The rectococcygeal muscles are two bands of smooth muscle tissue arising from the 2nd and 3rd

coccygeal vertebrae The coccyx ( : coccyges or coccyxes), commonly referred to as the tailbone, is the final segment of the vertebral column in all apes, and analogous structures in certain other mammals such as horses. In tailless primates (e.g. humans and other ...

, and passing downward and forward to blend with the rectal longitudinal smooth muscle fibers on the posterior wall of the

anal canal The anal canal is the part that connects the rectum to the anus, located below the level of the pelvic diaphragm. It is located within the anal triangle of the perineum, between the right and left ischioanal fossa. As the final functional seg ...

.Wu Y, Dabhoiwala NF, Hagoort J, et al. ''3D Topography of the Young Adult Anal Sphincter Complex Reconstructed from Undeformed Serial Anatomical Sections.'' Souglakos J, ed. PLoS ONE. 2015;10(8):e0132226. doi:10.1371/journal.pone.0132226

Structure

The rectococcygeal muscles are composed of smooth muscle and run from the anterior surface of the 2nd and 3rd

down the posterior wall of the rectum as a triangular shaped muscle before branching and inserting among the various muscles and fascial structures associated with the

pelvic diaphragm The pelvic floor or pelvic diaphragm is composed of muscle fibers of the levator ani, the coccygeus muscle, and associated connective tissue which span the area underneath the pelvis. The pelvic diaphragm is a muscular partition formed by the le ...

and

and collectively called longitudinal anal muscles.

Variation

There are some differences in the retrococcygeal muscle architecture between males and females. In males the muscle inserts with the fascia of the

levator ani The levator ani is a broad, thin muscle group, situated on either side of the pelvis. It is formed from three muscle components: the pubococcygeus, the iliococcygeus, and the puborectalis. It is attached to the inner surface of each side of the ...

to either side of the rectum or to other fascial elements of the pelvic diaphragm. In females the rectococcygeal muscle additionally runs around the sides of the rectum to connect to the rectovaginal fascia of the posterior

vagina In mammals, the vagina is the elastic, muscular part of the female genital tract. In humans, it extends from the vestibule to the cervix. The outer vaginal opening is normally partly covered by a thin layer of mucosal tissue called the hymen ...

l wall. There is also evidence suggesting that the retrococcygeal muscles are ~2-fold thicker in females.

Innervation

The rectoccygeal muscles are innervated by

autonomic nerves Autonomic can refer to: * Autonomic nervous system, a division of the peripheral nervous system that supplies smooth muscle and glands, and thus influences the function of internal organs *Autonomic computing Autonomic computing (AC) is distribu ...

associated with the

inferior hypogastric plexus The inferior hypogastric plexus (pelvic plexus in some texts) is a network () of nerves that supplies the organs of the pelvic cavity. The inferior hypogastric plexus gives rise to the prostatic plexus in males and the uterovaginal plexus in female ...

Function

The rectococcygeal muscles form part of the complex arrangement of muscle surrounding the rectum, sometimes termed the anal-sphincter complex, which act to stabilise and support the anal canal during defecation. The rectococcygeal muscle acts to lift the sphincter, thereby effectively shortening the rectum and aiding evacuation.

Other animals

In many animals with tails, such as horses and dogs, the rectococcygeal muscles are involved in the response to the raising of the tail during defecation.Evans HE, de Lahunta A, ''Miller's Anatomy of the Dog'', Elsevier Health Sciences, 2013, p.326. In tailed animals the muscle attaches to vertebrae in a more caudal position than in humans due to the additional vertebrae in the tail, in dogs there are connections to the 5th and 6th caudal vertebrae and in horses to the 4th or 5th. The rectococcygeal muscle in the rabbit is notable for being one of the fastest contracting mammalian

smooth muscles Smooth muscle is an involuntary non-striated muscle, so-called because it has no sarcomeres and therefore no striations (''bands'' or ''stripes''). It is divided into two subgroups, single-unit and multiunit smooth muscle. Within single-unit mus ...

known.

Other images

File:The_levator_and_coccygeus_muscles_seen_from_above._After_Toldt,_1919.tif, Pelvic region showing m. rectococcygeus.

External links

Rectococcygeus muscle
a
Systematized Nomenclature of Medicine - Clinical Terms

References

{{Authority control Muscles of the torso Pelvis