posterior median line posterior median line the posterior median line is a sagittal line on the posterior torso at the midline. posterior median lineillustration of a human back.posterior view of the thorax and shoulder girdle.detailsidentifierslatinlinea mediana posteriorta98a01.2.00.022ta270fma20311anatomical terminology a similar term is "vertebral line", which defined by the spinous processes. however, this term is not in terminologia anatomica.