In civil actions, where the burden of proof rests with the plaintiff, the plaintiff is entitled to the opening and concluding arguments except that if the defendant introduces no evidence or admits a prima-facie case, the defendant shall be entitled to open and conclude. In civil actions for personal injuries, the defendant shall be deemed not to have admitted a prima-facie case if such defendant introduces any evidence as to the extent of damages, other than cross-examination of the plaintiff and witnesses called by the plaintiff.