422 NERVES OF ENCEPHALON. 



nerves of motion, and arise each from the inner side of the 

 cms cerebri, close to the pons, its fihres heing traced to the 

 locus niger in the cms. These nerves penetrate the dura 

 mater at the posterior clinoid process, and proceed forward 

 along the outer wall of the cavernous sinus to the foramen 

 lacerum superius, through which they pass, and then di- 

 viding into two branches, supply five of the seven muscles 

 contained in the orhit. 



Fourth Pair of Nerves, Pathetici or TrocMeares, (Fig. 118.) 

 These are the smallest nerves of the brain, not larger than 

 an ordinary strand of cotton, and arise each by two or 

 three filaments from the valve of Vieussens, &nd.processus a 

 cerebello ad testem ; they are very delicate and easily broken, 

 and pursue a long course on the outer margin of the pons, 

 between the cerebrum and cerebellum, to the posterior cli- 

 noid process, where they enter a canal of the dura mater, 

 then proceed along the external wall of the cavernous sinus, 

 at first below the third, then above all the nerves at this 

 point, to the foramen lacerum superius or sphenoidal fissure, 

 through which the last pass to be distributed solely to the 

 superior oblique muscles of the eye. 



Fifth Pair, Trifacial or Trigemini, (Figs. 118, T4.) These 

 are compound nerves, having filaments both of sensation 

 and motion, hence they have been called the cranial-spinal 

 nerves. They are the largest of the cerebral nerves, and, 

 according to Dr. Alcock, arise by two roots from an emi- 

 nence, on a longitudinal tract of yellowish matter in front 

 of the floor of the fourth ventricle, which divides inferiorly 

 into two fasciculi, traceable downward to the spinal cord, 

 the one going to the anterior column, the other to the pos- 

 terior. The two roots having this origin, emerge on the 

 side of the pons Varolii, where it is continuous with the 

 crus cerebelli. Here they are separated by a narrow, trans- 

 verse fasciculus. The union of the two constitutes the fifth 

 nerve, which consists of from TO to 100 filaments bound to- 

 gether by pia mater. The nerve passes forward in an oval 

 opening or canal in the dura mater, formed by the separa- 

 tion of the two layers of this membrane, and then expands 



