1360 SUKFACE AND SUKGICAL ANATOMY. 



" Find also the zygomatic process (E), and the root of the zygoma (preauricular 

 point) (P), immediately above and in front of the external acoustic meatus. 

 Having found these five points, join EP, PS, and ET. Bisect EP and PS at N and 

 E. Join MN and ME. Bisect also AB at C, and draw CD parallel to AM." 



The line MA corresponds to the superior and inferior precentral sulci, and may 

 therefore be termed the pre-central line. The origins of the superior and inferior 

 frontal sulci may be indicated by the points of union of the upper and middle and 

 the middle and lower thirds of the line MA, the lower point being at the level 

 of the temporal crest. 



The line ET, termed the oblique or lateral line, intersects the pre-central line 

 at the point A, which overlies the pterion, and corresponds therefore to the lateral 

 point of the lateral cerebral fissure and to the anterior division of the middle meningeal 

 artery. AC overlies the posterior horizontal limb of the lateral fissure of the brain, 

 which terminates at the level of the temporal crest, in the inferior part of the 

 triangle HCB. This triangle contains the parietal tuber, and may, therefore, be 

 termed the supra-marginal triangle. The termination of the lateral line, at the 

 three-quarter sagittal point T, overlies the parieto-occipital fissure. 



By joining TE, EO, a triangle is mapped out which delimits the surface of the 

 occipital lobe ; the line TE corresponds to the lambdoidal suture, while EO corresponds 

 to, or lies a little above, the tentorium and the upper border of the transverse sinus. 



CD, the post-central line, corresponds to the superior post-central sulcus, and lies 

 a little behind the inferior post-central sulcus. 



The parallelogram AMDC overlies the Rolandic area, i.e. the anterior central 

 gyrus and the posterior central gyrus, separated by the central sulcus. 



The pentagon ABEPN maps out the temporal lobe, with the exception of its 

 apex, which is directed downwards, forwards, and inwards, a finger's-breadth in 

 front of the point N. 



A finger's-breadth below AB is the superior temporal sulcus, the posterior 

 extremity of which turns upwards to terminate at B, the point which indicates, 

 therefore, the position of the angular gyrus. 



The central sulcus of Rolando may be mapped out upon the scalp by drawing a 

 line downwards and forwards for a distance of 3| in. from a point half an inch behind 

 the mid-sagittal point M at an angle of 67 to the sagittal line (Hare). This angle 

 may readily be found by Chiene's plan of folding a sheet of paper first to half a right 

 angle and again to a quarter of a right angle (45 + 22-5 = 6 t 7'5). According to 

 Cunningham, the average angle which the fissure makes with the sagittal line is 70. 



Kronlein's scheme for projecting the more important cerebral areas on the 

 surface of the cranium is as follows: A base line, the same as that advocated % by 

 Eeid, is drawn from the infra-orbital margin backwards through the upper border of 

 the external acoustic meatus to the occipital region, which it strikes a little below 

 the inion, Fig. 1068. A second line is drawn backwards parallel to it from the supra- 

 orbital margin. Three vertical lines are now projected between these two parallels: 

 the anterior from the centre of the zygomatic arch (C), the middle from the pre- 

 auricular point (D), the posterior from the posterior border of the base of the 

 mastoid process (E). The latter is prolonged upwards to the sagittal line on the 

 cranial vault, and the direction of the central sulcus of Eolando is obtained by 

 drawing a line from this point obliquely downwards and forwards to the point 

 where the anterior vertical meets the superior horizontal line (Sylvian point). The 

 inferior extremity of the sulcus corresponds to the point where the middle vertical 

 line, prolonged upwards, meets the Eolandic line. The lateral fissure line is obtained 

 by bisecting the angle formed by the Eolandic line and the superior horizontal line. 



The topographical distribution of function in the cerebral cortex is shown in 

 Fig. 1068, in which the areas worked out by Grtinbaum and Sherrington in the 

 anthropoid apes have been transferred to the human brain. The above observers 

 have shown that, while the motor area occupies the whole length of the anterior 

 central convolution and of the central sulcus of Eolando (with the exception of its 

 very extremities), it nowhere extends on to the exposed surface of the posterior 

 central convolution ; nor does it extend as far down on the medial surface of the 

 hemisphere as the sulcus cinguli. Extirpation of the hand area, for example, is 



