title: Fetal Development of the Human Obturator Internus Muscle With Special Reference to the Tendon and Pulley.
abstract: To examine the development of the tendon pulley of the obturator internus muscle (OI), we observed paraffin sections of 26 human embryos and fetuses (∼6-15 weeks of gestation). The OI was characterized by early maturation of the proximal tendon in contrast to the delayed development of the distal tendon. At 6 weeks, the ischium corresponded to a simple round mass similar to the tuberosity in adults. At 8 weeks, before development of the definite lesser notch of the ischium, initial muscle fibers of the OI, running along the antero-posterior axis, converged onto a thick and tight but short tendon running along the left-right axis. Thus, at the beginning of development, the OI muscle belly and tendon met almost at a right angle. At 10 weeks, the OI tendon extended inferiorly along the sciatic nerve, but the distal part remained thin and loose and it was embedded in the gluteus medius tendon. At 15 weeks, in association with the gemellus muscles, the distal OI tendon was established. The mechanically strong sciatic nerve was first likely to catch the OI muscle fibers to provide a temporary insertion. Next, the ischium developing upward seemed to push the tendon to make the turn more acute along the cartilaginous ridge. Finally, the gemellus muscle appeared to provide inferior traction to the OI tendon for separation from the gluteus medius to create the final, independent insertion. Without such guidance, the piriformis tendon first attached to the OI tendon and then merged with the gluteus medius tendon.
authors: Department of Anatomy, Nihon University School of Medicine, Tokyo, Japan.
authors: Michiko
authors: M
authors: Naito
authors: Department of Anatomy, Akita University Graduate School of Medicine, Akita, Japan.
authors: Ryoji
authors: R
authors: Suzuki
authors: Department of Anatomy, Akita University Graduate School of Medicine, Akita, Japan.
authors: Hiroshi
authors: H
authors: Abe
authors: Department of Anatomy and Human Embryology II, Complutense University, Madrid, Spain.
authors: Jose Francisco
authors: JF
authors: Rodriguez-Vazquez
authors: Division of Internal Medicine, Iwamizawa Kojin-Kai Hospital, Iwamizawa, Japan.
authors: Gen
authors: G
authors: Murakami
authors: Department of Anatomy, Nihon University School of Medicine, Tokyo, Japan.
authors: Shin
authors: S
authors: Aizawa
mesh_terms: D047108:Embryonic Development / Q000502:physiology*; D006801:Humans; D007512:Ischium / Q000196:embryology*; D018482:Muscle, Skeletal / Q000196:embryology*; D013710:Tendons / Q000196:embryology*; D013848:Thigh / Q000196:embryology*
keywords: gemellus muscles; human fetus; ischium; obturator internus muscle; piriformis muscle; sciatic nerve; tendon pulley