<P> The superior and inferior articular processes are well - defined, projecting respectively upward and downward from the junctions of pedicles and laminae . The facets on the superior processes are concave, and look backward and medialward; those on the inferior are convex, and are directed forward and lateralward . The former are wider apart than the latter since in the articulated column, the inferior articular processes are embraced by the superior processes of the subjacent vertebra . </P> <P> The transverse processes are long and slender . They are horizontal in the upper three lumbar vertebrae and incline a little upward in the lower two . In the upper three vertebrae they arise from the junctions of the pedicles and laminae, but in the lower two they are set farther forward and spring from the pedicles and posterior parts of the vertebral bodies . They are situated in front of the articular processes instead of behind them as in the thoracic vertebrae, and are homologous with the ribs . </P> <P> Three portions or tubercles can be noticed in a transverse process of a lower lumbar vertebrae: the lateral or costiform process, the mammillary process, and the accessory process . The costiform is lateral, the mammillary is superior (cranial), and the accessory is inferior (caudal). The mammillary is connected in the lumbar region with the back part of the superior articular process . The accessory process is situated at the back part of the base of the transverse process . The tallest and thickest costiform process is usually that of L5 . </P> <P> The first lumbar vertebra is level with the anterior end of the ninth rib . This level is also called the important transpyloric plane, since the pylorus of the stomach is at this level . Other important structures are also located at this level, they include; fundus of the gall bladder, celiac trunk, superior mesenteric artery, termination of spinal cord, beginning of filum terminalis, renal vessels, middle suprarenal arteries, and hila of kidneys . </P>

Where are the mammillary processes located on a typical lumbar vertebra