(_d_) Forces applied to the occipital region travel inwards along the internal occipital crest to the strengthened margins of the foramen magnum, or are projected outwards along the lateral sinus ridges. In the former case, the force either passes forwards towards the dorsum ephipii and so again reaches the posterior clinoid process, or is directed more laterally towards the jugular process of the occipital bone, there meeting the fibrous tissue intervening between that process and the corresponding part of the temporal bone. 4. All forces, whether transmitted along the internal occipital crest, the temporal bone, the sphenoidal wings, or the crista galli of the ethmoid, are further transmitted to the dura mater attached to those prominences and ridges. The dura mater undoubtedly plays an important part in the reception and transmission of the forces. 5. The forces all show a tendency to converge towards the pituitary region, the great ‘water-cushion’ of the brain--a region bounded by the clinoid processes. That these processes receive a considerable part of the forces transmitted is confirmed by the fact that they are frequently torn away from their basic attachments. This is especially the case with respect to the attenuated base of the anterior clinoid process. It is obvious, therefore, that forces tend to be transmitted from the vault to the base, and yet the base is, in many respects, the weakest part of the skull. It is perforated by numerous foramina, it is hollowed out in places for the formation of air sinuses and for the reception of the integral portions of the auditory apparatus. Furthermore, it presents a more or less plane surface, one differing in all respects from the marked convexity of the vault. Those forces, therefore, which are received by the base of the skull are not subjected to that diffusion which forms so conspicuous a feature in the case of the vault. All these points tend to show that the base of the skull is more or less unsuited for the reception of severe blows, direct or transmitted, whilst, on the other hand, nature has taken into consideration and provided fairly adequately against the dangers incident to vault injuries. It is not proposed at this stage to discuss further the relative strength of vault and base. Points, other than those already enumerated, will be brought forward in subsequent sections. FRACTURES OF THE BASE OF THE SKULL Fractures of the base of the skull are produced in two ways:-- 1. By violence applied _directly_ to the base--perforating wounds of the orbit, bullet-wounds through the mouth and base of skull, the driving inwards of the bones of the face, the driving upwards of the condyle of the jaw (the ‘knock-out’ blow of the pugilist), and, as the result of heavy falls on to the feet or buttocks, the upward driving of the condyles of the occipital bone.