A head fixation device in the form of a skull clamp comprises an opening device having an actuator positioned along an upright portion of the skull clamp near where a pin assembly contacts a patient's head for stabilization. The opening device can be actuated such that the relative distance between arms of the skull clamp can be opened, closed, or adjusted. The opening device is substantially positioned within one of the arms of the skull clamp. In some versions the skull clamp further comprises an attachment feature having an offset configuration.