4. Force applied to The fracture follows the occipito-mastoid suture the mastoid region. to the jugular foramen, and is again continued on the opposite side of that foramen along the petro-occipital suture towards the apex of the petrous bone. It then passes across the sphenoidal body to the sphenoidal fissure of the opposite side, and so across the anterior fossa. It is especially common in this particular variety of fracture to find fissures diverging from the region of the sphenoidal sinus forwards towards the cribriform plate of the ethmoid, these fissures usually passing between the optic foramina. This fracture is also peculiar in so much that, when the degree of separation along the occipito-mastoid suture is excessive, there is special liability to a tearing of the lateral sinus wall as the sinus begins to turn downwards and inwards. [Illustration: FIG. 35. DIAGRAM OF LINES PURSUED BY BASIC FRACTURES. Force applied to the mastoid region.] 5. Force applied to The fracture passes across the thin cerebellar the lateral fossa and strikes the foramen magnum immediately occipital region. behind the condyle. Starting again from a similar point on the opposite side of the foramen, the fracture passes outwards to the jugular foramen. Again, two courses are now available, the fracture either cutting outwards across the body of the petrous, ‘external’ to the internal auditory meatus and cutting across the facial nerve in the region of the geniculate ganglion, and finally terminating in the roof of the middle ear, or else passing along the petro-occipital suture and so to the foramen lacerum medium, the sphenoidal fissure, and the anterior fossa as in the previous case. [Illustration: FIG. 36. DIAGRAM OF LINES PURSUED BY BASIC FRACTURES. Force applied to the lateral occipital region.]