The development of the Purkinje fibre system in the bovine fetal heart.

In the bovine fetal heart, subendocardial bundles of cells could be distinguished from the main myocardial mass. Their morphological characteristics suggest that they represent bundles of Purkinje fibres. An intense fluorescence after incubation in antisera against the intermediate filament protein skeletin also supports this suggestion. Further, the bundles exhibited different histochemical reaction from the main myocardial mass. During development the histochemical pattern changed. Bundle cells in mitosis were observed. With increasing fetal age, binucleate cells were seen progressively more frequently. Our observations indicate that the Purkinje fibres differentiate along a line separate from the ordinary myocardial cells and that they acquire their adult characteristics gradually.