A carefully done in vitro study is presented on the sagittal plane motion patterns of the human cervical spine as the various components (ligaments, disc and facet joints) are sequentially transected, and as an axial tensile load is applied in increments until the spine fails. Sound practices regarding preservation and maintenance of the physiological environment were utilized. A simple roentgenographic measuring echnique, using steel pins and needles as markers, provided reliable information about the displacement patterns of vertebrae. The results indicate that failure of the spine takes place when at least all the anterior or all the posterior plus two anterior components, have been transected. Also presented are the results of motion pattern changes, and their significance for developing a safe clinical test for evaluating spine injury.