There are many warnings of the danger of opening the skull, and of the necessity for definitely deciding beforehand that there is good reason for so doing. How carefully their observation had been made, and how well they had taken advantage of their opportunities, which were, of course, very frequent in those warlike times when firearms were unknown, hand-to-hand conflict common, and blunt weapons were often used, can be appreciated very well from some of the directions. For instance, they knew of the possibility of fracture by _contrecoup_. They say that "quite frequently, though the percussion comes in the anterior part of the cranium, the cranium is fractured on the opposite part." They even seem to have known of accidents such as we now discuss in connection with the laceration of the middle meningeal artery. They warn surgeons of the possibilities of these cases. They tell the story of "a youth who had a very small wound made by a thrown stone, and there seemed no serious results or bad signs. He died the next day, however. His cranium was opened, and a large amount of black blood was found coagulated about his dura mater." There are many interesting things said with regard to depressed fractures and the necessity for elevating the bone. If the depressed portion is wedged, then an opening should be made with the trephine, and an elevating instrument called a spatumen used to relieve the pressure. Great care should be taken, however, in carrying out this procedure, lest the bone of the cranium itself, in being lifted, should injure the soft structures within. The dura mater should be carefully protected from injury as well as the pia. Care should especially be exercised at the brow, and the rear of the head, and at the commissures (_proram et pupim et commissuras_), since at these points the dura mater is likely to be adherent. Perhaps the most striking expression, the word "infect" being italicized by Gurlt, is: "In elevating the cranium, be solicitous lest you should _infect_ or injure the dura mater."