The Orbital Region
The orbits are a pair of bony cavities that contain the eyeballs.
The Description of Orbit:
The orbit is a pyramidal cavity with its base anterior and its apex posterior. The orbital margin is formed above by the frontal bone, the lateral margin is formed by the processes of the frontal and zygomatic bones, the inferior margin is formed by the zygomatic bone and the maxilla, and the medial margin is formed by the processes of the maxilla and the frontal bone.
Roof: Formed by the orbital plate of the frontal bone, which separates the orbital cavity from the anterior cranial fossa and the frontal lobe of the cerebral hemisphere.
Lateral wall: Formed by the zygomatic bone and the greater wing of the sphenoid.
Floor: Formed by the orbital plate of the maxilla, which separates the orbital cavity from the maxillary sinus.
Medial wall: Formed from before backward by the frontal process of the maxilla, the lacrimal bone, the orbital plate of the ethmoid (which separates the orbital cavity from the ethmoid sinuses), and the body of the sphenoid.
Openings into the Orbital Cavity: Orbital opening lies anteriorly. About one sixth of the eye is exposed; the remainder is protected by the walls of the orbit.
Supraorbital notch (Foramen): The supraorbital notch is situated on the superior orbital margin. It transmits the supraorbital nerve and blood vessels.
Infraorbital groove and canal: Situated on the floor of the orbit in the orbital plate of the maxilla; they transmit the infraorbital nerve (a continuation of the maxillary nerve) and blood vessels.
Nasolacrimal canal: Located anteriorly on the medial wall; it communicates with the inferior meatus of the nose. It transmits the nasolacrimal duct.
Inferior orbital fissure: Located posteriorly between the maxilla and the greater wing of the sphenoid; it communicates with the pterygopalatine fossa. It transmits the maxillary nerve and its zygomatic branch, the inferior ophthalmic vein, and sympathetic nerves.
Superior orbital fissure: Located posteriorly between the greater and lesser wings of the sphenoid; it communicates with the middle cranial fossa. It transmits the lacrimal nerve, the frontal nerve, the trochlear nerve (4th CN), the oculomotor nerve (3rd CN) (upper and lower divisions), the abducent nerve (6th CN), the nasociliary nerve, and the superior ophthalmic vein.
Optic canal: Located posteriorly in the lesser wing of the sphenoid; it communicates with the middle cranial fossa. It transmits the optic nerve (2nd CN) and the ophthalmic artery.
The nasal cavity extends from the nostrils in front to the posterior nasal apertures or choanae behind, where the nose opens into the nasopharynx. The nasal vestibule is the area of the nasal cavity lying just inside the nostril. The nasal cavity is divided into right and left halves by the nasal septum. The septum is made up of the septal cartilage, the vertical plate of the ethmoid, and the vomer.
Walls of the Nasal Cavity: Each half of the nasal cavity has a ﬂoor, a roof, a lateral wall, and a Medial or septal wall.
Floor: The palatine process of the maxilla and the horizontal plate of the palatine bone.
Roof: The roof is narrow and is formed anteriorly beneath the bridge of the nose by the nasal and frontal bones, in the middle by the cribriform plate of the ethmoid, located beneath the anterior cranial fossa, and posteriorly by the downward sloping body of the sphenoid.
Lateral Wall: The lateral wall has three projections of bone called the superior, middle, and inferior nasal conchae. The space below each concha is called a meatus.
Sphenoethmoidal Recess: is a small area above the superior concha. It receives the opening of the sphenoid air sinus.
Superior Meatus The superior meatus lies below the superior concha .It receives the openings of the posterior ethmoid sinuses.
Middle Meatus The middle meatus lies below the middle concha. It has a rounded swelling called the bulla ethmoidalis that is formed by the middle ethmoidal air sinuses, which open on its upper border. A curved opening, the hiatus semilunaris, lies just below the bulla. The anterior end of the hiatus leads into a funnel-shaped channel called the infundibulum, which is continuous with the frontal sinus. The maxillary sinus opens into the middle meatus through the hiatus semilunaris.
Inferior Meatus The inferior meatus lies below the inferior concha and receives the opening of the lower end of the nasolacrimal duct, which is guarded by a fold of mucous membrane.
The medial wall is formed by the nasal septum. The upper part is formed by the vertical plate of the ethmoid and the vomer. The anterior part is formed by the septal cartilage. The septum rarely lies in the midline, thus increasing the size of one half of the nasal cavity and decreasing the size of the other.
The Paranasal Sinuses
The paranasal sinuses are cavities found in the interior of the maxilla, frontal, sphenoid, and ethmoid bones .They are lined with mucoperiosteum and filled with air; they communicate with the nasal cavity through relatively small apertures. The maxillary and sphenoidal sinuses are present in a rudimentary form at birth; they enlarge visibly after the eighth year and become fully formed in adolescence.
The maxillary sinus is pyramidal in shape and located within the body of the maxilla behind the skin of the cheek .The roof is formed by the ﬂoor of the orbit, and the ﬂoor is related to the roots of the premolars and molar teeth. The maxillary sinus opens into the middle meatus of the nose through the hiatus semilunaris.
The two frontal sinuses are contained within the frontal bone. They are separated from each other by a bony septum. Each sinus is roughly triangular, extending upward above the medial end of the eyebrow and backward into the medial part of the roof of the orbit. Each frontal sinus opens into the middle meatus of the nose through the infundibulum.
The two sphenoidal sinuses lie within the body of the sphenoid bone. Each sinus opens into the sphenoethmoidal recess above the superior concha.
The ethmoidal sinuses are anterior, middle, and posterior and they are contained within the ethmoid bone, between the nose and the orbit. They are separated from the orbit by a thin plate of bone so that infection can readily spread from the sinuses into the orbit. The anterior sinuses open into the infundibulum; the middle sinuses open into the middle meatus, on or above the bulla ethmoidalis; and the posterior sinuses open into the superior meatus.