s indicated.

_Rodent cancer_ may originate on the scalp, but usually spreads
thither from the face.

In operating for extensive tumours of the scalp the haemorrhage is
sometimes formidable. It may be controlled by an elastic tourniquet
applied horizontally round the head, or if, on account of the position
of the tumour or from other causes, this is not practicable, by
ligation or temporary clamping of the external carotid on one or on
both sides.

#Air-containing Swellings#--_Pneumatocele Capitis._--Cases have been
recorded in which, as a result of pathological or traumatic
perforations of the mastoid, and less frequently of the frontal cells,
air has passed under the pericranium and given rise to a tense rounded
tumour, resonant on percussion, and capable of being emptied by firm
pressure. Such swellings exhibit neither pulsation nor fluctuation;
and as they are painless, and give rise to almost no inconvenience,
they do not call for treatment.

_Emphysema of the scalp_ may follow fractures implicating any of the
air sinuses of the skull, the air infiltrating the loose cellular
tissue between the pericranium and the aponeurosis, and on palpation
yielding a characteristic crepitation. It usually disappears in a few
days.

#Vascular Tumours.#--_Naevi_ on the scalp present the same features as
elsewhere. If placed over one of the fontanelles, a naevus may derive
pulsation from the brain, and so simulate a meningocele.

_Cirsoid aneurysm_ is usually met with in the course of the temporal
artery, and may involve the greater part of the scalp. Large,
distended, tortuous, bluish vessels pulsating synchronously with the
heart are seen and felt. They can be emptied by pressure, but fill up
again at once on removal of the pressure. The patient complains of
dizziness, headache, and a persistent rushing sound in the head.
Ulceration of the skin over the dilated vessels, leading to fatal
haemorrhage, may take place.

They may be treated by excision, after division and ligation of the
larger vessels entering the swelling; or the dilated vessels may be
cut across at several points and both ends ligated. Krogius recommends
the introduction of a series of subcutaneous ligatures so as to
surround the whole periphery of the pulsating tumour, and interrupt
the blood flow. Ligation of the main afferent vessels, or of the
external or common carotid, has been followed by recurrence, owing to
the free anastomatic circulation in the