paranasal sinus ethmoid sinus MESH:D005005 Wikipedia:Ethmoid_bone_sinus FMA:84115 ethmoidal bone sinus The evaginations of the mucous membrane of the nasal cavity into the ethmoidal bony labyrinth, forming multiple small paranasal sinuses. NCIT:C12276 UMLS:C0015028 MA:0001792 ethmoidal sinus SCTID:181206009 GAID:356