The semispinalis muscles are a group of muscles located in the back. They include the semispinalis capitis, semispinalis cervicis, and semispinalis thoracis muscles. The semispinalis capitis originates at the transverse processes of the upper thoracic and lower cervical vertebrae, and inserts into the occipital bone at the base of the skull. The semispinalis cervicis originates at the transverse processes of the upper thoracic vertebrae, and inserts into the transverse processes of the upper cervical vertebrae. The semispinalis thoracis originates at the transverse processes of the thoracic vertebrae, and inserts into the spinous processes of the upper lumbar and lower thoracic vertebrae.

The main function of the semispinalis muscles is to extend the head and vertebral column. This movement is essential for activities such as looking upwards and arching the back, and helps to provide stability and support for the spine. The semispinalis muscles also assist in lateral flexion (bending to the side) and rotation of the vertebral column.