THE SKULL THE CRANIUM 



219 



ligament ; dorsal to the hook itself is the canal of Huguier for the 

 chorda tympani nerve. Straight across from these features, at the 

 inner end of the suture between the petrous and the sphenoid, and 

 at the anterior end of the septum of the bulla, is an opening into 

 the cranial cavity for the Yidian nerve. 



The inner wall of the tympanum faces outward, downward, and 

 forward. Its upper part is contributed by the petrous and the upper 

 part of the bullar septum. The septal part of the wall is smooth and 

 concave, but the petrous portion shows the features peculiar to its 

 surface, the promontory in front and the fenestra ovalis above and 



behind. 



FIG. 149. 



Sagittal Crest. 



Wall of Cranium 

 Cut Edge of Tentorium, 



Squamous. 



For Malleus. 

 Aqitxductus Fallopii. 

 Fenestra Ovalis. 

 For Incus. 

 Cochlea. 



Inner Chamber of Sulla. 

 ' Edge of Septum. 



Outer Chamber of Bulla. 

 Septum. 



Parietal. 



Tentorium C'erebellL 



-Squamous of Temporal. 



Cells in Petrous. 



For TENSOR TYMPANI. 



5? Fenestra Ovalis. 

 Slit for STAPEOIUS. 



'Z^f -Britiij' [Chambers of Bulla. 



:a C5t -Opening of Communication between Two 



Afa*tr>id of Temporal. 



Cochlea. 



'Posterior Rim of External Aitdito, 

 of Ectotympanic of Bulla. 



Entotympanic of Bulla. 

 Groove in Basfoceipital for Blood-vessel. 



Inner Chamber of Bulla. 

 TRANSVERSE VERTICAL SECTION OF SKULL THROUGH EXTERNAL AUDITORY MEATUS. 



The outer wall of the tympanum faces backward and inward and 

 somewhat upward ; it is little more than a ring surrounding the ex- 

 ternal auditory meatus. It is formed by the ectotynipauic, except the 

 upper part, which is derived from the squamous. It presents a cir- 

 cular elevated strip forming the margin of the auditory meatus. This 

 strip is wider in front and quite disappears behind and above. Around 

 this margin, below and in front, the wall is concave ; it ends at the 

 posterior wall at a point where the septum joins the edge of the auditory 

 meatus. Above this point is the outer part of the fossa for the incus 

 and malleus. 



