io THE NERVOUS SYSTEM 



situated between the superomedial border of the hemisphere 

 and the angular and supramarginal gyri. From the two 

 latter it is separated by the ramus horizontalis of the post- 

 central sulcus. It is believed to contain the centre for stereo- 

 gnosis, the sense by which objects can be identified by tactile 

 impressions only. When symptoms of cerebral tumour are 

 present, the development of astereognosis indicates that the 

 tumour is situated in the neighbourhood of the superior 

 parietal gyrus. Cases of astereognosis have also been 

 recorded in which the lesion has been confined to the supra- 

 marginal convolution (Fig. 3). 



The posterior part of the lateral surface of the cerebrum 

 belongs to the occipital lobe. This portion of the cortex 

 contains some of the higher visual centres, but as they appear 

 to be connected more intimately with the medial surface of the 

 occipital lobe, their description is deferred until that aspect 

 of the brain is described (p. 12). 



When the lips of the posterior ramus of the lateral fissure 

 are drawn apart, a submerged area of the cerebral cortex is 

 brought into view. This area is termed the Island (of Reil). 

 It is of value as a landmark in the study of sections of the 

 brain which pass through the anterior part of the cerebral 

 hemisphere (Fig. 18). Practically nothing is known about its 

 functions, and, although Campbell has suggested that its 

 anterior portion contains the higher centres for the sense of 

 taste, his views have no clinical evidence to support them. 



The Medial Surface of the Cerebral Hemisphere 



The most noticeable structure on the medial surface is the 

 Corpus Callosum. It consists of white matter, the fibres of 

 which run mainly in a transverse direction and connect cortical 

 areas of one hemisphere to the corresponding areas of the 

 other. The posterior extremity of the corpus callosum, which 

 is termed the spknium^ forms a rounded swelling, overhanging 

 the posterior aspect of the mid-brain (Fig. 5). The body 



