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.—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 mastoid, condyloid, and occipital, passing to the transverse (lateral) sinus; the parietal, which enters the superior sagittal (longitudinal) sinus; and a branch from the nose which traverses the foramen cæcum and enters the anterior end of the superior sagittal sinus.

The supra-trochlear, supra-orbital and auriculo-temporal branches of the trigeminal nerve, together with the greater and lesser occipital nerves, supply the scalp with sensation, while the muscles are supplied from the facial nerve.

The lymph vessels pass to the parotid, occipital, mastoid, and submaxillary groups of glands, the different areas of drainage being ill-defined.