Origin: Mamillary process
Insertion: Roots of spinous process of lumbar vertebra
Nerve: Dorsal rami of spinal nerves
Action: extension of the thoracic vertebrae, proprioceptive transducers that monitor the position and movements of the vertebral column.
The Rotatores (Rotatores spinae) lie beneath the Multifidus and are found only in the thoracic region; they are eleven in number on either side. Each muscle is small and somewhat quadrilateral in form; it arises from the upper and back part of the transverse process, and is inserted into the lower border and lateral surface of the lamina of the vertebra above, the fibers extending as far as the root of the spinous process. The first is found between the first and second thoracic vertebrae; the last, between the eleventh and twelfth. Sometimes the number of these muscles is diminished by the absence of one or more from the upper or lower end.