406 THE BRAIN 



posterior ram us of the lateral fissure, below. It lies between 

 the central and the precentral sulci and is the region of the 

 motor area of the brain. It is continuous, at its upper and 

 its lower ends, round the extremities of the central sulcus, 

 with the posterior central gyrus. From its posterior face 

 two buttresses, an upper and a lower, project backwards, as 

 pointed out on p. 403. The buttresses form excellent land- 

 marks for the delimitation of the parts of the motor area. 

 Anteriorly, the anterior central gyrus is continuous with the 

 superior, middle, and inferior frontal gyri, and, inferiorly, it 

 forms part of the fronto-parietal operculum (p. 401). Its 

 lower two-thirds are supplied by the middle cerebral artery, 

 and its upper third is supplied by the anterior cerebral 

 artery (Fig. 148). 



Gyrus Frontalis Superior. The superior frontal gyrus lies 

 above the superior frontal sulcus. It forms also part of the 

 supero-medial border and part of the medial surface of the 

 hemisphere. It is continuous, posteriorly, with the anterior 

 central gyrus, and, anteriorly, round the frontal pole, with 

 the gyrus rectus and the medial orbital gyrus of the inferior 

 surface of the frontal lobe. The supero-lateral part of the 

 superior frontal gyrus is frequently divided into upper and 

 lower parts by an interrupted furrow called the paramedial 

 frontal sulcus (Fig. 137). 



Gyrus Frontalis Medius. The middle frontal gyrus lies 

 between the superior and inferior frontal sulci. It is con- 

 tinuous, posteriorly, with the anterior central gyrus, and, 

 round the superciliary border, with the anterior orbital gyrus of 

 the inferior surface of the frontal lobe. The horizontal or 

 oblique limb of the inferior precentral sulcus cuts into its 

 posterior end (Fig. 138). 



Gyrus Frontalis Inferior. The centre for speech has been 

 associated with the posterior part of the inferior frontal gyrus 

 of the left side ; therefore the inferior frontal gyrus is a 

 region of special interest. It extends forwards, from the 

 inferior precentral sulcus, and is continuous, round the 

 superciliary border, with the lateral and posterior orbital gyri 

 of the inferior surface of the frontal lobe. The inferior 

 frontal gyrus is divided into three parts by the anterior 

 ascending and the anterior horizontal rami of the lateral 

 fissure. The posterior part is sometimes called the pars 

 basilaris ; it lies between the anterior ascending ramus of the 



