sphenoidal sinus
One of the paired paranasal sinuses, located in the body of the sphenoid bone and communicating with the highest meatus of the nasal cavity on the same side[MESH]. The sphenoidal sinuses (or sphenoid) contained within the body of the sphenoid vary in size and shape; owing to the lateral displacement of the intervening septum they are rarely symmetrical. The following are their average measurements: vertical height, 2.2 cm. ; transverse breadth, 2 cm. ; antero-posterior depth, 2.2 cm. [WP,unvetted].