Just like all the spinotransverse muscles, semispinalis thoracis is innervated by the medial branches of the posterior rami of adjacent spinal nerves. Dorsal branches of the posterior intercostal arteries provide its blood supply.

What is Semispinalis capitis innervated by?

Semispinalis capitis muscle receives its innervation through the greater occipital nerve (posterior ramus of C2 spinal nerve) and spinal nerve C3. Blood supply comes from the occipital artery that arises from the external carotid artery.

What nerve supplies Semispinalis capitis?

Cervical dorsal rami

The suboccipital nerve supplies the muscles of the suboccipital triangle and the semispinalis capitis. Sometimes it has a cutaneous branch that joins the greater or lesser occipital nerves.