of 22.5 deg. each. Three of
these angles taken together make up the 67.5 deg.. If the straight edge of
the paper be placed along the sagittal suture with the angle of
folding over the upper end of the fissure of Rolando, the folded edge
falls over the line of the fissure (Chiene).

[Illustration: FIG. 182.--To illustrate the site of various operations
on the skull.]

LUMBAR PUNCTURE

Quincke, in 1891, first suggested the withdrawal of cerebro-spinal
fluid from the theca in the lumbar region, as a means of relieving
excessive intra-cranial tension in tuberculous meningitis, and to
obtain specimens of the fluid for diagnostic purposes. The scope of
the procedure, both as a therapeutic and as a diagnostic measure, has
since been widely extended.

_Technique._--The puncture may be made with the patient either lying
on his left side, the spine being fully flexed by approximating the
knees and shoulders; or sitting on the table with the knees drawn up
and the body bent forward. The upper edge of the fourth lumbar spine
is identified by drawing a horizontal line across the back at the
level of the highest part of the iliac crests (Fig. 183). The space
between the fourth and fifth lumbar vertebrae being the widest, is that
usually selected. The skin having been purified, an exploring needle,
about three inches long, is introduced about half an inch below the
fourth lumbar spine in the middle line, and passed for about two
inches in a direction forwards and slightly upwards. The needle
usually encounters some resistance as it pierces the interspinous
ligament, and then enters the sub-arachnoid space. If bone is struck,
the needle should be withdrawn and introduced at a different level. If
the cerebro-spinal fluid does not escape at once, a stylet should be
passed through the needle to clear it of blood-clot or shreds of
tissue. When the intra-thecal tension is normal, the fluid trickles
away drop by drop, but if it is increased, as, for example, in
meningitis, intra-cranial tumour, hydrocephalus, or uraemia, it may
escape in a jet.

[Illustration: FIG. 183.--Localisation of site for introduction of
needle in Lumbar Puncture.]

The _normal cerebro-spinal fluid_ is clear and colourless, has a
specific gravity of 1004-1008, and contains a trace of serum globulin
and albumose, some chlorides, and a substance which reduces Fehling's
solution. Microscopically, it may contain some large endothelial cells
and a few lymphocyte