THE SKULL THE CEANIUM 



237 



the internal auditory meatus (Fig. 173) differs from the section shown 

 in Fig. 167 because it is oblique to the long axis of the petrous. It 

 establishes the exact position of the vestibule in relation to the 

 cochlea, the lamina spiralis, the cribriform spots of the internal 

 auditory meatus, the aqureductus Fallopii, and the tympanum. 



FIG. 173. 



External Ampulla. 



Aquxductus Fallopii 

 Bridge, j 



Fenestra Ovalis. . - 



Groove leading to 

 Scala Vestibuli. 



Fovea Hemisphxrica. 



Anterior Rim of 

 Fenestra Rotunda. 



Lamina Spiralis 

 Secunda. 



Base of Modiolus. 



.>(// n'or Ampulla. 



, l-'nvea Hemi-eUiptica. 



.To Aqusedudus Fallopii. 

 . To Superior Cribriform Spot. 



__...? Middle Cribriform Spot. 



-Spiral Cribriform Tract. 



Lamina Spiralis. 

 -Slit into Scala Vestibuli. 



Basioccipital. 



- - .Entotympanic Cavity of Bulla. 



TRANSVERSE VERTICAL SECTION THROUGH LEFT TEMPORAL. POSTERIOR ASPECT. 



(Enlarged Four Times.) 







% 



It will be observed that the inferior aspect of the transverse hori- 

 zontal section (Fig. 174) is almost a complement of the section illus- 

 trated in Fig. 169. The position and direction of the cochlea, and 

 the features on the roof of the vestibule, are well shown. 



The aquseductus Fallopii begins at the internal auditory meatus 

 and runs forward, outward, and slightly upward to a point anterior 

 and medial to the fossa for the tensor tympani muscle (Fig. 165). 

 Here it is joined by the branch from the hiatus Fallopii, and turns 

 abruptly backward and outward and curves over the medial part of 

 the tensor tympani fossa (Figs. 166, 167). It then leaves the petrous 

 (Fig. 168), and, turning downward and outward, passes between 

 the squamous bridge and the petrous (Fig. 173), then between the 

 mastoid and the tympanic, and ends at the stylo-mastoid foramen. 

 This terminal portion communicates with the jugular foramen by a 

 canal between the bulla, the mastoid, and the occipital, for the trans- 



