Face Muscles: Anatomy, Functions, and Comparative Notes

By Dr. Zubair Khalid, DVM, MS, PhD · 2026-09-19

Facial muscles are the skeletal muscles that insert into the skin of the face rather than into bone, and they pull that skin to produce expressions such as a smile, a frown, or a squint. They are also called the muscles of facial expression, and almost all of them are supplied by the facial nerve, cranial nerve VII (CN VII).

Those two facts, skin insertion and CN VII supply, are the fastest way to separate facial muscles from the chewing muscles. The masseter and temporalis move the jaw by pulling on bone and are supplied by a different nerve, the trigeminal (CN V). The muscles of expression move the surface of the face, and they exist so that a social signal can be produced in a fraction of a second. That signaling function explains why the anatomy differs so much between species: a horse needs mobile lips and flaring nostrils, a dog needs an ear that swivels and a platysma that ripples down the neck, and a human needs the fine lip and tongue control that speech requires. This guide covers the core anatomy, the origin, insertion, and action of each major muscle, how the system develops, and where the comparative differences show up.

What Counts as a Facial Muscle

A facial muscle is a striated (voluntary) skeletal muscle whose fibers end in the connective tissue of the skin or in a thin fibrous sheet called an aponeurosis, rather than in a tendon attached to a bone. The connective tissue layer that links these muscles to the skin is the superficial musculoaponeurotic system, or SMAS. The SMAS transfers the pull of a contracting muscle to the overlying skin, which is why a facial muscle can wrinkle the skin without moving a joint.

The architecture of the SMAS is not uniform. In a histological and three-dimensional reconstruction study of human tissue blocks, the cervical SMAS (around the platysma) was described as parallel deep and superficial fibrous septa connected by vertical communicating septa that enclose fatty compartments, a design that transfers platysmal contraction to the skin [1]. The facial SMAS shows different regional arrangements, which is one reason a contraction in one part of the face produces a different skin movement than the same contraction elsewhere.

Two practical consequences follow from this design. First, facial muscles have small mechanical advantage because they pull on soft tissue, so they produce small forces and large, precise displacements. Second, they are not wrapped around joints, so their "action" is described as the direction of skin movement, not as a joint motion.

A Summary Table of Key Facts

The embryonic origin is the deepest distinction. The muscles of mastication come from mesodermal progenitor cells in the first branchial arch, while the muscles of facial expression come from progenitor cells in the second branchial arch [2]. That shared origin is why every muscle of expression, without exception, is innervated by CN VII.

Development and Innervation

Facial expression muscles are not built from somites, the segmented blocks of mesoderm that form the trunk and limb muscles. They arise from unsegmented cranial paraxial mesoderm and migrate from the second branchial arch to their final positions in the face [2]. The migration is controlled by a chemokine signaling axis. In a study using mouse mutants and chick embryos, Cxcr4, the receptor, and SDF-1, its ligand, were shown to guide second-arch muscle progenitor cells. Muscles derived from the second arch failed to form in Cxcr4 mutants at embryonic days E13.5 and E14.5, while implanting SDF-1-loaded beads into the second arch attracted myogenic progenitor cells and expanded the expression of muscle markers toward the bead [3]. First-arch muscles were unaffected in the same mutants, which confirms that the two arch systems use partly separate molecular controls [3].

There is a further oddity worth remembering. The satellite cells associated with facial expression muscles share properties with heart muscle, which sets them apart from the satellite cells of trunk muscle [2]. This is a developmental detail, but it matters for anyone thinking about how facial muscle regenerates after injury.

The nerve supply is anatomically variable between individuals. In a study combining 30 anatomical dissections with 14 intraoperative electrical stimulations during parotid surgery, the peripheral branching of the facial nerve and the communicating branches between its divisions were highly variable from person to person [4]. The same study noted that the sphincter muscles, the orbicularis oris and orbicularis oculi, were anatomically protected and showed better nerve recovery, while the frontalis, depressor labii inferioris, and platysma showed little recuperation [4]. For a clinician, the practical message is that the branching pattern cannot be assumed. For a student, the message is that "the facial nerve supplies the muscles of expression" is a rule about the whole nerve, not a promise that any two people share the same branching map.

The Core Muscles of Expression

The muscles below are the ones that appear in every introductory treatment. Origins and insertions are given in standard textbook terms, and actions are described as the skin movement produced.

Orbicularis Oculi

The orbicularis oculi is a ring-shaped (sphincter) muscle that surrounds the eye. It has three parts. The orbital part is the outer ring that runs along the orbital rim. The palpebral part lies in the eyelid. The lacrimal part is a small deep slip near the medial corner.

• Origin: orbital part from the medial orbital margin and adjacent bone, palpebral part from the medial palpebral ligament, lacrimal part from the lacrimal crest.
• Insertion: fibers sweep around the orbit and interlace with each other and with the skin of the eyelid and lateral cheek.
• Action: the palpebral part closes the eyelid gently for blinking, the orbital part closes it forcefully for a squint, and the lacrimal part helps compress the lacrimal sac to move tears.

The orbicularis oculi is one of the muscles that interacts with the eyebrow position. A description of upper-face anatomy notes that the frontalis, corrugator supercilii, and orbicularis oculi act together to influence eyebrow position and movement [5]. That interaction is why the eyebrow is treated as a single functional unit rather than as the product of one muscle.

Orbicularis Oris

The orbicularis oris is the sphincter of the mouth. It is not a simple ring. It is a composite of fibers that blend with the fibers of the muscles that radiate into the lips, and its midline fibrous raphe is a landmark in the upper lip.

• Origin: fibers arise from the maxilla and mandible near the midline and from the buccinator and other muscles that converge on the mouth.
• Insertion: fibers encircle the oral opening and insert into the skin and mucous membrane of the lips.
• Action: closes the lips, protrudes them (as in a pucker), and resists the pull of the muscles that retract the mouth corners.

The orbicularis oris sits at the center of a mechanical tug-of-war. The muscles that radiate outward from the mouth corner pull it open, and the orbicularis oris pulls it closed. The balance between them sets resting lip posture.

Zygomaticus Major and Minor

The zygomaticus muscles are the main retractors of the mouth corner. They run from the cheekbone to the corner of the mouth.

• Origin: zygomaticus major from the lateral surface of the zygomatic bone, zygomaticus minor from the anterior surface of the zygomatic bone.
• Insertion: zygomaticus major into the modiolus (the dense fibromuscular node at the mouth corner) and the skin of the upper lip, zygomaticus minor into the upper lip.
• Action: pulls the mouth corner upward and outward, which produces a smile.

The modiolus is the convergence point where several muscles meet at the corner of the mouth. Its presence or absence varies between species. In a microanatomical study of the baboon facial mask, the labial commissure lacked a discrete modiolus, and the nasolabial region was organized as a continuous maxillonasolabialis rather than as separate named slips [6]. That is a real structural difference, not a naming quirk, and it changes how force is distributed around the mouth.

Levator Labii Superioris

The levator labii superioris lifts the upper lip. It lies just below the eye and runs down to the lip.

• Origin: the maxilla along the lower orbital margin, above the infraorbital foramen.
• Insertion: into the skin and muscle of the upper lip, blending with the orbicularis oris.
• Action: raises the upper lip, as in a sneer or in the expression of disgust.

In cattle, a broad insertion of the levator labii superioris indicates that the muscle is involved in both upper lip and nostril movement, and several muscles in that species appeared to influence nostril shape [7]. That broader role is a good example of how the same named muscle can have a wider functional footprint in one species than another.

Buccinator

The buccinator forms the wall of the cheek. It is sometimes grouped with the muscles of mastication because it helps position food, but it is a muscle of expression by origin and innervation.

• Origin: the alveolar processes of the maxilla and mandible, and the pterygomandibular raphe, a fibrous band between the jaws.
• Insertion: into the orbicularis oris at the mouth corner.
• Action: compresses the cheek against the teeth, which keeps food between the teeth during chewing and expels air from the mouth.

The buccinator is the muscle that makes a cheek trumpet possible. It also matters in nursing infants, where it helps maintain suction.

Platysma

The platysma is a broad, thin sheet that covers the front of the neck and extends onto the lower face.

• Origin: the fascia over the pectoralis major and deltoid muscles.
• Insertion: the lower border of the mandible and the skin and muscles of the lower face and mouth corner.
• Action: tenses the skin of the neck, pulls the mouth corner downward, and produces the vertical neck bands seen in a grimace.

The platysma is unusual because it is a muscle of expression that sits mostly outside the face. Its relationship to the skin has been studied in detail. Histological analysis of the cervical platysma-skin interface described a type V SMAS architecture of parallel fibrous septa linked by vertical septa that enclose fat compartments, a design that transmits platysmal contraction to the skin [1]. This is why a platysma contraction produces visible skin bands rather than a smooth bulge.

Table of Origins, Insertions, and Actions

How Facial Muscles Are Studied

Facial movement can be measured in several ways, and the method determines what you can claim from the data.

Surface observation and manual coding remain the foundation. The Facial Action Coding System, originally developed for humans, identifies distinct facial movements based on mimetic muscles. It has been adapted to other species. A study of the baboon developed a species-specific system, PapioFACS, after dissecting five adult craniofacial specimens (10 hemifaces) and identifying 15 facial muscles, 3 extrinsic auricular muscles, and 4 intrinsic auricular muscles. The coding system defined 20 Action Units, 12 Action Descriptors, and 3 Ear Action Descriptors, with final inter-coder agreement above 90% [6]. A parallel effort in cattle mapped 30 mimetic muscles by dissecting three heads, using skinning and facial mask preparation on opposite sides, and reported notable fiber blending in the lower face and ear region [7].

Instrumented measurement adds numbers to those observations. A comparison of a depth sensor (Kinect-V2) against a marker-based motion system in 100 healthy participants tested six movements: opening the mouth, smiling, eyebrow-lifting, forced eye closure, whistling, and frowning. Intra-method reliability was strong for the depth sensor, with intraclass correlation coefficients from 0.61 for forced eye closure to 0.85 for mouth opening, but the two methods disagreed on subtle expressions, with mean biases ranging from -0.99 for opening the mouth to 20.82 for frowning [8]. The lesson is that a sensor can be reliable with itself and still not agree with a different instrument.

Four-dimensional imaging captures the timing of a movement, not just its endpoint. In a study of 31 surgically managed unilateral cleft lip and palate cases and 34 matched non-cleft controls, a 3-second smile was captured as 180 three-dimensional images at 60 frames per second. The smile lasted about 2 seconds in the cleft group versus about 1.3 seconds in controls, and the philtrum on the cleft side moved more slowly (7.24 mm/s versus 8.22 mm/s) [9]. Speed and duration are separate variables from magnitude, and a normal-looking endpoint can hide a slower movement.

Electromyography and electrostimulation are used when the question is which nerve branch supplies which muscle. The dissection and stimulation study described earlier used systematic stimulation of each trunk and branch during parotid surgery to map penetrating points into the mimetic muscles [4].

Comparative Notes Across Species

The same basic plan, a set of second-arch muscles supplied by CN VII, is built differently in different lineages. The differences track what each animal needs to signal and to eat.

Dogs and Cats

Domestic dogs have a facial muscle anatomy shaped partly by domestication. Dissections of dog and wolf heads showed that the levator anguli oculi medialis, a muscle that raises the inner eyebrow strongly, is uniformly present in dogs but not in wolves. Behavioral data showed that dogs produce the eyebrow movement significantly more often and at higher intensity than wolves, and the highest-intensity movements were produced exclusively by dogs [10]. The proposed explanation is that the movement resembles a sad expression in humans and may trigger a nurturing response, giving expressive dogs a selection advantage [10].

The physiology differs too. A comparison of myosin fiber types in the zygomaticus and orbicularis oris of 6 domestic dogs and 4 gray wolves found that the sampled dogs had almost 100% fast-twitch (type II) fibers, while wolves had less than 50%. The authors note the small sample size and did not run statistical tests, but the pattern suggests dog faces can contract quickly while wolf faces are built to sustain a contraction [11].

Breed shape changes the muscles as well. A morphometric study comparing brachycephalic and dolichocephalic dogs measured mimic muscles and expressed them as ratios to head dimensions. Significant differences were found in all but two of the examined muscles when muscle length was scaled to head length, and the musculus levator nasolabialis was morphologically different between the groups, with muscle fibers located in the fold over the nasal bridge in brachycephalic dogs. The raphe of the orbicularis oris was not always apparent in brachycephalic dogs, and the proportions of muscle lengths and eye slot length to skull size had shifted considerably [12].

Cats and dogs both have a well-developed platysma and a set of auricular muscles that move the ear. The baboon study is a useful reminder that auricular musculature can be elaborate in a mammal: it identified 3 extrinsic and 4 intrinsic auricular muscles in that species, with a particularly well-developed auricular region [6].

Horses

Horses have specialized musculature for nostril flare and lip mobility. The comparative literature places horses alongside humans as species with a relatively diverse facial repertoire. A cattle study explicitly compared its findings with humans and horses and concluded that muscular differences suggest a slightly less diverse or different facial repertoire in cattle, with robust lips and a different lip-muscle arrangement likely restricting the marginal, upper lip, and lip-corner movements described in one or both comparison species [7]. In other words, the horse is the reference point for a mobile, expressive lower face among large domestic mammals.

Cattle

Cattle have 30 identified mimetic muscles, with fiber blending in the lower face and ear region. The eyebrow region is served only by a broad frontalis, which suggests fewer eyebrow movements than in humans and broader ones than in horses. Several muscles influence nostril shape, and the levator labii superioris has a broad insertion that involves it in both upper lip and nostril movement [7].

Humans

Humans have finer control of the lips and mouth for speech than the other species discussed here. The same muscles that produce expression also shape the vocal tract. The orbicularis oris, buccinator, and the muscles that position the mouth corner all contribute to the precise lip closures and constrictions that consonants require. This is a functional overlay on the same anatomical plan, not a separate set of muscles.

Reptiles and Birds

Facial muscles of the mammalian type are absent or reduced in reptiles and birds. These groups do not have the same sheet of second-arch muscles inserting into facial skin, and their facial movement is limited. This is a genuine difference in the Bauplan, and it is why a lizard cannot produce a mammalian-style facial expression.

A Comparative Summary

Clinical and Practical Relevance

Facial nerve function is the thread that ties the clinical picture together. Because every muscle of expression depends on CN VII, a lesion anywhere along the nerve produces weakness in the muscles it supplies. The pattern of weakness helps localize the lesion, and the variability of branching means the pattern is not perfectly predictable from one person to the next [4].

The sphincter muscles behave differently from the rest after injury. In the stimulation and dissection study, the orbicularis oris and orbicularis oculi were anatomically protected and showed better nerve recovery, while the frontalis, depressor labii inferioris, and platysma showed little recuperation [4]. That difference is worth knowing when discussing prognosis in general terms.

Muscle function also shows up in conditions that affect the lips. In the cleft lip and palate imaging study, reduced speed and magnitude of upper lip movement on the cleft side indicated restricted muscular activity [9]. The measurement was of movement, but the underlying cause is the muscle and its attachments.

Experimental work on nerve repair uses the facial nerve as a model. A rat study of the buccal branch of the facial nerve tested a heterologous fibrin biopolymer combined with photobiomodulation using a low-level laser. Nerve fiber diameter was 7.10 ± 0.25 µm in the repair group without laser and 8.00 ± 0.36 µm with laser, and axon diameter was 3.31 ± 0.19 µm versus 4.07 ± 0.27 µm. In the laser-treated repair group, the area of muscle fibers was similar to the control group, and functional parameters improved [13]. These are animal data and should not be read as a human protocol.

Comparative anatomy has a direct applied use in animal welfare. The cattle study was motivated by the fact that no standardized system for assessing the entire facial display in cattle exists, and that building one requires mapping the mimetic musculature first [7]. The baboon work has the same logic: anatomy first, then a coding system that links muscle to movement [6].

Common Mistakes and Limitations

The first mistake is confusing the muscles of expression with the muscles of mastication. Both move parts of the face, but they differ in insertion, nerve supply, and embryonic origin. If a muscle inserts into bone and is supplied by CN V, it is a chewing muscle.

The second mistake is treating the orbicularis oris as a simple ring. It is a composite that receives fibers from several directions, and its behavior depends on the balance of those fibers.

The third mistake is assuming that a named muscle has the same job in every species. The levator labii superioris is a good example. In cattle it has a broad insertion that involves it in nostril movement as well as upper lip movement [7].

The fourth mistake is reading a single measurement as a complete description of a movement. Speed, magnitude, and duration are separate variables, and a movement can look normal at its endpoint while being slower or longer than normal [9].

The fifth mistake is assuming that a measurement tool is interchangeable with another. Depth sensor and marker-based systems can each be reliable and still disagree, especially on subtle expressions [8].

The sixth mistake is overreading small studies. The dog and wolf fiber-type comparison had 6 dogs and 4 wolves and no statistical testing, so the result is a pattern worth noting, not a settled fact [11].

A final limitation is individual variation. Facial nerve branching differs between people, and the same dissection can look different on two sides of the same body [4]. Any statement about facial muscle anatomy is a statement about the typical pattern, not a guarantee for a specific individual. For anything involving a specific patient or animal, a qualified clinician or veterinarian needs to assess the case directly.

Quick Review

1. Facial muscles insert into skin or the SMAS, not into bone, and almost all are supplied by the facial nerve (CN VII).
2. They develop from second pharyngeal arch mesoderm and migrate under the control of the CXCR4/SDF-1 axis.
3. The orbicularis oculi and orbicularis oris are sphincters. The zygomaticus, levator labii, and platysma move the mouth and neck skin. The buccinator compresses the cheek.
4. The modiolus is the fibromuscular node at the mouth corner. Its structure varies between species.
5. Dogs have a levator anguli oculi medialis that wolves lack, plus fast-twitch dominant facial fibers.
6. Horses have specialized nostril flare and lip mobility. Cattle have 30 mimetic muscles with a broad frontalis and robust lips.
7. Reptiles and birds lack the mammalian sheet of facial expression muscles.

Frequently Asked Questions

What nerve controls the muscles of facial expression?

The facial nerve, cranial nerve VII, supplies the muscles of facial expression. This is the single most reliable rule in facial muscle anatomy. The muscles of mastication are supplied by a different nerve, the trigeminal (CN V).

Are facial muscles attached to bones?

They originate on bone or fascia but insert into skin or the superficial musculoaponeurotic system. That skin insertion is what allows them to create expressions rather than move joints.

What is the difference between the orbicularis oculi and the orbicularis oris?

The orbicularis oculi surrounds the eye and closes the eyelid. The orbicularis oris surrounds the mouth and closes and protrudes the lips. Both are sphincter muscles.

Do dogs have the same facial muscles as humans?

No. Dogs have a levator anguli oculi medialis that wolves lack, and their facial fibers are predominantly fast-twitch. Humans have finer lip control for speech, and their eyebrow musculature supports a wider range of eyebrow movements than cattle or horses show.

Why do horses move their nostrils and lips so much?

Horses have specialized musculature for nostril flare and lip mobility. Comparative studies use horses as a reference for a mobile lower face among large domestic mammals.

Do reptiles and birds have facial muscles?

Facial muscles of the mammalian type are absent or reduced in reptiles and birds. They do not have the same second-arch muscle sheet inserting into facial skin.

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