THE CRANIUM. 1165 
the mid-sagittal point M at an angle of 67° to the sagittal line (Hare). This 
angle may readily be found by Chiene’s plan of folding a sheet of paper first to 
half a right angle and again to a quarter of a right angle (45° + 22-5° = 67°5°). 
According to Cunningham, the average angle which the fissure makes with the 
sagittal line is 70°. 
The lateral ventricle may be tapped or drained at the commencement of the 
descending cornu, through the posterior half of the first temporal convolution, by 
Ze 3 
sy 
» 
a % 
KN QQ GC 
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Fic. 793.—CRANIO-CEREBRAL TOPOGRAPHY. 
Guiding lines (Chiene’s), blue ; sutures, green ; meningeal arteries, red ; sulci, black. 
G. Glabella. C. — Mid-point of AB. 
O. Inion. MA is divided into thirds at K and L. 
M. Mid-point between G and O. CD is drawn parallel to AM. 
T. Mid-point between M and O. ; Z. Post-auricular point. 
8. Mid-point between T and O. VW. Guide to anterior limit of lateral sinus. 
E. External angular process. Y.  Mastoid antrum. 
P. Root of zygoma (pre-auricular point). “1 Site at which subarachnoid space may be opened. 
N. Mid-point of EP. “2. Site for draining lateral ventricle (Kocher). 
R. Mid-point of PS. “3. Site for draining lateral ventricle (Keen). 
penetrating only 1 cm. of brain tissue. For this purpose the centre of the trephine 
should be placed a finger’s-breadth below the middle of CB. Or, secondly, the 
ventricle may be reached from above, by traversing brain tissue for a depth 
of 4 to 5 em. through the superior frontal sulcus, 14 in. (two fingers’-breadth) 
in front of the point K, the instrument being directed downwards and backwards 
(Kocher). 
