864 



NEUROLOGY 





\JC 



related to the posterior longitudinal bundle which lies against its ventro-lateral 

 aspect and many of its cells lie among the fibers of the posterior longitudinal bundle. 

 The nucleus of the oculomotor nerve contains several distinct groups of cells which 

 differ in size and appearance from each other and are supposed to send their axons 

 each to a separate muscle. Much uncertainty still exists as to which group supplies 

 which muscle. There are seven of these groups or nuclei on either side of the mid- 

 line and one medial nucleus. The cells of the anterior nuclei are smaller and are 

 supposed to give off the sympathetic efferent axons. The majority of fibers arise 

 from the nucleus of the same side some, however, cross from the opposite side and 

 are supposed to supply the Rectus medialis muscle. Since oculomotor and abducens 

 nuclei are intimately connected by the posterior longitudinal bundle this decussa- 

 $t tion of fibers to the Medial rectus may facili- 



m tate the conjugate movements of the eyes in 

 which the Medial and Lateral recti are espe- 

 cially involved. 



Many collaterals and terminals are given off 

 to the oculomotor nucleus from the posterior 

 longitudinal bundle and thus connect it with 

 the vestibular nucleus, the trochlear and ab- 

 ducens nuclei and probably with other cranial 

 nuclei. Fibers from the visual reflex center in 

 the superior colliculus pass to the nucleus. It 

 is also connected with the cortex of the occip- 

 ital lobe of the cerebrum by fibers which 

 pass through the optic radiation. The path- 

 way for voluntary motor impulses is probably 

 similar to that for the abducent nerve. 



The Optic Nerve or Nerve of Sight (77 cranial) 

 consists chiefly of coarse fibers which arise 

 from the ganglionic layer of the retina. They 

 constitute the third neuron in the series com- 

 posing the visual path and are supposed to 

 convey only visual impressions. A number of 

 fine fibers also pass in the optic nerve from 

 the retina to the primary centers and are sup- 

 posed to be concerned in the pupillary re- 

 flexes. There are in addition a few fibers which 

 pass from the brain to the retina ; they are sup- 

 posed to control chemical changes in the retina 

 and the movements of the pigment cells and cones. Each optic nerve has, accord- 

 ing to Salzer, about 500,000 fibers. 



In the optic chiasma the nerves from the medial half of each retina cross to enter 

 the opposite optic tract, while the nerves from the lateral half of each retina pass 

 into the optic tract of the same side. The crossed fibers tend to occupy the medial 

 side of each optic nerve, but in the chiasma and in the optic tract they are more 

 intermingled. The optic tract is attached to the tuber cinereum and lamina 

 terminalis and also to the cerebral peduncle as it crosses obliquely over its under 

 surface. These are not functional connections. A small band of fibers from the 

 medial geniculate body joins the optic tract as the latter passes over it and crosses 

 to the opposite tract and medial geniculate body in the posterior part of the chiasma. 

 This is the commissure of Gudden and is probably connected with the auditory 

 system. 



Most of the fibers of the optic tract terminate in the lateral geniculate body, 

 some pass through the superior brachium to the superior colliculus, and others 





FIG. 762. Figure showing the different groups 

 of cells, which constitute, according to Perha, 

 the nucleus of origin of the oculomotor nerve. 

 1. Posterior dorsal nucleus. 1'. Posterior ven- 

 tral nucleus. 2. Anterior dorsal nucleus. 2'. Ante- 

 rior ventral nucleus. 3. Central nucleus. 4. 

 Nucleus of Edinger and Westphal. 5. Anterc- 

 internal nucleus. 6. Antero-external nucleus. 8. 

 Crossed fibers. 9. Trochlear nerve, with 9', its 

 nucleus of origin, and 9", its decussation. 10. 

 Third ventricle. M, M. Median line. (Testut.) 



