6 THE NERVOUS SYSTEM 



(Fig. 3). The lowest part of the anterior central gyms con- 

 tains the motor centres for the face ', head and neck. 



Before the axons from the nerve-cells of the motor area of 

 the cortex reach their destination, they all, with certain 

 exceptions to be noted later (pp. 34 and 86), cross the 

 median plane. Cortical lesions in this situation, therefore, 

 produce their effects on the opposite side of the body and, 



2 3 



5 6 7 



FIG. 3. Lateral Aspect of Left Cerebral Hemisphere. 



7. Post-central sulcus. 



8. Supra -marginal gyrus. 



9. Post-parietal gyrus. 



" I Rami of lateral 



' J fissure (of Sylvius). 



1. Inferior frontal sulcus. 



2. Superior frontal sulcus. 



3. Inferior precentral sulcus. 



4. Superior precentral sulcus. 



5. Central sulcus (of Rolando). 



6. Posterior central gyrus. 



13. Superior temporal sulcus. 



owing to the extent of the anterior central gyrus, they are not 

 likely to involve the whole of the motor area. The effects 

 of the lesion may be irritative or paralytic, according to its 

 nature, or the second condition may ensue after a temporary 

 irritative stage. Irritative conditions of the motor cortex do 

 not necessarily depend on the existence of an organic lesion, 

 and in many cases of epilepsy no such lesion is present. 



