Unit 2 · Upper face
One elevator, three depressors, and the muscle you must never reach
The upper face is the most treated region in aesthetic practice and the least forgiving. The frontalis is the only brow elevator, it works against a glabellar complex of three depressors, and immediately behind that complex sits the levator palpebrae superioris — a muscle you never target and must never reach.
Learn · Forehead & scalp
The forehead is a single elevator against a bank of depressors
The forehead region contains the frontalis muscle, the primary brow elevator, alongside the corrugator supercilii and procerus — the primary brow depressors responsible for glabellar rhytids.
The depressor supercilii completes the group. Read together with Unit 1, the balance is asymmetrical by design: one muscle lifts the brow and several pull it down and in. That imbalance is why the forehead tolerates so little over-treatment on the elevator side.
Frontalis fibre distribution is not uniform between patients. Medial–lateral pattern variation is significant, and some individuals have a central gap in frontalis fibres. A standard template pattern applied to a non-standard muscle is one of the routine causes of an uneven forehead result.
Learn · Periorbital region
The orbit and the muscle behind it
The periorbital region contains the orbicularis oculi — the muscle responsible for eyelid closure, and a central player in crow's feet formation and lower eyelid aesthetics. The region also contains the levator palpebrae superioris, a skeletal muscle of extraocular origin, and the smaller muscles of the medial and lateral canthi.
The orbicularis oculi is a treatment target. The levator palpebrae superioris is not — it is the structure that defines the boundary of where product may safely go.
Learn · Muscle index
Upper face muscles
Select a muscle to read its full profile. Use this as a working index rather than a reading list — the muscles you are about to treat are the ones worth opening.
Muscle explorer · Upper face
Six muscles across two regions. Arrow keys move through the index.
Forehead & scalp
Periorbital
Forehead & scalp
Frontalis
M. frontalis
Elevates the brow and forehead skin; produces horizontal forehead lines.
Galea aponeurotica at the coronal suture level.
Skin and subcutaneous tissue of the forehead; blends with orbicularis oculi and corrugator at brow level.
Temporal branch of CN VII.
The only brow elevator. Over-treatment with neuromodulators can cause brow ptosis. Medial–lateral pattern variation is significant: some individuals have a central gap in frontalis fibres, requiring tailored injection patterns.
Forehead & scalp
Corrugator supercilii
M. corrugator supercilii
Draws the brow medially and inferiorly; produces vertical glabellar lines ("11 lines").
Medial supraorbital ridge (superciliary arch).
Skin of the medial eyebrow (deep and superficial heads).
Temporal branch of CN VII.
Has two heads (transverse and oblique). The transverse head runs in a deeper plane. Accurate injection requires appreciation of depth variation across the muscle's course.
Forehead & scalp
Procerus
M. procerus
Pulls the medial brow inferiorly; produces horizontal nasal root lines ("bunny lines" when over-recruited).
Fascia covering the lower nasal bones and upper lateral cartilages.
Skin between the eyebrows; blends with frontalis.
Temporal and buccal branches of CN VII.
Treated as a single midline injection point in standard glabellar protocols. Often under-treated in isolation, leading to residual horizontal lines at the nasal root.
Forehead & scalp
Depressor supercilii
M. depressor supercilii
Depresses the medial brow; contributes to glabellar complex activity.
Medial orbital rim (frontal process of maxilla).
Medial aspect of brow skin.
Temporal branch of CN VII.
Often functionally integrated with the corrugator supercilii. Some anatomists classify it as a component of the orbicularis oculi. Frequently targeted alongside corrugator in comprehensive glabellar treatment.
Periorbital
Orbicularis oculi
M. orbicularis oculi
Orbital part: forceful eye closure (blinking and squinting). Palpebral part: gentle eyelid closure. Lacrimal part: dilates lacrimal sac during blinking.
Medial palpebral ligament, frontal process of maxilla, lacrimal bone.
Encircles the orbit; fibres interdigitate laterally to form the lateral palpebral raphe.
Temporal and zygomatic branches of CN VII.
The lateral orbital fibres (orbital part) are the primary target for crow's feet neuromodulator treatment. The palpebral part lies within 1–2 mm of the orbital rim — injection here risks diffusion to the levator palpebrae, causing eyelid ptosis. Injections lateral to the orbital rim reduce this risk substantially.
Periorbital
Levator palpebrae superioris
M. levator palpebrae superioris
Elevates the upper eyelid.
Lesser wing of sphenoid, above the optic canal.
Superior tarsal plate and skin of the upper eyelid.
Oculomotor nerve (CN III), not CN VII.
Though not a target of aesthetic treatment, the levator palpebrae is the muscle implicated in the most feared complication of periorbital neuromodulator injection: upper eyelid ptosis. Diffusion through the orbital septum from glabellar or brow injections can transiently paralyse this muscle.
The frontalis muscle primarily functions to:
Select an option to commit. The reasoning appears afterwards.
The frontalis originates on the galea aponeurotica and inserts into the skin and subcutaneous tissue of the forehead. Contraction elevates the brow and forehead skin, and the horizontal forehead lines a patient presents with are the surface record of that action repeated over years.
The clinical consequence is that the frontalis is the only brow elevator. There is no second muscle to take up the work if it is over-treated, which is why brow ptosis follows excessive frontalis weakening and why the dose here is judged against the strength of the depressors below it rather than against the depth of the lines alone.
Predict · Glabellar complex
Four muscles treated as one region
The glabellar complex — frontalis, corrugator supercilii, procerus and depressor supercilii — is the most commonly treated region with neuromodulators in aesthetic practice. It is also the region where partial treatment produces the most recognisable failures. Commit to what those failures look like before you open the reveal.
Every muscle in the glabellar complex was correctly identified and product was placed in each — yet the result reads as lateral brow elevation on one side and residual oblique lines on the other. What has gone wrong?
Hold your answer before you open this. The value is in having committed to a mechanism first.
Understanding the relative contributions of each muscle is what prevents the characteristic complications of over- or under-treatment: lateral brow elevation, the "Spock brow", from selective frontalis weakening; medial brow ptosis; and residual oblique lines from incomplete corrugator treatment.
Treating the complex is not the same as treating each muscle equally. The corrugator has two heads, transverse and oblique, and the transverse head runs deeper — so a superficial pass over the whole complex predictably leaves oblique fibres active.
The procerus is treated as a single midline injection point in standard glabellar protocols and is often under-treated in isolation, which is the usual explanation for residual horizontal lines at the nasal root after an otherwise adequate glabellar treatment. The depressor supercilii is frequently targeted alongside the corrugator for the same reason: it is functionally integrated with it, and some anatomists classify it as a component of the orbicularis oculi.
The corrugator supercilii, when contracted, creates:
Select an option to commit. The reasoning appears afterwards.
The corrugator supercilii runs from the medial supraorbital ridge to the skin of the medial eyebrow. Contraction draws the brow medially and inferiorly, and the vertical glabellar lines, the "11 lines", are the skin folding along that vector.
The muscle has two heads and they do not sit at the same depth: the transverse head runs deeper than the oblique. Accurate treatment therefore requires appreciation of depth variation across the muscle's course, not a single plane applied along its length.
Predict · Eyelid ptosis
The complication that is caused by diffusion, not by placement
The levator palpebrae superioris is not a target and cannot be reached by a needle placed correctly. It is nonetheless the muscle behind the most feared complication in the region.
A glabellar or brow injection is placed in the correct muscle, at the correct depth, and the patient returns with upper eyelid ptosis. By what route did the product reach a muscle innervated by CN III?
Hold your answer before you open this. The value is in having committed to a mechanism first.
Upper eyelid ptosis following neuromodulator injection occurs via diffusion of toxin through the orbital septum to the levator palpebrae superioris. The risk is higher with injections placed medially and close to the orbital rim, particularly below the brow. The 1 cm above orbital rim rule for glabellar injections is based on the thickness and integrity of the septum at various positions.
Apraclonidine 0.5% eye drops, an alpha-2 adrenergic agonist, can partially ameliorate the ptosis by stimulating Müller's muscle, the superior tarsal muscle — an accessory elevator innervated by the sympathetic nervous system.
The palpebral part of the orbicularis oculi lies within 1–2 mm of the orbital rim. Injection at that position risks diffusion to the levator palpebrae and consequent eyelid ptosis. Placing crow's feet injections lateral to the orbital rim reduces this risk substantially, and the same reasoning governs the medial limit of any brow-level injection.
Which muscle is responsible for closing the eye and is the primary target when treating crow's feet with a neuromodulator?
Select an option to commit. The reasoning appears afterwards.
The orbicularis oculi encircles the orbit and closes the eye. Its orbital part performs forceful closure — blinking and squinting — and the lateral orbital fibres of that part are the primary target for crow's feet treatment. The palpebral part performs gentle eyelid closure and is not the target.
That distinction is a safety boundary as much as an anatomical one. The palpebral part lies within 1–2 mm of the orbital rim, and product placed there can diffuse to the levator palpebrae superioris and cause eyelid ptosis. Keeping injections lateral to the orbital rim reduces that risk substantially.
Unit 2 summary
Clinical takeaways
- The frontalis is the only brow elevator. It raises the brow and forehead skin and produces horizontal forehead lines. Over-treatment causes brow ptosis because nothing else lifts.
- The glabellar complex fails in recognisable patterns. Lateral brow elevation from selective frontalis weakening, medial brow ptosis, and residual oblique lines from incomplete corrugator treatment each point back to a specific muscle in the group.
- Crow's feet are treated in the orbital part, lateral to the rim. The orbicularis oculi closes the eye; its palpebral part sits within 1–2 mm of the orbital rim and is not the target.
- Eyelid ptosis is a diffusion complication. Product reaches the levator palpebrae superioris through the orbital septum, most often from medial injections close to the rim below the brow. The 1 cm above orbital rim rule for glabellar injections follows from septal thickness and integrity.