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A MANUAL OF PHYSIOLOGY 



and die out ; what molecular changes are associated with them ; 

 above all, how the molecular changes are translated into conscious- 

 ness how, for example, it is that a series of nerve-impulses from 

 the optic radiation flickering across the labyrinth of the occipital 

 cortex should light up there a visual sensation these are questions 

 to which we can as yet give no answer, and the answers to some of 

 which must for ever remain hidden from us. 



Functions of the Upper Part of the Central Stem and Basal 

 Ganglia. The function of the pons is sufficiently indicated by its 

 name. The grey matter so plentifully scattered, especially in its 

 ventral portion, may exercise a not unimportant influence on the 

 impulses that traverse it. But on the whole its main office is to 

 provide a bridge along which impulses may travel between other 

 portions of the nervous system. We have already seen that many 

 of its transverse fibres arising from the cells of the pontine grey 



Corpus striatum 



Anterior pillar of 

 the fornix 



Optic thalamus 

 Third ventricle 



FIG. 345. HORIZONTAL SECTION THROUGH BRAIN TO SHOW THE BASAL GANGLIA 

 AND THIRD VENTRICLE (HUMAN). 



matter, and then crossing the middle line to the opposite middle 

 peduncle, are the cerebellar segments of commissural arcs connecting 

 the cerebral with the opposite cerebellar hemispheres. The cerebral 

 segments of these arcs are the cortico-pontine fibres originating 

 in the prefrontal, temporal, and occipital portions of the cerebral 

 cortex, and passing through the corona radiata, internal capsule, 

 and crura cerebri, to end in the nuclei pontis. Many fibres and 

 collaterals of the pyramidal tract also terminate here. On the dorsal 

 aspect of the pons in the floor of the fourth ventricle are the nuclei 

 of origin (or reception) of the fifth, sixth, and seventh cranial 

 nerves. Various reflex centres are situated in this region e.g., that 

 for the closure of the eyelids, when the conjunctiva is stimulated. 



The posterior corpora quadrigemina and internal geniculate bodies 

 are connected with the cochlear division of the auditory nerves, and 

 form important stations on the auditory path to the cortex, 



