12 THE NERVOUS SYSTEM 



life of the patient. The condition, like all cerebral tumours, 

 is progressive; paral)tic symptoms appear gradually, and 

 paralysis of one side of the body is associated with vague 

 hemiplegic symptoms on the other ; a tendency to drowsiness 

 and stupidity supervenes. At the same time, none of the 

 cerebral nerves are directly involved, since none of them are 

 in intimate relation with the corpus callosum. 



Very little is known with regard to the functions of the 

 large cortical areas which lie above and in front of the corpus 

 callosum. This part of the medial surface is divided into 

 upper and lower areas by the sulcus cinguli (calloso-marginal 

 fissure), which ascends to the supero-medial border of the 

 hemisphere a little in front of the splenium (Fig. 6). The 

 upper area is termed the marginal gyrus and its posterior 

 part is termed the paracentral lobule. The latter is usually 

 cut into by the upper extremity of the central sulcus and it 

 contains some of the higher motor centres for the lower limb 

 of the opposite side (Fig. 6). 



The gyrus cinguli (callosal gyrus) lies between the sulcus 

 cinguli and the corpus callosum. When it is traced backwards 

 it curves downwards and forwards round the splenium and 

 becomes continuous with the hippocampal gyrus on the basal 

 surface of the cerebrum. These two gyri together constitute 

 the gyrus fornicatus (limbic lobe). 



Experimental and clinical evidence suggests that some of 

 the higher sensory centres are situated in the gyrus cinguli, and 

 lesions in this situation usually produce some alterations in 

 sensibility on the opposite side of the body. 



From the region of the occipital pole, the Calcarine Fissure 

 passes forwards and meets the Parieto-Occipital Fissure at an 

 acute angle below the splenium of the corpus callosum 

 (Fig. 6). The area contained between these sulci and the 

 supero-medial border of the hemisphere is known as the 

 Cuneus. It belongs to the occipital lobe and contains some 

 of the higher visual centres. A cortical lesion of the cuneus 

 produces blindness in the lower lateral quadrant of the 



