58 THE ANATOMY OF YERTEBRATED ANIMALS. 



muscles, and ultimately divides into two branches, one of 

 which is in relation with the mandibular, and the other with 

 the hyoidean arch. 



The five nerves which have just been mentioned are often 

 intimately connected together. Thus, in the Lepidosiren^ the 

 three motor nerves of the eyeball are completely fused with 

 the ophthalmic division of the fifth.* In the j\fyxinoid fishes 

 there are no motor nerves of the eyeball ; but, in the Lampre}', 

 the rectus externus and inferior^ and the ohllquus inferior^ are 

 supplied by the ophthalmic, while the oculomotor and the pa- 

 thetic unite into a common trunk, which gives branches to the 

 rectus superior and internus^ and ohllquus superior. The ocu- 

 lomotor, the pathetic, and the abducens, are more or less con- 

 founded with the ophthalmic in the Amphibia ; but in Tele- 

 ostei^ Ganoidei^ Elasraobranchii^ and in all the higher Verte- 

 brata^ the nerves of the muscles of the eye are distinct from 

 the fifth pair, except where the oculomotor unites with the 

 ophthalmic into the ciliary ganglion. 



The facial and the trigeminal nerves have common roots 

 in fishes. In Amp)hihia, though the roots are distinct, the 

 facial may be completely united with the ganglion of the tri- 

 geminal, as in the Frog. In all abranchiate Vertebrata the 

 two nerves are quite distinct. 



Whether the nerves are distinct or not, 2, pcdatine^ or vidi- 

 an^ nerve (which, in the higher Vertebrata^ is especially con- 

 nected with the facial), runs through, or beneath, the base of 

 the skull, parallel with its long axis ; and, after uniting with 

 the superior maxillary, and usually contributing to form the 

 sphenopalatine^ or Mechelian^ ganglion, is distributed to the 

 mucous membrane of the roof of the mouth ; and the mandib- 

 ular division of the seventh, or chorda tympani^ unites v/ith 

 the inferior maxillary division of the fifth nerve. 



The eighth pair \auditorii) is formed by, the nerves of the 

 org-an of hearing^. 



The ninth pair [r/lossopharyngei) is especially distributed to 

 the pharjmgeal and lingual regions of the alimentary canal, 

 and, primarily, supphes the boundaries of the second visceral 

 cleft. 



The tenth pair {pneumogastricl or vagi) consists of vcrj 



*I am ofreatly disposed to think that the motor nerves of the eye more 

 nearly retain their primary relations in Lepidosiren than in any other verte- 

 brated animal ; and that they are really the motor portions of the nerves of 

 the orbito-nasal cleft, the third and fourth appertaining to the inner division 

 of the ophthalmic, the sixth to its outer division. 



