Variable sized cavities located within the body of the sphenoid that communicate antero-inferiorly with the spheno-ethmoidal recess. Early in life they are simple extensions of the nasal epithelium that enlarge and cavitate the bone forming large sinuses by adolescence.

Sinus is Latin for a curve, fold, bay, or gulf. In anatomy it can describe anything from a large, hollow cavity to a concave groove-like channel.

Sinus sphenoidalis

Sinus sphénoïdal