THE FORE-BRAIN OR PROSENCEPHALON 



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from which it is separated by the lingual gyrus; in front, it is situated between the 

 hippocampal gyrus and the anterior part of the fusiform gyrus. 



The Sulcus Circularis (circuminsular fissure) (Fig. 731) is on the lower and lateral 

 surfaces of the hemisphere: it surrounds the insula and separates it from the 

 frontal, parietal, and temporal lobes. 



Lobes of the Hemispheres. By means of these fissures and sulci, assisted by 

 certain arbitrary lines, each hemisphere is divided into the following lobes: the 

 frontal, the parietal, the temporal, the occipital, the limbic, and the insula. 



Frontal Lobe (lobus frontalis*) . On the lateral surface of the hemisphere this lobe 

 extends from the frontal pole to the central sulcus, the latter separating it from 

 the parietal lobe. Below, it is limited by the posterior ramus of the lateral 

 fissure, which intervenes between it and the central lobe. On the medial sur- 

 face, it is separated from the cingulate gyrus by the cingulate sulcus; and on the 

 inferior surface, it is bounded behind by the stem of the lateral fissure. 



issures and lobes of the cerebrum viewed laterally. 





The lateral surface of the frontal lobe (Fig. 726) is traversed by three sulci which 

 divide it into four gyri: the sulci are named the precentral, and the superior and 

 inferior frontal; the gyri are the anterior central, and the superior, middle, and 

 inferior frontal. The precentral sulcus runs parallel to the central sulcus, and is 

 usually divided into an upper and a lower part; between it and the central sulcus is 

 the anterior central gyrus. From the precentral sulcus, the superior and inferior 

 frontal sulci run forward and downward, and divide the remainder of the lateral 

 surface of the lobe into three parallel gyri, named, respectively the superior, middle, 

 and inferior frontal gyri. 



The anterior central gyrus (gyrus centralis anterior; ascending frontal convolution; 

 precentral gyre) is bounded in front by the precentral sulcus, behind by the central 

 sulcus; it extends from the supero-medial border of the hemisphere to the posterior 

 ramus of the lateral fissure. 



The superior frontal gyrus (gyrm frontalis superior; super/rental gyre) is situated 

 above the superior frontal sulcus and is continued on to the medial surface of the 

 hemisphere. The portion on the lateral surface of the hemisphere is usually more 

 or less completely subdivided into an upper and a lower part by an antero- 



