, or failing
evidence of this, by a decompression operation in the temporal region.

INTRA-CRANIAL HAEMORRHAGE

Apart from the haemorrhage that accompanies laceration of brain tissue,
bleeding may occur inside the skull, either from arteries or from
veins. The effused blood may collect either between the dura mater and
the bone (_extra-dural haemorrhage_), or inside the dura (_intra-dural
haemorrhage_).

#Middle Meningeal Haemorrhage.#--The commonest cause of extra-dural
haemorrhage is laceration of the middle meningeal artery. This
artery--a branch of the internal maxillary--after entering the skull
through the foramen spinosum, crosses the anterior inferior angle of
the parietal bone, and divides into an anterior and a posterior branch
which supply the meninges and calvaria (Fig. 186). Either branch may
be injured in association with fractures, or from incised, punctured,
or gun-shot wounds. The vessel may be ruptured without the skull being
fractured, and sometimes it is the artery on the side opposite to the
seat of the blow that is torn. The most common situations for rupture
are at the anterior inferior angle of the parietal bone, in which case
the anterior branch is torn (90 to 95 per cent.); and on the inner
aspect of the temporal bone, where the posterior branch is torn (5 to
10 per cent.).

[Illustration: FIG. 186.--Relations of the Middle Meningeal Artery and
Lateral Sinus to the surface as indicated by Chiene's Lines.

(After Cunningham.)]

It is probable that the size of the haemorrhage depends on the nature,
extent, and severity of the injury to the head. The recoil of the
skull after the blow separates the dura from the bone, and if the
meningeal artery is lacerated or punctured, blood is effused into the
space thus formed (Fig. 187). A localised blow therefore results in a
small area of separation and a correspondingly small clot; while a
diffuse blow is followed by more extensive lesions. It is believed
that, once the dura is partly separated, the force of the blood poured
out from the lacerated artery is--on the principle of the hydraulic
press--sufficient to continue the separation.

[Illustration: FIG. 187.--Extra-Dural Clot resulting from haemorrhage
from the Middle Meningeal Artery.]

_Clinical Features._--The typical characteristics of middle meningeal
haemorrhage are met with only when the bleeding takes place between the
dura and the bone. Under these conditions the symptoms of concu