Parietal pelvic muscles
The musculature of the inner pelvic surface is divided by its topographical location into greater and lesser pelvis groups.
The iliopsoas muscle (m. iliopsoas) lies within the greater pelvis. Its fascial sheath has close anatomical connections and fuses with the lateral part of the inguinal ligament, as well as with the arcus iliopectineus. The muscle itself leaves the pelvic cavity and emerges onto the thigh through the muscular lacuna (lacuna musculorum), after which it inserts into the lesser trochanter of the femur.
The following key structures are located in the lesser pelvic cavity:
- Piriformis muscle (m. piriformis) — originates on the anterior surface of the sacrum and exits through the greater sciatic foramen into the gluteal region. It does not fill the foramen completely, forming the supra- and infrapiriform slits for the passage of neurovascular bundles and nerves.
- Obturator internus muscle (m. obturatorius internus) — begins on the inner surface of the anterolateral pelvic wall and the obturator membrane, passes through the lesser sciatic foramen, and leaves the obturator canal for vessels and nerves.
- Coccygeus muscle (m. coccygeus) — lies in the posterior regions, although it is not always well-developed.
Floor of the lesser pelvis cavity and pelvic diaphragm
The lesser pelvis cavity is bounded inferiorly by a robust musculo-fascial complex that forms two diaphragms: the pelvic and the urogenital.
The basis of the first one — the pelvic diaphragm (diaphragma pelvis) — is formed by the levator ani muscle (m. levator ani). It originates on the inner surface of the inferior pubic ramus, as well as on the tendinous arch of the pelvic fascia (arcus tendineus fasciae pelvis), which is a thickening of the fascia of the obturator internus muscle.
Additionally, the following features of the m. levator ani are distinguished:
- Muscle bundles originate from the posterior surface of the superior pubic ramus all the way to the ischial spine.
- The fibers attach to the ligaments (lig. sacrococcygeum anterius and lig. anococcygeum), as well as to the coccyx itself.
- The levator bundles connect with the opposite side and encircle the wall of the lower rectum, fusing with its muscular coat.
- An active interweaving of fibers with the external anal sphincter (m. sphincter ani externus) takes place.
Urogenital diaphragm
In the anterior regions of the pelvic floor, where the levator ani muscle does not close with its internal bundles, the urogenital diaphragm (diaphragma urogenitale) is located.
It lies inferior to the anterior parts of m. levator ani and precisely fills the angle formed by the inferior rami of the pubic and ischial bones. The main structural basis of this diaphragm is the deep transverse perineal muscle (m. transversus perinei profundus).
The external anal sphincter (m. sphincter ani externus) is also closely related to these structures. It originates from the lig. anococcygeum, circularly surrounds the rectum, and terminates by blending into the perineal body (centrum tendineum perinei).
Briefly: answers to topical questions
What passes through the suprapiriform foramen?
The superior gluteal neurovascular bundle passes through the suprapiriform foramen. It includes:
- Superior gluteal artery (a. glutea superior) — branches off from the posterior trunk of the internal iliac artery, dividing into superior and inferior branches;
- Superior gluteal veins (vv. gluteae superiores) — form a plexus that covers the artery;
- Superior gluteal nerve (n. gluteus superior) — located inferiorly and laterally relative to the vessels.
What passes through the obturator canal?
The obturator neurovascular bundle passes through the obturator canal. It includes:
- Obturator artery (a. obturatoria) — anastomoses with the medial femoral circumflex artery and the inferior gluteal artery;
- Obturator vein (v. obturatoria);
- Obturator nerve (n. obturatorius) — innervates the adductor muscles, gracilis muscle, and the skin of the medial thigh.
Anatomical rule: the iliopsoas passes through the lacuna to the lesser trochanter, the piriformis divides the greater sciatic foramen into two tiers for vessels and nerves, and the levator ani together with the deep transverse muscle form a two-layered pelvic floor.
Class and exam questions
Where does the iliopsoas muscle pass as it exits the pelvis?
The m. iliopsoas leaves the pelvic cavity and emerges onto the thigh through the muscular lacuna (lacuna musculorum), after which it inserts into the lesser trochanter of the femur.
What structures pass through the infrapiriform foramen?
The sciatic nerve, inferior gluteal neurovascular bundle, posterior cutaneous nerve of the thigh, and pudendal neurovascular bundle pass through the infrapiriform foramen.
Which muscle forms the basis of the urogenital diaphragm?
The basis of the urogenital diaphragm (diaphragma urogenitale) is formed by the deep transverse perineal muscle (m. transversus perinei profundus).
What else to study on this topic
- Topography of the supra- and infrapiriform foramina
- Detailed structure of the tendinous arch of the pelvic fascia
- Connections of the levator ani muscle with the anal sphincter
- Mutual arrangement of the pelvic and urogenital diaphragms
- Topographo-anatomical features of the obturator canal
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