Posterior Exposure of Foramen Magnum and Vertebral Canal. Extensive soft tissue and bony resection has exposed the rostral vertebral canal and anterior surface of the posterior cranial fossa. A portion of the cranial dura has been removed to demonstrate the clivus and the tectorial membrane, the latter a continuation of the posterior longitudinal ligament connecting the body of the axis to the clivus. Stumps of cranial nerves V, VI, VII, VIII, IX, X, XI, and XII are shown approaching their respective foramina of exit. The left anterior inferior cerebellar artery, a branch of the basilar artery, is seen coursing with the facial (CNVII) and vestibulocochlear (CNVIII) nerves. It provides the labyrinthine artery that accompanies these nerves into the internal auditory meatus. The atlantic part of the vertebral artery is shown laying in grooves on the superior surface of the posterior arch of the atlas. The spinal cord has been transected at the level of the third cervical segment. Ventral and dorsal rootlets of the C3 spinal nerve are visible. Between these rootlets (and continuing inferiorly) are the denticulate ligaments, white glistening condensations of pia mater that connect the lateral borders of the cord to the spinal dura. The dorsal rootlets of C2 segment consolidate to form the dorsal root of the C2 spinal nerve. This root ends in a swelling, the dorsal root or spinal ganglion, near the intervertebral foramen. It joins the ventral root to form the definitive C2 spinal nerve. After exiting the intervertebral foramen it divides into dorsal and ventral primary rami (the latter not labeled). (Image courtesy of PA Rubino)