Chapter 47: The scalp, auricle and face
The scalp (fig. 47-1) is
comprised of five layers:
1. Skin, usually hairy.
2. Dense subcutaneous tissue containing vessels and nerves. The scalp gapes when cut, and the blood vessels are held open by the dense connective tissue, resulting in bleeding that should be arrested by pressure.
3. Aponeurosis and occipitofrontalis muscle. The galea aponeurotica (epicranial aponeurosis) is a fibrous helmet between the occipitalis and frontalis muscles and is anchored to the occipital bone. The occipitofrontalis muscle comprises two occipital bellies (attached to the occipital and temporal bones) and two frontal bellies (which end in the skin of the forehead), united by the galea and supplied by the facial nerve. The muscle moves the scalp and elevates the eyebrows.
4. Loose subaponeurotic tissue containing the emissary veins and allowing free movement of layers 1 to 3 as a unit. Layer 4 is a "dangerous area" because it allows spread of infection even, by way of the emissary veins, to intracranial structures.
5. Pericranium, the periosteum on the outside of the skull.
It should be noticed that the initial letters of the names of the layers form the word scalp.
The nerves and vessels of the scalp (fig. 47-2) ascend in layer 2. Surgical flaps of the scalp are cut so as to remain attached inferiorly. The scalp is supplied successively by the branches of divisions 1 to 3 of the trigeminal nerve and by the cervical plexus and dorsal rami of the cervical nerves (see fig. 47-6). The trigeminal and cervical territories are commonly equal in area, but overlapping does occur. The arterial supply, although partly by the internal carotid artery, is mainly by branches of the external carotid artery. Anastomoses are abundant, so partially detached pieces of scalp may be replaced successfully. The superficial temporal artery, a terminal branch of the external carotid artery, arises in the parotid gland, crosses the zygomatic arch, and divides into frontal and parietal branches. The pulsations of the superficial temporal artery can be felt over the zygomatic arch. The posterior auricular and occipital arteries, also branches of the external carotid artery, run superiorward and posteriorward to the scalp.
The auricle, a part of the external ear, consists of elastic cartilage covered by skin. The chief topographic features of the auricle are shown in figure 47-3. The lobule consists merely of fibrous tissue and fat. The auricle is connected with the fascia on the side of the skull by unimportant anterior, superior, and posterior auricular muscles, which are supplied by the facial nerve.
The auricle is supplied by both cranial (auriculotemporal nerve from cranial nerve V; probably also twigs from cranial nerves VII, IX, and X) and spinal (lesser occipital and great auricular) nerves (see fig. 47-6).
The eyelids, nose, and lips are discussed elsewhere.
Muscles of facial expression (fig. 47-4).
The muscles of facial expression are very superficial (being attached to or influencing the skin) and are all supplied by the facial nerve. In addition to those of the scalp and auricle, already mentioned, muscles are arranged around the openings of the orbits, nose, and mouth.
The orbicularis oculi (fig. 47-4A), a sphincter around the rim of the orbit, comprises (1) an orbital part, attached mainly to the medial margin of the orbit; (2) a palpebral part, contained in the eyelids and anchored medially and laterally; and (3) a lacrimal part, posterior to the lacrimal sac. The orbicularis protects the eye and brings the eyelids together in blinking and sleep. Its antagonists are the levator palpebrae superioris and the frontalis muscles. Paralysis of the orbicularis causes drooping of the lower eyelid (ectropion) and spilling of tears (epiphora), as occurs in facial palsy.
The muscles around the nose and mouth are shown in figure 47-4B and C. The orbicularis oris is a complicated sphincter that closes the lips and can also protrude them. The buccinator arises from the maxilla and mandible and is inserted in a complicated manner into the orbicularis oris and lips. It is overlain by the buccal fat pad, and both are pierced by the parotid duct. The buccinator keeps the cheek taut, preventing injury from the teeth.
All the muscles of facial expression develop from pharyngeal arch 2 and hence are supplied by the facial nerve. The facial nerve traverses successively (1) the posterior cranial fossa, (2) the internal acoustic meatus, (3) the facial canal in the temporal bone, and (4) the parotid gland and face. After it gives off the posterior auricular nerve, the facial nerve divides within the parotid gland into its terminal branches, which form the parotid plexus. The branches emerge under cover of the parotid gland, radiate as they procede anteriorward in the face, communicate with the branches of the trigeminal nerve, and innervate the muscles of facial expression, including the platysma. The terminal branches are usually classified as temporal, zygomatic, buccal, marginal (along the mandible), and cervical (fig. 47-5A).
The facial artery, a branch of the external carotid artery in the neck, winds around the inferior border of the mandible and proceeds superomedially on the face (fig. 47-5B). It is very tortuous and participates in many anastomoses. In the face, the facial artery supplies the lips (by inferior and superior labial arteries) and the anterior part of the nose and ends as the angular artery. This artery ends at the medial angle of the eye by anastomosing with branches of the ophthalmic artery, thereby establishing a communication between the external and internal carotid arteries. The labial arteries of the two sides anastomose across the median plane: hemorrhage from a cut lip is controlled by compressing both sides of the cut between the index fingers and thumbs.
The facial vein (fig. 47-5B) is posterior to the artery, somewhat more superficial and is not as tortuous. Its origin, the angular vein, communicates with the cavernous sinus by way of the ophthalmic veins. In the cheek, the facial vein receives the deep facial vein from the pterygoid plexus, and it usually ends directly or indirectly in the internal jugular vein. Because of its connections with the cavernous sinus and the pterygoid plexus and the consequent possibility of spread of infection, the territory of the facial vein around the nose and upper lip has been termed the "danger area" of the face.
The "vertex-ear-chin line" indicates the boundary between the cranial (trigeminal) and spinal innervations (fig. 47-6). The ophthalmic, maxillary, and mandibular branches of the trigeminal nerve separate before emerging from the base of the skull, and their cutaneous distributions must be tested separately; this is usually done over the forehead, the prominence of the cheek, and the chin.
The spinal innervation of the skin (see fig. 3-3) should be considered from the perspective of dermatomes and in terms of the supply by named peripheral nerves. Dermatomes may be considered as successive areas of distribution for each spinal nerve, both ventral and dorsal rami. Peripheral nerve distribution overlaps dermatomes because ventral rami combine to form plexi (e.g., the cervical plexus) in which the individual rami become regrouped to form named nerves (e.g., great auricular) (fig. 47-6).
47-1 List the layers of the scalp.
47-2 What are the antagonists of the orbicularis oculi?
47-3 Which is the main muscle of the cheek?
47-4 What is the orbicularis oris?
47-5 How do the facial muscles develop?
47-6 How is hemorrhage from a cut lip controlled?
47-7 Why is the area around the nose and upper lip termed the "danger area" of the face?
47-8 What is the boundary line between the cranial and spinal areas of cutaneous innervation of the head and neck?
47-9 What are the two main modes of spinal innervation of the skin?
47-10 Where is the trigeminal ganglion and what is its significance?
Figure 47-1 Section through the scalp, skull, and meninges
Figure 47-2 Innervation and blood supply of the scalp, superior aspect. In this instance the trigeminal territory extends posterior to the vertex of the head. The abundant arterial anastomoses are omitted. (After Grant.)
Figure 47-3 Right auricle, lateral aspect.
Figure 47-4 Muscles of facial expression. A, Anterior aspect, showing the muscles around the openings of the orbit and nose. B, Muscles of the mouth. The course of the fibers that constitute the orbicularis oris is shown schematically on the right half of the face. C, Lateral aspect, showing the muscles of the scalp and auricle. The orbicularis oculi and orbicularis oris are shown also. In A, B, and C the unbroken leaders indicate the bony attachments of the muscles. D, Left-sided facial paralysis caused by a lesion of the facial nerve at its exit from the skull. The patient has been asked to "shut the eyes" tightly and to open the mouth. Note the deviation of the lips, characteristic triangular shape of the mouth, and failure to close the affected eye. (From a photograph by Pitres and Testut.)
Figure 47-5 A, The facial nerve in the face. Variations are common, but two chief divisions (temporofacial and cervicofacial) are generally found. The intricacies of the parotid plexus have been omitted. B, The facial vessels in the face. The vein is posterior, more superficial, and less tortuous.
Figure 47-6 Cutaneous innervation of the head and neck. The vertex-ear-chin line separates the trigeminal territory from that of the cervical nerves. Although the central portion of the face is supplied by the trigeminal nerve only, it is believed that most of the skin of the face and neck "is supplied from a combination of trigeminal and upper cervical nerve roots" (L. Kruger and R. F. Young, in The Cranial Nerves, ed. by M. Samii and P. J. Jannetta, Springer, Berlin, 1981). A.-T., auriculotemporal n. (from the mandibular); GA, great auricular n. (C2, 3); asterisk, probably branches from cranial nerves and the vagus nerve; 1, 2, 3, ophthalmic, maxillary, and mandibular nn.; V-C, vertex-ear-chin line.