640 MANUAL OF PHYSIOLOGY. 



turn, or great sensory tract, is directly connected with the optic 

 thalamus. 



BASAL GANGLIA. 



The great masses of gray and white matter seen on the floor 

 of the lateral ventricles are called the corpora striata and optic 

 thalami, and together are spoken of as the basal ganglia. The 

 exact relationship borne by their functions to those of the mes- 

 encephalon and cerebral cortex is not perfectly understood, 

 though it is, no doubt, intimate. The following are some of the 

 more important points in the evidence on the subject : 



Corpora Striata. The motor tracts, coming from below, 

 lie in the lower part of the crus cerebri, and thence one on each 

 side passes into the corresponding corpus striatum. Anatomi- 

 cally, then, this part may be regarded as the ganglion of the 

 motor tract. 



Destructive lesion of one corpus striatum is followed by loss of 

 power of the muscles of the other side of the body. This is 

 equally true of lesions artificially produced in animals and those 

 resulting from disease in man. When the crura on both sides are 

 destroyed the animal remains motionless and prostrate. 



Electrical stimulation of one of the corpora striata causes uni- 

 lateral motions of the other side of the body. This fact, however, 

 does not teach us much concerning the functions of the particular 

 cells of its gray matter, since the stimulus cannot be kept from 

 affecting the fibres passing through the corpus striatum to go 

 directly to the motor tract. 



In dogs, and still more so in rabbits, the corpora striata seem 

 to be able to carry out some complex motions which in man are 

 believed to require the cooperation of the higher cerebral centres. 

 It has been stated that a dog whose cerebral cortex is completely 

 destroyed can perform movements that in man can only be evoked 

 by the cortex of the hemispheres. 



It would appear then that the gray matter of the corpus striatum 

 is a motor ganglion, nearly related in function to the cerebral 

 cortex. The cells of this ganglion are the first agents working 

 under the direction of the cortical centres, and carry out the 

 organization and distribution of voluntary motor impulses. In 



