The subcostal nerve or nervus subcostalis in Latin is the twelfth thoracic ventral ramus (T12) inferior to the last rib (costae XII). It generally supplies the abdominal wall and the gluteal skin. The innervation of the chest wall consists mainly of the thoracic ventral rami of the intercostal nerves (T1-T11) that lie in the intercostal spaces between adjacent ribs.
Spinal nerve T12 (subcostal) is larger than the rest; it gives off the dorsolumbar nerve, a communicating branch, to the first lumbar ventral ramus. It supplies a collateral branch, like the intercostal nerve, and accompanies the subcostal vessels along the twelfth rib’s inferior border. It then runs posterior to the lateral arcuate ligament and kidney, and anterior to the upper aspect of the quadratus lumborum muscle. The aponeurosis of the transversus abdominis is perforated by the subcostal nerve that soon passes forwards between both the transversus abdominis muscle and the internal oblique. It is distributed afterwards in the same manner as the lower intercostal nerves.
The subcostal nerve connects with the iliohypogastric nerve that originates from the lumbar plexus, and then sends off a branch to the pyramidalis muscle. It pierces the internal and external oblique muscles as well via its lateral cutaneous branch, and innervates the lowest slip of the latter. The subcostal nerve then descends about 5 cm behind the anterior superior iliac spine, over the iliac crest, where it distributes to the anterior gluteal skin. Some filaments reach as far as the femur’s greater trochanter.
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