The lumbar region and its layers up to the parietal abdominal fascia, fascia abdominis parietalis can be considered as the posterior abdominal wall. Many of the parts are the same contents of the posterior and anterolateral abdominal walls.
Deep to the parietal fascia, there is the retroperitoneal space, spatium retroperi-toneale, a part of the abdominal cavity limited anteriorly by the parietal peritoneum.
LUMBAR REGION, REGIO LUMBALIS
The surface landmarks of the region are: spinous processes of two inferior thoracic and all lumbar vertebrae, XII pair of ribs, and iliac crests. Over the horizontal line connecting the supreme points of the iliac crests, the apex of the L IV spinous process is palpated.
In cerebrospinal punctures, a needle is entered into the space between the L IV and V spinous processes.
The spinous process of the L IV is a mark to identify spinous processes of the vertebrae lying upwards and downwards.
The posterior median line of the body (the spinous processes line) divides the region into two symmetrical halves.
Limits of the lumbar region. The superior limit is the XII rib; the inferior one - the iliac crest and the relating half of the sacrum; the lateral limit is the posterior axillary line or the vertical line corresponding to it from the extremity of the XI rib to the iliac crest; and the medial limit is the posterior median line of the body (the spinous processes' line).
Within the region, two parts are distinguished: the medial, with the vertebral column and the erector spinae muscle, m. erector spinae, and the lateral one with the broad abdominal muscles. At this spot, the inferior lumbar triangle, trigonum lumbale inferius and the superior lumbar triangle (quadrangle), trigonum (tetragonum) lumbale superius are marked.