<prompt> First sinus to develop -EthmoidMaxillarySphenoidFrontal  <response>: Ans. is b i.e., Maxillary Development of the maxillary sinus begins by the 65th day of gestation, making it the first sinus to develop in utero ___Essential otolaryngologyo Most common sinus affected by sinusitis overall- Maxillaryo Most common sinus affected in adult- Maxillaryo Most common sinus affected in children- Ethmoido Least common sinus affected- Sphenoido Sinuses involved in order of frequency- Maxillary Frontal Ethmoid Sphenoid 