ABSTRACT
I GROSS ANATOMY The spinal cord extends from the foramen magnum to approximately the L1-L2 disc space. It is continuous with the medulla oblongata and terminates in the conus medullaris. Below this level the nerve roots running inferiorly are collectively called the cauda equina (Fig. 1A-D). The cauda equina runs within the spinal canal, which is bordered anteriorly by the vertebral bodies and posteriorly by the dorsal bony arch. The spinal canal measures approximately 45 cm in length in males and 42 cm in females (1). There are two enlargements in the spinal cord that run from C4 to T1 and from L2 to S3. These enlargements correspond to areas of upper and lower extremity innervation. In all there are 31 nerve roots that branch from the spinal cord (8 cervical, 12 thoracic, 5 lumbar, 5 sacral, and 1 coccygeal). In cross-section the cord is slightly flatter in the AP plane. It reaches its maximum transverse diameter between C3 and C6, which is approximately 13 to 14 mm (2).
