The thoracic spinal nerve 3 (T3) is a spinal nerve of the

thoracic segment The spinal cord is a long, thin, tubular structure made up of nervous tissue, which extends from the medulla oblongata in the brainstem to the lumbar region of the vertebral column (backbone). The backbone encloses the central canal of the spi ...

.American Medical Association
Nervous System -- Groups of Nerves It originates from the

spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform composition) found in all chordat ...

from below the thoracic vertebra 3 (T3).

References

Spinal nerves {{neuroanatomy-stub