NERVE 189 



VI. THE DISCHARGING SIDE OF THE CEREBRAL ARC. 



In the previous section the way in which changes in the 

 external Avorld act upon the body and the consciousness has 

 been considered. 



The reactions of the body through the spinal arcs in 

 reflex action have also been dealt with, and the way in 

 which these reactions are controlled and adjusted by the 

 concomitant action of the proprioceptive mechanisms of 

 the muscles and joints on the one hand, and of the vestibule 

 and semicircular canals on the other, has been explained 

 (p. 121). 



I. The Basal Ganglia. 



The way in which all incoming impulses are interrupted 

 and associated in the thalamus has been considered (p. 113). 



The thalamus is connected not only with the cortex, but 

 also with the different nuclei of the corpus striatum and 

 with the red nucleus from which fibres pass down the cord 

 in front of the crossed pyramidal tract (fig. 97). 



In man and apes the functions of these connections have 

 been largely handed over to the control of the cortex, but in 

 lower mammals they are of primary importance. 



Corpus Striatum. — There is some evidence that the 

 corpus striatum plays a part in controlling temperature 

 (p. 269). It was found that stimulation leads to increased 

 heat production, which must be due to increased chemical 

 change in the muscles. More recently it has been found 

 that stimulation by means of cold leads to a rise of tem- 

 perature, while stimulation by heat leads to a fall, the 

 first causing a constriction of the blood-vessels of the skin, 

 the second causingf a dilatation. 



'O 



II. The Discharging Area of the Cortex Cerebri. 



The wav in which movements are oriofinated and 

 dominated by the cortex cerebri, as the result of the 

 integration of the stimuli falliug on the body, and their 

 association with one another and with the impressions of 



