Focal Symptoms. 



589 



In the mammalians the pyramidal tract arises within a definite area (the 

 psychomotor zone), which in the cases of the carnivora is accurately known. It 

 converges towards the white matter of the hemisphere and occupies a narrow space 

 in the internal capsule placed laterally to the optic thalamus. From here it passes 

 to the pons and medulla where either the whole of it or the greater part passes to 



Fig. 79. Diagram of the system of coordination. Tlie sensory parts are on the 

 right, the motor parts on the left and the centers concerned in the middle. Cr. 

 cerebrum. Tli. M. C. qu. optic thalamus, methalamus and corpora quadrigemina, 

 Cbl. cerebellum. M. sp. spinal cord. Stimuli from the skin, muscles, tendons and 

 joints pass either to the spinal cord by way of the sensory roots or to the medulla 

 by way of the sensory root of the trigeminus (not shown in the figure). Some 

 are connected by the reflex collaterals directly with the motor cells in the cord 

 and medulla and others through Sp. Cbl. to the cerebellum, Sp. M. in the neigh- 

 borhood of the thalamus through Sp. Cr. to the cerebrum and then to the motor 

 cells in these centers. The motor impulses produced pass from the cortex by the 

 motor path Cr. Sp., from the thalamus by M. Sp. and from the cerebellum by 

 Cbl. Sp. to the motor cells in the cord and medulla. The cerebellum also receives 

 sensory impulses from the semicircular canals by way of the free vestibular nerve 

 (N. v.), the thalamus and corp. quad, from the organs of vision by way of the 

 optic nerve (N. o. ) and these are conveyed to the motor cells in the central 

 organs and cerebrum by the paths Cbl. Cr. 'and M. Cr. (Adapted from O. Forster). 



the other side to be continued in the lateral column of the spinal cord. The fibers 

 composing this nerve path accompany the peripheral motor path, both in the brain 

 and in the spinal cord, so that a connection is established between the cortex of the 

 brain and the peripheral motor nerves without touching the subcortical centers. In 



