Final answer:
The fibrils distributed throughout the ventricles, representing the end of the cardiac conduction system, are called Purkinje fibers.
Step-by-step explanation:
The thousands of fibrils distributed throughout the ventricles, which represent the end of the cardiac conduction system, are called the Purkinje fibers. These fibers are specialized myocardial conduction fibers that arise from the bundle branches and spread the impulse to the myocardial contraction fibers of the ventricles.