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Updated: Apr 15, 2026

Method to Measure Tone of Axial and Proximal Muscle
Published on: December 14, 2011
Ontogenetic changes of trunk muscle structure in the Japanese black salamander (Hynobius nigrescens)
Ayano Omura1, Wataru Anzai, Daisuke Koyabu
1Graduate School of Agricultural and Life Sciences, The University Museum, The University of Tokyo, 7-3-1 Hongo, Bunkyo-ku, Tokyo 113-0033, Japan.
Abstract:
We investigated ontogenetic changes in the trunk muscles of the Japanese black salamander (Hynobius nigrescens) before, during and after metamorphosis. Given that amphibians change their locomotive patterns with metamorphosis, we hypothesized that they may also change the structure of their trunk muscles. The trunk muscles were macroscopically observed, and the weight ratios of each trunk muscle group were quantified at six different developmental stages. Immediately after hatching, we found that the lateral hypaxial muscle was composed of one thick M. ventralis, from ventral edge of which M. transversus abdominis arose later, followed by M. obliquus externus and M. rectus abdominis. The weight ratios of the dorsal and abdominal muscles to the trunk muscles increased with growth. We suggest that a single thick and large lateral hypaxial muscle facilitates swimming during early developmental stages. The increase in the weight ratios of the dorsal and abdominal muscles with growth possibly assists with gravity resistance necessary for terrestrial life.
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