What is "sphenoidal sinus"

n. (alternative form of sphenoid sinus English)

Each of the paired sphenoidal sinuses (components of the paranasal sinuses) is contained within the body of the sphenoid. They vary in size and shape and owing to the lateral displacement of the intervening septum they are rarely symmetrical. They cannot be palpated during an extraoral examination.

The following are their average measurements: vertical height, 2.2 cm.; transverse breadth, 2 cm.; antero-posterior depth, 2.2 cm.