The inferior and posterior of the three elements forming the periotic bone.

The opisthotic is the posterior of the two bones making up the otic capsule and is usually fused to the prootic, the anterior otic bone. The opisthotic is an endochondral bone. It is usually the largest contributor to the paroccipital process and to the structures of the middle and inner ear. It normally contacts all of the occipital bones and the prootic, and may contact the basisphenoid. It often forms part of the edge of the foramen ovale, the door to the inner ear.