<prompt> Sinus absent at the birth:Maxillary sinusEthmoidal sinusFrontal sinusTemporal sinus  <response>: Ans. c Frontal sinusRef: Dhingra 5th Ed. 203 Please refer to above table The first sinus that starts to develop in human embryo is maxillary sinus. It starts to develop around 10 weeks of intra-uterine life. The last sinus to develop in human embryo is frontal sinus . This sinus is absent at the time of birth starts to develop postnatally. Frontal sinus can be visualized radiologically at 6 yrs of age. 