1340 



CLINICAL AND TOPOGRAPHICAL ANATOMY 



The position of the chief sulci will now be given: — 



Lateral (Sylvian) fissure (fig. 1089). — The point of appearance of this, on 

 the outer side of the brain, practically corresponds to the pterion (p. 1332, fig. 

 1085) — a point which lies in the temporal fossa, about 3.7 cm. (1| in.) behind the 

 zygomatic process and about the same distance above the zygoma. From this 

 point the lateral fissure, which here separates the frontal and parietal from the 

 temporal lobe, runs backward and upward, ascending gently, at first in the line 

 of the squamo-parietal suture, then crossing this suture about its centre and 

 thence, ascending more rapidly, it climbs up to the temporal ridge, to end 1.8 cm. 

 (I in.) below the parietal eminence. Its termination is surrounded by the 

 supramarginal convolution, to which the parietal eminence corresponds with 

 sufficient accuracy. Such being the surface-marking of the chief or posterior 

 horizontal limb of the lateral fissure (s^, fig. 1089), it remains to indicate briefly 

 the two shorter limbs which bound the inferior frontal convolution, which, on the 

 left side, contains the centre for speech (Broca's convolution), and corresponds 

 to a point lying three fingers' breadth vertically above the centre of the zygo- 

 matic arch. (Stiles.) Of these, the anterior horizontal (s^, fig. 1089) runs for- 

 ward across the termination of the coronal, just above the line of the spheno- 

 parietal suture. The ascending limb (s^, fig. 1089) runs upward for about 



Fig. 1090. — Lateral View op the Skull, Showing the Topography of the Middle 

 Meningeal Artery and the Transverse Sinus. 



Anterior branch 



of middle 



meningeal art. 



Posterior 

 branch of 

 middle menin- 

 geal art. 



Transverse 

 (lateral) sinus 



2.5 cm. (1 in.) just behind the termination of the coronal suture, or 5 cm. (2 in.) 

 behind the zygomatic process. 



The central sulcus (fissure of Rolando). — This most important fissure, in 

 front of which, in the precentral convolution of the frontal lobe, lie the motor 

 centres for the opposite side of the body, is situated under the parietal bone. 

 It may be marked out with sufficient precision in the following way (Thane) : 

 The sagittal line, from glabella to external occipital protuberance, is bisected, 

 and a point 1.2 cm. (^ in.) behind the centre represents the superior Rolandic point. 

 From this point a line drawn downward and forward 9 cm. (3f in.) long, at an angle 

 of 67^2° with the sagittal line (i. e., f of a right angle) will represent the central 

 sulcus. The lower extremity of this line is known as the inferior Rolandic point. 



This method is open to the objection that it only applies to the average adult skull, and not 

 to skulls of all sizes. To obviate this difficulty the method of Kronlein may be employed in 

 addition (fip;. 108.5). A base line BIj is drawn thro>ip;h the lower border of the orbit and the 

 upper border of the external acustic meatus. Parallel to this an upper horizontal line UH is 

 marked out at the level of the upper margin of the orbit. Three lines vertical to the base line 

 arc; now drawn, f 1) at the posterior border of the mastoid process MHi (2) througli the condyle 

 of the lower jaw (Clij), and (3) from the mid-point of the zygoma (ZS). The point Ri, where 

 tlio first vertical joins the sagittal suture is the superior Rolandic point. The point S where 

 the third vertical ZS cuts the line VM marks the junction of the three lirrd)S of the lateral fissure. 

 A line joining Ri and S will cut the second vertical CR2 at the inferior Rolandic point, Rj. 



