Superficial Structures of the Face and Scalp
The subcutaneous tissue of the face and scalp is highly vascular and is traversed by several nerves. Most of the nerves are sensory to skin and include branches of the trigeminal (V) and upper cervical spinal nerves. In addition, there are branches that are motor from the facial (VII) nerve to a group of muscles in the subcutaneous tissues of the face, scalp and front of the neck, known as the muscles of facial expression.
Muscles of facial expression
In general, these muscles are arranged as sphincters or dilators around the orifices of the face (Fig. 7.18). Most are anchored to bone at one end and attached to skin at the other.
The sphincter of the palpebral fissure (the gap between the eyelids) is orbicularis oculi, which is divided into inner palpebral and outer orbital parts. The palpebral part lies within the eyelids and is attached to the medial and lateral palpebral ligaments. The orbital portion is attached only to the medial palpebral ligament, and its fibres lie around the orbital margin. Both parts close the palpebral fissure, the palpebral part gently and the orbital part forcefully as when ‘screwing up the eyes’. The palpebral part also helps sweep tears medially across the cornea from lacrimal gland to lacrimal canaliculi. The dilator components are provided by levator palpebrae superioris within the orbit (p. 380), and by occipitofrontalis in the scalp. The latter muscle has two bellies, occipital and frontal, linked by an extensive intermediate tendon, the epicranial aponeurosis, which forms a mobile layer over the vault of the skull. From its posterior extremity the occipital belly (occipitalis) descends to its attachment on the highest nuchal line of the occipital bone (Fig. 7.19); from its anterior end the frontal belly (frontalis) descends in the forehead and its fibres interdigitate with those of orbicularis oculi and attach to skin near the eyebrow. Occipitalis fixes the epicranial aponeurosis allowing frontalis to raise the eyebrows.
Around each nostril is nasalis with two feeble parts, alar and transverse, which dilate and compress the nostrils, respectively.
Orbicularis oris, the sphincter of the mouth, is embedded in the lips and attaches near the midline to the mandible and maxilla.
In addition, there are dilators around the mouth whose fibres continue into orbicularis oris. The most medial dilator of the upper lip is levator labii superioris alaeque nasi. This muscle attaches near the medial margin of the orbit and runs to the alar cartilage of the nose and to the upper lip. Levator labii superioris is attached to bone beneath the orbital margin, whereas levator anguli oris lies slightly deeper and its fibres incline towards the angle of the mouth. Two of the dilator muscles take attachment from the zygoma: zygomaticus major and minor. Attached to the mandible are three muscles, called, from lateral to medial, depressor anguli oris, depressor labii infe- rioris and mentalis.
The buccinator muscle (Figs 7.18 & 7.20) lies deep to the other dilator muscles in the wall of the cheek. Anteriorly, it blends with the deep surface of orbicularis oris. Posteriorly, it gains attachment to the outer surface of the mandible from the level of the first to the third molar teeth. Passing behind the third molar tooth, buccinator is attached to the pterygomandibular raphe and the pterygoid hamulus. The muscle attachment continues forwards along the outer surface of the maxilla as far as the first upper molar tooth. Buccinator controls the size of the vestibule of the mouth (that part of the buccal cavity lying between the cheek and the teeth).
The platysma (Fig. 7.21), the most extensive muscle of facial expression, descends in the subcutaneous tissue of the neck from the inferior border of the mandible and fades out on the anterior surface of the thorax. A few fibres may run horizontally from the angle of the mouth as risorius. Platysma is most easily seen in action during respiratory distress when the skin of the neck is pulled taut.
In the human, the auricular muscles are almost vestigial.
All the muscles of facial expression derive their motor nerve supply from the facial (VII) nerve. Occipitalis and some of the auricular muscles are innervated by the posterior auricular branch of the nerve (p. 340); the remaining muscles are supplied by the five sets of branches (Fig. 7.22) that emerge from the anterior border of the parotid gland (p. 339). The temporal branch of the facial nerve ascends to supply the remaining auricular muscles and frontalis. The zygomatic branch is directed towards the eye and supplies muscles above and below the palpebral fissure. The third branch, the buccal, runs horizontally forwards to innervate buccinator and the muscles of the upper lip. The mandibular branch supplies the muscles of the lower lip, dipping below the mandible in its course. The cervical branch descends to supply platysma.
Blood supply of face
Most of the superficial structures of the face obtain their blood supply from the facial artery (Fig. 7.22), a branch of the external carotid artery. The facial artery enters the face by hooking under the inferior border of the mandible, where it is easily palpated. The vessel then pursues a tortuous course across the face towards the inner angle of the orbit. The area of the face in front of the ear is supplied by the transverse facial artery, an anterior branch of the superficial temporal artery. Emerging from the orbit to supply the forehead are the supraorbital and supratrochlear branches of the ophthalmic artery.
Blood from the face drains into the facial vein (Fig. 7.22), which accompanies the facial artery. The vein also receives the supratrochlear and supraorbital veins and thus communicates with ophthalmic veins in the orbit. Blood from the lateral part of the face drains into the superficial temporal vein.
The sensory nerve supply of the face is conveyed in branches of the three divisions of the trigeminal (V) nerve (Fig. 7.23).
The scalp (Fig. 7.24) extends from the superior nuchal line posteriorly to the superior orbital margin anteriorly, and to the external acoustic meatus and zygomatic arch laterally. It comprises two functional layers applied to the outer surface of the vault of the skull. Close to the bones lies the pericranium, which forms the periosteum of the skull. This is loosely attached over each constituent bone but is firmly bound to the sutures so that subperiosteal bleeding is limited to the area of the bones involved. Superficial to the pericranium, but separated from it by a layer of loose connective tissue, lie the epicranial aponeurosis (intermediate tendon of occipitofrontalis) and the skin of the scalp, firmly bound to each other so that they move as one over the underlying pericranium and skull.
The arteries and nerves that supply the scalp enter at its circumference and because they accompany each other, they will be described together, starting anteriorly. Near the midline are the supratrochlear and supraorbital nerves, arteries and veins. The nerves are derived from the ophthal- mic division of the trigeminal (V) nerve. The vessels communicate with their ophthalmic counterparts within the orbit.
Lateral to the orbit the zygomatico-temporal nerve from the maxillary division of the trigeminal nerve, accompanied by its vessels, ascends a short distance into the scalp. Just in front of the ear, the auriculotemporal nerve from the mandibular division of the fifth cranial nerve passes into the scalp. The superficial temporal artery and vein follow a similar course.
The area of the scalp behind the ear is supplied by the lesser occipital nerve (C2 anterior ramus) accompanied by the posterior auricular artery and vein. Posteriorly near the midline the scalp receives the greater occipital nerve (C2 posterior ramus) and the occipital artery and vein.
In addition, venous blood may drain via the diploic veins of the skull into the intracranial venous sinuses. Scalp wounds bleed profusely, making suturing difficult. To diminish bleeding, circumferential pressure may be temporarily applied with an elastic bandage.