LOBES AND GYRI OF THE CONVEX SURFACE. 59 



considers the occipito-parietal sulcus a true fissure because in the 

 embryo it produces a ventricular eminence, though it disappears 

 during development.* 



LOBES AND GYRI OF THE CONVEX SURFACE. 



(1) The frontal lobe (lobus frontalis) comprises the anterior 

 polar region of the hemisphere and forms a part of all three sur- 

 faces (Figs. 22, 28 and 26).. On the convex surface, it extends 

 as far back as the central sulcus and the lateral cerebral fissure; 

 on the basal surface, it is bounded behind by the stem of the 

 lateral cerebral fissure and the anterior perforated spot; and it is 

 limited posteriorly by the sulcus cinguli on the medial surface 

 of the cerebral hemisphere. 



On the convex surface, the frontal lobe has the following sulci 

 and gyri (Figs. 23 and 24): 



Superior precentral (s. prascentralis superior) 

 Inferior precentral (s. praecentralis inferior) 

 . j Superior frontal (s. frontalis superior) 

 ^ Inferior frontal (s. frontalis inferior) 

 Middle frontal (s. frontalis medius) 

 . Paramedial (s. paramedialis). 



f Anterior central (g. centralis anterior) 

 . j Superior frontal (g. frontalis superior) 

 I Middle frontal (g. frontalis medius) 

 I Inferior frontal (g. frontalis inferior). 



The precentral sulci (Fig. 23) are parallel with the central 

 sulcus and are located about a half inch in front of it, the lower 

 end of the inferior precentral being insinuated between the central 

 sulcus and the ascending ramus of the lateral fissure of the cere- 

 brum. They form the anterior boundary of the anterior central 

 gyrus. The superior frontal sulcus and the inferior frontal sulcus 

 are respectively continuous with the corresponding precentral 

 sulcus from which they trend downward and forward parallel 



*The name of this sulcus is written "occipito-parietal" rather than 

 "parieto-occipital;" this is a simpler word to pronounce as it avoids 

 having "oocc" in the middle of it. 



