SCALP
The scalp extends from the superciliary arches anteriorly to the external occipital protuberance and superior nuchal lines posteriorly and to the temporal lines laterally. It consists of five layers (see Fig. 12.2). Conveniently, the first letters of each layer together spell SCALP, making recall easier. The first three layers are intimately bound together and move as a unit.
Skin. This is thick and hair bearing and contains numerous sebaceous glands. Connective tissue beneath the skin. This is a dense fibrofatty layer containing fibrous septa that unite the skin to the underlying epicranialaponeurosis. This layer contains numerous blood vessels. The arteries are derived from both the external and internal carotid arteries, and free anastomoses occur between them. Aponeurosis (epicranial). This is a thin, tendinous sheet that unites the occipital and frontal bellies of the occipitofrontalis muscle (see below and Fig. 12.14). The lateral margins of the aponeurosis are attached to the temporal fascia. The subaponeurotic space is the potential space deep to the epicranial aponeurosis. It is limited in front and behind by the origins of the occipitofrontalis muscle, and it extends laterally as far as the attachment of the aponeurosis to the temporal fascia. Loose areolar tissue. This occupies the subaponeurotic space (see Fig. 12.2) and loosely connects the epicranial aponeurosis to the periosteum of the skull (the pericranium). This is the plane of movement of the scalp, that is, when the scalp moves, the first three layers (SCA) slide along this layer relative to the underlying periosteum. The areolar tissue contains a few small arteries, but it also contains some important emissary veins. The emissary veins are valveless and connect the superficial veins of the scalp with the diploic veins of the skull bones and with the intracranial venous sinuses. Pericranium. The pericranium is the periosteum covering the outer surface of the skull bones. The pericranium is continuous with the periosteum on the inner surface of the skull bones (endosteum) at the sutures between the individual skull bones.