Since the days of Pithecanthropus erectus, man has been paying for the privilege of walking on his hind legs. Nature designed the human body for four-legged locomotion, and evolution has not yet accomplished the structural changes required by this relatively new mode of progression. As a result, certain inherent anatomic weaknesses are expressed in the form of peculiarly human maladies. Some of the more common are flat feet, varicose veins, hemorrhoids, cystocele, hernia, backache, and sciatica. The latter condition is usually due to posterior protrusion or rupture of the intervertebral disk immediately above or below the fifth lumbar vertebra.
A knowledge of the anatomy of the parts is necessary for an understanding of this condition (fig. 1). The mamalian spine consists of bony vertebrae separated by intervertebral disks. These cartilaginous structures are designed to give flexibility to the spine but not to bear weight. Along the anterior surface of the bodies of the vertebrae runs the longitudinal anterior spinal ligament, which is very dense and strong. The posterior spinal ligament is a less dense structure running longitudinally along the posterior surfaces of the vertebral bodies within the spinal canal. The intervertebral disk consists of two cartilaginous plates which are adherent to the flat surfaces of the bodies of the adjoining vertebrae. The nucleus pulposus is an ovoid, semigelatinous cushion in the center of the disk, surrounded by the dense, heavy fibers of the annulus fibrosus. This annulus is thicker in front and at the sides than at the back, where. . .