Hiatus semilunaris is present in
Middle meatus: Uncinate process is a hook-like structure running in from anterosuperior to the posteroinferior direction in the middle meatus. It&;s postero superior border is sharp and runs parallel to the anterior border of bulla ethmoidalis. This gap between the two is called hiatus semilunaris .it is two-dimensional space of 1-2 mm width. (Ref: Diseases of Ear, Nose and Throat and head and neck surgery, Dhingra 7th edition, Pg no. 150)
Nose and paranasal sinuses
superior meatus
Middle meatus
Inferior meatus
Sphenoethmoidal recess
Middle meatus