THE HEAD, ANTERIOR. 21 



by continuing the line from the last point downward and back- 

 ward to the inion, following for the posterior two-thirds of 

 its extent the superior curved line of the occipital bone. 



The lower border of the cerebellum is indicated by a 

 line drawn forward and downward from the inion to the pos- 

 terior border of the mastoid process at its base. 



The Lateral Sinus. This corresponds to a band one- 

 fourth of an inch wide extending from the inion, following 

 the curved course of the superior nuchal line forward to a 

 point one inch directly behind the external auditory meatus. 



The Nasolambdoidal Line. This is a line connecting 

 the nasofrontal groove with a point five-twelfths to five- 

 eighths of an inch above the lambda. 



The Fissure of Sylvius. 



The Horizontal Portion. This is indicated by drawing 

 a line backward and slightly upward from the " Sylvian 

 point" to a point three-fourths of an inch below the most 

 prominent portion of the parietal eminence. 



The posterior two inches of this line coincides with the 

 nasolambdoidal line. 



The vertical limb of the Sylvian fissure corresponds to a 

 line one inch long drawn vertically upward from the hori- 

 zontal limb at a point three-fourths of an inch from its 

 beginning, or two inches distant from the E. A. P. 



The Fissure of Rolando. Take 57 per cent, of the 

 distance from the glabella to the inion, or (preferably) five- 

 sixths of an inch, behind the mid-point between the nasion 

 and the inion, this will indicate the central extremity of 

 the fissure of Rolando. 



From this point draw a line three and three-eighths 

 inches long downward and forward so as to make an angle 

 with the median line of 71.5 degrees. (Cunningham.) 



