THE CEREBRUM 419 



the same manner. By that expedient the fibres of the corpus 

 callosum may be traced into individual gyri. 



Cingulum. Examine the deep surface of the gyms cinguli, 

 which has been torn away, and note that a large bundle of 

 longitudinally directed fibres is embedded in its substance. 

 The bundle is the cingulum. It is a longitudinarassociation 

 bundle, composed of several systems of fibres which run only 

 for short distances within it and then pass into the adjacent 

 parts of the gyrus fornicatus. It curves round the convexity 

 of the corpus callosum, commencing, in front, at the anterior 

 perforated substance and terminating, posteriorly, in the 



Precuneus S} i FTl J-- Gyrus cinguli 



Corpus callosum 



Medial parieto- 



occipital fissure 





***>** 



Posterior cuneo-^\/-*> Anterior part of the 



lingual deep gyrus calcanne fissure 



FIG. 158. Posterior part of medial surface of the Left Hemisphere. The 

 calcarine and the parieto-occipital fissures are widely opened up to show 

 the deep gyri within them. 



hippocampal gyrus (Fig. 156). It can be easily displaced 

 from its bed by the exercise of a very slight degree'of traction. 



The fissures and sulci and gyri on the medial surface of 

 the left hemisphere should now be studied. 



The Fissures and Sulci on the Medial Surface of the Hemi- 

 sphere are the medial part of the parieto-occipital fissure ; 

 the posterior part of the calcarine fissure ; the callosal sulcus ; 

 the sulcus cinguli ; the subparietal sulcus ; and, possibly, the 

 upper end of the central sulcus. 



Fissura Parieto-occipitalis. The medial part of the parieto- 

 occipital fissure descends on the posterior part of the medial 

 surface of the hemisphere between the occipital and parietal 

 lobes. It terminates a short distance behind the posterior 

 end of the corpus callosum, and close to the medial occipital 

 border, by joining the calcarine fissure. If the dissector 

 in 27 a 



