The scalp extends from the supraorbital margins anteriorly to the highest nuchal lines at the back of the skull and down to the ears and zygomatic arches at the sides. The forehead, from eyebrows to hairline (or where it should be), is common to the face and scalp. The composition of the scalp is traditionally recalled from the five letters of the words that indicate its five layers: Skin; Connective tissue; Aponeurosis with muscle at the front and back; Loose areolar tissue; and Pericranium.
The skin of the scalp is the thickest in the body and is thickest of all in the occipital region. Apart from being usually the hairiest part of the body it also contains a high concentration of sebaceous glands. Many of the fibres of the scalp muscle are inserted into it. Elsewhere it is firmly attached by dense connective tissue (the second layer) to the underlying muscle and aponeurosis. The vessels and nerves run within this firm tissue which unites the first and third layers.
Occipitofrontalis consists of occipitalis and frontalis muscular parts with an intervening epicranial aponeurosis (galea aponeurotica) into which they are inserted at the back and front respectively.
Occipitalis arises from the highest nuchal line and passes forwards into the aponeurosis which lies over the top of the skull. The muscle bellies are separated across the midline by the aponeurosis which extends backwards to be attached to the external occipital protuberance and the most medial part of the highest nuchal line. Laterally the aponeurosis blends with the temporoparietal fascia (superficial temporal fascia) and comes down over the deep temporal fascia (see p. 357) to the zygomatic arch. Frontalis arises from the front of the aponeurosis and passes forwards to become attached to the upper part of orbicularis oculi and the overlying skin of the eyebrow. It has no attachment to the skull. The right and left frontalis muscles meet in the midline. The midline fibres blend with procerus, a small muscle that arises from the nasal bone and cartilage and inserts into the skin of the lower forehead; its contraction produces transverse wrinkles over the bridge of the nose.
Nerve supply. By the facial nerve; the posterior auricular branch to occipitalis, and temporal branches to frontalis.
Action. While occipitalis can pull the scalp back in certain individuals, usually it merely anchors the aponeurosis while frontalis elevates the eyebrows and produces wrinkles in the skin of the forehead.
Beneath the muscles and aponeurosis is a small amount of loose areolar tissue providing a plane above which the rest of the scalp can be moved and through which avulsion can occur (scalping).
Through this plane a flap of the overlying scalp can be rotated on a vascular pedicle as a surgical procedure. This subaponeurotic space extends down beneath orbicularis oculi into the eyelids.
Bleeding anywhere beneath the aponeurosis may appear as a ‘black eye’ by the blood tracking down through the space.
The pericranium is the periosteum of the vault of the skull. This is rather loosely attached to the bone and is easily stripped up by a subperiosteal haematoma. Such a haematoma outlines the bone concerned, since the pericranium is very firmly attached at the sutures at the margins of the bone.
Blood supply
The arteries of the scalp are derived from the external carotid artery by the occipital, posterior auricular and superficial temporal branches, and from the internal carotid artery by the supraorbital
and supratrochlear branches. All these arteries anastomose very freely with each other. The arterial walls are attached to the dense connective tissue of the second layer of the scalp and tend to be held open and bleed profusely when cut. Scalping does not cause necrosis of the bones of the vault, most of whose blood comes from the middle meningeal artery.
The occipital artery emerges from the apex of the posterior triangle and runs with the greater occipital nerve to supply the back of the scalp up to the vertex. The smaller posterior auricular artery runs with the lesser occipital nerve to supply the scalp behind the ear.
The superficial temporal artery is a terminal branch of the external carotid. Running up behind the temporomandibular joint and in front of the ear and the auriculo-temporal nerve, it crosses the zygomatic arch, where its pulsation can be felt, and branches out widely into the skin that overlies the temporal fossa. One branch, the middle temporal artery, pierces the fascia, supplies temporalis and anastomoses with the deep temporal branches of the maxillary artery.
The supraorbital and supratrochlear arteries (from the ophthalmic) run with the corresponding nerves. The supraorbital is the larger and supplies the front of the scalp up to the vertex. Its anastomosis with the superficial temporal artery connects the internal and external carotid systems.
The veins of the scalp run back with the arteries. In forehead, temple and occipital regions they receive diploic veins from frontal, parietal and occipital bones.
The supraorbital and supratrochlear veins drain by the angular vein into the facial vein. The superficial temporal veins run into the retromandibular vein, and occipital veins reach the plexus around the suboccipital muscles which drains into the vertebral vein. The posterior auricular vein drains the scalp behind the ear to the external jugular vein; it also receives the mastoid emissary vein from the sigmoid sinus. Spread of infection to this emissary vein from mastoid air cells can be dangerous or fatal, from retrograde thrombosis of cerebellar and medullary veins. At the vertex a parietal emissary vein on either side of the midline connects scalp veins with the superior sagittal sinus.
Lymph drainage
There are no lymph nodes within the scalp; lymphatic channels from the posterior half of the scalp drain to occipital and mastoid nodes, and from the anterior half to preauricular (parotid) nodes. The lymph eventually reaches the nodes of the deep cervical chain.
Nerve supply
The main sensory nerves run with the arteries. Posteriorly the greater occipital and third occipital nerves (posterior rami of C2 and C3 respectively) extend to the vertex and the posterior scalp respectively. The lesser occipital (anterior ramus of C2) supplies skin behind the ear. The temple is supplied by the auriculotemporal and the zygomaticotemporal nerves, and the forehead and front of the scalp by the supratrochlear and supraorbital nerves.
Temporal fossa and zygomatic arch
The temporal fossa is the area bounded by the temporal lines above and the zygomatic arch below (see Fig. 8.1, p. 525). Its roof (lateral wall) is the temporalis fascia and its floor (medial wall) is the
part of the side of the skull that includes the pterion, where the frontal, the parietal and the squamous part of the temporal bones articulate with the greater wing of the sphenoid. (It lies on the course of the anterior branch of the middle meningeal artery and marks the position of the stem of the lateral cerebral fissure.) The zygomatic processes of the frontal bone, the zygomatic bone, and the maxilla are in the anterior wall. The fossa is filled by the temporalis muscle which arises from the floor and the overlying fascia. Deep to the arch, at the level of the infratemporal crest of the greater wing of the sphenoid (Fig. 6.19), the fossa becomes continuous with the lateral part of the infratemporal fossa (see p. 361).
The zygomatic arch is formed by processes of the squamous temporal and zygomatic bones, which meet at a suture sloping downwards and backwards. The arch is completed anteriorly by the zygomatic process of the maxilla.
Nerves crossing the arch are vulnerable in incisions or in fractures. The auriculotemporal nerve crosses well back, just in front of the ear, and temporal and zygomatic branches of the facial nerve cross the arch, to reach the frontalis and orbicularis oculi muscles.
The temporal fascia (deep temporal fascia) is attached to the superior temporal line and passes down to the upper border of the zygomatic arch. Above the arch it splits into two layers, one attached to the lateral and the other to the medial margin of the upper border of the arch. The space between these two layers is occupied by fat, which is traversed by a branch of the superficial temporal artery and the zygomaticotemporal branch of the maxillary nerve. The temporal and zygomatic branches of the facial nerve, the superficial temporal vessels and the auriculotemporal nerve lie in or just deep to the overlying temporoparietal fascia (superficial temporal fascia, see p. 356). In surgical procedures in this region, the temporal fascia is divided at a high level and the space between its two layers entered at a lower level via the deep layer to access the zygomatic arch, thereby safeguarding the overlying neurovascular structures.
Temporalis
This muscle (one of the muscles of mastication) arises from the temporal fossa over the whole area between the inferior temporal line and the infratemporal crest, and from the deep surface of the temporalis fascia. The most anterior fibres are vertical and the most posterior are horizontal, turning downwards in front of the temporomandibular joint. The fan-shaped muscle converges towards the coronoid process of the mandible, becomes tendinous, and is inserted into a bevelled surface on the medial aspect of the coronoid process adjacent to its posterior border, apex and anterior border.
From the anterior part of this insertion, two tendinous bands extend downwards and forwards to the posterior end of the alveolar process enclosing the retromolar fossa between them. The deep, larger tendinous band is attached to a slight (temporal) crest on the mandible, and is palpable through the vestibule of the mouth; a useful guide when performing an inferior alveolar nerve block.
The blood supply of the muscle is derived from the temporal branches of the maxillary and superficial temporal arteries.
Nerve supply. Two or three deep temporal branches of the mandibular nerve enter the deep surface of the muscle.
Action. Temporalis elevates the mandible when the open mouth is closed, and it retracts the
protruded mandible.