Deep intrinsic muscles are located under the erector spinae. They are a group of short muscles, associated with transverse and spinous processes of the vertebral column.
Three major muscles in this group are-
The semispinalis is the most superficial muscles in this group. Much like the intermediate muscles, The semispinalis can be divided by its superior attachments into thoracic, cervicis and capitis.
Function: Contralaterally rotates and extends the head and vertebral column.
The multifidus is located under the semispinalis muscle. Multifidus is best developed in the lumbar area.
Function: Stabilizes the vertebral column.
The rotators are the most prominent muscle in the thoracic region.