Anatomical facts and location:. v The largest para-nasal sinuses.v Situated in the maxilla.v Has pyramidal shape.v Lateral nasal bone forms its base.. . v Apex headed towards the zygomatic bone. v Canine fossa, orbital floor and hard palate form the pyramidal walls. v Communicates with nasal cavity through maxillary ostium, in the posterior end of hitus simlunaris of middle meatus. .