Sinus not present at bih is:: (A) Ethmoid, (B) Maxillary, (C) Sphenoid, (D) Frontal
Answer is D. Frontal-Absent at bih-Adult size in20 years-Invades frontal bone(2-4yrs),size increases until teens. Ref.Scott Brown 7/e,Vol 2,p 1320.