-82 MAN 



CMicc between the ant hrcjpoids and man in this feature of the l^rain is the 

 miieh more marked degree of eomplexitx' m the mchx idual eomponents ol the 

 Sylvian fissure due to greater mtrieae\ ui the eonx olutions surrounding them. 

 The arrangement ol the \arious sul)di\ isions ot the Sylvian suleus is subjeet 

 to some variation. For further details m this regard the reader is referred to 

 standard works on the anatomy of the human brain. 



The Fissi re of Rolando. The Rolandie or eentral fissure of the 

 brain extends obliquely aeross the lateral surfaee of the hemisphere in such 

 a way as to interrupt the general longitudinal course of the gyri and sulci 

 of this region. It is bounded by two long oblique convolutions, the j)recentral 

 and postcentral gyres. The fissure begins near the vertex in relation \\ ith the 

 superior longitudinal fissure and often incises the mesial surface of the hemi- 

 sphere. Its point of origin on the vertex is slightly behmd the midpoint of 

 the superior longitudinal fissure, a little further back in man than in the great 

 anthropoids. I^rom this ]:)oint it passes outward, downward and forward to end 

 near the middle of the fissure of Syhius whose posterior limb it sometimes, 

 though rar(.'l\, joins. At the junction of its upper and middle thirds the fis- 

 sure of Rolando presents a deep curve with the concavity directed lorward. 

 The upper and lower limits of this bend in the fissure constitute the su|)erior 

 and inferior genu respectively. The lower or inlerior genuot the fissure extends 

 almost verticall\ and terminates in close relation with the fissure of Syl\-ius. 

 The'angle of inclination of the central fissure with the mesial plane in the 

 adult brain averages 71."^". This angle is essentially the same as in the great 

 anthropoids, although in man\ instances in llu' lower primates the angle is 

 much nearer ()()°. In certain exceptional instances among the great anthro- 

 poids this angle varies from 75° to 80°. 



The Parieto-Occh^it.al Fisslre. The parieto-occipital fissure is best 

 seen upon the mesial surface and has but slight representation upon the 

 lateral convexity in man. On this surface, as the parietal incisure, it is con- 



