The embryonic development of skeleton and muscles of the shoulder girdle was studied in two turtles: Emys orbicularis (Emydidae) and Trionyx sinensis (Trionychidae). The skeletal muscles and ligaments, being fixed on the dermis, were found to play an important role in the formation and growth of dermal ossification. The morphological variability of the epiplastra and entoplastron correlate with differences in the structure of the turtle muscular system. The morphogenetic processes responsible for an uncommon shape of ento- and epiplastrons of Trionychidae are described. A hypothesis of a unique origin of the plastra plates in species of this family is not confirmed by the data oh ontogenesis.