336 NERVOUS SYSTF.I\I. 



Third Fair, or M of ores Ocular tun. 



Take their origin, by several filaments, from the inward parts 

 of the crura cerebri, about their middle. The trunk of either 

 nerve, thus formed, first runs obliquely outward, across the back 

 of the crus, then tuins downward and enters the cavernous sinus, 

 wherein it is covered by a sheath of dura mater, and continues its 

 course through the foramen lacerum orbitale, inwardly placed to 

 the other nerves, into the orbit. In entering the cavity, the nerve 

 divides into two branches. The smaller is generally received by 

 a single muscle — the levator oculi. The larger branch sub- 

 divides into several others : the longest of these runs round the 

 eye-ball and penetrates the obliquus inferior; the two or three 

 others run to the adductor and depressor muscles. 



Ophthalmic Ganglion. — Upon the outward side of the optic 

 nerve, between it and that part of the motor oculi from which 

 the branch nerves spring, is situated the ophthalmic ganglion. 

 This little body is principally constituted of branches from the 

 third pair; but it also receives a filament or two from the sixth. 

 The nervous threads transmitted by the ganglion, surround the 

 sheath of the optic nerve, and, pursuing their course over it, pene- 

 trate the globe of the eye, and run to be dispersed upon the 

 iris. 



Fourth Pair, or Pathetic. 



These, the slenderest of the cerebral nerves, take a filamentous 

 origin from the summits of the testes, whence they proceed out- 

 ward between those bodies and the crura cerebelli, creep round 

 the cura cerebri, and are seen at the border of the tentorium 

 entering the cavernous sinus. Having coursed the anterior 

 boundary of the sinus, encased in dura mater, the nerve takes 

 refuge again in a small bony canal, constructed for its passage, 

 in front and rather to the outward side of the foramen lacerum, 

 which conducts it into the orbit. It destination is the superior 

 oblique muscle of the eye, to which it exclusively distributes its 

 ramifications. 



Fifth Pair, or Par Trigeminuni. 



These are the largest of the nerves of the brain. They take 

 their beginning by a multitude of filaments from the crura cere- 

 belli, and forthwith run for security into the cavernous sinuses, 

 where they are covered and protected by distinct sheaths of dura 

 mater. Each nerve within the sinus suddenly swells in bulk, 

 and thus is said to form a ganglion : and certainly the enlarged 

 portion is darker coloured than the nerve itself, albeit, it does 

 not put on the common appearance of, nor is it of the same 



