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Insertion: Into the lateral side of the proximal phalanx of the big toe.
both bellies can move the whole scalp on the underlying loose fascia.
Action: Adduction of the big toe.
• Orbicularis oculi
Nerve supply: Lateral plantar nerve.
In two parts. The orbital part surrounds the whole eye, blending with
• Flexor digiti minimi brevis Actions: The frontal belly lifts the eyebrows when looking upwards and
Origin: From the base of the 5th metatarsal. the frontal belly of occipitofrontalis. It closes the eye tightly. The
Insertion: Into the proximal phalanx of the little toe. palpebral part is in the eyelid and closes the eye gently as in sleep.
Action: Flexion of the little toe. • Orbicularis oris
Nerve supply: Lateral plantar nerve. Surrounds the whole mouth and blends in with the surrounding muscles
• Interossei: that are shown in Fig. 67.1. Closes the mouth and protrudes the lips.
• Dorsal • Buccinator
Origin: From adjacent sides of the metatarsals. Origin: From the pterygomandibular ligament, where it is continuous
Insertion: Into the dorsal extensor expansions and the sides of the with the superior constrictor of the pharynx.
proximal phalanges. Insertion: Blends in with the orbicularis oris. Tightens the cheeks and
Actions: Abduction of the toes; flexion of the metatarsophalangeal keeps them in contact with the gums, thus preventing food collecting in
joints and extension of the interphalangeal joints. the vestibule of the mouth.
Nerve supply: Lateral plantar nerve. • Platysma
• Plantar Origin: From the skin over the upper part of the chest, crossing the
Origin: From the bases of three of the metatarsals. mandible to blend in with the orbicularis oris. Pulls down the corners of
Insertion: Into the dorsal extensor expansions and the sides of the the mouth and has an antisphincteric action on the neck as in loosening
proximal phalanges. a tight collar.
Actions: Adduction of the toes and assisting the other actions of the Nerve supply of the muscles of facial expression: All the muscles of
dorsal interossei. facial expression are supplied by the facial nerve.
Nerve supply: Lateral plantar nerve. • Trapezius
Origin: From the superior nuchal line, the ligamentum nuchae and the
The head and neck spines of all the thoracic vertebrae.
The muscles of mastication Insertion: Into the spine of the scapula, the lateral edge of the acromion
• Temporalis and the lateral third of the clavicle.
Origin: From the lateral side of the skull below the temporal line. Actions: Extends the head on looking upwards, raises the tips of the
Insertion: To the coronoid process of the mandible, extending down the shoulders, braces the shoulders back, and helps serratus anterior to
anterior border as far as the third molar tooth. It passes deep to the rotate the scapula during abduction of the arm.
zygomatic arch. Nerve supply: Spinal accessory nerve.
Actions: Closes the mouth and clenches the teeth. The posterior fibres • Sternocleidomastoid
are horizontal and help to retract the mandible when closing the mouth. Origin: From the front of the manubrium (by a narrow rounded tendon)
• Masseter and the medial third of the clavicle.
Origin: From the lower border of the zygomatic arch. Insertion: To the mastoid process and the lateral part of the superior
Insertion: To the lateral side of the mandible in the region of the angle. nuchal line.
Actions: Closes the mouth and clenches the teeth. Actions: Rotates the head to the opposite side and flexes the cervical
• Lateral pterygoid spine to the same side, thus bringing the ear nearer to the shoulder of the
Origin: From the lateral pterygoid plate. same side. Both muscles acting together can flex the cervical spine
Insertion: To the neck of the mandible and the intra-articular disc of the against resistance. An accessory muscle of respiration.
temporomandibular joint. Nerve supply: Spinal accessory nerve.
Actions: It protrudes the mandible and moves the head of the mandible • Scalenus anterior
onto the articular eminence when the mouth is opened. Origin: From anterior tubercles of the transverse processes of several
• Medial pterygoid cervical vertebrae.
Origin: From the lateral pterygoid plate. Insertion: To the scalene tubercle on the medial border of the 1st rib, by
Insertion: To the medial surface of the mandible near the angle. means of a narrow pointed tendon.
Action: Helps to close the mouth. Actions: Flexes the cervical spine, produces lateral flexion to the
Nerve supply of the muscles of mastication: The muscles of mastication same side and rotation to the opposite side. An accessory muscle of
are all supplied by the mandibular division of the trigeminal nerve. respiration.
Nerve supply: Cervical spinal nerves.
The muscles of facial expression • Scalenus medius
The principal muscles of facial expression are shown in Fig. 67.1, from Origin: From the posterior tubercles of the transverse processes of
which their actions can be deduced. Only a few of them will be most of the cervical vertebrae.
described here. Insertion: Into a large area on the 1st rib behind scalenus anterior.
• Occipitofrontalis Actions: Similar to those of scalenus anterior.
Origin: The frontal belly extends backwards from the forehead region Nerve supply: Cervical spinal nerves.
and the occipital belly extends forwards from the occipital bone. • Other muscles
Insertion: Both parts are inserted into the galea aponeurotica (epicra- Other muscles of the neck, such as the strap muscles, are described
nial aponeurosis). fully in the text.
Muscle index 167