CORTICAL LOCALIZATION OF FUNCTION 



965 



The Sylvian Fissure. The position of the sylvian fissure is marked by a line starting 

 from a point 3 cm. (\\ inches) horizontally behind the external angular process of the frontal 

 bone to a point 2 cm. (* inch) below the most prominent point of the parietal eminence. The 

 first 2 cm. (-|- inch) will represent the basisylvian fissure, the remainder the sylvian fissure proper. 

 The sylvian point is therefore 5 cm. (2 inches) behind and about 1 cm. (| inch) above the level 

 of the" external angular process. The presylvian ramus of the fissure passes upward from this 

 point parallel to, and immediately behind, the coronal suture. 



The Tentorial Hiatus or Transverse Fissure. This is between the cerebrum and cere- 

 bellum, and corresponds to a line drawn from the inion to the external auditory meatus. 



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FIG. 716. Kronlein's method for determining the portions of certain fissures of the brain. 



Central Fissure. To find the dorsal end of the central fissure, a measurement should be 

 taken from the glabella to the external occipital protuberance. The position of the top of the 

 fissure will be, measuring from in front, 55.6 per cent, of the whole distance from the glabella to 

 the external occipital protuberance. Professor Thane adopts a somewhat simpler method. He 

 divides the distance from the glabella to the external occipital protuberance over the top of the 

 head into two equal parts, and, having thus defined the middle point of the vertex, he takes a 

 point half an inch behind it as the top of the siilcus. This is not quite so accurate as the former 

 method; but it is sufficiently so for all practical purposes, and on account of its simplicity is very 

 generally adopted. From this point the fissure runs downward and forward for 9 to 10 cm. 

 (3;! to 4 inches), its axis making an angle of about 70 degrees with the middle line. In order 

 to mark this groove, two strips of metal may be employed one, the shorter, being fixed to the 

 middle of the other at the angle mentioned. If the longer strip is now placed along the sagittal 

 suture so that the junction of the two strips is over the point corresponding to the top of the furrow, 



