70 



OSTEOLOGY. 



smaller petrosal nerve. 5. Near tine apex of the bone is seen the termination of 

 the carotid canal, the wall of which in this situation is deficient in front. 6. Above 

 this canal is a shallow depression for the reception of the Casserian ganglion. 



The posterior surface forms the front boundary of the posterior fossa of the 

 skull, and is continuous with the inner surface of the mastoid portion of the bone. 

 It presents three points for examination. 1. About its centre is a large orifice, 

 the meatus auditorius internus. This aperture varies considerably in size ; its 

 margins are smooth and rounded; and it leads into a short canal, about four lines 

 in length, which runs directly outwards. The end of the canal is closed by a 

 vertical plate, divided by a horizontal crest into two unequal portions. It trans- 

 mits the auditory and facial nerves, and auditory artery. 2. Behind the meatus 

 auditorius is a small slit, almost hidden by a thin plate of bone, leading to a 

 canal, the aquaeductus vestibuli ; it transmits a small artery and vein, and lodges 

 a process of the dura mater. 3. In the interval between these two openings, but 



Fig. 32. Petrous Portion. Inferior Surface. 



"F^y f carotid wnd 

 Canalfor Jaco^on's aervf 



or Arnold'* n 



Jit<fitf<ar fvssa 

 Vaginal jjrocett 

 jStylaid process 

 Stylo- mastoij foramen 

 Juyii.la,r Surface 

 Auricular 



above them, is an angular depression which lodges a process of the dura mater, 

 and transmits a small vein into the cancellous tissue of the bone. 



The inferior or lasilar surface (fig. 32) is rough and irregular, and forms part 

 of the base of the skull. Passing from the apex to the base, this surface presents 

 eleven points for examination. 1. A rough surface, quadrilateral in form, which 

 serves partly for the attachment of the Levator palati, and Tensor tympani muscles. 

 2. The opening of the carotid canal, a large circular aperture, which ascends at 

 first vertically upwards, and then, making a bend, runs horizontally forwards and 

 inwards. It transmits the internal carotid artery, and the carotid plexus. 3. The 

 aquseductus cochleae, a small triangular opening, lying on the inner side of the 

 latter, close to the posterior border of the petrous portion ; it transmits a vein from 

 the cochlea, which joins the internal jugular. 4. Behind these openings is a deep 

 depression, the jugular fossa, which varies in depth and size in different skulls; it 



