Some of the celebrated surgeons of the last century insisted that the course pursued by basic fractures was to be explained on anatomical grounds, but their views have been neglected and theories based on experimental evidence have been accepted in their place. All experiments, such as those previously mentioned, are useless, and definite conclusions can only be gained by carrying out in every case the following method of investigation: (1) by obtaining in the first case an accurate history as to the manner in which the injury was received; (2) by noting all visible and palpable signs of external injury; (3) by careful observation of all the clinical symptoms during the progress of the case; (4) by comparison of such with the lesions found in case of death. Over 300 cases have been investigated by me after these principles. In about 30 per cent. of the cases sufficient evidence was obtained to show that the basic fracture resulted and extended from a primary fracture of the vault. These cases were to be explained by Aran’s theory of irradiation. This theory, however, errs in stating further that the fracture follows the shortest anatomical route to the base. This is not correct, for the line of fracture corresponds to the direction of the applied force and is influenced to a very large extent by the resistance offered, the weaker areas being picked out and the strong buttresses avoided. It is only in the most severe cases that the fracture travels to and traverses across the base in such a direction as to show that, for the time being, all laws are in abeyance. In about 5 per cent. of cases the fracture resulted from bilateral compression, from falls on to the buttocks, &c., and from blows applied to the angle of the jaw. These cases afforded examples of the bursting and compression theories. On the other hand, in over 60 per cent. of cases, the injury was received over one of the following situations: (1) in front, over the frontal eminence or supra-orbital ridges; (2) in the antero-lateral region, over the external angular frontal process; (3) in the lateral region, over the lower temporal, auricular, and mastoid regions; (4) in the posterior region, over the superior curved line of the occipital bone or over the external occipital protuberance. In all these cases, therefore, the blow was inflicted at or near the level of the base of the skull, the resultant fracture being a fracture by direct violence, the fracture traversing the base and splitting it much in the same way as a chisel splits a board of wood. The ‘grain’ of the wood may be regarded as representing the weaker basic lines, and any ‘knot’ the resistance offered by the strong basic buttresses, the forces being momentarily turned aside, but soon again passing onwards, parallel to the original direction, but not necessarily in the same straight line.