fected, has nothing in common with a hernia cerebri.

SURGICAL AFFECTIONS OF THE CRANIAL NERVE

Irritation, or paralysis, of one or more of the cranial nerves may
result from lesions implicating their centres or trunks.

When the trunk of the nerve is affected, the paralysis is on the same
side as the lesion, and is of the lower neurone type; when the
cortical centre or the upper axons are involved, it is on the opposite
side, and is of the upper neurone type (p. 334). The lesions of the
cerebral centres with which nerve symptoms are most frequently
associated are: laceration of the brain, haemorrhage, meningitis,
tumour, and syphilitic gumma.

The nerve-trunks may be contused or torn across, especially in basal
fractures which traverse their foramina of exit; blood may be effused
into their sheaths as a result of injuries not attended with fracture;
or they may be pressed upon by an inflammatory effusion, a tumour, a
gumma, or an aneurysm invading the base of the skull. When the nerve
is merely contused, or pressed upon by blood-clot, the paralysis tends
to pass off in the course of a few days. When it is torn across, or
compressed by a new growth, the paralysis is permanent. In some
traumatic cases paralysis does not come on until a few days after the
injury, and is then due either to gradually increasing pressure from
blood-clot, or more probably to the onset of meningitis or of
ascending neuritis.

I. The branches of the _Olfactory Nerve_ may be ruptured as they pass
through the cribriform plate in fractures implicating the anterior
fossa of the skull, and there results complete and permanent loss of
smell (_anosmia_). Haemorrhage into the nerve sheath or contusion of
the nerve may cause a transitory loss of smell. The trunk of the nerve
may be implicated also in tumours and meningitis in the anterior
fossa. In all cases in which anosmia results there is also
interference with the power of recognising different flavours, thus
greatly impairing the sense of taste.

II. _Optic Nerve._--Temporary paralysis of one or both optic nerves is
a comparatively common result of traumatic effusion of blood into
their sheaths; the resulting blindness may pass off in a few days, or
may last for some weeks. When a large effusion takes place, the
prolonged pressure on the nerve may result in optic atrophy and
permanent blindness. Complete severance of the nerve by a bullet, the
point of a sharp instrument, or a fragment of