THE CEEEBEAL NERVES. 73 



side of tlie maxillary process, while tlie inferior maxillary 

 appertains to the anterior region of the first visceral arch. 

 The superior maxillary commonly unites with the outer, 

 or lachrymal, division of the ophthalmic ; the inferior maxil- 

 lary with the anterior division of the facial. 



In the higher Vertebrata, the trigeminal nerve usually 

 has two very distinct roots, a dorsal sensoiy, provided with 

 a ganglion (the Casserian ganglion), and a ventral motor, 

 non-ganglionated. The fibres of the latter pass almost ex- 

 clusively into the inferior maxillary division. In addition, 

 the ophthalmic division may have a ganglion (ciliary) ; the 

 superior maxillary another {sphenopalatine or Meckelian), 

 and the inferior maxillary a third (otic). 



The sixth pair (ahclucentesj issues from the inferior sur- 

 face of the brain, at the junction of the myelencephalon 

 with the metencephalon. It supplies the external straight 

 muscles of the eye; with the muscles of the nictitating 

 membrane, and the retractor htdhi, or musculus choanoides, 

 when such muscles exist. 



The seventh pair (faciales) supplies the siipei-ficial facial 

 miiscles, 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 Lejndosiren, 

 the three motor nerves of the eyeball are completely fused 

 with the ophthalmic division of the fifth.* In the Myxinoid 

 fishes there are no motor nerves of the eyeball ; but, in the 

 Lamprey, the rectus externus and inferior, and the ohliqims 

 inferior, are supplied by the ophthalmic, while the oculo- 

 motor and the pathetic unite into a common trunk, which 

 gives branches to the rectus superior and internus, and 

 obliquus superior. The oculomotor, the pathetic, and the 



* I am greatly disposed to think portions of tlie nerves of the or- 



that the motor nerves of the eye bitonasal cleft, the third and 



more nearly retain their primary fourth appertaining to the inner 



relations in Lejiidosiren than in division of the ophthalmic, the 



any other vertebrated animal ; sixth to its outer division, 

 and that they are reallj' the motor 



