66 



TEMPORAL BONE. 



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 



Fig. 29. 



Fig. 30.t 



auditorius internus. Above the meatus 

 auditori us internus is a small oblique fis- 

 sure, and a minute foramen ; the former 

 lodges a process of the dura mater, arid 

 the foramen gives passage to a small vein. 

 Further outwards, towards the mastoid 

 portion of the bone, is a small slit, 

 almost hidden by a thin plate of bone ; 

 this is the aqu&ductus vestibuli, and 

 transmits a small artery and vein of the 

 vestibule and a process of dura mater. 

 Below the meatus, and partly concealed 

 by the margin of the posterior border of 

 the bone, is the aquceductus cochlea, 

 through which passes a vein from the cochlea to the internal jugular vein, 

 and a process of dura mater. 



The meatus auditorius internus is about one-third of an inch in depth, 

 and pursues a slightlv oblique course in relation to the petrous portion of 



the temporal bone, but a course directly out- 

 wards in relation to the cranium. At the bot- 

 tom of the meatus, and upon its anterior as- 

 pect, is a reniform fossa, the concave border 

 of which is directed towards the entrance of 

 the meatus. The reniform fossa is divided 

 into an upper and lower compartment by a 

 sharp ridge, which is prolonged for some dis- 

 tance upon the anterior wall of the meatus, 

 and sometimes as far as its aperture ; in either 

 case it marks the situation of the two nerves, 

 facial and auditory, which constitute the se- 

 venth pair, awJ enter the meatus. Along the convexity of the reniform 

 fossa, and arnrfiged in a curved line from above downwards, are four or 



* 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 

 rrnistoid 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 immediately internal to the mastoid process. 

 8. The occipital groove. 9. The groove for the lateral sinus. 10. The elevation upon 

 tne anterior surface of the petrous bone marking the situation of the perpendicular semi- 

 circular 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 downwards to 

 the sharp edge which conceals the opening of the aquseductus cochlea?, while the num- 

 ber itself is situated on the bony lamina which overlies the opening of the aqua'ductiis 

 vestibuli. 14. The styloid process. 15. The stylo-mastoid foramen. 1C. The carotid 

 Jbramen. 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, 

 hear its apex. 19. The extremity of the petrous bone which gives origin to the levator 

 j,!ati and tensor tympani muscles. 



IA. The reniform fossa of the meatus auditorius internus; right temporal bone. 



The ridge dividing the reniform fossa into two compartments. 2. The opening of 

 ti* aquieductus Fallopii. The openings following that of the aquseductus Fallopii in 

 u curved direction require no reference. 3. The cluster of three or four oblique 



