1362 



SUEFACE AND SUEGICAL ANATOMY. 



horizontal ramus of the lateral cerebral fissure, occupies a level midway 

 between it and the temporal line. The anterior horn of the ventricle is 

 opposite the lower part of the coronal suture while the posterior horn is opposite 

 the posterior part of the temporal line. The inferior horn corresponds to the 

 second temporal gyrus. 



The lateral ventricle may be tapped or drained from above, by traversing brain 

 tissue for a depth of 4 to 5 cm. through the superior frontal sulcus, 1J in. (two 

 fingers'-breadth) in front of the point X 2 , Fig. 1067, the instrument being directed 

 downwards and backwards (Kocher).i 



FIG. 1068. SCHEME SHOWING RELATIVE TOPOGRAPHY OP THE CHIEF SUBDIVISIONS OF THE MOTOR AREA 

 (adapted from Griinbaum and Sherrington). Guiding lines, red ; sulci, blue. 



Keen drains the ventricles through an opening 1J in. behind the external 

 acoustic meatus and the same distance above Eeid's base-line (a line drawn back- 

 wards from the inferior margin of the orbit through the centre of the external 

 acoustic meatus, X 3 , Fig. 106*7), the instrument being passed into the brain towards 

 the summit of the opposite auricle. If the ventricle is not distended it will be 

 reached at a depth of two inches from the surface. 



To open the subarachnoid space, the pin of a small trephine is placed over the 

 mid-point of the line EA, Fig. 1067 ; the dura is incised as it crosses the stem of the 

 lateral fissure of the brain from the frontal lobe to the anterior extremity of the 

 temporal lobe. Care must be taken to keep in front of the middle meningeal artery. 



The cisterna cerebello-medullaris, situated between the under surface of the 

 cerebellum and the medulla obloiigata, may be reached by turning down a flap of soft 

 parts, and removing a circle of bone immediately above the foramen magnum. The 



