Intermediate muscles of the back

The longissimus is the muscle lateral to the semispinalis. It is the longest subdivision of the erector spinae that extends forward into the transverse processes of the posterior cervical vertebrae.

The iliocostalis is the muscle immediately lateral to the longissimus that is the nearest to the furrow that separates the epaxial muscles from the hypaxial. It lies very deep to the fleshy portion of the serratus ventralis (serratus posterior).