40 APPLIED ANATOMY. 



at the asterion. Its anterior third is well marked, but as it crosses the coronal suture 

 it fades away and gradually broadens out, its upper margin being called the superior 

 and its lower the inferior temporal ridge. The superior ridge marks the attachment 

 of the superficial layer of the temporal fascia, the inferior, the deep layer. 



External Angular Process. This is the outer extremity of the frontal bone, 

 where it articulates with the malar. The line of the suture can be distinctly felt in 

 the living. 



Malar Tubercle. This is the small bony projection on the posterior edge of 

 the malar bone, 1.25 to 2 cm. (}4 to ^ in.) below the frontomalar suture. 



Stephanion. The point where the temporal ridge crosses the coronal suture. 



TOPOGRAPHICAL POINTS. 



Pre-auricular Point. The depression in front of the ear and just behind the 

 conclyle of the lower jaw. 



Sylvian Point. Where the anterior ascending and anterior horizontal limbs 

 come off from the posterior horizontal limb of the fissure of Sylvius. It lies 4 cm. 

 ( i y% in. ) posterior and a little above the external angular process, at the junction of 

 the parietal, sphenoid, and temporal bones. 



Superior Rolandic Point. Where the upper end of the line marking the 

 Rolandic fissure crosses the median line. 



Inferior Rolandic Point. Where the lower end of the line marking the 

 Rolandic fissure crosses the line of the Sylvian fissure. 



THE LOWER LEVEL OF THE BRAIN. 



The lower level of the brain is marked by a line beginning in the median line 

 I cm. (f- in.) above the nasion, thence above the orbit i cm. from its edge to the 

 external angular process; from here it goes to the middle of the zygoma, thence 

 backward along its upper border, above the auditory meatus and along the supe- 

 rior curved line to the inion (occipital protuberance). 



FISSURES AND CONVOLUTIONS. 



The conformation of the various fissures and convolutions varies so much within 

 normal limits that it is not possible to outline them on the surface of the scalp or 

 skull with absolute exactness. The various lines which are laid out to indicate their 

 course are, therefore, only approximate, but they are sufficiently accurate for opera- 

 tive purposes. To allow for variations, the openings made are usually large, and the 

 motor areas are sometimes identified by the application of an electrode. 



Fissure of Sylvius (fissura cerebri lateralis). To indicate the course of 

 the Sylvian fissure, a line is drawn from the external angular process of the frontal 

 bone through a point 2 cm. (^ in.) below the most prominent part of the parietal 

 eminence and ending 1.5 cm. ($/% in.) above the lambda. The main portion of the 

 Sylvian fissure begins 2 cm. (3/ in.) behind the angular process; 2 cm. farther back 

 or 42 mm. ( i ^ in. ) behind the angular process is the Sylvian point, where the 

 anterior horizontal and anterior ascending limbs are given off. From this point the 

 posterior horizontal limb passes backward to 2 cm. ( 3/ in. ) below the highest point 

 of the parietal eminence and then curves upward and backward for a distance of 

 1.25 cm. to 2 cm. (^ to 3/ in.). 



Central Fissure, or Fissure of Rolando (sulcus centralis). The line of 

 the central fissure begins at the upper Rolandic point, 1.5 cm. (^ in.) behind the 

 middle of a sagittal line passing from the glabella to the inion. It then passes 

 down and forward at an angle of approximately 70 (67^, Chiene) toward the 

 middle of the zygoma (Le Fort) to end at the lower Rolandic point, where it inter- 

 sects the Sylvian line. It is about 9 cm. (3^ in.) long. The central fissure stops 

 I cm. above the Sylvian line or fissure. 



Parieto-occipital Fissure (fissura parieto-occipitalis). The position of 

 this fissure is quite variable, an average being 1.5 cm. (^ in.) above the lambda, and 

 extending 1.25 cm. (^ in.) out from the median line. It is about 6 cm. (2^ in.) 

 above the inion and on or below the line of the Sylvian fissure. 



