The muscles of the pelvis are:

  • Obturator internus.
  • Piriformis.
  • Levator ani.
  • Coccygeus.

Obturator Internus

The obturator internus is a thick, fan-shaped muscle that covers the majority of the lateral wall of the pelvis.

Origin

It originates from:

  • Obturator membrane.
  • Margins of the obturator foramen (with the exception of at the obturator canal).
  • Pelvic outermost layer of the ileum between the obturator foramen and the greater sciatic notch.

Insertion

The fibres converge posteroinferiorly to create a powerful tendon that hooks around the lesser sciatic notch nearly at right angle and crosses the posterior aspect of the hip joint to be added into the medial surface of greater trochanter.

Nerve Supply

It’s provided by the nerve to obturator internus (L5; S1, S2), a particular nerve from the sacral plexus.

Actions

  • It helps to stabilize the hip joint.
  • It’s the lateral rotator of femur in erect bearing and the abductor of femur when the hip joint is bent.
  • The pelvic outermost layer of the obturator internus is covered by a dense layer of fascia- the obturator fascia. Between the body of pubis and the ischial spine, the fascia creates a linear thickening known as the tendinous arch of obturator fascia.

Piriformis

The piriformis is a triangular muscle 1 on either side on the very front of the posterior wall of true pelvis.

Origin

It originates from the pelvic outermost layer of the middle 3 sections of sacrum by 3 digitations.

Insertion

The fibres converge inferolaterally, go through the greater sciatic notch, to goes into the gluteal region in the place where they create a rounded tendon that is added into the tip (i.e., top) of the greater trochanter.

Nerve Supply

It’s provided by ventral rami of first and 2nd sacral nerves (S1, S2).

Actions

  • It helps to stabilize the hip joint.
  • It’s the lateral rotator of femur when the hip joint is extended and its abductor when the joint is bent.

Levator Ani

Both levator ani are the wide curved, thin sheets of muscles. They slope from the side wall of the pelvis toward the median plane in the place where they fuse with every other to create the gutter-like floor of the true pelvis, and divides it from the ischiorectal fossae.

Origin

The levator ani muscle has a linear origin from the pelvic outermost layer of the body of pubis, a tendinous arch of obturator fascia, and the pelvic surface of the ischial spine.

Insertion

The groups of fibres brush backwards, downward and medially to be added as follows:

  • The anterior fibres create a sling around the prostate (levator prostatae) or vagina (sphincter vaginae) and are added into the perineal body (a mass of fibrous tissue) in front of the anal canal.
  • The intermediate fibres (puborectalis) create a sling around the anorectal junction to be fit in the anococcygeal raphe (a fibrous raphe which goes from the anorectal junction to the tip of coccyx).
  • The posterior fibres (iliococcygeus) are added in the anococcygeal raphe and the coccyx.

Nerve Supply

  • It’s by the perineal branch of 4th sacral nerve (S4) from its pelvic surface.
  • It’s by the perineal branch of the pudendal nerve (S2, S3) from its perineal surface.

Actions

  • The levator ani muscles of 2 sides together support the pelvic viscera and resist the intra-abdominal pressure during striving and expulsive efforts of the anterior abdominal wall muscles.
  • They also subserve a sphincteric activity on the anorectal junction to keep continence of faeces in both genders and vagina in female.

Coccygeus (Ischiococcygeus)

The coccygeus is a small triangular muscle situated behindthe levator ani muscle.

Origin

It originates by its apex from the pelvic surface of ischial spineand sacrospinous ligament.

Insertion

From its base into the sides of upper 2 sections of coccyxand the last bit of sacrum.

Nerve Supply

It’s by the ventral rami of 4th and 5th sacral nerves (S4, S5).

Actions

  • The coccygeus muscles help the levator ani muscles to support the pelvic viscera.
  • They can also create small movements of the coccyx.

 

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