ORIGIN: Spinal cord segment T9.

COURSE/DISTRIBUTION: This nerve takes origin from spinal cord segment T9 and leaves the vertebral canal by passing through the intervertebral foramen between T9 and T10 vertebrae. It immediately divides into two rami- dorsal and ventral rami.

Dorsal ramus:

It immediately turns backwards, close to T9 costotransverse joint and divides into medial and lateral branches.

bulletThe medial branch immediately passes between the joint and the superior costotransverse ligament with the corresponding intertransversarii. It runs between the semispinalis thoracis and multifidus. Its cutaneous branches now enter the skin at the side of T9 vertebra to supply the medial part of posterior aspect of T9 dermatome.
bulletThe lateral branch runs laterally and occupies the interval between the superior costotransverse ligament and the intertranversarii. It then turns on the medial aspect of the T9 levator costae. It runs between the longissimus thoracis and iliocostalis thoracis. Its muscular branches supply these muscles before it then pierces the skin of the remaining lateral part of the T9 dermatome to supply it with cutaneous branches.

Ventral ramus:

bulletContinues as the ninth intercostal nerve, which runs in the costal groove of the 9th rib under the 9th posterior intercostal artery. The 9th superior anterior intercostal artery later replaces this artery in the same groove. It later passes through the digitations of the diaphragm and the transversus abdominis. It lies in the interval between the internal oblique muscle of abdomen and the transversus abdominis. It enters the rectus sheath and passes to the rectus abdominis by piercing its lateral wall. It supplies all these muscles of the anterior abdominal wall.


bulletCutaneous branches
bulletMuscular branches
bulletDorsal ramus
bulletVentral ramus
  1. Continues as 9th intercostal nerve.


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