6. Force applied to The resultant fracture varies according to the the posterior direction of the applied force. A force which is occipital applied to the posterior occipital region at right region. angles to the transverse axis of the skull results in a fracture which, on reaching the posterior margin of the foramen magnum, is continued again on the opposite side of the foramen along the dorsum ephipii. When the force is more oblique in direction (as is usually the case) the fracture traverses the thin cerebellar fossa to the outer margin of the jugular foramen, and then follows one of the two courses indicated in the previous case. More commonly the fracture cuts across the petrous bone. [Illustration: FIG. 37. DIAGRAM OF LINES PURSUED BY BASIC FRACTURES. Force applied to the posterior occipital region, the fracture following the course _a. a._ or _b. b._, according to the direction of the applied force.] =Summary.= Basic fractures tend to follow certain definite paths, this transbasic course varying according to the direction of the force applied and the site of application of the same. Whether the fracture completely traverses the base depends on the character of the force and the resistance offered, for bases, as well as vaults, vary greatly in strength. To every rule there must be exceptions, and cases are at hand in which the fracture appears to have obeyed no law, or in which the force applied was of so forcible a nature that the fracture traversed the base, regardless of all the ordinary rules. The principles enumerated above were formulated by me some four years ago, and, in spite of certain adverse criticisms, I am more than ever convinced that the rules are correct, and that time and research are alone required to add to the strength of my assertions. SYMPTOMS RESULTING FROM FRACTURE OF THE BASE OF THE SKULL The symptoms resulting from a fracture of the base of the skull vary according to the particular fossa fractured. From a general point of view, the following symptoms require consideration:-- Hæmorrhages. Escape of cerebro-spinal fluid. Escape of brain-matter. Escape of air from the air-sinuses into the surrounding tissues. Involvement of certain cranial nerves. Symptoms pointing to fracture of the Anterior Fossa.