THE NOSE AND PARANASAL SINUSES
of the orbital roof about the ninth year. Thereafter the sinus extends for a
variable distance as a result of absorption of cancellous bone between the
outer and inner tables of the frontal bone. The anterior wall is formed by the
outer table; the posterior wall is related to the inner table which separates it
from the frontal lobe of the brain; its floor forms part of the orbital roof; and
the medial wall is a septum separating the two frontal sinuses. The opening of
Fig. 11. Lateral wall of right nasal cavity. 1, Frontal sinus; 2, Cell of the agger nasi; 3, Sphenoidal
sinus; 4, Large spheno-ethmoidal cell; 5, Anterior ethmoidal cell.
the frontal sinus is in its floor, and communicates with the middle meatus
through the nasofrontal duct (Fig. 11).
The ethmoid sinuses constitute a cell labyrinth and are present at birth as
prolongations of the nasal mucosa into the lateral mass of the ethmoid bone.
In adult life they vary in number, size and shape, and for clinical purposes
they are classified as anterior or posterior, depending upon whether they
communicate with the middle or the superior meatus. The cell labyrinth lies
between the upper half of the nasal cavity medially and the orbit from which
the cells are separated laterally by the lamina papyracea. The cells abut
anteriorly on the frontal process of the maxilla, and posteriorly they lie
against the sphenoid bone. The anatomical details may be seen in Figs. 11
The sphenoid sinus occupies the body of the sphenoid bone, and may be
present at birth as a small indentation of nasal mucosa. The sinus varies
greatly in size in the adult. The lateral wall is contiguous with the internal
carotid artery and the cavernous blood sinus; the roof is related to the frontal