466 THE BRAIN 



the medial surface of the hemisphere. It commences on the 

 lower portion of the anterior part of the medial surface, curves 

 first upwards and then posteriorly. Finally, turning upwards, 

 it cuts the supero-medial border of the hemisphere a short 

 distance behind the upper end of the sulcus centralis, and 

 terminates on the lateral surface of the parietal lobe. It 

 separates the anterior portion of the medial surface into a 

 marginal and a central area. The central part is the gyrus 

 cinguli (O.T. callosal gyrus). The marginal part is separ- 

 ated into two portions by a branch of the sulcus cinguli, which 

 projects upwards above the middle of the corpus callosum. 

 The anterior part is the medial area of the superior frontal 

 gyrus ; the posterior part is the paracentral lobule. 



Boundaries of the Frontal Lobe. The frontal is the largest 

 of the cerebral lobes. On the lateral surface of the hemisphere 

 it is bounded posteriorly by the central sulcus, and below by 

 the posterior branch of the lateral fissure. On the medial 

 surface it is limited by the sulcus cinguli ; whilst on the inferior 

 surface of the hemisphere the stem of the lateral fissure 

 forms its posterior boundary. 



Lateral Surface of the Frontal Lobe. On the lateral 

 surface of the frontal lobe the following sulci and gyri may be 

 recognised : 



Sulci x 



Sulcus prsecentralis in- 

 ferior. 



Sulcus prsecentralis su- 

 perior. 



Sulcus paramedialis. 



Sulcus frontalis superior. 



Sulcus frontalis medius. 



Sulcus frontalis inferior. 



Sulcus diagonalis. 



Sulcus fronto-marginalis. 



Gyri 



Gyrus centralis anterior. 

 Gyrus front- /Pars superior, 

 alis superior \Pars inferior. 

 Gyrus front- /Pars superior, 

 alis medius \ Pars inferior. 

 Pars basilaris. 

 Gyrus front- 1 Pars triangu- 

 alis inferior. "1 laris. 



I Pars orbitalis. 



Sulcus Prcecentralis Inferior (Fig. 186). The inferior prae- 

 central sulcus consists of a vertical and a horizontal part, 

 and, when present in a well-marked form, it presents a figure 

 like the letter T or F. The vertical portion lies anterior to 

 the lower part of the central sulcus (O.T. fissure of Rolando), 

 and the horizontal portion extends antero-superiorly into the 

 middle frontal gyrus. 



Sulcus Prczcentralis Superior (Fig. 186). This is a short 

 vertical sulcus which lies anterior to the upper part of the 



