Sinus absent at the birth:

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.