THE BRAIN. 



43 



given. Draw a mid- or sagittal line from opposite the highest point of the supra-orbital arches 

 to the external occipital protuberance. From the midpoint on this line draw another to the 

 pre-auricular point at the level of the upper border of the meatus. This is the frontal line. 

 From the most prominent point of the external angular process draw a line to the junction of 

 the middle and lower thirds of the frontal line and prolong it i^ in. beyond. 



The Sylvian fissure begins between i> and iy 2 in. behind the angular process or % of 

 the distance between that point and the frontal line. The bifurcation is i ^4 to 2 in. behind the 

 angular process or yV of the distance between it and the frontal line, the fissure then runs to an 

 equal distance behind the frontal line, and up for ^ in. parallel to the frontal line. The fissure 

 of Rolando runs from a point |4 in. behind the midsagittal point to one y of an inch in front of 

 the intersection of the frontal line and line of the Sylvian fissure. The parieto-occipital fissure 

 is T T _T of the distance from the midsagittal point to the inion. It lies near the apex of the lamb- 

 doid suture. 



The Lateral Ventricles. The lateral ventricles sometimes become distended by serous or 

 purulent effusions or, as in apoplexy, by blood. In order to tap them Keen (" Reference Hand- 



Fissure of Rolando 



Lateral ventricle 



Middle men- 

 ingeal artery 

 anterior 

 branch 



Posterior horn of 

 lateral ventricle 



Lateral sinus 



Middle nieningeal artery, posterior 

 branch ; inferior horn of lateral ven- 

 tricle seen beneath 



FIG. 53. Tapping the lateral ventricles and trephining for cerebral abscess. Semidiagrammaticview of head, show- 

 ing relation of Rolandic and Sylvian fissures and lines. 



book of the Medical Sciences," vol. viii., p. 229) has given three points, as follows: (i) One- 

 half to three-fourths of an inch (1.25 to 2 cm.) on either side of the median line and one-third 

 of the distance from the glabella to the upper end of the central (Rolandic) fissure. This is 

 high enough to avoid the frontal air-sinuses and is in advance of the motor area. A grooved 

 director is to be thrust in the direction of the inion. The ventricle is reached at a depth of 5 to 

 6.5 cm. (2 to 2 l / 2 in.) through the first frontal convolution. (2) Midway between the inion 

 and upper end of the central (Rolandic) fissure 1.25 to 2 cm. (% to ^ in.) from the median 

 line. The director is to be thrust toward the inner end of the supra-orbital ridge of the same 

 side. The ventricle will be reached at a depth of 5.5 to 7 cm. (2^ to 2^ in.) from the sur- 

 face. (3) Three centimetres (i% in.) behind the external auditory meatus and the same above 

 Reid's base line (from the lower border of the orbit through the centre of the external auditory 

 meatus). The director is to be thrust toward a point 6.25 to 7.5 cm. (2% to 3 in.) directly 

 above the opposite external meatus. The ventricle will be reached 5 to 5.75 cm. (2 to 2^4 in.) 

 from the surface. The director passes through the second temporal convolution; this is the 

 preferred method. 



