THE DIENCEPHALON AND THE OPTIC NERVE 



227 



mis sure of Gudden, which crosses the median plane in the posterior part of the 

 optic chiasma and, for the most part at least, connects the medial geniculate 

 bodies of the two sides. These are the fibers which form the medial root of the 

 optic tract. 



The Optic Radiation. The superior colliculus is a reflex center, and the fibers 

 of the optic nerve, which terminate in it, subserve optic reflexes. On the other 

 hand, the visual impulses, brought to the external geniculate body and the pul- 



Superior oblique muscle 

 Retina 



Optic nerve 

 Optic chiasma 



Commissure of Gudden 

 Trochlear nerve 

 O.ptic trad 

 Thalamus 



Medial geniculate body 

 Lateral genictilate body 



"~ -Superior colliculus 

 ~~- Inferior colliculus 

 ^^Nucleus oftrochlear nerve 

 radiation 



Cuneus 



Occipital pole 



Fig. 162. Schematic representation of the optic pathways. The index line to the commissure of 



Gudden does not reach that structure. 



vinar of the thalamus, are relayed to the cerebral cortex and give rise to visual 

 sensations. These two parts of the diencephalon are connected with the cere- 

 bral cortex on both sides of the calcarine fissure by projection fibers, which 

 form a conspicuous bundle that sweeps backward through the retrolenticular 

 portion of the internal capsule into the occipital lobe. It is known as the optic 

 radiation (Fig. 162). In addition to corticipetal fibers arising in the pulvinar 

 and lateral geniculate body, the optic radiation contains corticifugal fibers 



