THE NERVOUS SYSTEM. ,, t : 101 



be marked off into centres which control the motion of a 

 smaller group of muscles, as of a part of the arm. The 

 area of the arm would thus be the sum total of centres for 

 the various movements of which all the parts of the arm 

 are capable. The areas affect the movements of the 

 muscles of the opposite side of the body, so that stimu- 

 lating the area of the arm on the right cerebral cortex 

 will result in movements of the left arm. Locate the 

 main motor and sense areas from the following diagram. 



Ro 



Ant. 



FIG. 9. The left cerebral hemisphere. Sy is the fissure of Sylvius; 7?o, the 

 fissure of Rolando ; P.O., the parieto-occipital fissure ; If, the area for hear- 

 ing ; V, the area for vision ; S, the area for smelling. 



C. The Cranial Nerves. 



If the cranial nerves have been severed close to the 

 brain, they should be studied in the interior of the skull. 

 Observe carefully the points of exit of the roots of the 

 nerves. 



a. The olfactory nerves arise from the olfactory lobes. 



b. The optic nerves arise from the optic tracts just 

 anterior to the crura cerebri. 



