A COMPARATIVE MORPHOLOGIQAL STUDY OF THE AXIAL MUSCULATURE IN THE PELVIC REGIONS OF ACONTIAS PLUMBEUS AND MABUYA CAPENSIS (REPTILIA: SCINCIDAE), WITH REFERENCE TO THEIR RESPECTIVE MODES OF LOCOMOTION

Abstract

The epaxial musculature of the limbless, subterrestrial Acontias plumbeus is better developed than that of the normal limbed Mabuya capensis. This correlates with the fact that locomotion in the former is completely axial whereas that of the latter is primarily appendicular. The increase in cross-sectional area of the epaxial musculature in A. plumbeus has been accompanied by a decrease in the cross-sectional areas of its hypaxial musculature, visceral cavity, and vertebrae. This prevented the development of a body with a relatively large diameter which would have made subterrestrial locomotion energetically more costly. The hypaxial musculature of M. capensis, which is better developed than that of A. plumbeus, not only protects the viscera but also assists in keeping the body suspended between the two girdles during locomotion. In A. plumbeus the body rests on the substrate and the function of its hypaxial musculature is therefore essentially only to protect the viscera.