The semispinalis muscle is a type of transversospinalis muscle found in the human body. The transversospinalis muscle group is a very deep layer of muscles located on either side of the spine. The semispinalis muscle is the most superficial layer of this muscle group.

The semispinalis muscle is located in the back and is very long; in fact, it is the largest muscle mass in the posterior part of the neck. This muscle is responsible for maintaining posture and for movement of the head and the vertebral column. It is subdivided into three different muscles: semispinalis dorsi, semispinalis cervicis, and semispinalis capitis.

The semispinalis comes from the transverse processes of the lower vertebrae. (The transverse processes are areas of bone that stick out of the sides of the vertebrae.) It then reaches up across several vertebrae and inserts at the spines of some vertebrae. The muscle reaches up to about half of the vertebral column.