Anatomy Which of the following cavities are separated from the middle cranial fossa by a thin layer of bone? A Auditory tube and bony orbit B Middle ear cavity and sphenoid sinus C Sigmoid sinus and frontal sinus D Sphenoid sinus and ethmoid sinus 💡 Explanation Which of the following cavities are separated from the middle cranial fossa by a thin layer of bone? ✓ Correct Answer: B. Middle ear cavity and sphenoid sinus