The gradual changes of morphology from one vertebra to another do not occur in all parts on the same rate. Those of the costal joint surface were found to occur in a very restricted manner (Shinohara, 1997). The transformations in the structural elements of vertebrae were found to be under the control of Hoxgenes (Kostic & Capecchi, 1994).
In the lower thoracic vertebrae (T9 to T12) multifidus takes its origin from a bony tubercle (mamillary tubercle) which is situated posterosuperiorly on the transverse process. This tubercle is situated posterolateral to the superior articular process. The mamillary tubercle of T12 is much more prominent (Pal & Routal, 1999). In the lumbar vertebrae multifidus takes its origin from a bony protuberance (mamillary process), which is situated on the posterior border of the superior articular process (Chadha et aI., 2003).