The spinalis muscle is the most medial of the erector spinae group of muscles, and is lateral to the multifidus group. The spinalis detaches from medial side of the longissimus thoracis and travels forward near thoracic vertebral spinous processes to cervical vertebral spinous processes. It may be divided into two parts:
In the pig and the horse, the spinalis muscle forms a common muscle belly, therefore sometimes termed as "spinalis thoracic et cervicis (thoracic and cervical spinal muscle)", whereas in ruminants and carnivores, the thoracic and cervical spinalis muscles receive additional muscular strands from the the mamillary and transverse processes of some vertebrae, and the fibers of the spinlais musccles are closely related to and often difficult to separate form the semispinalis muscle. Therefore, some authors use the compound name "thoracic and cervical spinal and semispinal muscle" to describe this muscular complex.
Origin: extends across the spinous processes of one or more thoracic vertebrae, and sometimes last cervical vertebra
Insertion: spinous processes of Vth to 2nd cervical vertebrae
Action: fixes the thoracic vertebral column and extends the neck
Nerve: Dorsal branches of the cervical, thoracic and lumbar nerves