Medial Wall of the Nasal Cavity
The medial wall of the nasal cavity is formed by both bony elements and cartilage. Posteriorly the perpendicular plate of the ethmoid bone forms the superior septum and the vomer forms the inferior part of the septum. Further posteriorly the crest of both the maxilla and palatine bone complete the posterior septum. The anterior septum is formed entirely of the quadrangular cartilage which divides the cavity in the midline. The nasal septum can be deviated in some and is a sign of nasal trauma or abnormal growth.
The horizontal Plate of the Palatine bone is a rectangular shaped bone that projects medially and forms a right angle with the perpendicular plate of the ethmoid. The nasal surface of the bone forms part of the inferior meatus of the nose, the serrated anterior maxillary surface articulates with the maxilla. Laterally the bone articulates with the perpendicular plate, and superior portion of the plate forms the posterior part of the nasal cavity. The inferior surface of the plate is rough and provides attachment to the oral mucosa of the hard palate.
The perpendicular plate of the ethmoid bone is the superoposterior part of the bony nasal septum and articulates superiorly with the cribriform plate. The posterior border articulates superiorly with the sphenoidal crest and with the vomer by its inferior border. The vomer is an unpaired bone of the skull. It is located in the mid sagittal plane and articulates with the ethmoid, both palatine bones and both maxillary bones.
The choana is an opening at the back of the nasal passage that empties into the nasopharynx, close to where the adenoids are. The passage way forms an outflow from the nasopharynx into the mouth and throat. The cribriform plate is found in the midline on the anterior floor of the anterior cranial fossa. It can be descried as a thin bony plate of perforated bone through which the fibres of the olfactory nerve ascend and reach the entorhinal cortex. The plate is divided by the crista galae in the midline.
Palate and Oropharynx
The pharyngeal opening of the auditory tube can be described as a triangular opening surrounded by a raised, firm prominence known as the ‘torus’. The most medial end of the cartilage causes the elevation of the mucous membrane. The Hard Palate is a horizontal plate of bone formed by both the palatine process of the maxilla and the horizontal plate of the palatine bone. Its function is to form a separation between the nasopharynx and oropharynx. Insufficiency in this structure can cause difficulty with swallowing. The Soft Palate is also referred to as the ‘velum’. This is a continuation of the hard palate posteriorly but has no bony structure. This structure is constituted of 5 muscles crucial for swallowing. These are the tensor veli palatine (innervated by the mandibular branch of the trigeminal nerve), palatoglossus, the palatopharyngeus which has a crucial role in breathing, the levator veli palatini which elevates the soft palate to encompass the bolus of food, and the musculus uvulae which move the uvula. The uvula has an essential role in human speech and works with the posterior part of the tongue to create ‘guttural’ sounds. The palatine process of the maxilla is a structure that forms 75% of the hard palate with the remaining 25% by the horizontal plate of the palatine bone. This bony structure has numerous perforations to allow for the passage of nutrient vessels.
Cartilages and Other Structures
The posterior part of the cartilage of the nasal septum is expanded to form the posterior process. This expansion is formed at the junction with the lateral nasal cartilage. The septal cartilage is approximately 3-4mm thick. It divides the nasal cavity into two halves. The anteroinferior part of the cartilage has an expansion known as the ‘footplate’ which is 4-8mm wide. This foot plate lies in free contact with the membranous septum. The cartilage is expanded in other regions, namely the junction with the lateral nasal cartilage termed the posterior process. The cartilage is firmly adhered to the nasal bone by taut collagen fibres.
The nasal septum is a structure consisting of both bony and cartilaginous components. The bony components are the perpendicular plate of the ethmoid superoinferiorly, the vomer posteroinferiorly, the crests of the maxillary bone anteroinferiorly and the crest of the palatine bone inferior to the vomer. The cartilage of the septum is also termed the ‘quadrangular cartilage’ due to its shape. The posterior nasal spine is a sharp pointed projection of the posterior border of the palatine bone. The Musculus uvula gains its attachment here. The pharyngeal tonsil is also known as the adenoid. It is a mass of lymphatic tissue located in the roof of the nasopharynx. The structure degrades with age and is almost entirely absent at puberty. The torus tubarius is also known as the tubar tonsil. It resides at the base of the cartilaginous section of the Eustachian tube.