38 TEMPORAL BONE. 



applied against the internal surface of the squamous and mastoid 

 portions, and the apex being received into the triangular interval be- 

 tween the spinous process of the sphenoid and basilar process of the 

 occipital bone. For convenience of description it is divisible into 

 three surfaces anterior, posterior, and basilar ; and three borders 

 superior, anterior, and posterior. 



Surfaces. The anterior surface, forming the posterior boundary 



of the middle fossa of the interior 

 Fi - 15 * of the base of the skull, presents 



for examination from base to apex, 

 first an eminence caused by the 

 projection of the perpendicular se- 

 micircular canal ; next, a groove 

 leading to an irregular oblique 

 opening the hiatus Fallopii for 

 the transmission of the petrosal 

 branch of the Vidian nerve ; 

 thirdly, another and smaller ob- 

 lique foramen, immediately be- 

 neath the preceding, for the pas- 

 sage of the nervus petrosus su- 

 perficialis minor, a branch of 



Jacobson's nerve ; and lastly a large foramen near the apex of the 

 bone, the termination of ttye carotid canal. 



The posterior surface forms the front boundary of the posterior 

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

 of the meatus audilorius internus. The meatus pursues a course 

 directly outwards ; it is about one-third of an inch in length, and 

 terminates in two deep depressions (nearly one-eighth of an inch in 

 depth) separated by a sharp, horizontal ridge. The superior depres- 

 sion, the smaller of the two, is divided at its extremity, by a vertical 

 ridge, into an anterior portion, which is the commencement of the 

 aquasductus Fallopii, for the transmission of the facial nerve ; and 

 a posterior portion which corresponds with the upper part of the 

 inner wall of the vestibule, and is pierced by numerous openings for 



* 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 magna. 5. The bevelled edge of the squamous border of the 

 bone. 6. The zygoma. 7. The digastric fossa immediately internal to the mastoid 

 process. 8. The occipital groove. 9. The groove for the lateral sinus. 10. The ele- 

 vation upon the anterior surface of the petrous bone marking the situation of the per- 

 pendicular semicircular canal. 11. The opening of termination of the carotid canal. 

 12. The meatus auditorius internus. 13. A dotted line leads upwards from this number to 

 the narrow fissure which lodges a process of the dura mater. Another line leads down- 

 wards to the sharp edge which conceals the opening of the aquseductus cochleae, while 

 the number itself is situated on the bony lamina which overlies the opening of the 

 aquffiductus vestibuli. 14. The styloid process. 15. The stvlo-mastoid 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 vein 

 of the cochlea. 18. The notch for the fifth nerve upon the upper border of the petrous 

 bone, near to its apex. 19. The extremity of the pelrous bone which gives origin to 

 the levator palati and tensor tympani muscles. 



