THE EXTERNAL CONFIGURATION OF THE CEREBRAL HEMISPHERES 



235 



frontal lobe. Within it one may identify three chief sulci, which are, however, 

 subject to considerable variation. The precentral sulcus is more or less parallel 

 with the central sulcus and is often subdivided into two parts, the superior and 

 inferior precentral sulci (Fig. 168). The superior frontal sulcus usually begins 

 in the superior precentral sulcus and runs rostrally, following in a general way 

 the curvature of the dorsal border of the hemisphere which it gradually ap- 

 proaches. The inferior frontal sulcus usually begins in the inferior precentral 

 sulcus and extends rostrally, arching at the same time toward the base of the 

 hemisphere. 



Between the precentral and central sulci lies the anterior central gyrus in 

 which is found the motor area of the cerebral cortex. The remainder of this 



Anterior central gyrus 



Superior precentral sulcus \ 



Superior frontal gyrus 



Superior frontal sulcus ----- .^^ 

 Middle frontal gyrus-. 

 Middle frontal sulcus -/^ 

 Inferior frontal sulcus V_ ~,~* 



Inferior precentral sulcus I 



Inf. (Parsopercularis -1 ~_~~~ 



front. \ Pars triang. -4 



gynts\ Pars orbitalis-\ _ 



Lateral ( Ant. nor. ram. 

 cerebral] Ant. ascend, ram.'' / 

 fsstire ( Post, ram..''' 



Superior temporal siikus*'' 

 Superior temporal gyrus 



, Posterior central gyrus 

 Postccntral sulcus 



,,Supramarg. gyrusl 

 ^Angular gyrus 



''Superior parietal lobule 

 Interparielal sulcus 



Trans, occipital sulcus 



Sulcus lunatus 

 * \Infer tor temporal gyrus 

 \ Middle temporal sulcus 

 Middle temporal gyrus 



Fig. 168. Sulci and gyri on the lateral aspect of the human cerebral hemisphere. 



surface of the frontal lobe is composed of three convolutions, the superior, 

 middle, and inferior frontal gyri, separated from each other by the superior and 

 inferior frontal sulci. The inferior frontal gyrus, which in the left hemisphere 

 is also known as Broca's convolution, is subdivided by the two anterior rami of 

 the lateral sulcus into three parts, known as the orbital, triangular, and oper- 

 cular portions. The orbital part of the inferior frontal gyrus lies rostral to the 

 anterior horizontal ramus of the lateral sulcus; the triangular part is a wedge- 

 shaped convolution between the two anterior rami of that fissure; while the 

 opercular portion lies in the frontal operculum between the precentral sulcus 

 and the anterior ascending ramus of the lateral fissure. 



The Temporal Lobe. Ventral to the lateral fissure is the long tongue-shaped 



