Posterior view of caudal cerebellum and proximal spinal cord. Removal of occipital bone and laminectomy of the cervical vertebrae provides in situ continuity of the central nervous system (CNS). The posterior inferior cerebellar arteries, the largest branches of the vertebral arteries, can be seen proximal to the foramen magnum. The dorsal columns of the spinal cord convey somatosensory information from the body below the neck. In the cervical cord here, they are comprised of two separate tracts: the gracile and cuneate fasciculi. The gracile fasciculi represent the medial portion of the dorsal columns and carry somatosensory input from the lower trunk (T7 and below) and lower body. The cuneate fasciculi are located lateral to the gracile fasciculi and convey sensory input for the upper trunk (above T7), arms, and neck. Posterior (dorsal) roots of cervical spinal nerves emerge from the dorsolateral segments of the cervical cord. Distally, the cell bodies of these sensory neurons are contained within dorsal root (spinal) ganglia near intervertebral foramina. The spinal portion of the spinal accessory nerve can be seen as a single trunk that ascends through the foramen magnum to unite with its cranial portion, which arises from the medulla. The spinal portion arises from fibers from ventral horn cells between C1 and C5 segments. These fibers emerge from the cord between the ventral and dorsal spinal nerve roots before joining to form a single trunk. In this view, the vertebral arteries are shown ascending within transverse foramina of the C2 and C1 vertebrae. The vertebral arteries consist of several parts or segments. The cervical part (V2 segment) runs through the transverse foramina of C6 to C2 vertebrae. The atlantic part (V3 segment) emerges from the transverse foramen of C2, extends upward through the transverse foramen of C1, and wraps around posterior to the lateral mass to lay in a groove on the superior surface of the posterior arch of the atlas. It then passes into the vertebral canal beneath the posterior atlantooccipital membrane. The last part, the intracranial part (V4 segment) of the vertebral arteries, pierce the dura mater and course medially and in front of the medulla. At the lower border of the pons they unite to form the basilar artery. (Image courtesy of AL Rhoton, Jr.)