CRANIO-CEREBRAL TOPOGRAPHY. 9 



upper and lower Rolandic points, and gives the general direction of the fissure of 

 Rolando. The line forms an angle (the Rolandic angle) anteriorly with the median 

 line of about 70 (varying in individual cases from 64 to 75) ; and if prolonged 

 downwards it crosses the zygomatic arch about the middle (Le Fort). The fissure of 

 Rolando is not quite so long as the Rolandic line, since the margin of the hemi- 

 sphere does not quite reach the median line above, while below, the fissure of Rolando 

 usually ends about 1 cm. above the Sylvian fissure or lower Rolandic point. The 

 Rolandic line coincides most nearly with the upper part of the fissure, the inferior 

 genu of which projects somewhat in front of the line a little below its centre, 

 a spot which is placed from 5 to 15 mm. above the lower temporal line on the 

 parietal bone. 



The precentral sulci are situated about 15 mm. in front of the fissure of Rolando, 

 with which they are nearly parallel ; from the lower of these the inferior frontal 

 sulcus arches forwards and downwards beneath the temporal crest of the frontal 

 bone, which can be felt through the skin ; and the position of the superior frontal 

 sulcus may be indicated approximately by a line running forwards from the superior 

 precentral sulcus slightly internal to the centre of the interval between the temporal 

 crest and the median line of the forehead. 



The postcentral sulci being also nearly parallel to, and about 15 mm. distant 

 from, the fissure of Rolando, the average position of the longitudinal portion of the 

 intraparietal sulcus may be marked by a line drawn from the centre of the Rolandic 

 line to a spot 35 mm. external to the lambda, or 15 mm. from the end of the parieto- 

 occipital line. 



Lastly, the seat of the parallel fissure may be determined by the above- 

 mentioned line from the marginal tubercle of the malar bone to the lambda. 



Island of Reil, basal ganglia, and lateral ventricles. The Sylvian point marks 

 the position of the pole of the insula, and a spot on the Sylvian line 35 mm. behind 

 this point will correspond to its posterior angle. The upper limit of the insula may 

 then be indicated by a line, slightly convex upwards, drawn from its posterior angle 

 to the upper end of the anterior ascending branch of the Sylvian fissure, and 

 continued forwards for a distance of 15 mm. beyond the vertical passing through 

 the Sylvian point ; the lower limit by a line directed from the posterior angle down- 

 wards and forwards to a spot on the parallel line immediately below the Sylvian 

 point ; and the anterior limit by a line joining the anterior extremities of the two 

 foregoing lines. The area of the insula thus marked out will serve as a guide to 

 the position of the basal ganglia, which extend slightly beyond the limits of the 

 island, and are circumscribed by a strongly-curved line corresponding to the outer 

 border of the main part of the lateral ventricle. This line may be traced, beginning 

 at the anterior extremity of the ventricle 1 cm. in front of the foremost point of the 

 insula, and passing backwards in an arch, which follows the margin of the anterior 

 horn and body of the cavity, an equal distance above the upper limit of the island 

 to a spot 2 cm. behind its posterior extremity. Thence, the inferior horn runs 

 forwards and downwards, to end about 1 cm. below the level of the parallel fissure 

 and somewhat in advance of the coronal plane passing through the lower Rolandic 

 and preauricular points. From the back of the loop thus indicated the posterior 

 horn extends a variable distance towards the hindmost point of the hemisphere, 

 which is placed a little higher than the occipital pole, beneath the occipital point of 

 the skull. 1 



1 For more detailed information as to cranio-cerebral topography, reference may be made to the 

 memoir by D. J. Cunningham, Contribution to the Surface Anatomy of the Cerebral Hemispheres, with 

 a Chapter on Cranio-Cerebral Topography, by Victor Horsley. The subject is also fully illustrated by 

 the series of models prepared under the direction of the former anatomist, showing the relations of the 

 cerebral hemispheres in situ in a number of individuals of both sexes and at various periods of life, from 

 infancy to old age. 



