Background : It has been recognized that most skeletal muscle develops before birth, and almost
;. all the remainder is formed by the end of the first year in human. However, controversies on the origin and development of the limb muscles still remain, and furthermore, morphometric informations are extremely rare. Therefore, the authors performed this study to determine the developmental (or growth) pattern of the limb muscle; especially the Sartorius muscle.
Materials and Methods .; 5gm-thick paraffin sections of the Sartorius muscles, obtained from 44 normally developed` human fetuses of either sex aged between 17 and 36 weeks gestation, stained with routine hematoxylin and eosin or PAS(periodic acid-Schiff) reaction were used for light microscopy and morphometric analysis. The thickness of muscle fiber was measured, and the number of muscle fibers per unit area(2,025 grri) and the number(of nuclei) of satellite cells of the muscle fibers per unit area(6,860pM) were counted according to the method of Aherne and Dunnill(1982). Linear regression_ analysis was performed and p values less than 0.01 were considered to be statistically significant.
Results : Muscle fibers which composed of myofibrils were coarsely embedded in loose mesenchy-Mal connective tissue between 17 and 19 weeks gestation. Muscle fibers and surrounding connective tissue were dense with fetal age and showed characteristic features including cross striation as seen in the skeletal muscle fibers of an adult by 24-28 weeks gestation. Relatively well developed blood vessels and nerve endings appreared in the connective tissue. Nerve -endings seemed to be in
close relation with the muscle fibers with fetal age. Statellite cells of the muscle fibers were ! mononucleated and had heterochromatins. The number of satellite cells per unit area was constant with fetal age (p> 0.1), however, the number of muscle fibers per unit area decreased and the thickness of muscle fiber increased with fetal age (p G 0.01).
Conclusion It is likely that most limb muscle fibers complete their morphogenensis before birth between 24 and 28 weeks gestation and then grow mainly by hypertrophy of the intracellular structures in close relation with extracellula.r matrix and nerve endings.
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