The histochemistry of the posterior cricoarytenoid (PCA) muscle in the dog, compared with the diaphragm, the sternothyroid and the sternomastoid muscle.

The canine posterior cricoarytenoid (PCA) muscle was compared histochemically with pieces of the diaphragm (Dia), an infrahyoid muscle (the sternothyroid, ST), and with a reference skeletal muscle (the sternomastoid, SM) taken from the same animal. The muscle fibre type composition in the PCA, Dia and ST differed very little and showed a slight type II preponderance. In the SM there was a strong type II preponderance. A subgrouping of the type II muscle fibres could not be carried out in any of the muscles. The oxidative activity was greater in the PCA than in the other three muscles and greater in type I than in type II fibres for all muscles except the Dia. In the Dia, some type I fibres had a larger cross-sectional area and showed a greater oxidative activity and contained less glycogen than the rest of the type I fibres in the muscle. These fibres seemed to represent a separate subgroup of type I fibres possibly serving quiet respiration.