70 



lateral sinus, and, with a similar depression on the margin of the jugular process 

 of the occipital bone, forms the foramen lacerum posterius or jugular foramen ; 

 5, a small foramen for the passage of Jacobson's nerve (the tympanic branch of 

 the glosso-pharyngeal) : this foramen is seen in front of the bony ridge dividing 



Canals for Eustachian tube and 



Rough quadrilateral surface. 



Opening of carotid canal. 



Canal for Jacobson's nerve. 



Aquseductus cochlese. 



Canal for Arnold's nerve. 



Jugular fossa. 



Vaginal process. 



Styloid process. 

 Stylo-mastoid foramen 

 Jugular surface. 

 Auricular fissure, 



STYLO-PHARYNGEUS 



FIG. 35. Petrous portion. Inferior surface. 



the carotid canal from the jugular fossa ; 6, a small foramen on the wall of the 

 jugular fossa, for the entrance of the auricular branch of the pneumogastric 

 (Arnold's) nerve ; 7, behind the jugular fossa a smooth, square-shaped facet, the 

 jugular surface ; it is covered with cartilage in the recent state, and articulates 

 with the jugular process of the occipital bone ; 8, the vaginal process, a very 

 broad, sheath-like plate of bone, which extends backward from the carotid canal and 

 gives attachment to part of the Tensor palati muscle ; this plate divides behind 

 into two laminae, the outer of which is continuous with the tympanic plate, the 

 inner with the jugular process; 9, between these laminae is the ninth point for 

 examination, the styloid process, a sharp spine, about an inch in length : it is 

 directed downward, forward, and inward, varies in size and shape, and sometimes 

 consists of several pieces united by cartilage; it affords attachment to three 

 muscles, the Stylo-pharyngeus, Stylo-hyoideus, and Stylo-glossus, and two liga- 

 ments, the stylo-hyoid and stylo-maxillary; 10, the stylo-mastoid foramen, a rather 

 large orifice, placed between the styloid and mastoid processes: it is the termina- 

 tion of the aquaeductus Fallopii, and transmits the facial nerve and stylo-mastoid 

 artery; 11, the auricular fissure, situated between the tympanic plate and mastoid 

 processes, for the exit of the auricular branch of the pneumogastric nerve. 



Borders. The superior, the longest, is grooved for the superior petrosal sinus, 

 and has attached to it the tentorium cerebelli ; at its inner extremity is a seniilunar 

 notch, upon which the fifth nerve lies. The posterior border is intermediate in 

 length between the superior and the anterior. Its inner half is marked by a groove, 

 which, when completed by its articulation with the occipital, forms the channel 



