410 ANATOMY OF THE CENTRAL NEEVOUS' SYSTEM. 



parts of the brain mentioned. To all these "primary optic centers" come 

 fibers from the optic radiations, beginning in the occipital lobe. These 

 extend along the lateral side of the posterior horn, and under the inferior 

 parietal lobule, on their way from the cortical origin to the primary optic 

 centers. From this fact arise visual disturbances, having the character of 

 cortical lesions, which have been noticed in disease of this lobule or by ex- 

 perimental lesion of the corresponding locus in animals. 



The fibers of the optic tract pass to the chiasm. There the larger 

 portion passes to the opposite side, while a smaller portion, up to this point 

 not separated from the bundle, remains on the same side. The long- 

 cherished dispute about the chiasm has recently been decided, as stated 

 above, finally and convincingly by Singer and Mlinzer. The bundle which 

 does not cross over is very unimportant in some animals, and is entirely 

 wanting in certain orders. In the latter case there is, accordingly, a total 

 decussation. 



The optic tract must, in addition, contain the pupillary fibers from the 

 oculo-motorius. It has not yet been definitely demonstrated how they join it. 



The central course of the olfactorius was described in its relations, in 

 Chapter XIII. Compare especially Fig. 144, relating to this subject. 



