Cross-section of the spinal column through a vertebra (vertebrae and subarachnoid space).

Sagittal section of lumbar area of spinal column showing pertinent anatomy. Needle inserted between vertebrae into cerebral spinal fluid (CSF).

Cross-sections of the brain, midbrain, pons, medulla, cervical spinal cord and thoracic spinal cord showing the efferent corticospinal tract leading to a skeletal muscle (without labels).

Cross-sections of the brain, midbrain, pons, medulla, cervical spinal cord and thoracic spinal cord showing the efferent corticospinal tract leading to a skeletal muscle.

Two cross-sections of spinal area showing congenital defect in which part of vertebral column is absent (top) and more extreme case where spinal cord protrudes beyond vertebral absence (bottom).

Transverse section showing the arterial supply and venous drainage of the spinal cord (posterior part, top; anterior part; bottom).

Sagittal section of lumbar area of spinal column showing pertinent anatomy. Needle inserted into epidural space between L3 and L4 vertebrae.

Sagittal section of spinal cord at 12 weeks' gestation, showing the nerves, vertebral bodies, and cervical (pink), thoracic (orange), lumbar (yellow), sacral (brown), and coccygeal (green) segments.

Sagittal section of lumbar area of spinal column showing pertinent anatomy. Needle is removed leaving catheter in place between L3 and L4 vertebrae.

Cross-section of thorax at L3-L4 disc showing relevant lumbar anatomy; two spinal needles illustrate the medial and lateral approaches into the subarachnoid space where the cerebrospinal fluid is located.

Spinal cord, cross-section