Ans. c (Middle meatus). (Ref. Bhargaw, 5th ed.151)THE LATERAL NASAL WALL# It consists anteriorly of the nasal bone, frontal process of maxilla & the lacrimal bone.# Posterior to lacrimal bone, the lateral wall of nasal cavity is formed by ethmoid labyrinth, maxillary & inferior concha.# Perpendicular plate of palatine bone & the medial pterygoid plate form the most posterior portion.# Within the nasal cavity, scrolls of bone on the lateral walls, the conchae, projected medially to divide the cavity into meatuses.# Superior & middle conchae are part of ethmoid bone, but the inferior conchae are separate pair of bones.# A turbinate is a concha, meaning a soft tissue bone complex.# Superior, middle & inferior meatuses that are formed under & lateral to respective conchae, have increased contact with nasal surface to permit effective warming & moistening of inspired air.Superior turbinate meatus- Post ethmoidal air cells drain into it & sphenoid sinus drain via sphenoethmoidal recess.Middle turbinate meatus- Most important area, forms OMC where anterior-middle ethmoid air cells, maxillary & frontal sinuses drain into it.- Anterior to frontal recess & anterior end of middle turbinate is the bony prominence of frontal process of maxilla known as agger nasi, cells in it drains into ethmoid infundibulumInferior turbinate meatus- Largest turbinate. Nasolacrimal duct drains into its anterior part.Osteomeatal unit/complex (OMC)- OMC is the normal aerated channel which provides airflow & mucocilliary clearance for sinuses.- It is the key area for pathogenesis of chronic sinus diseases.- It is the cross road (confluence) for drainage of most paranasal sinuses.- It is the center of interest due to functional endoscopic sinus surgery (FESS).