The Lips

• These are mobile muscular folds that surround the mouth, the entrance of the oral cavity.

• The lips (L. labia) are covered externally by skin and internally by mucous membrane.
• In between these are layers of muscles, especially the orbicularis oris muscle.

• The upper and lower lips are attached to the gingivae in the median plane by raised folds of mucous membrane, called the labial frenula.

Sensory Nerves of the Lips

• The sensory nerves of the upper and lower lips are from the infraorbital and mental nerves, which are branches of the maxillary (CN V²) and mandibular (CN V³) nerves.

• This is the second cranial nerve (CN II) and is the nerve of sight.

->The sides and base of the skull are formed partly by these bones.
->Each bone consists of four morphologically distinct parts that fuse during development (squamous, petromastoid, and tympanic parts and the styloid process).
->The flat squamous part is external to the lateral surface of the temporal lobe of the brain.
->The petromastoid part encloses the internal ear and mastoid cells and forms part of the base of the skull.
->The tympanic part contains the bony passage from the auricle (external ear), called the external acoustic meatus. The petromastoid part also forms a portion of the bony wall of the tympanic cavity (middle ear). The meatus and tympanic cavity are concerned with the transmission of sound waves.
->The slender, pointed styloid process of the temporal bone gives attachment to certain ligaments and muscles (e.g., the stylohyoid muscle that elevates the hyoid bone).
->The temporal bone articulates at sutures with the parietal, occipital, sphenoid, and zygomatic bones.
->The zygomatic process of the temporal bone unites with the temporal process of the zygomatic bone to form the zygomatic arch. The zygomatic arches form the widest part of the face.
->The head of the mandible articulates with the mandibular fossa on the inferior surface of the zygomatic process of the temporal bone.
->Anterior to the mandibular fossa is the articular tubercle.
->Because the zygomatic arches are the widest parts of the face and are such prominent facial features, they are commonly fractured and depressed. A fracture of the temporal process of the zygomatic bone would likely involve the lateral wall of the orbit and could injure the eye.

The Eye and Orbit

• The orbit (eye socket) appears as a bony recess in the skull when it is viewed from anteriorly.
• It almost surrounds the eye and their associated muscles, nerves and vessels, together with the lacrimal apparatus.

• The orbit is shaped somewhat like a four-side pyramid lying on its side, with its apex pointing posteriorly and its base anteriorly.

Levator Palpebrae Superioris Muscles

• This is a thin, triangular muscle that elevates the upper eyelid.
• It is continuously active except during sleeping and when the eye is closing.

• Origin: roof of orbit, anterior to the optic canal.
• Insertion: this muscle fans out into a wide aponeurosis that inserts into the skin of the upper eyelid. The inferior part of the aponeurosis contains some smooth muscle fibres that insert into the tarsal plate.
• Innervation: the superior fibres are innervated by the oculomotor nerve (CN III), and the smooth muscle component is innervated by fibres of the cervical sympathetic trunk and the internal carotid plexus.

Illnesses involving the Levator Palpebrae Superioris

• In third nerve palsy, the upper eyelid droops (ptosis) and cannot be raised voluntarily.
• This results from damage to the oculomotor nerve (CN III), which supplies this muscle.

• If the cervical sympathetic trunk is interrupted, the smooth muscle component of the levator palpebrae superioris is paralysed and also causes ptosis.
• This is part of Horner's syndrome.

The Rectus Muscles

• There are four rectus muscles (L. rectus, straight), superior, inferior, medial and lateral.

• These arise from a tough tendinous cuff, called the common tendinous ring, which surrounds the optic canal and the junction of the superior and inferior orbital fissures.
• From their common origin, these muscles run anteriorly, close to the walls of the orbit, and attach to the eyeball just posterior to the sclerocorneal junction.

• The medial and lateral rectus muscles attach to the medial and lateral sides of the eyeball respectively, on the horizontal axis.
• However, the superior rectus attaches to the anterosuperior aspect of the medial side of the eyeball while the inferior rectus attaches to the anteroinferior aspect of the medial side of the eye.

The Oblique Muscles

The Superior Oblique Muscle

• This muscle arises from the body of the sphenoid bone, superomedial to the common tendinous ring.
• It passes anteriorly, superior and medial to the superior and medial rectus muscles.
• It ends as a round tendon that runs through a pulley-like loop called the trochlea (L. pulley).
• After passing though the trochlea, the tendon of the superior oblique turns posterolaterally and inserts into the sclera at the posterosuperior aspect of the lateral side of the eyeball.

The Inferior Oblique Muscle

• This muscle arises from the maxilla in the floor of the orbit.
• It passes laterally and posteriorly, inferior to the inferior rectus muscle.
• It inserts into the sclera at the posteroinferior aspect of the lateral side of the eyeball.

Muscles Around the Mouth

• The sphincter of the mouth is orbicularis oris and the dilator muscles radiate outward from the lips like the spokes of a wheel.

Orbicularis Oris Muscle

• This muscle encircles the mouth and is the sphincter of the oral aperture
• This muscle (1) closes the lips, (2) protrudes them and (3) compresses them against the teeth.
• It plays an important role in articulation and mastication. Together with the buccinator muscle, it helps to hold the food between the teeth during mastication.

Zygomaticus Major Muscle

• It extends from the zygomatic bone to the angle of the mouth.
• It draws the corner of the moth superolaterally during smiling and laughing.

Zygomaticus Minor Muscle

• This is a narrow slip of muscle, and passes obliquely from the zygomatic bone to the orbicularis oris.
• It helps raise the upper lip when showing contempt or to deepen the nasolabial sulcus when showing sadness.

The Buccinator Muscle

• This is a thin, flat, rectangular muscle.
• It is attached laterally to the alveolar processes of the maxilla and mandible, opposite the molar teeth and the pterygomandibular raphe.
• Medially, its fibres mingle with those of orbicularis oris.Innervation: the buccal branch of facial.

• It aids mastication and swallowing by pushing the cheeks against the molar teeth during chewing.