Because only thin shelves of bone separate the sphenoidal sinuses from the nasal cavities below and hypophyseal fossa above, the pituitary gland can be surgically approached through the roof of the nasal cavities by passing first through the anteroinferior aspect of the sphenoid bone and into the sphenoidal sinuses and then through the top of the sphenoid bone into the hypophyseal fossa.
Innervation of the sphenoidal sinuses is provided by: the posterior ethmoidal branch of the ophthalmic nerve [V1], and the maxillary nerve [V2] via orbital branches from the pterygopalatine ganglion.
The sphenoidal sinuses are supplied by branches of the pharyngeal arteries from the maxillary arteries.
Walls, floor, and roof
The medial wall of each nasal cavity is the mucosa-covered surface of the thin nasal septum, which is oriented vertically in the median sagittal plane and separates the right and left nasal cavities from each other.
The nasal septum (Fig. 8.236) consists of: the septal nasal cartilage anteriorly, posteriorly, mainly the vomer and the perpendicular plate of the ethmoid bone, small contributions by the nasal bones where they meet in the midline, and the nasal spine of the frontal bone, and contributions by the nasal crests of the maxillary and palatine bones, rostrum of the sphenoid bone, and the incisor crest of the maxilla.
The floor of each nasal cavity (Fig. 8.237) is smooth, concave, and much wider than the roof. It consists of: soft tissues of the external nose, and the upper surface of the palatine process of the maxilla and the horizontal plate of the palatine bone, which together form the hard palate.
The naris opens anteriorly into the floor, and the superior aperture of the incisive canal is deep to the mucosa immediately lateral to the nasal septum near the front of the hard palate.
The roof of the nasal cavity is narrow and is highest in central regions where it is formed by the cribriform plate of the ethmoid bone (Fig. 8.238).
Anterior to the cribriform plate the roof slopes inferiorly to the nares and is formed by: the nasal spine of the frontal bone and the nasal bones, and the lateral processes of the septal cartilage and major alar cartilages of the external nose.
Posteriorly, the roof of each cavity slopes inferiorly to the choana and is formed by: the anterior surface of the sphenoid bone, the ala of the vomer and adjacent sphenoidal process of the palatine bone, and the vaginal process of the medial plate of the pterygoid process.
Underlying the mucosa, the roof is perforated superiorly by openings in the cribriform plate, and anterior to these openings by a separate foramen for the anterior ethmoidal nerve and vessels.
The opening between the sphenoidal sinus and the spheno-ethmoidal recess is on the posterior slope of the roof.
The lateral wall of each nasal cavity is complex and is formed by bone, cartilage, and soft tissues.
Bony support for the lateral wall (Fig. 8.239A) is provided by: the ethmoidal labyrinth, superior concha, middle concha and uncinate process, the perpendicular plate of the palatine bone, the medial pterygoid plate of the sphenoid bone, the medial surfaces of the lacrimal bones and maxillae, and the inferior concha.
In the external nose, the lateral wall of the cavity is supported by cartilage (lateral process of the septal cartilage and major and minor alar cartilages) and by soft tissues. The surface of the lateral wall is irregular in contour and is interrupted by the three nasal conchae.