Some histochemical properties of the fiber types in the pectoralis muscle of an emu (Dromaius novaehollandiae)

The muscle fibers of the cranial slip of M. pectoralis pars thoracica of an emu (Dromaius novaehollandiae) were studied histochemically for intracellular lipid, succinic dehydrogenase, myofibrillar adenosine triphosphatase, and acetylcholinesterase. It was concluded that the muscle consisted of approximately 28% slow‐tonic and 72% fast‐twitch glycolytic fibers. The tonic fibers were considered to be characteristic of a postural muscle, and the fasttwitch glycolytic fibers to reflect the inability of the muscle to engage in sustained activity. The general absence of slow‐tonic fibers from the pectoralis of other avian species so far studied may be attributed to inadequate sampling of the deeper regions of the muscle.