NERVOUS SYSTEM. '229 



fundibulum and the large petuitary gland. The pineal gland 

 (95. A. c?,) with its small peduncles, is seen between the 

 optic lobes and the hemispheres, as in higher classes, and is 

 composed chiefly of cineritious substance. 



From the great extent of the cranial cavity and the small- 

 ness of the brain, the cerebral nerves have a long free course 

 from their origin to their cranial foramina. In the osseous 

 fishes the optic nerves (96. q,} generally cross each other with- 

 out uniting or intermingling their fibres, but in the plagiostome 

 fishes they unite and decussate, as in mammalia. Fromthegreat 

 size of the organs of vision in this class, and of the muscles 

 which move them, not only the optic nerves are proportion- 

 ally large, but also the third, fourth and sixth pairs, or oculo- 

 motory, trochlear and abducent nerves, which are the motor 

 filaments of these muscles. The abducent nerves advance 

 forwards from the inferior surface of the medulla oblongata, 

 where they arise between the posterior fibres of the large 

 trigemini. This large fifth pair (Fig. 96. m,) arising from 

 the sides of the lobes of the medulla oblongata immediately 

 beneath the cerebellum (96. c,) gives off the ophthalmic (96. 

 p,) which passes forwards through the orbit above the eye 

 to be distributed on the upper part of the face ; the supe- 

 rior maxillary (96. o,) which passes under the eye to ramify 

 on the sides of the face ; and the inferior maxillary (96. n,) 

 which supplies chiefly the palate and lower jaw. The prin 

 cipal branches of the seventh or facial nerve (96. I,) are dis- 

 tributed on the posterior part of the face and neck. The 

 great pneumo-gastric nerves (96. &,) arising behind the trige- 

 mini, from the sides of the medulla oblongata present a large 

 ganglion, from which branches pass downwards to the 

 branchiae, and backwards along the oesophagus to the sto- 

 mach, and air sac or rudimentary lungs ; and before these is 

 a branch analagous to the glosso-pharyngeal, which supplies 

 the tongue and anterior branchial arch. This great ganglion 

 of the pneumo-gastric (96. k,) is sometimes close to the 

 origin of the nerve, and sometimes remote ; and a branch 

 from this nerve, like the accessary of Willis, extending lon- 

 gitudinally on the side of the whole body near the lateral line 

 sends filaments to the surface. The pneumo-gastric supplies 

 nerves also to the electrical organs of the torpedo. The 

 acoustic nerve, arising between the trigeminus and the great 



