...M. J. Duxson; Y. Usson ABSTRACT Mammalian muscles develop from two populations of myotubes; primary myotubes appear first and are few in number; secondary myotubes appear later and form most of the muscle fibres. We have made an ultrastructural study to investigate how primary and secondary...

.... Soleus and lumbrical muscles in these animals had reduced numbers of muscle fibres, and quantitative examination of embryonic muscles revealed that this was due solely to a decreased formation of secondary myotubes; the number of primary myotubes remained normal. Undernutrition did not affect the number...

...J. J. Ross; M. J. Duxson; A. J. Harris ABSTRACT Numbers of myoblasts, primary myotubes and secondary myotubes in developing rat embryo hindlimb IVth lumbrical muscles were counted at daily intervals up until the time of birth, using electron mi-croscopy. Motoneurone death at the spinal cord level...

... tension measurements showed that all myotubes in partly innervated muscles examined on E21 contracted in response to nerve stimulation. Primary myotubes were formed and maintained at normal numbers in muscles with innervation reduced throughout development, but a diminished number of secondary myotubes...