Dissection View of Anterior Surface of Posterior Cranial Fossa and Vertebral Canal. The brainstem, cerebellum, and rostral segment of the cervical spinal cord have been removed to expose the vertebrobasilar arterial tree, stumps of cranial nerves entering cranial foramina, and components of spinal nerves. The atlantic portions of the vertebral arteries pierce the spinal dura and arachnoid at the foramen magnum to continue as the intracranial portions of the arteries. These give rise to the posterior inferior cerebellar arteries before uniting to form the basilar artery lying on the clivus. The anterior inferior cerebellar arteries quickly arise from the basilar artery and course toward the internal auditory meatus in company with the facial (CNVII) and vestibulocochlear (CNVIII) nerves. Toward the midline, the stumps of the abducens (CNVI) nerves can be seen piercing clival dura. The glossopharyngeal (CNIX), vagus (CNX), and spinal accessory (CNXI) nerves are visible in their rostral-caudal relationship as they approach the location of the jugular foramen. The spinal accessory nerve arises from the lateral surface of the first five cervical segments of the spinal cord between dorsal and ventral rootlets of spinal nerves. It ascends through the foramen magnum. Rootlets of the hypoglossal (CNXII) nerve penetrate dura in their course to the hypoglossal canal. The denticulate ligament is a lateral white glistening condensation of pia mater located between dorsal and ventral roots. Dorsal rootlets of the C2 and C3 spinal nerves are shown leaving the spinal cord. The rootlets join to form a dorsal root, demonstrated by C2, which ends at a swelling, the dorsal root or spinal ganglion. Here, the dorsal root joins its ventral root to form the short, definitive spinal nerve. This nerve exits the intervertebral foramen between the atlas and axis vertebrae before quickly dividing into the dorsal and ventral rami. On the dorsal surface of the spinal cord is a narrow midline depression, the posterior median sulcus. Immediately lateral to this are the fasciculi gracilis and lateral to this, the fasciculi cuneatus, both components of the dorsal columns. Ventral to the transected spinal cord is a portion of the arachnoid, raised by the metal probe. (Image courtesy of PA Rubino)