146 



THE SKELETON. 



bone which brings into view the oval expanded orifice of a canal leading into 

 the tympanum, the meatus auditorius externus. This canal is situated between 

 the mastoid process and the posterior and middle roots of the zygoma; its 

 upper margin is smooth and rounded, but the greater part of its circumference 

 is surrounded by a curved plate of bone, the auditory process, the free margin 

 of which is thick and rough, for the attachment of the cartilage of the external 

 ear. 



The apex of the petrous portion, rough and uneven, is received into the 

 angular interval between the spinous process of the sphenoid and the basilar 

 process of the occipital ; it presents the anterior or internal orifice of the 

 carotid canal, and forms the posterior and external boundary of the foramen 

 lacerum medium. 



The anterior surface of the petrous portion (Fig. 98) forms the posterior bound- 

 ary of the middle fossa of the skull. This surface is continuous with the squa- 



Fig. 98. Left Temporal Bone. Inner Surface. 

 *' 



i 



mous portion, to which it is united by a suture, the temporal suture, the remains 

 of which are distinct even at a late period of life. It presents six points for 

 examination. 1. An eminence near the centre, which indicates the situation of 

 the superior vertical semicircular canal. 2. On the other side of this eminence 

 a depression, indicating the position of the tympanum, the layer of bone which 

 separates the tympanum from the cranial cavity being extremely thin. 3. A 

 shallow groove, sometimes double, leading backwards to an oblique opening, 

 the hiatus Fallopii, for the passage of the petrosal branch of the Vidian nerve. 

 4. A smaller opening, occasionally seen external to the latter, for the passage 

 of the smaller petrosal nerve. 5. Near the apex of the bone the termination 

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

 6. Above this canal, a shallow depression for the reception of the Casserian 

 ganglion. 



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



