642 HANDBOOK OF PHYSIOLOGY. 



quadrigeminum and the lateral corpus geniculatum to the sense of 

 sight. 



Centre for Cutaneous Sensations. Physiological experiments, as well 

 as clinical and pathological observations, now show pretty certainly that 

 the cortical centre for sensations of touch, and probably of pain and 

 temperature, are essentially identical with the motor areas, that is to 

 say, in the central convolutions. Owing, however, to the wide distribu- 

 tion of afferent impulses, through the multiplication of their means of 

 getting to the brain, the area of these sensory centres is not as strictly 

 limited as that of other special centres. 



TJie Centre for Muscular Sensations. A great deal of evidence is ac- 

 cumulated to show that the most important area in which these sensa- 

 tions are brought to consciousness is in the inferior parietal lobule. 



FUNCTIONS OF CORPORA STRIATA AND OPTIC THALAMI. 



The Corpora Striata. The idea formerly held that the corpora 

 striata are concerned in the transmission of motor impulses, or that they 

 are the great motor ganglia at the base of the brain, rests upon insuffi- 

 cient evidence. Lesions of the corpora striata produce hemiplegia only 

 because of the pressure-effects they exercise upon the internal capsule 

 close by. 



The caudate nucleus is connected with the opposite side of the cere- 

 bellum by fibres which conduct downward, and the lenticular nucleus is 

 connected with the cerebellum by fibres from the tegmeuturn and su- 

 perior cerebellar peduncles which conduct upward. It is suggested that 

 the corpora striata are central organs analogous to the cerebral cortex 

 itself. " The analogy to those parts of the cortex that are connected 

 with the cerebellum is rendered still greater by the fact that a lesion, 

 even an extensive lesion, may exist in either the caudate or lenticular 

 nucleus, and so long as it does not interfere with the functions of the 

 motor or sensory parts of the internal capsules it causes no persistent 

 symptoms." (Gowers.) 



On the whole, however, it must be said that the functions of the 

 corpora striata are unknown, and it is possible that in man they are very 

 subsidiary, if not even rudimentary, bodies. 



Tlie Optic Tlialami. That the optic thalami are the great sensory 

 centres at the base of the brain which was a view held by many until 

 recently does not seem to be based upon sufficiently accurate observa- 

 tions. The important relation to the tegmentum of its own side would 

 make it appear as being specially concerned with the sensory fibres pass- 

 ing to the cerebrum, for which it probably forms a relay. 



Its connection with the optic nerves has been commented upon 

 above. Fibres connect the optic thalamus too with the superior pe^ 

 duncle of the cerebellum of the opposite side, 



