The skeletal muscles develop from mesenchyme derived from one of the following three sources: somites (and somitomeres), (2) somatic mesoderm of the body wall, and (3) mesenchyme of the pharyngeal arches.
Whatever the source, development of the skeletal muscle is preceded by differentiation of myoblasts from the mesenchyme. The newly formed myoblasts increase in number by mitotic division. The newly formed myoblasts become elongated and continue to form parallel bundles. Adjacent myoblasts then fuse together to form cylindrical structures called myotubes. Each myotube is a mul-tinucleated cell in which the nuclei are
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located at the cell periphery. Myo- der and urethera, etc, also develops from
filaments are formed in the cytoplasm the splanchnic mesoderm. Smooth mus-
of the myotubes during or after the cle in the walls of the blood vessels and
fusion of myoblasts. Soon myofibrils lymphatic vessels arises from the so-
are seen in the cytoplasm and, by the matic mesoderm. As mentioned earlier,
end of the 12th week of develop- the smooth muscle of thfe iris and
ment,characteristic cross-striations myoepithelial cells are derived from ecto-
can be seen in these cells, which are derm.