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HANDBOOK OF PHYSIOLOGY. 



ward and terminates in three distinct nuclei, viz., the pulvinar of the 

 optic thalamus, the anterior corpus quadrigeminum and the lateral 

 corpus geniculatum. These nuclei waste if the eyes are removed fron 

 an adult animal ; and if from a newly born animal they do not develop. 

 The optic chiasma in its course gives off fibres which are connected witli 

 the nucleus of the third nerve. 



It appears that some of the fibres of the optic tract pass directly intt 

 the cerebral cortex without joining with the optic thalamus, corpus quad- 

 rigeminum or corpus geniculatum. 



It was shown above that the fibres of the cerebral cortex, known as 

 the optic radiation, pass from the occipital region to the three nuclei 

 about which we are speaking, viz., into the pulvinar of the optic thala- 

 mus, the anterior corpus quadrigeminum and lateral corpus geniculatum. 



Fig. 386. -The Cortical Centres. 



and it is known that when the occipital cortex is removed, these three 

 waste. It has been further shown that in a newly born animal the 

 removal of such a region is followed by imperfect development of the 

 parts in question. 



If one optic nerve be divided blindness of the corresponding eye 

 results, but if one optic tract be divided there is a half blindness, 

 which is called hemianopsia, hemianopia, or hemiopia, right or left, 

 according as the right or left field of vision is cut off. It is highly 

 probable that the occipital lobe (figs. 382, 386), and particularly 

 the cuneus, is concerned as a so-called visual centre, since not only is 

 it connected with the optic nerves, as we have seen, but also because the 

 removal of the right occipital lobe in an animal (monkey), is followed 

 by left hemiopia, removal of the left by right hemiopia, and removal of 

 both occipital lobes by total blindness. Some have connected the angular 



