Embryonic skeletal muscles originate from metameric mesodermal structures called somites, which are formed according to a craniocaudal gradient from the paraxial mesoderm. In addition to providing all of the striated musculature of the body, somites give rise to the dorsal dermis and the axial skeleton. In birds, microsurgical experiments have been performed on newly formed somites to study their derivatives (1 ,2 ). It has been demonstrated that the somite contains a dorsal compartment providing the dermomyotome from which striated muscle and dermis originate and a ventral compartment forming the sclerotome from which the axial skeleton develops (for review,seeref.3 ).
