786 MAN 



from each other by correspondingly tortuous fissures. The superior frontal 

 gyrus is situated between the margin ot the hemisphere and the superior 

 frontal sulcus; it corresponds to the upper part ol the hemisphere and is 

 mucli longer than any of the other frontal convohitions upon the lateral 

 surface. It is continued mesially to the marginal gyre on the mesial surface 

 and joins the central convolution by means of a lateral bridge at the upper 

 end of the precentral fissure. The middle frontal gyrus is parallel to the 

 superior frontal eoinolution in a general way, separated from it by the 

 superior frontal sulcus. The superior and inferior precentral sulci separate 

 this gyre from the central con\()hition although a well-marked deep annec- 

 tent gyrus usuallx connects them. The inferior frontal eoinolution, the 

 smallest of the three gyres in this region, is in some respects the most impor- 

 tant of them all. It is situated in relation with the horizontal and ascending 

 branches of the SyKian fissure. These branches di\ide the inferior frontal 

 convolution into three parts, the anterior frontal operculum (pars orbitalis), 

 the intermediate frontal operculum (pars triangularis) and the posterior 

 frontal operculum (pars basalis). The left inferior frontal eoinolution is 

 often called Broca's convolulion and it is regarded as the motor speech center. 

 In man it is more dcxcloped upon the left side m right-handed indniduals. 

 This greater development i:)articularly aflects the triangufar part of the con- 

 volution which ma\' cntirel\ separate the horizontal and ascending branches 

 of the Sylvian fissure. 



The Parietal I.ohc. The |)arictal lobe presents an extensive and irregular 

 C|uadrilateral outline. It is bounded b\ the l^olaiidic fissure in front, below 

 by the fissure of S\l\ius, and behind by the imaginary line connecting the 

 pre-occipital notch with the external portion of the pancto-occipital fissure. 

 Upon Its lateral surfai'e the parietal lobe is di\ ided b\ an interruptc'd fissure, 

 the intraparietal sulcus, into three coinolutions, the post-central, sujicrior 

 parietal and inferior parit'tal gyres. The intraparii'tal sulcus commences at 



