THE NERVOUS SYSTEM. 



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reach the valve of Vieusseus, where they decussate in the middle line 

 and appear at the front of the pons at the lateral edge of the crus. The 



Fig. 365. Fourth ventricle with the medulla oblongata and the corpora quadrigemina. The 

 roman numbers indicate superficial origins of the cranial nerves, while the other numbers in- 

 dicate their deep origins, or the position of their central nuclei. 8, 8', 8", 8'", auditory nuclei 

 nerves; , funiculus teres; A., B, corpora quadrigemina ; c.g, corpus geniculatum; p. c, pedun- 

 culus cerebri; m, c, p, middle cerebellar peduncle; s, c, p, superior cerebellar peduncle; i, c,p, 

 inferior cerebellar peduncle ; I, c, locus caeruleus ; e, t, eminentia teres ; a, c, ala cinerea ; a, w, 

 accessory nucleus; o, obex; c, clava; /, c, funiculus cuneatus; /, g, funiculus gracilis. 



nucleus of the fourth nerve on either side is connected with those of the 

 third and sixth nerves. 



Functions. The IVth nerve is exclusively motor, and supplies only 

 the trochlearis or obliquus superior muscle of the eyeball. 



The Vth Nerve (Trigeminus) . 



Origin. The Vth or Trigeminal nerve resembles, as already stated, 

 the spinal nerves, in that its branches are derived through two roots ; 

 namely, the larger or sensory, in connection with which is the Gasserian 

 ganglion, and the smaller or motor root which has no ganglion, and 

 which passes under the ganglion of the sensory root to join the third 

 branch or division which ensues from it. The fibres of origin of the 

 fifth nerve come from the floor of the fourth ventricle. The motor root 

 to the inside of the sensory, about the middle of each lateral half. The 

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

 far as the upper part of the cord. From the motor nucleus there 

 stretches forward as far as the anterior corpus quadrigeminum a bundle 

 of long fibres termed the descending root, which has attached to it sparse 

 spheroidal nerve-cells. It is also connected with the locus caeruleus. 

 The sensory nucleus outside the motor has connected with it a tract of 



