What are the functions of “expert witnesses” in medical malpractice cases?

As to the function of “expert witnesses” Anderson v. Chasney, 1949 CanLII 236 (MB CA), [1949] 4 D.L.R. 71, deals with what I accept as the law where Coyne, J.A., at p. 81 says: “His counsel argued that if a general practice of surgeons is followed, negligence cannot be attributed, and that expert evidence is conclusive. But if that were correct the expert witnesses, would, in effect, be the jury to try the question of negligence. That question however, must continue to be one for the petit jury empanelled to try the case if it is a jury case, and for the court where it is not. The experts remain witnesses to give their expert opinions in assistance of the jury or the court to determine whether there is negligence or not. The opinions of experts are not conclusive.”