# Lecture 10: Face and Scalp ## Unit 1.5: Human Gross Anatomy III - Pelvis and Head/Neck --- ## Learning Objectives By the end of this lecture, students will be able to: 1. Describe the layers of the scalp and their clinical significance 2. Identify the muscles of facial expression and their innervation 3. Describe the sensory innervation of the face (trigeminal nerve divisions) 4. Identify the blood supply of the face and scalp 5. Describe the anatomy of the parotid gland and facial nerve 6. Correlate anatomical features with clinical conditions --- ## Scalp The scalp is the soft tissue covering of the calvaria, extending from the supraorbital margins anteriorly to the superior nuchal lines posteriorly, and laterally to the zygomatic arches. Its structure is conveniently remembered using the mnemonic SCALP, which denotes its five layers from superficial to deep. The skin is the outermost layer and is notably thick, being the thickest skin of the body, and hair-bearing. The dense connective tissue layer lies immediately beneath the skin and contains a rich neurovascular network including the scalp arteries, veins, and cutaneous nerves. This layer is firmly attached to both the overlying skin and the underlying aponeurosis, and these three layers move as a functional unit. The aponeurosis, or galea aponeurotica, is a strong tendinous sheet that connects the occipitalis muscle posteriorly to the frontalis muscle anteriorly and is continuous laterally with the temporoparietal fascia. The loose areolar tissue constitutes the fourth layer and is clinically termed the "danger space" because it allows free movement of the scalp over the underlying pericranium and also permits the spread of blood or infection across extensive areas. This layer is continuous anteriorly with loose tissue in the upper eyelids, explaining how scalp hematomas can track forward to produce periorbital ecchymosis (black eyes). The pericranium is the periosteum of the skull bones and is loosely attached to the outer table except at the sutures, where it is firmly bound. Scalp wounds have characteristic features reflecting this layered anatomy. Because the vessels run in the dense connective tissue layer and are tethered by fibrous septa, they cannot retract or undergo vasoconstriction when cut, leading to profuse bleeding. The attachment of the first three layers also causes wound edges to gape rather than fall together. Panel A: Coronal section through the scalp showing thick hair-bearing skin (brown) and dense connective tissue (pink) with embedded arteries and nerves. Panel B: Galea aponeurotica (white fibrous layer) connecting frontalis and occipitalis muscles. Panel C: Loose areolar tissue (pale yellow) labeled as the danger space and pericranium (thin dark layer) on the outer table of the skull. Panel D: Arrows showing how the first three layers (skin, connective tissue, aponeurosis) move as a unit. --- ## Muscles of the Scalp The epicranius muscle is the principal muscle of the scalp, comprising the frontalis anteriorly and occipitalis posteriorly, joined by the galea aponeurotica. The frontalis originates from the galea aponeurotica and inserts into the skin of the forehead and the eyebrows. When it contracts, it raises the eyebrows and produces horizontal wrinkles across the forehead, the facial expression associated with surprise. The occipitalis arises from the superior nuchal line and mastoid process and inserts into the galea aponeurotica. Its contraction retracts the scalp posteriorly, providing a fixed point against which the frontalis can act. The temporoparietalis is a thin muscle located above the ear, connecting the galea aponeurotica to the temporal fascia. In most individuals it is functionally weak or vestigial. All scalp muscles receive motor innervation from the facial nerve (CN VII). The frontalis is supplied by the temporal branches of the facial nerve, while the occipitalis receives the posterior auricular branch. Panel A: Lateral view of the frontalis muscle overlying the frontal bone. Panel B: Broad galea aponeurotica (translucent white sheet) connecting frontalis to the occipitalis muscle posteriorly. Panel C: Thin temporoparietalis muscle visible laterally above the ear. Panel D: Facial nerve branches (temporal and posterior auricular) shown in yellow approaching their target muscles. --- ## Blood Supply of the Scalp The scalp receives an exceptionally rich blood supply from five paired arteries, with extensive anastomotic connections. This redundant supply explains both the profuse bleeding from scalp wounds and the excellent healing capacity of scalp tissue. The anterior scalp receives blood from internal carotid system derivatives via the ophthalmic artery. The supratrochlear artery emerges at the superomedial orbital margin and ascends to supply the medial forehead. The supraorbital artery exits through the supraorbital notch or foramen and supplies the central forehead and anterior scalp toward the vertex. The lateral and posterior scalp are supplied by branches from the external carotid artery. The superficial temporal artery, one of the terminal branches of the external carotid, emerges anterior to the ear where it is readily palpable against the zygomatic arch. It divides into frontal and parietal branches supplying the temporal and lateral scalp regions. The posterior auricular artery ascends behind the ear to supply the scalp posterior to the auricle. The occipital artery passes posteriorly deep to the sternocleidomastoid and splenius capitis muscles, emerging to pierce the trapezius and supply the posterior scalp. The veins of the scalp generally accompany the arteries. The supratrochlear and supraorbital veins unite to form the angular vein, which continues as the facial vein. The superficial temporal veins drain into the retromandibular vein. The occipital and posterior auricular veins contribute to the external jugular vein. Critically, emissary veins pass through foramina in the skull to connect the scalp veins with the dural venous sinuses. Because these veins lack valves, they can permit bidirectional flow, creating a potential pathway for the spread of infection from the scalp to the intracranial venous sinuses. Panel A: Superior view of scalp vasculature with supratrochlear and supraorbital arteries (red) anteriorly from the ophthalmic artery. Panel B: Superficial temporal artery (red) laterally converging toward the vertex. Panel C: Posterior auricular and occipital arteries (red) posteriorly with corresponding veins in blue. Panel D: Emissary veins (dotted lines) connecting scalp veins through skull to underlying dural sinuses. --- ## Innervation of the Scalp Sensory innervation of the scalp is derived from the trigeminal nerve (CN V) anteriorly and from the cervical plexus (C2-C3) posteriorly, with the boundary roughly corresponding to a line between the ears passing over the vertex. The anterior scalp to the vertex is supplied by branches of the trigeminal nerve. From the ophthalmic division (V1), the supratrochlear nerve provides sensation to the medial forehead, while the supraorbital nerve supplies the forehead and anterior scalp extending to the vertex. The maxillary division (V2) contributes the zygomaticotemporal nerve to the temple. The mandibular division (V3) provides the auriculotemporal nerve, which supplies the temple and the anterior aspect of the external ear. The posterior scalp, behind the vertex, receives sensory innervation from the cervical plexus. The lesser occipital nerve (from the anterior ramus of C2) supplies the area behind the ear. The greater occipital nerve (from the posterior ramus of C2) is the principal nerve of the posterior scalp, emerging between the atlas and axis and piercing the trapezius to supply a large territory extending nearly to the vertex. The third occipital nerve (from the posterior ramus of C3) supplies the lower posterior scalp. Motor innervation to the scalp muscles comes exclusively from the facial nerve, as described above. Panel A: Lateral view of V1 branches (green) -- supratrochlear and supraorbital -- covering the forehead and anterior scalp. Panel B: V2 territory (yellow) with zygomaticotemporal nerve at the temple and V3 territory (orange) with auriculotemporal nerve at the temple and anterior ear. Panel C: Cervical plexus territories (blue) showing lesser occipital behind ear, greater occipital across posterior scalp, and third occipital inferiorly. Panel D: Boundary line at vertex indicated between trigeminal and cervical plexus territories. --- ## Muscles of Facial Expression The muscles of facial expression constitute a unique group of skeletal muscles that arise from bone or fascia but insert into the skin of the face rather than crossing joints. This arrangement allows them to produce the subtle movements of facial skin that convey emotion. All muscles of facial expression are derived from the second pharyngeal arch and are therefore innervated by the facial nerve (CN VII). Unlike most skeletal muscles, they lack surrounding fascial coverings, allowing direct skin attachment. The muscles around the eye include the orbicularis oculi, the sphincter muscle encircling the orbit. Its orbital part produces forceful eye closure (as when squinting in bright light), while the palpebral part produces gentle closure (as in blinking). The lacrimal part surrounds the lacrimal sac and aids in tear drainage. The corrugator supercilii draws the eyebrows together and downward, producing the vertical furrows associated with frowning. The procerus draws the medial eyebrows downward, creating transverse wrinkles over the nasal bridge. The muscles around the nose include the nasalis, which has transverse and alar parts that compress and dilate the nostrils respectively. The depressor septi pulls the nasal tip downward. The levator labii superioris alaeque nasi elevates both the upper lip and the nasal ala. The muscles around the mouth are numerous and complex, reflecting the importance of this region for speech and facial expression. The orbicularis oris is the sphincter muscle of the mouth, closing and protruding the lips. Multiple muscles elevate the upper lip and oral commissure: the levator labii superioris elevates the upper lip, the levator anguli oris elevates the corner of the mouth, the zygomaticus major draws the angle upward and laterally (the muscle of smiling), and the zygomaticus minor assists in elevating the upper lip. Depressors of the lower lip include the depressor labii inferioris, which pulls the lower lip downward, and the depressor anguli oris, which draws the corner of the mouth inferiorly. The mentalis protrudes and wrinkles the chin. The risorius draws the corners of the mouth laterally in a grinning expression. The buccinator forms the muscular foundation of the cheek, compressing the cheek against the teeth to keep food in position during mastication and aiding in forceful exhalation. The platysma, though extending into the neck, is considered a muscle of facial expression; it tenses the skin of the neck and can depress the mandible and corners of the mouth. The muscles around the ear include the anterior, superior, and posterior auricular muscles, which are largely vestigial in humans, though some individuals retain the ability to move their ears. Panel A: Anterior view of periorbital muscles (orbicularis oculi, corrugator) in blue with arrows indicating direction of action. Panel B: Nasal muscles (nasalis, procerus) in green with underlying bony attachments shown faintly. Panel C: Perioral muscles (orbicularis oris, levators, depressors, zygomaticus major and minor, buccinator) in red with arrows indicating direction of action. Panel D: Platysma shown extending from mandible to clavicle with action arrows. --- ## Facial Nerve Motor Distribution The facial nerve (CN VII) provides motor innervation to all muscles of facial expression. Its course can be understood in three segments: intracranial, within the facial canal, and extracranial. Intracranially, the facial nerve exits the brainstem at the cerebellopontine angle, immediately lateral to the abducens nerve. It enters the internal acoustic meatus along with the vestibulocochlear nerve (CN VIII) and the labyrinthine artery. Within the facial canal of the petrous temporal bone, the nerve makes two bends. At the first bend, the nerve expands to form the geniculate ganglion, which contains the cell bodies for taste and sensation. Here, the greater petrosal nerve branches off, carrying parasympathetic fibers that will eventually innervate the lacrimal gland (via the pterygopalatine ganglion). Continuing posteriorly, the nerve gives off the nerve to stapedius (controlling the stapedius muscle in the middle ear) and the chorda tympani, which carries taste fibers from the anterior two-thirds of the tongue and parasympathetic fibers to the submandibular and sublingual glands. The facial nerve exits the skull through the stylomastoid foramen. Immediately after emerging, it gives off the posterior auricular nerve (to occipitalis and posterior auricular muscles) and branches to the stylohyoid and posterior belly of digastric. The main trunk then enters the parotid gland, within which it divides into its terminal branches. Though the nerve passes through the gland, it does not innervate it. Within the parotid, the branches form the parotid plexus and emerge as five terminal groups, remembered by the mnemonic "To Zanzibar By Motor Car": the temporal branches cross the zygomatic arch to supply the frontalis and upper orbicularis oculi; the zygomatic branches supply the lower orbicularis oculi; the buccal branches run across the cheek to innervate the buccinator and upper lip muscles; the marginal mandibular branch runs along or below the mandible to supply the lower lip and chin muscles; and the cervical branch descends to innervate the platysma. The temporal branch is vulnerable as it crosses the zygomatic arch, and the marginal mandibular branch is at risk during surgery near the mandible because it may loop below the mandible before ascending to reach its target muscles. Panel A: Lateral view showing facial nerve exiting stylomastoid foramen with posterior auricular branch ascending. Panel B: Main trunk entering parotid gland (shown as translucent) and forming the parotid plexus. Panel C: Five emerging terminal branches labeled -- temporal (to forehead), zygomatic (to lower eyelid), buccal (to cheek), marginal mandibular (to lower lip and chin), and cervical (to platysma). Panel D: Each branch shown in different color with target muscle regions indicated. --- ## Sensory Innervation of the Face Sensory innervation of the face is provided by the three divisions of the trigeminal nerve (CN V), with territories arranged roughly from superior to inferior. The ophthalmic division (V1) supplies the forehead, upper eyelid, and external nose (including the tip). Named branches include the supratrochlear nerve (medial forehead and upper eyelid), supraorbital nerve (forehead and anterior scalp), infratrochlear nerve (medial upper eyelid and side of nose), external nasal nerve (tip and dorsum of nose), and lacrimal nerve (lateral upper eyelid). The maxillary division (V2) supplies the lower eyelid, cheek, side of the nose, and upper lip. Its principal cutaneous branch is the infraorbital nerve, which emerges from the infraorbital foramen below the orbit to supply the lower eyelid, side of the nose, and upper lip. Additional branches include the zygomaticofacial nerve (over the cheek prominence) and zygomaticotemporal nerve (at the temple). The mandibular division (V3) supplies the lower lip, chin, and jaw (except the angle). The mental nerve emerges from the mental foramen on the mandible to supply the lower lip and chin. The buccal nerve supplies sensory fibers to the cheek (note that motor innervation to buccinator comes from the facial nerve, not this nerve). The auriculotemporal nerve supplies the temple and anterior ear. Importantly, the angle of the mandible is not supplied by the trigeminal nerve but rather by the great auricular nerve from the cervical plexus (C2, C3). This distinction is clinically relevant when performing local anesthesia or assessing facial sensation. Panel A: V1 territory (green) covering forehead, upper eyelid, and nose tip with branches (supratrochlear, supraorbital, external nasal) emerging from their foramina. Panel B: V2 territory (yellow) covering lower eyelid, cheek, and upper lip with infraorbital nerve emerging from infraorbital foramen. Panel C: V3 territory (orange) covering lower lip, chin, and jaw with mental nerve at mental foramen and auriculotemporal nerve at temple. Panel D: Angle of mandible (blue) indicated as C2-C3 territory distinct from trigeminal distribution. --- ## Arterial Supply of the Face The face receives its principal arterial supply from the facial artery, a branch of the external carotid artery. The facial artery arises in the neck, passes deep to the submandibular gland (grooving its deep surface), and crosses the lower border of the mandible just anterior to the insertion of the masseter muscle, where its pulsation is readily palpable. From there it ascends tortuously toward the medial angle of the eye, ending as the angular artery which anastomoses with branches of the ophthalmic artery. Along its course, the facial artery gives off the inferior labial artery to the lower lip, the superior labial artery to the upper lip (which also sends a branch to the nasal septum, making this a preferred site for nasal packing), and the lateral nasal artery to the side of the nose. The superficial temporal artery, a terminal branch of the external carotid, emerges anterior to the ear and supplies the temporal region. Its pulsation is palpable against the zygomatic arch and may be visible in elderly individuals. It is the artery biopsied when giant cell (temporal) arteritis is suspected. The transverse facial artery branches from the superficial temporal artery and runs anteriorly across the masseter muscle, roughly parallel to and below the zygomatic arch. These arteries form extensive anastomoses across the midline and with branches of the ophthalmic artery (itself from the internal carotid system), providing excellent collateral circulation and accounting for the face's remarkable healing capacity. Panel A: Lateral view of the facial artery crossing the mandible anterior to the masseter and ascending tortuously toward the medial eye angle. Panel B: Labeled branches of the facial artery -- inferior labial, superior labial, and lateral nasal -- along its course. Panel C: Superficial temporal artery anterior to the ear with transverse facial branch crossing the masseter. Panel D: Anastomotic connections indicated by arrows, particularly the connection between the angular artery and ophthalmic vessels. --- ## Venous Drainage of the Face The facial vein begins at the medial angle of the eye as the angular vein, formed by the union of the supratrochlear and supraorbital veins. It descends across the face, running posteroinferior to the facial artery (unlike most head and neck veins, the facial vein does not closely accompany its artery). The facial vein joins with the anterior division of the retromandibular vein to form the common facial vein, which drains into the internal jugular vein. The "danger area of the face" is a triangular region bounded roughly by the corners of the mouth and the bridge of the nose. This area is significant because the facial vein makes critical communications with the intracranial venous sinuses via two pathways. First, the angular vein communicates with the superior ophthalmic vein, which drains into the cavernous sinus. Second, the deep facial vein connects the facial vein to the pterygoid plexus, which in turn communicates with the cavernous sinus. These connections gain clinical importance because the facial veins, like most veins of the head and neck, lack valves. Under normal circumstances, blood flows from superficial to deep, but increased pressure (as during straining or infection) can reverse this flow. Infections within the danger area, such as furuncles (boils) or severe acne, can therefore spread along these valveless veins to reach the cavernous sinus, potentially causing life-threatening cavernous sinus thrombosis. Panel A: Facial vein descending from the medial eye angle with major tributaries labeled. Panel B: Angular vein connecting to superior ophthalmic vein leading to cavernous sinus through the orbit. Panel C: Deep facial vein connecting to pterygoid plexus with communication pathway to cavernous sinus. Panel D: Danger area of the face outlined as a triangle (corners of mouth to nasal bridge) with arrows indicating potential paths of infection spread to cavernous sinus. --- ## Parotid Gland The parotid gland is the largest of the three major salivary glands and produces purely serous (watery) secretions. It is located in the preauricular region, anterior and inferior to the external acoustic meatus, superficial to the masseter muscle and the ramus of the mandible. The gland occupies the parotid bed, bounded superiorly by the zygomatic arch, inferiorly by the angle of the mandible and posterior belly of digastric, anteriorly by the masseter and medial pterygoid muscles, and posteriorly by the mastoid process and sternocleidomastoid muscle. A deep process of the gland extends medially behind the mandible toward the parapharyngeal space. Several important structures pass through the parotid gland, arranged from superficial (lateral) to deep (medial). Most superficial is the facial nerve with its branches, which enters the gland posteriorly after exiting the stylomastoid foramen and forms the parotid plexus within the substance of the gland. Although the nerve traverses the gland, it does not innervate it. Deep to the nerve lies the retromandibular vein, formed by the union of the superficial temporal and maxillary veins. Deepest of the three is the external carotid artery, which divides within or just above the gland into the superficial temporal and maxillary arteries. A useful mnemonic for these relationships is "Face, Vein, Artery" from superficial to deep. The parotid duct (Stensen's duct) emerges from the anterior border of the gland, crosses the masseter muscle superficially, turns sharply medially to pierce the buccinator muscle, and opens into the oral vestibule opposite the upper second molar tooth. The duct can be palpated as a cordlike structure over the masseter when the muscle is contracted. Parasympathetic secretomotor innervation to the parotid follows a complex pathway. Preganglionic fibers originate in the inferior salivatory nucleus, travel in the glossopharyngeal nerve (CN IX), exit via the tympanic nerve, traverse the middle ear as the tympanic plexus, emerge as the lesser petrosal nerve, and synapse in the otic ganglion. Postganglionic fibers hitchhike on the auriculotemporal nerve to reach the gland. Sympathetic fibers arrive from the superior cervical ganglion via periarterial plexuses and regulate blood flow to the gland. Panel A: Lateral view of parotid gland (semi-transparent yellow) with facial nerve branches (yellow lines) as the most superficial structure passing through it. Panel B: Retromandibular vein (blue) intermediate and external carotid artery (red) deepest within the gland substance. Panel C: Parotid duct emerging anteriorly, crossing the masseter, and piercing the buccinator to open at the upper second molar (inset of open mouth). Panel D: Otic ganglion and parasympathetic innervation pathway to the parotid gland shown in diagram. --- ## Clinical Correlations Scalp lacerations gape rather than fall together due to the fibrous connections between the skin, connective tissue, and galea. They bleed profusely because the vessels in the connective tissue layer are held open by these same fibrous attachments and cannot retract. Infections in the loose areolar layer (the danger space) can spread widely beneath the scalp and may track forward into the eyelids. Bell's palsy is an idiopathic lower motor neuron facial nerve palsy, often attributed to viral infection or inflammation within the narrow facial canal. Because it is a lower motor neuron lesion, all branches of the facial nerve are affected on the ipsilateral side, including those to the forehead (frontalis). This distinguishes it from an upper motor neuron lesion such as stroke, where forehead movement is typically spared because the frontalis receives bilateral upper motor neuron input. Patients with Bell's palsy present with inability to close the eye, drooping of the mouth, and loss of the nasolabial fold on the affected side. Parotitis (inflammation of the parotid gland) is most classically seen in mumps, a viral infection that causes painful bilateral parotid swelling. Complications include orchitis (which may lead to sterility), pancreatitis, and meningitis. Bacterial parotitis may occur in dehydrated or debilitated patients due to retrograde spread of oral bacteria through the parotid duct. Parotid tumors and surgical procedures on the parotid gland carry significant risk to the facial nerve because it traverses the gland. The nerve is carefully identified and preserved during parotidectomy. Frey syndrome (auriculotemporal syndrome or gustatory sweating) is a complication of parotid surgery in which aberrant regeneration of parasympathetic fibers (intended for the parotid gland) to sweat glands of the overlying skin causes sweating over the parotid region during eating. Trigeminal neuralgia (tic douloureux) is a condition of severe, lancinating pain in the distribution of one or more divisions of the trigeminal nerve, most commonly V2 or V3. The pain is often triggered by light touch, chewing, or exposure to cold and is frequently caused by vascular compression of the trigeminal nerve root at the brainstem. Cavernous sinus thrombosis is a life-threatening complication of facial infections, particularly those in the danger area. It presents with proptosis (forward displacement of the eye), ophthalmoplegia (impaired eye movement due to involvement of cranial nerves III, IV, and VI within the sinus), and sensory changes in the V1 and V2 distributions. Fever, headache, and altered mental status indicate the severity of the condition. Panel A: Bell's palsy facial appearance showing unilateral forehead drooping, inability to close eye, and drooping mouth corner. Panel B: Parotid gland swelling in mumps with bilateral enlargement. Panel C: Parotid tumor with facial nerve at risk during surgical exposure. Panel D: Cavernous sinus thrombosis showing proptosis and periorbital edema with arrow indicating infection spread pathway from the danger area. --- ## Summary The scalp comprises five layers remembered as SCALP: skin, connective tissue (dense), aponeurosis (galea aponeurotica), loose areolar tissue (danger space), and pericranium. The first three layers move as a unit and contain the neurovascular structures. The muscles of facial expression arise from bone and insert into skin, all innervated by the facial nerve, which exits via the stylomastoid foramen and divides into five terminal branches within the parotid gland: temporal, zygomatic, buccal, marginal mandibular, and cervical. Sensory innervation of the face follows the three divisions of the trigeminal nerve: V1 supplies the forehead and nose tip, V2 supplies the cheek and upper lip, and V3 supplies the lower lip and chin (but not the angle of the mandible, which is C2-C3 territory). The facial artery supplies most of the face and anastomoses with ophthalmic branches at the medial eye angle, creating connections between the external and internal carotid systems. The danger area of the face is significant because infections can spread via valveless facial veins to the cavernous sinus, potentially causing cavernous sinus thrombosis. The parotid gland is traversed by the facial nerve, retromandibular vein, and external carotid artery, with its duct opening opposite the upper second molar. --- ## Key Terms | Term | Definition | |------|------------| | Galea aponeurotica | Tendinous aponeurosis connecting the frontalis and occipitalis muscles, forming the central layer of the scalp | | Danger area of the face | Triangular region where infections may spread via valveless veins to the cavernous sinus | | Bell's palsy | Lower motor neuron facial nerve palsy affecting all ipsilateral facial muscles including the forehead | | Parotid duct | Stensen's duct; drains the parotid gland and opens into the mouth opposite the upper second molar | | Pterion | Thin skull region overlying the middle meningeal artery, vulnerable to fracture | | Emissary veins | Valveless veins connecting scalp veins to dural sinuses, permitting potential infection spread | --- *This content is subject to the [MIT License](https://opensource.org/licenses/MIT). © 2024–2026 Hibbert School of Medicine.*