Fig. 39. To show the Relation of a Typical Basic Fracture to the Middle Ear and its Adjuncts. A, Malleus; B, Middle ear and aditus; C, Geniculate ganglion (facial nerve); D, Groove for great superficial petrosal nerve; E, Canal for tensor tympani muscle; F, Processus cochleariformis; G, Eustachian tube; H, External auditory meatus; I, Membrana tympani; J, Mastoid cells.
![[Larger illustration]](#432681327980907716_illo103lg.jpg.id-5953187879040634357.wrap-0.html.html){kind=link}
In the second group of cases a different picture is obtained. Usually the result of blows applied to the occipital region, the fracture traverses the thin cerebellar fossa towards the outer angle of the jugular foramen, thence cutting across the petrous bone, external to the internal auditory meatus, and terminating, usually by comminution, in the tegmen tympani. It is in the transpetrous part of the fracture that the damage is done, for, not only is the facial nerve cut across in the region of the ganglion, but the auditory apparatus is also severed into two parts. The exact line of the fracture is shown in [Figs. 40] and [41].
A
B
Fig. 40. To show the Relation of Basic Fractures to the Petrous Bone. A, The basic fracture, resulting from a force applied to the left occipital region, follows the course depicted in [Fig. 36]. B, The inner half of the petrous bone, being loose, is thrown forward so as to show the relation of the fracture to the integral parts of the petrous bone.
In this class of fracture, though facial paralysis and deafness are both immediate in onset and permanent in duration, there is, in many cases, no bleeding from the ear as the membrana tympani may be uninjured.