Unit 3 · Mid & lower face
Fifteen muscles converging on two structures
From the nasal root to the chin, almost every muscle in this region either acts on the upper lip or inserts into the modiolus at the oral commissure. That convergence is why a single misplaced injection here changes speech, smile symmetry or oral competence rather than simply softening a line.
Learn · Regional framing
Three regions, one mechanical system
The nasal muscles are small, often overlooked, and clinically relevant in both neuromodulator practice — nasal tip elevation, bunny lines, nostril flare reduction — and in understanding the dynamics of the upper lip complex.
The midface contains the largest and most complex grouping of facial muscles, including the zygomaticus major, the primary smile muscle, and the buccinator, masseter and several lip elevators. This region is also traversed by the parotid duct and facial artery, making thorough anatomical knowledge critical for safe treatment.
The perioral region is dominated by the orbicularis oris, the sphincter of the mouth, and surrounded by multiple depressor and elevator muscles that converge at the modiolus. This complex is central to lip aesthetics, gummy smile treatment and marionette line formation.
The three regions are separated for study, not for planning. The levator labii superioris alaeque nasi elevates the upper lip and dilates the nostril, so it belongs to both the nose and the perioral complex; the depressor septi nasi animates the upper lip downward during smiling. A gummy smile is a nasal, midface and perioral problem simultaneously.
Learn · Muscle index
Mid and lower face muscles
Fifteen muscles across three regions. Select the muscle you need rather than reading the set — the index is built to be returned to during treatment planning, not memorised in one pass.
Muscle explorer · Mid & lower face
Fifteen muscles across three regions. Arrow keys move through the index.
Nose
Cheek & midface
Perioral
Nose
Nasalis (transverse part)
M. nasalis, pars transversa
Compresses the nostril (nose flaring, reversed).
Target for nostril flare reduction; blends with procerus superiorly.
Nose
Nasalis (alar part)
M. nasalis, pars alaris
Dilates the nostril.
Treatment here risks compromising nasal patency; rarely indicated.
Nose
Depressor septi nasi
M. depressor septi nasi (DSN)
Depresses the nasal tip and columella; animates the upper lip downward during smiling.
Primary target for nasal tip elevation, by injection at the nasal spine; relevant in gummy smile treatment.
Nose
Procerus
M. procerus
Pulls the medial brow inferiorly; produces horizontal nasal root lines.
Treated with the corrugator and glabellar complex; also a target for bunny lines at the nasal root. Full profile appears in the Unit 2 index.
Nose
Levator labii superioris alaeque nasi
M. levator labii superioris alaeque nasi
Elevates the upper lip and dilates the nostril.
Contributes to nasal flare and gummy smile; the longest named muscle in the body.
Cheek & midface
Zygomaticus major
M. zygomaticus major
Draws the oral commissure superiorly and laterally — the primary muscle of smiling.
Zygomatic bone, anterior to the zygomaticotemporal suture.
Modiolus, the fibromuscular node at the oral commissure, and skin of the upper lip.
Buccal and zygomatic branches of CN VII.
Bifid zygomaticus major (double zygomaticus) occurs in a significant proportion of patients and is associated with cheek dimples. Understanding its pathway is important when treating the nasolabial fold with filler — inadvertent injection into or around this muscle can impair smile symmetry.
Cheek & midface
Zygomaticus minor
M. zygomaticus minor
Elevates the upper lip; contributes to nasolabial fold deepening during smiling.
Zygomatic bone, medial to zygomaticus major.
Upper lip, lateral to levator labii superioris.
Buccal branch of CN VII.
When present, an anatomical variant in approximately 40% of individuals, the zygomaticus minor contributes to the dynamics of the nasolabial fold and medial cheek. Appreciation of this variation is relevant in surgical and filler midface work.
Cheek & midface
Levator labii superioris
M. levator labii superioris
Elevates and everts the upper lip; deepens the nasolabial fold.
Infraorbital margin (maxilla).
Upper lip, skin and muscle.
Buccal branch of CN VII.
One of the muscles implicated in gummy smile (class II). Treatment with a neuromodulator in the infraorbital region targets this muscle. Careful dosing is required to avoid undue lip ptosis or asymmetry.
Cheek & midface
Masseter
M. masseter
Primary jaw closer; elevates the mandible for chewing.
Zygomatic arch (superficial head) and deep surface of the zygomatic arch (deep head).
Lateral surface of the ramus and angle of the mandible.
Masseteric nerve, a branch of CN V3, the mandibular division of the trigeminal nerve.
A primary target for jaw slimming and bruxism treatment with neuromodulators. Masseteric hypertrophy treatment requires injection into the lower third of the muscle bulk, palpated at the angle of the mandible. High injections risk weakening the zygomaticus, buccinator or risorius.
Cheek & midface
Buccinator
M. buccinator
Compresses the cheeks against the teeth; involved in blowing, chewing and sucking.
Alveolar processes of maxilla and mandible, opposite the molar teeth; pterygomandibular raphe posteriorly.
Modiolus; blends with orbicularis oris.
Buccal branch of CN VII; sensory supply from the buccal branch of CN V3.
The parotid duct (Stensen's duct) pierces the buccinator at the level of the upper second molar. Filler injections in the mid-buccal region carry a risk of duct injury — rare but described. The buccal fat pad lies immediately lateral to the buccinator and is a key volumetric structure in midface aesthetics.
Cheek & midface
Risorius
M. risorius
Retracts the commissure laterally, producing a "grimace" smile.
Parotid fascia.
Modiolus; skin at the corner of the mouth.
Buccal and mandibular branches of CN VII.
A variable muscle with significant individual anatomy. When over-dominant relative to the zygomaticus, the risorius contributes to a wide, flat smile. Rarely a direct injection target but relevant in understanding smile mechanics and commissure position.
Perioral
Orbicularis oris
M. orbicularis oris
Closes and purses the lips; involved in speech, kissing and whistling.
No bony origin; formed by interdigitation of surrounding muscles converging at the modiolus.
Skin and mucosa of the lips.
Buccal and mandibular branches of CN VII.
The perioral vertical lines ("lipstick lines") are caused by repeated contraction of the orbicularis oris in combination with age-related volume loss and dermal thinning. Neuromodulator treatment of this muscle requires low doses and careful placement to preserve lip function. Filler is generally the preferred treatment for lip lines.
Perioral
Depressor anguli oris
M. depressor anguli oris (DAO)
Pulls the oral commissure inferiorly; contributes to the downturned mouth appearance and marionette lines.
Oblique line of the mandible.
Modiolus and skin at the oral commissure.
Marginal mandibular branch of CN VII.
A primary neuromodulator target for the downturned commissure. The DAO runs in a fairly consistent pathway from the mandibular body laterally upwards to the modiolus. Injection is typically 1–1.5 cm lateral to the commissure and 1 cm above the mandibular border. Medial placement risks the depressor labii inferioris and can impair speech and oral competence.
Perioral
Depressor labii inferioris
M. depressor labii inferioris (DLI)
Pulls the lower lip inferiorly and laterally; contributes to lower lip eversion and lower dental show.
Anterior mandible, along the oblique line between the mental foramen and the symphysis.
Skin and muscle of the lower lip.
Marginal mandibular branch of CN VII.
Treated for smile asymmetry, where one side shows excessive lower lip depression, and as part of lip flip refinement. The marginal mandibular nerve runs close to the DLI — inadvertent blockade causes lower lip asymmetry and drooping.
Perioral
Mentalis
M. mentalis
Raises and wrinkles the chin skin; protrudes the lower lip.
Incisive fossa of the mandible, below the lower incisors.
Skin of the chin.
Marginal mandibular branch of CN VII.
Hyperactive mentalis produces the characteristic "cobblestone" or "pebbly" chin — a common neuromodulator target. Over-treatment can soften the chin pad excessively, reducing projection. The mental nerve exits the mental foramen just lateral to the midline — a key anatomical landmark during chin filler injection.
Predict · Nasal tip dynamics
A tip that drops on smiling is a muscle problem
Botulinum toxin type A (BTX-A) is not usually thought of as a nasal treatment, yet one of the most reliable small interventions in the face sits at the base of the columella. Commit to the muscle and the injection point before you open the reveal.
A patient's nasal tip visibly drops each time they smile, and the same animation shortens the upper lip. Which muscle is doing that, and where would you place product to change it?
Hold your answer before you open this. The value is in having committed to a mechanism first.
The depressor septi nasi pulls the nasal tip inferiorly during animation, a feature particularly noticeable during smiling. Treatment of the DSN with 2–4 indicative BTX-A reference units at the nasal spine, the columellar base, is a well-described technique for nasal tip elevation.
The same injection often contributes to improvement in a dynamic gummy smile. The key injection point is in the midline, at the base of the columella — superficial, subcutaneous, with the needle bevel up.
The DSN is one of three contributors a gummy smile can be attributed to, alongside the levator labii superioris, implicated in class II gummy smile and treated in the infraorbital region, and the levator labii superioris alaeque nasi, which elevates the upper lip and dilates the nostril. Establishing which of the three is dominant on animation is what determines whether the nasal spine injection is sufficient on its own.
A patient requests nasal tip elevation on animation. The muscle to target, and the injection point described for it, are:
Select an option to commit. The reasoning appears afterwards.
The depressor septi nasi depresses the nasal tip and columella and animates the upper lip downward during smiling. Weakening it at the nasal spine, in the midline at the base of the columella, is the described technique for nasal tip elevation. Placement is superficial and subcutaneous, with the needle bevel up.
The same injection frequently improves a dynamic gummy smile, which is why the assessment is done on animation rather than at rest. A tip that sits well statically and drops on smiling is a DSN problem, and no amount of structural work elsewhere in the nose will address it.
Predict · Midface variation
The smile muscle is not the same muscle in every patient
The zygomaticus major draws the oral commissure superiorly and laterally and is the primary muscle of smiling. It is also one of the most anatomically variable muscles in the face.
A nasolabial fold is treated with filler using a technique that has been reliable for years, and this patient returns with an asymmetric smile. What anatomical variation would explain it?
Hold your answer before you open this. The value is in having committed to a mechanism first.
Bifid zygomaticus major, or double zygomaticus, occurs in a significant proportion of patients and is associated with cheek dimples. Understanding its pathway matters when treating the nasolabial fold with filler: inadvertent injection into or around this muscle can impair smile symmetry.
The zygomaticus minor is a second source of variation. It is present in approximately 40% of individuals, and where it is present it contributes to the dynamics of the nasolabial fold and medial cheek.
Masseteric hypertrophy treatment requires injection into the lower third of the muscle bulk, palpated at the angle of the mandible. Injections placed high risk weakening the zygomaticus, buccinator or risorius, which presents as an altered smile rather than as a jawline result. The parotid duct pierces the buccinator at the level of the upper second molar, and filler in the mid-buccal region carries a described, though rare, risk of duct injury.
A patient treated for masseteric hypertrophy returns with an altered smile on the treated side rather than the expected change in jaw contour. The most likely explanation is:
Select an option to commit. The reasoning appears afterwards.
Masseteric hypertrophy treatment requires injection into the lower third of the muscle bulk, palpated at the angle of the mandible. High injections risk weakening the zygomaticus, buccinator or risorius — all muscles of expression that sit superior and anterior to the intended field.
The lesson generalises beyond the masseter. Where a large muscle is treated adjacent to smaller expressive ones, the boundary of the injection field is defined by what lies outside it. Palpating the angle of the mandible and staying in the lower third is not a technique preference; it is what keeps the effect inside the target.
Learn · Perioral depressors
The narrow margin around the depressor anguli oris
The DAO runs in a fairly consistent pathway from the mandibular body laterally upwards to the modiolus, which makes it one of the more predictable targets in the lower face. The margin around it is nonetheless small: the depressor labii inferioris sits medial to it, and the marginal mandibular branch of CN VII supplies both.
DAO injection is typically 1–1.5 cm lateral to the commissure and 1 cm above the mandibular border. Medial placement risks the depressor labii inferioris and can impair speech and oral competence. The marginal mandibular nerve runs close to the DLI, and inadvertent blockade causes lower lip asymmetry and drooping.
The perioral depressors and elevators all converge at the modiolus, and the orbicularis oris has no bony origin at all — it is formed by the interdigitation of the surrounding muscles at that node. A change introduced in any one of them is therefore distributed across the whole complex, which is why perioral neuromodulator treatment uses low doses and why filler, rather than a neuromodulator, is generally the preferred treatment for lip lines.
The depressor anguli oris draws the corner of the mouth downward. Relaxing it with a neuromodulator addresses:
Select an option to commit. The reasoning appears afterwards.
The DAO runs from the oblique line of the mandible to the modiolus and skin at the oral commissure, pulling the commissure inferiorly. Its unopposed resting tone is what produces the downturned mouth appearance and contributes to marionette lines, so weakening it is the described treatment for the downturned commissure.
Placement decides whether that result is achieved cleanly. Injection is typically 1–1.5 cm lateral to the commissure and 1 cm above the mandibular border; medial placement risks the depressor labii inferioris and can impair speech and oral competence. The correct muscle at the wrong coordinate is a functional complication, not a cosmetic one.
Unit 3 summary
Clinical takeaways
- The modiolus is the shared endpoint. Zygomaticus major, buccinator, risorius and the perioral depressors all insert there, and the orbicularis oris is formed from their interdigitation. A change in one is distributed across the complex.
- Nasal tip depression on smiling is the depressor septi nasi. Injection at the nasal spine, in the midline at the columellar base, elevates the tip and often improves a dynamic gummy smile.
- Midface anatomy varies between patients. Bifid zygomaticus major occurs in a significant proportion of patients and the zygomaticus minor in approximately 40%. A reliable technique applied to a variant anatomy is how smile asymmetry arises after nasolabial filler.
- Boundaries define lower face safety. Masseter injections stay in the lower third at the angle of the mandible; DAO injections stay 1–1.5 cm lateral to the commissure and 1 cm above the mandibular border. Both limits exist to keep the effect out of an adjacent muscle.