MORPHOLOGICAL AND HISTOCHEMICAL ASPECTS OF THE EXTRAOCULAR-MUSCLES OFTHE SOUTH-AMERICAN OPOSSUM (DIDELPHIS-ALBIVENTRIS)

The extraocular muscle fibres of the South-American opossum were deter mined according to their metabolic profiles using NADH-diaforase, and myofibrilar ATPase after pre-incubation in both acid (pH 4.3) and alka line (pH 10.4) media. Three muscles were selected to study the arrange ment of the fibres (obliquous dorsalis, rectus dorsalis and rectus lat eralis muscles). It was demonstrated that they are organized in two la yers: the orbital layer composed by small diameter fibres and the glob al layer with three-limes thicker fibres than the former. The global l ayer has three fibre types: white, red and intermediate; while the orb ital layer presents two fibre types, which react differently to the AT Pase.