The Lateral Wall of the Orbit

• This wall is thick, particularly its posterior part, which separates the orbit from the middle cranial fossa.
• The lateral wall is formed by the frontal process of the zygomatic bone and the greater wing of the sphenoid bone.

• Anteriorly, the lateral wall lies between the orbit and the temporal fossa.

• The lateral wall is partially separated from the roof by the superior orbital fissure.

The Nasal Mucosa

• Mucosa lines the entire nasal cavities except for the vestibule of the nose.
• The nasal mucosa is firmly bound to the periosteum and perichondrium of the supporting structures of the nose.
• It is continuous with the adjoining cavities to which the nasal cavity communicates (e.g., the nasopharynx and paranasal sinuses).

• The inferior 2/3 of the nasal mucosa is called the respiratory area and air passing over this is warmed and moistened before it passes into the lungs.
• The superior 1/3 is called the olfactory area.

The Olfactory Area of Nasal Mucosa

• This area contains the peripheral organ of smell.
• Sniffing draws air into this area
• Olfactory receptor cells (from the olfactory nerve, CN I, are located in the mucosa of this area in the nose.

Nerves to the Respiratory Area of Nasal Mucosa

• The inferior 2/3 of the nasal mucosa are supplied chiefly by the trigeminal nerve (CN V).

• The mucous membrane of the nasal septum is supplied chiefly by the nasopalatine nerve, a branch of the maxillary nerve (CN V²).
• Its anterior portion is supplied by the anterior ethmoidal nerve (a branch of the nasociliary nerve) which is derived from the ophthalmic nerve (CN V¹).

• The lateral walls of the nasal cavity are supplied by branches of the maxillary nerve (CN V²); the greater palatine nerve, and the anterior ethmoidal nerve.

Arteries of the Nasal Mucosa

• The blood supply of the mucosa of the nasal septum is derived mainly from the maxillary artery.

• The sphenopalatine artery, a branch of the maxillary, supplies most of the blood of the nasal mucosa.
• It enters by the sphenopalatine foramen and sends branches to the posterior regions of the lateral wall and to the nasal septum.

• The greater palatine artery, also a branch of the maxillary, passes through the incisive foramen to supply the nasal septum.

• The anterior and posterior ethmoidal arteries, branches of the ophthalmic artery, supply the anterosuperior part of the mucosa of the lateral wall of the nasal cavity and nasal septum.

• Three branches of the facial artery (superior labial, ascending palatine, and lateral nasal) also supply the anterior parts of the nasal mucosa.

Veins of the Nasal Mucosa

• The veins of the nasal mucosa form a venous network of plexus in the connective tissue of the nasal mucosa.
• Some of the veins open into the sphenopalatine vein and drain to the pterygoid plexus.
• Others join the facial and infraorbital veins.
• Some empty into the ophthalmic veins and drain into the cavernous sinus.

Initially, four clefts exist; however, only one gives rise to a definite structure in adults.

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.

The Lateral Pterygoid Muscle

• This is a short, thick muscle that has two heads or origin.
• It is a conical muscle with its apex pointing posteriorly.

• Origin: superior head—infratemporal surface and infratemporal crest of the greater wing of the sphenoid bone, inferior head—lateral surface of lateral pterygoid plate.
• Insertion: neck of mandible, articular disc, and capsule of temporomandibular joint.
• Innervation: mandibular nerve via lateral pterygoid nerve from anterior trunk, which enters it deep surface.

• Acting together, these muscles protrude the mandible and depress the chin.
• Acting alone and alternately, they produce side-to-side movements of the mandible.

-> This bone forms much of the base and posterior aspect of the skull.
-> It has a large opening called the foramen magnum, through which the cranial cavity communicates with the vertebral canal.
-> It is also where the spinal cord becomes continuous with the medulla (oblongata) of the brain stem.
-> The occipital bone is saucer-shaped and can be divided into four parts: a squamous part (squama), a basilar part (basioccipital part), and two lateral parts (condylar parts).
-> These four parts develop separately around the foramen magnum and unite at about the age of 6 years to form one bone.
-> On the inferior surfaces of the lateral parts of the occipital bone are occipital condyles, where the skull articulates with C1 vertebra (the atlas) at the atlanto-occipital joints.
-> The internal aspect of the squamous part of the occipital bone is divided into four fossae: the superior two for the occipital poles of the cerebral hemispheres, and the inferior two, called cerebellar fossae, for the cerebellar hemispheres.