THE SKULL THE CRANIUM 



233 



posterior aspect of such a section (Fig. 166) that is, the posterior 

 surface of the anterior of the two pieces thereby produced exhibits 

 the following features : 



In the superior part are the cells of the petrous forming the 

 antrum of the tympanum ; just under these is the oval section of the 

 aquseductus Fallopii, to the outer side of which is the deep fossa for 

 the tensor tynipaui muscle forming the upper part of the tympanum. 

 Lower down is the large oval section of the vestibule ; its upper out- 

 line is notched medially by a section of the beginning of the common 

 canal of the non-ampullar ends of the superior and posterior semi- 

 circular canals ; the emargination in its upper outline is produced 

 by the front of the superior ampulla ; the deep emargination in its 

 lower outline is part of the posterior ampulla, The upper arcuate 



FIG. 167. 



Aquseductus Fallopii. 



FOSSa for TENSOR TYMPANI 



Fovea Hemi-elliptirn 



Rim of Fenestra Ovalis. 

 Opening into Scala 



Vestibu/i. 

 Lamina Spiralis Secunda. 



Lamina Spiralis. 



Rim of Fenestra Rotun In. 



Superior Ampulla. 

 Superior and Posterior 

 ..--" Semicircular Canals. 



Opening of Aquxductus 



Vestibuli. 



Fovea Hemisphxrica. 

 Posterior Ampulla. 



SECTION OF LEFT PETROUS TRANSVERSE TO LONG AXIS. POSTERIOR 

 ASPECT. (Enlarged Four Times.) 



portion of the outer outline is formed by the rim of the fenestra 

 ovalis, which can be seen on the outer aspect. A notch in the upper 

 part of the rim is the section of a groove in Avhich is fastened the mem- 

 branous partition which closes the fenestra. The wall of the vestibule 

 exposed to view comprises the anterior wall and parts of the upper 

 and inner walls. Along the outer side is the opening into the scala 

 tympani ; at the upper part are the fovea hemi-elliptica and the ves- 

 tibular crest ; lower down is the fovea hemisphserica, and still lower, 

 in the outer part of the posterior ampulla, are the fine pores from 

 the foramen singulare. These areas are all in the part of the wall 

 contributed by the posterior wall of the internal auditory meatus ; the 

 rest of the wall is formed by the posterior part of the modiolus and 

 the lamina spiralis. 



If the section be made transverse to the long axis of the petrous 



