SENSE AREAS AND ASSOCIATION AREAS. 207 



brain undergo secondary degeneration and their course can be 

 traced microscopically to the brain. By this means it has been 

 shown that in man and the mammaha there is a partial decus- 

 sation of the optic fibers in the chiasma. The fibers from the 

 inner side of each retina cross at this point to the opposite optic 

 tract; those from the outer side of the retina do not decussate, 



Occipital lobe. 



Occipito-thalamic radiation. 

 Superior colliculus. 



Lateral geniculate. 

 Thalamus. 



Optic tract. 



Optic chiasm. 



Fig. 92.— Diagram to indicate the general course of the fibers of the optic nerves and the 

 bilateral connection between cortex and retina. 



but pass into the optic tract of the same side. The fibers of the 

 optic tract end mainly in the gray matter of the lateral genicu- 

 late body, but some pass also to the thalamus (pulvinar) and 

 some to the superior colliculus of the corpora quadrigemina. 

 These locations, therefore, particularly the lateral geniculates, 

 must be considered as the primary optic centers. From these 

 points the path is continued toward the cortex by new neurons 

 whose axons constitute a special bundle, the occipitothalamic 

 radiation, lying in the occipital part of the internal capsule 

 (see Fig. 82, D). A schema representing this course of the 

 optic fibers is given in the accompanying diagram (Fig. 92). 



