PRACTICAL CONSIDERATIONS : THE BRAIN. 



1215 



Anderson and Mackins suggest : (i) a median sagittal line from the glabella to 

 the inion ; (2) a frontal line from the mid-sagittal point to the depression just in front 

 of the ear at the level of the upper border of the meatus ; (3) a squamosal line from 

 the most external point of the external angular process, at the level of the superior 

 border of the orbit to the junction of the middle and lower thirds of the frontal line, 

 and prolonged for about 3. 7 cm. ( i ^ in. ) behind the frontal line. The upper ex- 

 tremity of the central fissure was found by them to lie between the mid-sagittal point 

 and a point 18 mm. (^ in.) behind it, and the lower extremity of this fissure they 

 located near the squamosal line, about 18 mm. (^ in.) in front of its junction with 

 the frontal line. The commencement of the lateral portion of the Sylvian fissure is 

 not at a definite fixed point, but will usually be hit at a point from 3. 7-5 cm. ( i ^2 

 in. ) behind the angular process, the course of the horizontal portion of this 

 fissure corresponding closely to the squamosal line (Mills). 



Fissure of Rolando 



FIG. 1044. 



Bregma 



Line for Rolandic fissure 



Interparietal fissure 



External parieto- 

 occipital fissure 



Parietal eminence 



Inion 



Lateral sinu 



Posterior limb 

 of Sylvian fissure 



Line for 

 Sylvian fissure 



Vertical limb 

 of Sylvian fissure 



Horizontal limb 

 of Sylvian fissure 

 Glabella 



Nasion 



Semidiagrammatic view of head, showing relation of Rolandic and Sylvian fissures and lines. 



The fissure of Sylvius begins anteriorly, approximately, at a point 3 cm. ( I % 

 in. ) behind the external angular process of the frontal bone ; and ends posteriorly at 

 a point 1 8 mm. (^ in.) below the parietal eminence. A straight line between these 

 two points will represent the fissure, which is about 10 cm. (4 in. ) long. The an- 

 terior 1 8 mm. (34 in.) of this line will correspond to the main portion of the fissure 

 and the remainder to the horizontal limb. The vertical limb ascends for about 

 2.5 cm. (i in.) from the posterior end of the main fissure. Around the posterior 

 end of the horizontal limb, and approximately under the parietal eminence lies the 

 supramarginal convolution. It is continuous in front with the ascending parietal 

 convolution, and behind with the angular gyrus. 



The parieto-occipital fissure is most marked on the mesial surface of the brain. 

 The external limb passes outwards, almost at right angles to the longitudinal fissure 

 on the external surface for about 2.5 cm. and lies from 2-3 mm. in front of the lambda. 



The frontal lobe is divided into three main convolutions by the superior and in- 

 ferior frontal sulci. The line for the superior frontal sulcus passes directly backward 



