THE ONTOGENETIC DEVELOPMENT OF THE SOMATIC MUSCULATURE OF THE TRUNK OF THE AGLOSSAL ANURAN XENOPUS LAEVIS (DAUDIN)

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Abstract
The secondary somatic muscles of the trunk develop by means of proliferations from the primary muscles. The dorsal part of the “Urwirbelfortsatz” contains the elements of both the m. obliquus abdominis internus and m. obliquus abd. externus. The m. ileolumbalis of the adult is formed by the fusion of the m. ileolumbalis, pars medialis and pars lateralis. A separate m. coccygeo‐sacralis is present in the young post‐metamorphic stage. A true horizontal myoseptum is absent. A well‐developed m. rectus abdominis superficialis can be distinguished during metamorphosis and even in the young post‐metamorphic stage. The ontogenesis proves the allegedly primitive features concerning the m. rectus abdominis, the m. ileolumbalis and the m. coccygeo‐sacralis to be specializations. Xenopus must be regarded as a very specialized anuran.