Distribution of muscle fibre types in the thoracic and lumbar epaxial muscles of Japanese macaques (Macaca fuscata)

Histochemical properties are investigated in the thoracic and lumbar epaxial muscles of Japanese macaques, Macaca fuscata. Whole transverse sections of the muscles were removed at the different levels of the thoracic and lumbar vertebrae and muscle fibre types were classified into type I and type II fibres on the basis of their histochemical profiles. In the lumbar region the iliocostalis and longissimus muscles have many type II fibres. In the thoracic region the iliocostalis muscle has more type I fibres than the longissimus muscle. The intermammillares and mammilloaccessorii muscles which lie medially and deep to the longissimus muscle in the lumbar region have an extremely large number of type I fibres. These differences in the distribution of muscle fibre types among and within muscles suggest that functional differentiation exists among and within the muscles.