CEREBRUM. 125 



The Superior frontal convolution is bounded internally by the longitu- 

 dinal fissure, and externally by the superior frontal fissure ; it is connected 

 with the superior end of the frontal convolution, and runs downward and 

 forward to the anterior extremity of the frontal lobe, where it turns back- 

 ward, and rests upon the orbital plate of the frontal bone. 



The Middle frontal convolution, the largest of the three, runs from be- 

 hind forward, along the sides of the lobe, to its anterior part ; it is bounded 

 above by the superior and below by the inferior frontal fissures. 



The Inferior frontal convolution winds around the ascending branch 

 of the fissure of Sylvius, in the anterior and inferior portion of the 

 cerebrum. 4- 



Parietal Lobe. The Ascending parietal convolution is situated just be- 

 hind the fissure of Rolando, running downward and forward; above, it 

 becomes continuous with the upper parietal convolution, and below, winds 

 around to be united with the ascending frontal. 



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. 



Te7nporo-sphenoidal Lobe. Contains three well-marked convolutions, 

 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 contains 

 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 tem- 

 poro-sphenoidal lobes. 



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 for- 

 mation 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 



