THE BRAIN AND THE WALLS OF THE CRANIAL CAVITY 729 



fissure is iimnediately above the posterior horizontal limb of the fissure of Sylvius; 

 it Hes beneath the point of intersection of the auriculo-bregniatic line with a line 

 drawn from the stephanion (the point where the temp{jral ridge cuts the coronal 

 suture) to the asterion (Macalister). In skulls of a sagittal length of 18 cm. and 

 over this i)()int is 45-5 per cent, of the horizontal arc from the glabella to tlie inion. 

 and in skulls of less than 18 cm. it is 46 per cent, of the same arc posterior to the 

 glabella. 



The i)<)siti()n of the posterior horizontal limb of the fissure of Sylvius varies; its 

 posterior part is always under cover of the parietal bone and it terminates either in 

 front of or below the parietal eminence, but the anterior part may be above, 

 l)eneath, or below the squamo-parietal suture. In the adult the anterior part of 

 the fissure runs upwards and backwards from the posterior end of the spheno- 



FiG. 433. — Drawing of a Cast of the Head of an Adult Male. 

 (Prepared by Professor Cunningham to illustrate cranio-cerebral topography.) 



POSITION OF 

 FRONTAL EMINENCE 



FISSrjlE OF 

 STL vies 



MIDDLE 



TEMPORAL 



FISSURE 



l)arietal suture along the anterior part of the squamo-i)arietal suture to its highest 

 point; thence it continues in the same direction beneath the parietal bone towards 

 the laml)da, terminating either in front of or below tlie parietal eminence. In the 

 child, however, the fissure is considera])ly above the line of the squamo-parietal 

 suture (fig. 434), which it gradually approaches, attaining its adult position about 

 the ninth year; this cliange of position, which occurs during the first nine years, is 

 • Kie i)artly to the ascent of the sutural line and partly to the descent of the fissure 

 on the surface of tlie l)rain. 



The upi)er end of the external parieto-occipital fissure usually lies about 5 nun. 

 in front of the lambda, and the course of the fissure may be indicated liy a line 

 drawn from 5 mm. in front of the lambda to a point"^ immediately above the 

 asterion. and. as the latter point corresponds with the i)re-occipital notch on, the 



