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A MANUAL 0* PHYSIOLOGY 



corpus quadrigeminum, the nucleus of the oculo-motor nerve in the 

 wall of the Sylvian aqueduct, and the fibres which it carries to the 

 iris, form a reflex arc for the contraction of the pupil to light, as re- 

 presented in Fig. 258, p. 720. 



The functions of the optic thalami have not been satisfactorily 

 defined either by experiment or pathological observation. Lying as 

 they do in the isthmus of the brain, begirt by the great motor and 

 sensory paths, it is to be expected that lesions of the thalami should 

 affect also the internal capsule, and give rise to the symptoms of 

 motor and sensory paralysis. But no definite defect of motor power 



or common sensation 

 has ever been unequi- 

 vocally connected with 

 a lesion restricted to 

 the thalami. They 

 have, however, exten- 

 sive connections with 

 the cerebral cortex, 

 each of the thalamic 

 nuclei being connected 

 with a definite cortical 

 region in such a way 

 that destruction of the 

 cortical area in young 

 animals or human be- 

 ings leads to degenera- 

 tion of the correspond- 

 ing nucleus. It is the 

 afferent paths to the 

 cortex with which they 

 FIG. 261. LONGITUDINAL SECTION OF THE GREY are specially related as 

 MATTER OF A LAMELLA OF THE CEREBELLUM centres o f relay The 

 (DIAGRAMMATIC, AFTER KoLLiKER). posterior portion of the 



gr, a 'granule' cell with its axon, ; ', bifurcation thalamus, Or pulvinar, 

 of , in the molecular layer, into two fine longitudinal f/-j rrn Q rnrt nf thp rpn 

 branches; m, a Purkinje's cell; ', dendritic antler IOr , mS .P a " 

 process (Golgi's method). tral visual apparatus; 



for (a) it is found to 



be undeveloped in animals from which the eyeballs have been re- 

 moved soon after birth ; (b) a portion of the optic tract is certainly 

 connected with it ; (c) in some cases of atrophy of the occipital 

 cortex, which, as we shall see, is undoubtedly a central area for 

 visual sensations, atrophy of the pulvinar has also been noticed ; (d) a 

 lesion of the pulvinar may give rise to hemianopia (p. 719). 



Haemorrhage into the caudate or lenticular nucleus of the corpus 

 striatum often causes hemiplegia, but this is always due to implication 

 of the internal capsule. Experimental lesions in dogs and rabbits 

 are followed by disturbances of the heat-regulating mechanism and 

 rise of temperature. 



Certain structures, belonging to the primary fore-brain, which have 

 now no functional importance, may nevertheless be mentioned as 



