Muscle fibre types in the external eye muscles of the pigeon, Columba livia.

Fibre typing with antisera raised against specific myosin types from muscles of known physiological properties were used to characterise the fibre types within the oculorotatory muscles of pigeons. Fibres reacting strongly to antiserum anti-ALD (specific for tonic fibre myosin) were found lying along the global margin of the muscle and also in a layer lying immediately beneath a discrete band of fibres running along the orbital margin. These fibres resembled those of the skeletal muscle ALD in their type properties. Using another antiserum, anti-I, specific for slow twitch and to a lesser extent, slow tonic myosins, it was possible to identify another slow fibre type which formed the orbital layer and also lay scattered randomly through the body of the muscle. No equivalent to this type was found in the skeletal muscles ALD or iliofibularis. The remaining fibres which did not react with either anti-ALD or anti-I formed 58% of the fibre population and reacted with an antiserum specific for fast myosin. However, their response to alkali preincubation suggests that the fast fibres of eye muscles also contain a myosin which is different from those in skeletal muscle.