This is a small triangular fossa or shallow area inferior to the arcuate eminence. It sits posterior and slightly superior to the internal acoustic meatus just below the groove for the greater petrosal nerve. This shallow impression usually contains a small foramen. This foramen transmits a small vein with a slip of the dura mater. In the newborn skull this region is a deep fossa that extends laterally as a blind tunnel under the anterior semicircular canal of the vestibular system. With growth it is reduced to the small foramen. Internal to this region of bone is the posterior semicircular canal.

Sub is Latin for below. Arcuate, from the Latin arcus, refers to a bow or curving structure. Fossa comes from the Latin fodere meaning to dig. Therefore, the Latin fossa literally translates as a ditch, trench, or hole.

Fossa subarcuata