Define the following terms and give their location:
$(a)$ Purkinje fibres
$(b)$ Bundle of His

(N/A) Purkinje fibres: These are specialized cardiac muscle fibres that conduct electrical impulses from the $AV$ node to the ventricular myocardium. They are located in the subendocardial surface of the ventricular walls.
$(b)$ Bundle of His: This is a collection of heart muscle cells specialized for electrical conduction that transmits the electrical impulses from the $AV$ node to the point of the apex of the fascicular branches. It is located in the interventricular septum of the heart.