Hitherto unknown detailed muscle anatomy in an 8‐week‐old embryo

Abstract

Congenital muscle diseases, such as myopathies or dystrophies, occur relatively frequently, with estimated incidences of up to 4.7 per 100 000 newborns. To diagnose congenital diseases in the early stages of pregnancy, and to interpret the results of increasingly advanced in utero imaging techniques, a profound knowledge of normal human morphological development of the locomotor system and the nervous system is necessary. Muscular development, however, is an often neglected topic or is only described in a general way in embryology textbooks and papers. To provide the required detailed and updated comprehensive picture of embryologic muscular anatomy, three‐dimensional (3D) reconstructions were created based on serial histological sections of a human embryo at Carnegie stage 23 (8 weeks of development, crown–rump length of 23.8 mm), using amira reconstruction software. Reconstructed muscles, tendons, bones and nerves were exported in a 3D‐PDF file to permit interactive viewing. Almost all adult skeletal muscles of the trunk and limbs could be individually identified in their relative adult position. The pectoralis major muscle was divided in three separate muscle heads. The reconstructions showed remarkable highly developed extraocular, infrahyoid and suprahyoid muscles at this age but surprisingly also absence of the facial muscles that have been described to be present at this stage of development. The overall stage of muscle development suggests heterochrony of skeletal muscle development. Several individual muscle groups were found to be developed earlier and in more detail than described in current literature.

Return of the intestinal loop to the abdominal coelom after physiological umbilical herniation in the early fetal period

“…; Warmbrunn et al. ). However, the bilateral rectus muscles are still separated in the midsagittal region, from which the umbilical cord arises.…”

“…The abdominal wall should grow sufficiently before it returns, to prepare for rapid abdominal expansion (Mall, 1898). The elasticity of the abdomen may be limited in the craniocaudal and latero-lateral directions, as the abdominal muscles such as the rectus and external and internal oblique muscles develop before the return phase Warmbrunn et al 2018). However, the bilateral rectus muscles are still separated in the midsagittal region, from which the umbilical cord arises.…”

Complete Adipose Replacement of Bilateral Medial Gastrocnemius Muscle - A Cadaveric Case Report

“…[1,10] Embryologically, skeletal muscles, including the GM, derive from the paraxial mesoderm. [12] As a part of mesoderm of an embryo, the mesenchyme can be found throughout the whole life span and is able to develop into connective tissues like muscles and adipose tissues, cartilage, and bones. [13] Adipose tissue comprises adipose stem cells, adipocytes, and various other cells; and can deposit in various places of human body including skeletal muscles.…”

“…Literature has exerted that adipocytes exist in skeletal muscles and the number of these cells can increase if the muscle is injured. [6,12] However, it is still unknown which and how a specific muscle or muscles would respond more to the injury. Sartorius is a slender strap muscle with parallel muscle fiber arrangement, while the gastrocnemius is a big and wide pennate muscle with feather-like fiber arrangement, indicating adipose tissue infiltration very likely into the original muscle cells.…”

Relationship between rectal abdominis muscle position and physiological umbilical herniation and return: A morphological and morphometric study

“…The RAM formed distinct bundles of muscle at CS21. The RAM reached the umbilicus at CS23 (8 weeks), in which myotube formation was observed histologically (Mekonen, Hikspoors, Mommen, Köhler, & Lamers, 2015; Nichol et al, 2012; Warmbrunn, de Bakker, Hagoort, Alefs‐de Bakker, & Oostra, 2018). Finally, the RAM extends between the rib cage and pubis.…”