THE FIFTH NERVE, OR TRIGEMINAL 



551 



ventral to the aqueduct of Sylvius, and the inferior corpus quadrigeminum. 

 The fibers from both sides sweep dorsally around the central gray matter, and 

 reach the valve of Vieussens, where they decussate in the mid-line of the roof, 

 then pass forward along the lateral aspect of the crus. The nucleus of the 

 fourth nerve on either side is connected with those of the third and sixth nerves 

 and with the optic reflex center previously described. 



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 



nVLK 



VJ1I 



FIG. 385. Section Across the Pons, About the Middle of the Fourth Ventricle, py, Pyramidal 

 bundles; po, transverse fibers passing po\, behind, and pOn, in front of py; r, raphe; o.s, su- 

 perior olive; a. V, bundles of ascending root of V. nerve enclosed in a prolongation of the sub- 

 stance of Rolando; VI, the sixth nerve; nVl, its nucleus; VII, facial nerve; VII. a, intermediate 

 portion, nVIl, its nucleus; VIII, auditory nerve, nVIIl, lateral nucleus of the auditory. (After 

 Quain.) 



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 sensory, 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. It is also connected with the locus ceruleus. 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 



