BONES OF THE SKULL. 



sellae); the angles of the ridge project anteriorly and exter- 

 nally as tubercles (posterior clinoid processes). [169] 



More laterally the posterior angles of the lesser sphenoidal 

 wings project (anterior clinoid processes) backward. Just be- 

 hind the optic foramen an S-shaped (carotid) groove descends 

 on the side of the body of the sphenoid to an orifice (carotid 

 canal) , in the apex of the petrous temporal, which opens into 

 the foramen lacerum medium, an irregular aperture. Just ex- 

 ternal to this foramen is an oval one (foramen ovale) , and just 

 external to and behind this is a small one (foramen spinosum) . 

 There is a large cleft (sphenoidal fissure) anteriorly between 

 the wings of the sphenoid; just below its inner end is an open- 

 ing (foramen rotundum) into the spheno-maxillary fossa; be- 

 hind this foramen is a small one (foramen Vesalii). [169] 



The superior, or anterior, surface of the petrous temporal 

 presents near its apex a depression for the Gasserian ganglion. 

 Near its centre is an elevation (arcuate eminence) over the su- 

 perior semicircular canal. Just in front of this is a slit-like 

 opening (hiatus Fallopii), of the aqueductus Fallopii, which 

 presents two foramina at its bottom; a groove leads from the 

 hiatus to the foramen lacerum medium. Just external to the 

 hiatus is a small foramen, for the lesser superficial petrosal 

 nerve. Behind this, and in front of the eminence, is the thin 

 roof (tegmen tympani) of the tympanum. [169] 



Posterior Fossa. This is the largest and lies behind the pos- 

 terior clinoid processes and superior borders of the petrous 

 bones. The foramen magnum pierces the floor in the midline; 

 on either side of this is a foramen (anterior condylic) ; over- 

 hanging and external to this is a rounded bridge of bone (tu- 

 berculum jugulare). External to this is an irregular opening 

 (jugular foramen), which may be divided by a projection 

 (processus intra-jugulare) . Behind this, and close to the fora- 

 men magnum, there may be another foramen (posterior con- 

 dylic). [170] 



The petrous temporal presents on its posterior surface the 



[15] 



