supplying the digastric 

 muscle. 



The Trigeminus of the second, or terrestrial, type, suffers 

 no reduction through the loss of the lateral line organs, since 

 it has nothing directly to do with them, but the four original 

 branches become reduced to three through the loss of the deep 

 ophthalmic element, which seems, in part at least, to fuse with 

 the superficial branch of the same nerve to form the " first 

 branch " of human anatomy, the ophthalmicus. The maxil- 

 laris and mandibularis show but little change and form the 

 second and third branches, respectively, thus giving the reason 

 for the name "Trigeminus" first applied in Man. 



The great increase in the size of the lingual branch of the 

 mandibularis has already been noticed ; otherwise the most im- 

 portant innovation is found in the new relations of the Tri- 

 geminus with the Facialis, the Glosso-pharyngeus, and the 

 sympathetic ganglia. The first of these has already been 

 treated in detail. The Glosso-pharyngeus sends a communi- 

 cating branch (tympanic [Jacobson's~\ nerve) to the otic gan- 

 glion, which rests upon the base of ramus mandibularis; the 



