A, Meckel’s cave, the cistern, which extends forward from the posterior fossa along the posterior trigeminal root to the level of the mid portion of the ganglion, has been exposed by removing the lateral dural wall of the cave. The motor root arises rostral to the sensory root and passes through Meckel’s cave on the medial side of the posterior sensory root and ganglion. B, The dura has been removed to expose the posterior root and ganglion and the three trigeminal divisions. There are diffuse anastomoses between the rootlets posterior to the ganglion. C, Enlarged view of the diffuse anastomosis in the region of Meckel’s cave. D, Four motor rootlets, which arise around the rostral margin of the sensory root, have been elevated to expose the anastomoses between the motor and sensory roots. The cerebellar lip projects forward and may hide the junction of the sensory root with the pons in the retrosigmoid approach. E, A cleavage plane has been started anteriorly and extended backward to the level of the posterior root. The first-division fibers are rostromedial within the posterior root and the third-division fibers caudolateral with the second division being in an intermediate location. (Images courtesy of AL Rhoton, Jr.)