uire to be
emptied with a hollow needle.

These effusions are to be distinguished from the _cephal-haematoma_, in
which the blood collects between the pericranium and the bone. This is
oftenest seen in newly born children as a result of pressure on the
head during delivery, and is characterised by its limitation to one
particular bone--usually the parietal--the further spread of the blood
being checked by the attachment of the pericranium at the sutures.
Occasionally a permanent thickening of the edges of the bone remains
after the absorption of the extravasated blood. This condition is to
be diagnosed from traumatic cephal-hydrocele (p. 390).

#Wounds of the Scalp.#--So long as a scalp wound, however extensive,
is kept free from infection, it involves comparatively little risk,
but the introduction of organisms to even the most trivial wound is
fraught with danger, on account of the ease and rapidity with which
the infection may spread along the emissary veins to the meninges and
intra-cranial sinuses.

The deeper the wound, the greater is the risk. If the epicranial
aponeurosis is divided, the "dangerous area" between it and the
pericranium is opened, and if infection occurs, it may lead to
widespread suppuration. Should the wound extend through the
pericranium, infection is more liable to spread to the bone and to the
cranial contents.

The usual varieties of wounds--incised, punctured, contused, and
lacerated--are met with in the scalp, and they vary in degree from a
simple superficial cut to complete avulsion. For medico-legal purposes
it is important to bear in mind that a scalp wound produced by the
stroke of a blunt weapon, such as a stick or baton, may closely
simulate a wound made with a cutting instrument.

On account of the density of the integument and its close connection
with the aponeurosis, scalp wounds do not gape unless the epicranial
aponeurosis is widely divided. This facilitates union in incised
wounds, but interferes with drainage in the long narrow tracts which
result from punctures, and which are so liable to be infected and to
implicate the sub-aponeurotic space, the pericranium, or even the
bone. It also favours the inclusion in the wound of a foreign body,
such as the broken point of a knife, or a piece of glass. The bleeding
from scalp wounds is often profuse and difficult to control, because
the vessels, fixed as they are in the dense subcutaneous tissue,
cannot retract and contract