5. Face & Scalp

Musculi Faciei

Fig. 5.1 Superficial musculi faciei

Anterior view. The superficial layer of muscles is shown on the right side of the face. Certain muscles have been cut on the left to expose deeper muscles. The musculi faciei are the superficial layer of muscles that arise either directly from the periosteum or from adjacent muscles and insert onto other musculi faciei or directly into the connective tissue of the skin. Because of their cutaneous attachments, the musculi faciei are able to move the facial skin (an action that may be temporarily abolished by botulinum toxin injection). They also serve a protective function (especially for the eyes) and are active during food ingestion (closing the labial fissure). The musculi faciei are innervated by branches of the nervus facialis (CN VII). As these muscles are located in the subcutaneous fat, and because the superficial body fascia is absent in the face, surgeons must be particularly careful when dissecting this region. The lack of fascia on the face and the loose connective tissue between the cutaneous attachments of the musculi faciei also means that facial lacerations, following a blow to the face for example, tend to gape widely. This necessitates careful suturing of these lacerations to approximate the edges of the wound and to prevent scarring. The loose nature of the connective tissue also provides a place for blood and fluid to accumulate, leading to swelling and bruising of the face. Such swelling may also be apparent following an inflammatory insult, such as a bee sting. The muscles of mastication lie deep to the musculi faciei. They control the movement of the mandibula and are innervated by branches of the nervus trigeminus (CN V).

Fig. 5.2 Superficial musculi faciei

Lateral view. The aponeurosis epicranialis (galea aponeurotica) is a tough tendinous sheet stretching over the calvaria; it is loosely attached to the periosteum. The muscles of the calvaria that arise from the aponeurosis epicranialis (musculi temporoparietalis and occipitofrontalis) are collectively known as the “epicranial muscles.” The musculus occipitofrontalis has two bellies: venter frontalis and venter occipitalis. The musculi trapezius and sternocleidomastoideus are superficial neck muscles.

Musculi Faciei: Calvaria, Ear, & Eye

Fig. 5.3 Musculi faciei: calvaria and ear

A Anterior view of calvaria. B Left lateral view of musculi auriculares.

Fig. 5.4 Musculi faciei: rima palpebrarum and nose

A Anterior view. The most functionally important muscle of this region is the musculus orbicularis oculi, which closes the rima palpebrarum (a protective reflex against foreign matter). As the musculus orbicularis oculi closes the rima palpebrarum, it does so by closing from lateral to medial, thus spreading lacrimal secretions across the cornea (p. 243). If the action of the musculus orbicularis oculi is lost because of facial nerve paralysis, the loss of this protective reflex will be accompanied by drying of the cornea from prolonged exposure to the air. The function of the musculus orbicularis oculi is tested by asking the patient to squeeze the eyelids tightly shut. Other symptoms of facial nerve paralysis (Bell palsy) include ipsilateral drooping of the corner of the mouth, eyebrow, and lower eyelid, and the inability to smile, whistle, blow out cheeks, or wrinkle the forehead (due to paralysis of the other musculi faciei).

B The musculus orbicularis oculi has been dissected from the left orbit to the medial canthus of the eye and reflected anteriorly to demonstrate its lacrimal part (pars profunda musculi orbicularis oculi, the Horner muscle). This part of the musculus orbicularis oculi arises mainly from the crista lacrimalis posterior, and its action is a subject of debate (it may have a functional role in drainage of the saccus lacrimalis).

Fig. 5.5 Changes of facial expression: rima palpebrarum and nose

Anterior view.

A Musculus corrugator supercilii. B Musculus orbicularis oculi. C Musculus nasalis. D Musculus levator labii superioris alaeque nasi.

Musculi Faciei: Mouth

Fig. 5.6 Musculi faciei: mouth

A–D Left lateral view. E Anterior view.

A Musculi zygomatici major and minor. B Musculi levator labii superioris and depressor labii inferioris (exposed by removal of the musculus depressor anguli oris). C Musculi levator anguli oris and depressor anguli oris. D Musculus buccinator. E Musculi faciei of the mouth.

Fig. 5.7 Changes of facial expression: mouth

Anterior view.

A Musculus orbicularis oris. B Musculus buccinator. C Musculus zygomaticus major. D Musculus risorius. E Musculus levator anguli oris. F Musculus depressor anguli oris. G Musculus depressor labii inferioris. H Musculus mentalis.

Neurovascular Topography of the Anterior Face & Scalp: Superficial Layer

Fig. 5.8 Neurovasculature of the superficial layer of the anterior face

Anterior view. Removed: Skin and fatty tissue. The musculi faciei have been partially removed on the left side to display underlying musculature and neurovascular structures. The musculi faciei receive motor innervation from the nervus facialis (CN VII), which emerges laterally from the glandula parotidea. The muscles of mastication receive motor innervation from the nervus mandibularis of the nervus trigeminus (CN V₃). The face receives sensory innervation primarily from the terminal branches of the three divisions of the nervus trigeminus (CN V), but also from the nervus auricularis magnus, which arises from the plexus cervicalis (see pp. 316 and 317). The face receives blood supply primarily from branches of the arteria carotis externa, though these do anastomose on the face with facial branches of the arteria carotis interna (see Fig. 3.12).

Fig. 5.9 Scalp

The scalp consists of five layers. From superficial to deep, these are Skin, Connective tissue, epicranical Aponeurosis (galea aponeurotica), Loose areolar tissue, and Pericranium.

Scalp infections are able to spread easily through the loose connective tissue layer. They may spread intracranially to the sinus durae matris through venae emissariae, causing meningitis, or to the eyelids or nose because the frontalis muscle inserts into the skin and subcutaneous tissue but does not attach to bone. Infections that spread to the eyelid cause rapid swelling because the skin of the eyelid is very thin and it covers a loose connective tissue layer. Scalp infections are unable to spread into the neck because the ventri occipitales of the musculi occipitofrontales attach to the os occipitale and the processus mastoideus of the os temporale. Likewise they are prevented from spreading laterally beyond the arci zygomatici because the aponeurosis epicranialis is continuous with the fascia temporalis, which attaches to the arci zygomatici.

Scalp lacerations bleed profusely because the arteries entering the periphery of the scalp bleed from both ends owing to extensive anastomoses. Furthermore, the arteries do not contract to arrest bleeding because they are held open by the dense connective tissue layer of the scalp. The musculus occipitofrontalis may go into spasm following scalp laceration causing the wound to gape. Scalp lacerations should be sutured or otherwise controlled as soon as possible after injury to prevent serious, sometimes fatal, loss of blood.

Fig. 5.10 Venous “danger zone” in the face

The superficial veins of the face have extensive connections with the deep veins of the head (e.g., the plexus pterygoideus) and sinus durae matris (e.g., the sinus cavernosus) (see p. 66). Veins in the triangular danger zone are, in general, valveless. There is therefore a particularly high risk of bacterial dissemination into the cavitas cranii. For example, bacteria from a boil on the lip may enter the vena facialis and cause meningitis by passing through venous communications with the sinus cavernosus.

Neurovascular Topography of the Lateral Head: Superficial Layer

Fig. 5.11 Neurovasculature of the superficial layer of the lateral head

Left lateral view. The arteries supplying the lateral head arise from branches of the arteria carotis externa (see Fig. 5.12). Blood drains primarily into the venae jugulares interna, externa, and anterior (see p. 62). The musculi faciei receive motor innervation from the nervus facialis (CN VII), which emerges laterally from the glandula parotidea (see p. 133). The muscles of mastication receive motor innervation from the nervus mandibularis division of the nervus trigeminalis (CN V₃, see p. 128). The sensory innervation of the face is shown in Fig. 5.13.

Fig. 5.12 Superficial arteries of the head

Left lateral view. The superficial face is supplied primarily by branches of the arteria carotis externa (e.g., arteriae facialis, temporalis super-ficialis, and maxillaris). However, there is a limited contribution from branches derived from the arteria carotis interna in the region of the orbital rim.

Note: The arteria carotis interna is colored purple and the anterior, medial, posterior, and terminal branches of the arteria carotis externa are colored red, blue, green, and yellow, respectively.

Fig. 5.13 Sensory innervation of the lateral head and neck

Left lateral view. The head receives sensory innervation primarily from the nervus trigeminus (orange), the plexus cervicalis (green and gray), and the ramik posteriores of the nervi spinales (blue). Sensory supply to the face is primarily from the terminal branches of the three nervus trigeminus divisions. The occiput and nuchal region are supplied primarily by rami posteriores of the nervi spinales. The rami anteriores of the first four nervi spinales combine to form the plexus cervicalis. The plexus cervicalis gives off four cutaneous branches that supply the lateral head and neck (nerves listed with their associated spinal nerve fibers): nervus auricularis minor (C2, occasionally C3), nervus auricularis major (C2–C3), nervus transversus cervicalis (C2–C3), and nervi supraclaviculares (C3–C4) (see Fig. 12.3).

Neurovascular Topography of the Lateral Head: Intermediate & Deep Layers

Fig. 5.14 Nerves of the intermediate layer of the lateral head

Left lateral view. The glandula parotidea has been removed to demonstrate the structure of the plexus intraparotideus of the nervus facialis (see Fig. 4.88). The occiput receives sensory innervation from the greater occipital nerve, which arises from the ramus posterior of C2, and the nervus occipitalis minor, which arises from the plexus cervicalis (rami anteriores of C2).

Fig. 5.15 Neurovasculature of the lateral face

Left lateral view. The musculus masseter and arcus zygomaticus have been windowed to reveal the deep structures. Also, the ramus and corpus of the mandibula have been opened to demonstrate neurovascular structures that traverse it.