288 



ANATOMY OF THE CENTRAL NERVOUS SYSTEM. 



ciently confirmed by the various methods of investigation, we may prob- 

 ably at present regard it as firmly established that optic-nerve fibers arise 

 and terminate in the corpus geniculatum laterale, in the superficial medulla 

 of the anterior corpus qiiadrigeminum, and in the outermost layers of the 

 pulvinar. These last-named gray masses are designated as the primary 

 optic centers. 



A connection letiueen these centers and the cortex of the occipital lohe has 

 been proved in a definite and satisfactory manner. The fibers concerned in 

 this form the radiatio thalamo-occipitalis, the optic radiation, or the bundle 

 of Gratiolet: a not inconsiderable fiber-tract which develops from the pri- 

 mary centers in separate bundles and passes backward from there to become 

 lost in the cortex of the cuneus and in about the region of the second and 

 third occipital gyrus. 



In the territory from which they originate (the cortex) and along the 



Fig. 184. — Section through the corpus geniculatum laterale of the cat. 

 Silver method. Sho^\'S the entering optic fibers and the splitting-up of the same 

 into terminal, brush-like arborizations. (After P. EamOn y Cajal.) 



proximal part of their course while passing away from there, the coronal 

 fibers to the separate optic centers (or terminals) are to be separated from 

 one another only with difficulty. Farther anteriorly, however, it is recog- 

 nized that the fibers to the pulvinar occupy the dorsal, and the fibers to the 

 geniculatum laterale the ventral, portion of the tract. Only in the most 

 posterior division of the internal capsule, just before the entrance into the 

 primary centers (Mg. 165), are the separate parts of the optic radiation 

 sharply separated from one another. The pedicle to the corpus geniculatum 

 lies close to this as the lateral medullary field, or area. It arises from the 

 cuneus, perhaps from the lobus lingualis also. Dorsal to it, the fibers of 

 the optic radiation arising from the two occipital gyri enter the pulvinar. 



