SURFACE MARKINGS OF SPECIAL REGIONS OF HEAD AND NECK 1293 



only be regarded as approximately correct, yet they are all sufficiently accurate 

 for surgical purposes. The longitudinal fissure corresponds to the medial line of 

 the scalp between the nasion and inion. In order to mark out the lateral cerebral 

 (Sylvian) fissure a point, termed the Sylvian point, which practically corresponds 

 to the pterion, is defined 35 mm. behind and 12 mm. above the level of the fronto- 

 zygomatic suture; this point marks the spot where the lateral fissure divides. 

 Another method of defining the Sylvian point is to divide the distance between 

 the nasion and inion into four equal parts; from the junction of the third and 

 fourth parts (reckoning from the front) draw a line to the frontozygomatic suture; 

 from the junction of the first and second parts a line to the auricular point. These 

 two lines intersect at the Sylvian point and the portion of the first line behind 

 this point overlies the posterior ramus of the lateral cerebral fissure. The position 



Fio. 1198. Relations of the brain and middle meningeal artery to the surface of the skull. 1. Nasion. 2. Inion. 

 {.Lambda. 4. Lateral cerebral fissure. 5. Central sulcus. A A . Reid's base line. B. Point for trephining the anterior 

 branch of the middle meningeal artery. C. Suprameatal triangle. D. Sigmoid bend of the transverse sinus. E. 

 Point for trephining over the straight portion of the transverse sinus, exposing dura mater of both cerebrum and 

 cerebellum. Outline of cerebral hemisphere indicated in blue; course of middle meningeal artery in red. 



of the posterior ramus can otherwise be obtained by joining the Sylvian point to a 

 point 2 cm. below the summit of the parietal eminence. The anterior ascending 

 ramus can be marked out by drawing a line upward at right angles to the line 

 of the posterior ramus for 2 cm. and the anterior horizontal ramus by a line of the 

 same length drawn horizontally forward both from the Sylvian point. To define 

 the central sulcus (fissure of Rolando) two points are taken; one is situated 1.25 

 cm. behind the center of the line joining the nasion and inion; the second is at 

 the intersection of the line of the posterior ramus of the lateral cerebral fissure 

 with a line through the preauricular point at right angles to Reid's base line. The 

 upper 9 cm. of the line joining these two points overlies the central sulcus and forms 

 an angle, opening forward, of about 70 with the middle line of the scalp. An 

 alternative method is to draw two perpendicular lines from Reid's base line to the 

 top of the head; one from the preauricular point and the other from the posterior 



