234 THE CEREBRUM. 



corticifugal fibers in the temporo-thalamic radiation; they are 

 probably reflex in function. 



The optic, or occipito-thalamic radiation (Figs. 70, 38, 45 and 

 55) rises in the lateral geniculate body and in the pulvinar of the 

 thalamus. It continues the visual conduction path through the 

 retrolentiform region of the internal capsule to the cortex of the 

 lingual and cuneate gyri. Half -blindness in the same side of 

 both retinae results from section of the optic radiation. The 

 corticifugal fibers in the occipito-thalamic radiation are believed 

 by Campbell to be axones of the solitary giant cells (Meynert's) 

 in the occipital cortex. They run through the lateral geniculate 

 body and brachium superius to the superior colliculus of the 

 corpora quadrigemina, where they end in contact with the neu- 

 rones of the anterior longitudinal bundle. Their function is 

 reflex. 



II. COMMISSURAL FIBERS. 



They connect opposite sides of the cerebrum and, like the 

 projection fibers, are continuous with the radiations of Mey- 

 nert. They are contained chiefly in the corpus callosum, the 

 anterior commissure, and the commissura hippocampi; but are 

 also found in the posterior commissure, commissura hebenularum, 

 inferior (Gudden's) and superior (Meynert's) commissures. 



The corpus callosum, as already described, is the great link 

 between the cerebral hemispheres (Figs. 34, 27 and 73). Its 

 fibers connect both similar and dissimilar parts of the cortices; 

 within the hemisphere, they form a prominent radiation, called 

 the radiatio corporis callosi. The corpus callosum is made up 

 almost wholly of cortical axones, a few of them being projection 

 fibers; of a small number of afferent projection fibers, and of 

 collaterals from the association and projection fibers. All callosal 

 fibers, except the few efferent projection fibers, end on the opposite 

 side in arborizations within the cortex. It is the corpus callosum, 

 chiefly, that makes it possible for the two hemispheres of the 

 cerebrum to act together as one organ. Philogenetically, it is 

 of recent development, since it is not found below mammals. 



The anterior commissure (Figs. 73, 40 and 30) joins the 



