6l2 



THE NERVOUS SYSTEM 



Functions. The fourth nerve is exclusively motor, and supplies only the 

 trochlearis or superior oblique muscle of the eyeball. 



The Fifth Nerve, or Trigeminal. Origin. The fifth or trigeminal 

 nerve resembles the spinal nerves in that it has two roots; namely, the larger 

 or sensory, in connection with which is the Gasserian ganglion, and the small 

 or motor root, which has no ganglion, and which passes under the ganglion 

 of the sensory root. The fibers of origin of the fifth nerve come from the 

 floor of the fourth ventricle. The motor root arises to the inside of the sen- 



FIG. 409. Fourth Ventricle with the Medulla Oblongata and the Corpora Quad- 

 rigemina. The Roman numbers indicate superficial origins of the cranial nerves, while the 

 other numbers indicate their deep origins, or the position of their central nuclei. 8, 8', 8", 

 Auditory nuclei nerves; t, funiculus teres; A, B, corpora quadrigemina; c.g, corpus genic- 

 ulatum; p.c. pedunculus cerebri; m.c.p, middle cerebellar peduncle; s.c.p, superior cere- 

 bellar peduncle; i.c.p, inferior cerebellar peduncle; l.c, locus ceruleus; e.t, eminentia teres; 

 a.c, ala cinerea; a.n, accessory nucleus; o, obex; c, clava; f.c, funiculus cuneatus; f.g, funicu- 

 lus gracilis. 



sory about the middle of each lateral half of the fourth ventricle. The 

 sensory fibers, however, can be traced down in the medulla oblongata as far 

 as the upper part of the cord. The motor nucleus stretches forward as far 

 as the superior corpus quadrigeminum, giving rise to a bundle of long fibers 

 termed the descending root. The sensory nucleus receives a tract of sensory 

 fibers from the trigeminus extending as low as the second cervical nerve, 

 and this forms a tract at the tip of the posterior cornu, between it and the 

 restiform body. The cells of origin of the sensory tract are in the Gas- 



