POSTNATAL-DEVELOPMENT OF SEMITENDINOSUS MUSCLE IN THE DOG

In this study the differentiation of postnatal muscle fibres in dog se mitendinosus muscle has been characterized. Several histochemical tech niques for myosin ATPase and metabolic activity were used in animals a ged between 1 day and 2 months. The results show that at birth there a re two types of fibre, whose ATPase activity gradually changes during postnatal development, so that several types of fibre can be identifie d after 2 months. These finally become the four types of the adult: I, IIA, IIDog, IIC. The main conclusions of the study are that the use o f mATPase techniques is appropriate for showing the differentiation be tween muscle fibres, even at early stages of postnatal development, an d that the origin of the four different fibres of the adult can be tra ced back to early postnatal stages.