CEREBRUM. 139 



The Upper parietal convolution is situated between the parietal and 

 longitudinal fissures. 



The Supra- marginal convolution winds around the superior extremity 

 of the fissure of Sylvius. 



The Angular convolution, a continuation of the preceding, follows the 

 parietal fissure to its posterior extremity, and then makes a sharp angle 

 downward and forward. 



Temporo-sphenoidal Lobe. Contains three well-marked convolu- 

 tions, the superior, middle and inferior, separated by well-defined fissures, 

 and continuous posteriorly with the convolutions of the parietal lobe. 



The Occipital Lobe lies behind the parieto-occipital fissure, and con- 

 tains the superior, middle and inferior convolutions, not well marked. 



The Central Lobe, or Island of Reil, situated at the bifurcation of the 

 fissure of Sylvius, is a triangular-shaped cluster of six convolutions, the 

 gyri operti, which are connected with those of the frontal, parietal, and 

 temporo-sphenoidal lobes. 



Upon the inner or mesial aspect of the hemisphere are found (Fig. 15) 



1. The Par acentral lobule, lying in the region of the upper extremity of 

 the fissure of Rolando; it contains the large giant cells of Betz. Injury to 

 this convolution is followed by degeneration of the motor tract. 



2. The Gyrus fornicatus, lying below the calloso-marginal fissure. 

 Running parallel with the corpus callosum, it terminates at its posterior 

 border in the hippocampal gyms. 



3. The Gyrus hippocampus (H) is formed by the union of the preceding 

 convolution with the occipito-temporal. It runs forward and terminates 

 in a hooked extremity uncus. 



4. The Quadrate lobule or precuneus lies between the upper extremity 

 of the calloso marginal fissure and the parieto-occipital. 



5. The Cuneus lies posteriorly to the quadrate lobule. It is a wedge- 

 shaped mass enclosed by the calcarine and parieto-occipital fissures. 



Structure. The Gray matter of the cerebrum, about one-eighth of an 

 inch thick, is composed of five layers of nerve cells : (i) a superficial layer, 

 containing few small multipolar ganglion cells ; (2) small ganglion cells, 

 pyramidal in shape; (3) a layer of large pyramidal ganglion cells with 

 processes running off superiorly and laterally ; (4) the granular formation 

 containing nerve cells; (5) spindle-shaped and branching nerve cells of 

 moderate size. 



The White matter consists of three distinct sets of fibres : 



I. The diverging or peduncular fibres are mainly derived from the 



