1504 A MANUAL OF ANATOMY 



The posterior limb of the stem of the fissure of Sylvius is long, 

 and is directed, for the most part, horizontally backwards for fully 

 2 inches, after which it turns upwards into the parietal lobe for a 

 short distance. The line which indicates the course of the posterior 

 limb is called the Sylvian line. It extends from the Sylvian point 

 backwards for fully 2 inches, and then vertically upwards for about 

 I inch towards the region of the parietal eminence. The parietal 

 lobe and a small portion of the frontal lobe lie above the Sylvian 

 line, and the temporal lobe lies below it. 



The superior Rolandlc point is situated ^ inch behind the centre 

 of the sagittal line, which connects the nasion and the inion. This 

 point approximately represents the upper extremity of the fissure 

 of Rolando. 



The inferior Rolandic point is situated on the Sylvian line about 

 I inch behind the Sylvian point, and 2 inches above the pre- 

 auricular point. It indicates the point where the fissure of Rolando, 

 if sufficiently prolonged, would meet the posterior limb of the stem 

 of the fissure of Sylvius. 



The Rolandic line is represented by a line connecting the superior 

 and inferior Rolandic points. 



The Rolandic angle is the angle which the Rolandic line forms 

 with the sagittal line. It ranges from 65 to 70 degrees. The 

 Rolandic line, if sufficiently prolonged, would cross the zygomatic 

 arch at its centre. It indicates, in a general way, the course of the 

 fissure of Rolando, but this fissure usually ceases at a point i inch 

 above the Sylvian line. The cerebral convolutions directly in front 

 of, and behind, the Rolandic line are (i) the precentral, or ascending 

 frontal, convolution (motor area) in front, and (2) the post-central, 

 or ascending parietal, convolution (sensory area) behind. The 

 Rolandic line represents the boundary-line between the frontal and 

 parietal lobes of the cerebral hemisphere. 



The base-line of Reid represents a line drawn backwards from the 

 centre of the infra-orbital margin through the pre-auricular and 

 auricular points to the inion. The fissure of Rolando may be deter- 

 mined from Reid s base-hne in the following manner : Two lines are 

 drawn upwards to the sagittal line perpendicular to the base-line, 

 one from the pre-auricular point and the other from the posterior 

 border of the mastoid process close to its root. These two lines, 

 together with the sagittal and Sylvian lines, enclose a quadrilateral 

 area, and the diagonal connecting the postero-superior and antero- 

 inferior angles represents the fissure of Rolando except at its superior 

 and inferior limits. 



The parietal eminence, which is usually indefinite, corresponds to 

 the region situated | inch behind the centre of a line connecting 

 the pre-Rolandic and pre-auricular points. It indicates the position 

 of the supramarginal gyrus of the parietal lobe of the cerebral 

 hemisphere. 



The frontal eminence corresponds to the middle frontal convo- 

 lution. 



