40 BOXES OF THE HEAD. 



ear. It forms a short canal, the meatus audifornis exfernns, directed 

 inwards and a little forwards, narrower in the middle than at its- 

 extremities, and leading into the cavity of the f//nij)anum, part of 

 which is seen from the exterior in the macerated bone. It is bounded 

 superiorly by the posterior root of the zygoma, and in the remainder of 

 its circumference ehielly by the external aiiditonj jn-ocess, a curved 

 uneven border, to which the cartilage of the ear is attached. This 

 process is the thickened outer extremity of the fj/Dipa/u'c plate, a lamina 

 one surface of which forms the anterior wall of the external auditory 

 meatus and the tympanum, while the other looks towards the glenoid 

 fossa. The upper margin of the tympanic plate is separated from the 

 glenoid fossa by the Jisa are of GJaser, while its lower margin descends as 

 a sharp edge, the vaijhial jirocess, which partly surrounds the front of 

 the styloid process at its base. The styloid process is long and tapering, 

 and is directed doAvnwards and forwards. It is placed in front of the 

 digastric fossa, and has immediately behind it the foramen which forms the 

 outlet of the canalof the facial neiwe, named stijlo-mastuid from its position 

 between the styloid and mastoid processes. A smooth rouncled and. 

 deep depression, the _/'///////«;• /os.sff, lies internal to the styloid process ^ 

 it is close to the posterior margin of the bone, and completes with the 

 jugular notch of the occipital bone the foramen lacerum posterius. lu 

 front and a little to the inside of the jugular fossa is the carotid foramen, . 

 the inferior extremity of the carotid canal; and internal to the carotid 

 foramen is a rough surface which gives attachment to the levator palati 

 muscle, and is continued into the rough inner extremity, or apex of the 

 petrous bone. The carotid canal ascends at first perpendicularly, then 

 turns horizontally forwards and inwards, and emerges at the apex, close 

 to the anterior margin. It transmits the internal carotid artery. In the 

 angle between the petrous and squamous portions of the bone is the 

 anterior opening of the Evstacliian canal. 



The posterior surface looks backwards and inwards, and forms part of 

 the posterior fossa in the base of the skull. It presents a large orifice 

 leading into a short canal which is directed outwards, the mecdus cuidi- 

 torius interniis. This canal is terminated by a plate of bone, the lamina 

 crilirosa, presenting in the loAver part small apertures through which the 

 divisions of the auditory nerve pass, while in its upper part is the com- 

 mencement of the canal called aqaedtict of Fallopius, which transmits 

 the facial nerve. This canal takes a somewhat circuitous course' 

 through the petrous bone, passing outwards and backwards over the 

 labyrinth of the ear, and then downwards to terminate at the stylo- - 

 mastoid foramen. 



The anterior or upper .v/rfare looks upwards and forwards, and forms 

 part of the middle fossa in the base of the skull. A depression near 

 the apex marks the position of the Gasserian ganglion. A narrow- 

 groove runs obliquely backwards and outwards to a foramen named the 

 Jrifffns Falloiiii, which leads to the aqueduct of Fallo]-)ius, and transmits 

 the large superficial petrosal nerve. Farther back is a rounded emi- 

 nence, indicating the situation of the superior semicircular canal. 



The superior harder is grooved for the superior petrosal sinus. The 

 anterior dorder is very short, and forms at its junction with the 

 squamous part an angle in which is situated the orifice of the Eusta- 

 chian canal, the osseous portion of a tube of the same name, which 

 leads from the pharynx to the tympanum ; and above this, partially 



