THE TEMPORAL BONES. 25 



diameter and from two to four lines in depth. At the 

 bottom is placed a vertical, cribriform plate, through 

 which the auditory nerve passes to the labyrinth. At 

 the upper part of the vertical plate is a foramen, about 

 the size of a broom-straw. It leads into a canal called 

 the aquaeductus Fallopii, and transmits the facial nerve. 

 External to the auditory meatus is a canal called the 

 aquaeductus vestibuli, which communicates with the 

 vestibule of the labyrinth and transmits a small vein. 

 A sharp process of bone gives attachment to the dura 

 mater. The inferior surface is very irregular, and pre- 

 sents twelve points for examination. These are placed 

 along the anterior and posterior borders, and a few mid- 

 way between. Those along the posterior border, begin- 

 ning at the apex, are: (1) the quadrilateral rough 

 surface; (2) the aquaeductus cochlea; (3) the jugular 

 fossa, near the anterior portion of which is seen (4) a 

 foramen which transmits the auricular branch of the 

 pneumogastric nerve. External to the jugular fossa is 

 (5) the jugular surface for articulation with the jugular 

 process of the occipital bone. Along the anterior bor- 

 der,, beginning at the apex, we have : the quadri- 

 lateral rough surface ; (6) the opening of the carotid 

 canal ; (7) the vaginal process which passes backward, 

 inclosing (8) the styloid process, posterior to which, and 

 at its base, is observed (9) the stylo-mastoid foramen, 

 the termination of the aquaeductus Fallopii ; external to 

 the stylo-mastoid foramen is (10) the auricular fissure 

 for the transmission of a branch of the pneumogastric 

 nerve ; in the partition between the carotid canal and 

 the jugular fossa is (11) Jacobsen's foramen for the 

 transmission of a branch of the glosso-pharyngeal nerve 

 to the tympanum ; in the angle between the petrous and 

 squamous portions is (12) the Eustachian tube, leading 



