Fig. 2. A tracing of a sagittal X-radiograph of the lower thoracic and lumbosacral spine (excised, unloaded, ligamentous) of a 2.34 kg male Macaca fascicularis. In contrast to the in vivo dorsal curve during sitting (see Figs 1 and 3), here the lumbosacral spine is hyper-extended. P, S, L and T indicate the pelvis and the sacral, lumbar and thoracic vertebrae, respectively. The length of the lumbar column (L1-L6) is approximately 10cm. The calculation in this study focuses on the lumbar column; the angles between these unloaded lumbar intervertebral joints were estimated by measuring the angles between lines drawn parallel to the long axes of the vertebral centra.