The dorsal axial musculature of certain primitive permian tetrapods

The development of the dorsal axial musculature is traced from Eryops, through Diadectes, to Dimetrodon. lguana, a modern form, is used for comparison. The axial muscles of a primitive form, such as Eryops, were thick, fleshy, and metameric; those of more advanced types, such as Dimetrodon, were light, highly tendinous, and largely unsegmented. Diadectes represents an intermediate stage. The changes in the muscles and related changes in the axial skeleton are closelyassociated with the development of active, terrestrial animals.