g of the tendon. Recovery usually takes place under massage
and passive movements. Failing this, the thickened portion of the
tendon is pared down to its normal size; if it is the sheath of the
tendon that is narrow, it is laid freely open.

[Illustration: FIG. 176.--Trigger Finger.

(Photograph lent by Sir George T. Beatson.)]

#Drop# or #mallet finger# is described on p. 121.

CHAPTER XI

THE SCALP

Surgical Anatomy--Injuries: _Contusion_; _Haematoma_;
_Cephal-haematoma_; _Wounds_; _Avulsion_--Diseases: _Infective
conditions_; Cystic and solid tumours; Air-containing swellings;
Vascular tumours.

#Surgical Anatomy.#--The _skin_ of the scalp is intimately united to
the _epicranial aponeurosis_ by a network of firm fibrous tissue
containing some granular fat, and representing the subcutaneous
connective tissue. These three layers constitute the scalp proper, and
they are so closely connected as to form a single structure which can
be moved to a certain extent by the action of the epicranius muscle.
The epicranius (occipito-frontalis) muscle with its aponeurosis
extends from the superciliary ridge in front to the superior nuchal
(curved) line of the occipital bone behind, and laterally to the level
of the zygoma where it blends with the temporal fascia. Between the
scalp proper and the _pericranium_ is a quantity of loose areolar
tissue, in the meshes of which extravasated blood or inflammatory
products can rapidly spread over a wide area. Blood extravasated under
the pericranium is limited by the attachments of this membrane at the
sutures.

The _blood supply_ of the frontal region is derived from the internal
carotid arteries through their supra-orbital branches; the remainder
of the scalp is supplied from the external carotids through their
temporal, posterior auricular and occipital branches. The vessels,
which run in the subcutaneous tissue, superficial to the epicranial
aponeurosis, anastomose freely with one another and across the middle
line. The main branches run towards the vertex, and incisions should,
as far as possible, be directed parallel with them.

The _venous return_ is through the frontal, temporal, and occipital
veins. These have free communications, through the _emissary veins_,
with the intra-cranial sinuses, and by these routes infective
conditions of the scalp may readily be transmitted to the interior of
the skull. The most important of the emissary veins are: the