ORIGIN: Spinal cord segment T3.

COURSE/DISTRIBUTION: This nerve takes origin from spinal cord segment T3 and leaves the vertebral canal by passing through the intervertebral foramen between T3 and T4 vertebrae. It immediately divides into two rami- dorsal and ventral rami.

Dorsal ramus:

It immediately turns backwards, close to T3 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. After supplying these muscles, it enters the rhomboideus major, minor and the trapezius. Its cutaneous branches now enter the skin at the side of T3 vertebra to supply the medial part of posterior aspect of T3 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 T3 levator costae. It runs between the longissimus thoracis and iliocostalis thoracis. Its muscular branches supply these muscles; it then pierces the skin of the remaining lateral part of the T3 dermatome to supply it with cutaneous branches.

Ventral ramus:

Continues as the third intercostal nerve, which runs in the costal groove of the 3rd rib under the 3rd posterior intercostal artery. The 3rd superior anterior intercostal artery later replaces this artery in the same groove.


bulletCutaneous branches
bulletMuscular branches
bulletDorsal ramus
bulletVentral ramus
  1. Continues as 3rd intercostal nerve.


Tip:  T1-T6 nerves have the same course.



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