Tatsuo Sato1, Ji Hyun Kim2, Kwang Ho Cho3, Shogo Hayashi4, José Francisco Rodríguez-Vázquez5, Gen Murakami6. 1. Emeritus Professor of Tokyo Medical and Dental University, Tokyo, Japan. 2. Department of Anatomy, Jeonbuk National University Medical School, Geunji-ro 20, Deokjin-gu, Jeonju, Jeonbuk, 54907, Republic of Korea. 407kk@hanmail.net. 3. Department of Neurology, Wonkwang University School of Medicine and Hospital, Institute of Wonkwang Medical Science, Iksan, Korea. 4. Department of Anatomy, School of Medicine, International University of Health and Welfare, Narita, Japan. 5. Department of Anatomy and Embryology, Faculty of Medicine, Complutense University, Madrid, Spain. 6. Division of Internal Medicine, Cupid Clinic, Iwamizawa, Hokkaido, Japan.
Abstract
PURPOSE: The longissimus (LO) and iliocostalis (IC) of adults consist of myofibers extending from the superolateral to the inferomedial side of the back and, because of the same course, they are fused in the thoracolumbar region. The LO also has a medial attachment to the long myofibers of the transversospinalis (TS) showing a course from the superomedial to the inferolateral side. However, there is apparently no information regarding when and how these similar longitudinal muscles differentiate from a cluster of dorsomedial myotome cells. METHODS: We examined sagittal and horizontal sections of the trunks of 39 human embryos and fetuses (18-330 mm crown-rump length). RESULTS: At 6-7 weeks gestational age (GA), the surface aponeurosis appeared prior to and independent of the thoracolumbar fascia. At 6-9 weeks GA, the LO myofibers had a postero-inferior course, from the transverse process to the initial aponeurosis, whereas the TS myofibers had a postero-superior course, from a lateral extension of the intertransverse ligament to the aponeurosis. However, the IC consisted of supracostal longitudinal myofibers and was distant from the LO until 12 weeks GA. Because of the lack of ligamentous attachments and ribs, myofibers of the TS, LO, and IC took a similar inferior course in the lumbar region. When the early TS was represented by the transverso-aponeurotic muscle, consequently, the LO corresponded to the aponeuro-transversal muscle and was independent from the IC. CONCLUSION: The classical model of TS and LO development does not recognize the essential role of the aponeurosis identified here.
PURPOSE: The longissimus (LO) and iliocostalis (IC) of adults consist of myofibers extending from the superolateral to the inferomedial side of the back and, because of the same course, they are fused in the thoracolumbar region. The LO also has a medial attachment to the long myofibers of the transversospinalis (TS) showing a course from the superomedial to the inferolateral side. However, there is apparently no information regarding when and how these similar longitudinal muscles differentiate from a cluster of dorsomedial myotome cells. METHODS: We examined sagittal and horizontal sections of the trunks of 39 human embryos and fetuses (18-330 mm crown-rump length). RESULTS: At 6-7 weeks gestational age (GA), the surface aponeurosis appeared prior to and independent of the thoracolumbar fascia. At 6-9 weeks GA, the LO myofibers had a postero-inferior course, from the transverse process to the initial aponeurosis, whereas the TS myofibers had a postero-superior course, from a lateral extension of the intertransverse ligament to the aponeurosis. However, the IC consisted of supracostal longitudinal myofibers and was distant from the LO until 12 weeks GA. Because of the lack of ligamentous attachments and ribs, myofibers of the TS, LO, and IC took a similar inferior course in the lumbar region. When the early TS was represented by the transverso-aponeurotic muscle, consequently, the LO corresponded to the aponeuro-transversal muscle and was independent from the IC. CONCLUSION: The classical model of TS and LO development does not recognize the essential role of the aponeurosis identified here.
Entities:
Keywords:
Back muscles; Erector spinae aponeurosis; Facial ectoskeleton concept; Human fetus; Iliocostalis; Longissimus
Authors: Hayelom K Mekonen; Jill P J M Hikspoors; Greet Mommen; S Eleonore KÖhler; Wouter H Lamers Journal: Clin Anat Date: 2016-09-28 Impact factor: 2.414