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. Anatomically, this part may be regarded as the ganglion of the motor tract.

Destructive lesion of one corpus striatum is followed by loss of motion of the other side. 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 corpus striatum causes movement of the other side. 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 and forming the direct motor tract.

Diagram of Brain and Medulla Oblongata. (Cleland).

Fig. 256. Diagram of Brain and Medulla Oblongata. (Cleland).

a, Spinal cord; b, b, Cerebellum divided, and above it the valve of Vieussens partially divided; c, Corpora quadrigemina; d, d, Optic thalami; e, pineal body; f,f, Corpora striata; g,g, Cerebral hemispheres in section; h, Corpus callosum: i. Fornix: l, l, Lateral ventricles; 3, Third ventricle; 4, Fourth ventricle; 5, Fifth ventricle, bounded on each side by septum lucidum.

In dogs, and still more 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 that the gray matter of the corpus striatum is motor, being nearly related in function to the cerebral cortex. The cells of this ganglion are probably agents working under the direction of the cortical centres, organizing and distributing certain motor impulses. In animals whose hemispheres are less complexly developed, such as the dog or rabbit, the "basal agent" seems capable of carrying on more elaborate work, independent of the guidance of the higher motor centres in the gray matter of the brain.