Medial dorsal sacrocaudal muscle

Origin: Small processes that are dorsolateral to the caudal edge of the caudal vertebrae. Direct extension of the multifidus muscle.

Insertion: Mamillary processes of the fifth through last caudal vertebrae.

Action: Extension of the tail and possibly lateral flexion.

Nerve: Branches of the plexus caudalis dorsalis.

Variation:

In equids, the medial dorsal sacrocaudal muscle is composed of robust, oblique bundles that follow one another. It originates from the spinous processes of the last three sacral vertebrae and the first coccygeal vertebrae. The first three bundles terminate with short tendons on the mammillary processes of the coccygeal vertebrae. From the fourth bundle onward, the tendons become progressively thinner and join with the tendons of the lateral dorsal sacrocaudal muscle at the level of the rough areas that serve as mamillary processes.