TEMPORAL BONE. 



31 



hardness and density. It is a three-sided pyramid, projecting hori- 

 zontally forwards into the base of the skull, the base being applied 

 against the internal surface of the squamous and mastoid portions, and 

 the apex being received into the triangular interval between the spi- 

 nous process of the sphenoid and the basilar process of the occipital 

 bone. For convenience of description it is divisible into three sur- 

 faces anterior, posterior,i and basilar ; and three borders superior, 

 anterior, and posterior. 



Surfaces. The anterior surface, forming the posterior boundary 

 of the middle fossa of the interior of the base of the skull, presents for 

 examination from base to apex, first, an eminence caused by the pro- 

 jection of the perpendicular semicircular canal ; next, a groove lead- 

 ing to an irregular oblique opening, the hiatus Fallopii, for the 

 transmission of the pe- 

 trosal branch of the 

 Vidian nerve ; thirdly, 

 another and smaller 

 oblique foramen, imme- 

 diately beneath the pre- 

 ceding, for the passage 

 of the nervus petrosus 

 superficialis minor, a 

 branch of Jacobson's 



nerve ; and lastly, a 

 large foramen near the 

 apex of the bone, the 

 termination of the caro- 

 tid canal. 



The posterior surface 

 forms the front boun- 

 dary of the posterior 

 fossa of the base of the skull ; near its middle is the oblique entrance 



* The left temporal bone, seen from within. 1. The squamous portion. 2. 

 The mastoid portion. The number is placed immediately above the inner 

 opening of the mastoid foramen. 3. The petrous portion. 4. The groove for 

 the posterior branch of the arteria meningea media. 5. The bevelled edge of 

 the squamous border of the bone. 6. The zygoma. 7. The digastric fossa im- 

 mediately internal to the mastoid process. 8. The occipital groove. 9. The 

 groove for the lateral sinus. 10. The elevation upon the anterior surface of 

 the petrous bone marking the situation of the perpendicular semicircular canal. 

 11. The opening of termination of the carotid canal. 12. The meatus audito- 

 rius internus, 13. A dotted line leads upwards from this number to the nar- 

 row fissure which lodges a process of the dura mater. Another line leads 

 downwards to the sharp edge which conceals the opening of the aquaeductus 

 cochleae, while the number itself is situated on the bony lamina which overlies 

 the opening of the aquaeductus vestibuli. 14. The styloid process. 15. The 

 stylo-niastoid foramen. 16. The carotid foramen. 17. The jugular process. 

 The deep excavation to the left of this process forms part of the jugular fossa, 

 and that to the right is the groove for the eighth pair of nerves. 18. The notch 

 for the fifth nerve upon the upper border of the petrous bone, near to its apex. 

 19. The extremity of the petrous bone which gives origin to the levator palati 

 and tensor tympani muscles. 



