226 



MAMMALIAN ANATOMY 



the planes of the three intersect one another nearly in right angles, 

 but do not correspond with the planes of the skull, nor even with 

 the planes of the petrous. 



The plane of the superior canal is frequently said to be transverse 

 and vertical ; it slopes, however, from the vestibule on the outside, 

 inward and backward, and from above, downward and inward. The 

 plane of the posterior canal is usually described as longitudinal and 



FIG. 1GO. 



Aqumluctus Ventibuli. . Superior Ampulla. 



External Ampulla. 

 United Superior and Posterior 

 Semicircular Canals. , 



Posterior Ampulla. 



,-Fovea Hemi-elliptica. 



.Vestibule; Inferior Cribriform Spot. 

 ,' Fovea Hemisphxrica. 

 . Scala I'estibtili. 



Scala Tympani, beyond, the 

 Aquseductus Cochleae. 



...~- Scala Tympani. 



Lamina Spiralis 



Secunda. 



~~\"-- Scala Vestibuli. 

 Apex of Cochlea. 



METAL CAST OP LEFT BONY LABYRINTH AND AUDITORY BULLA. 

 MEDIAL ASPECT. (Enlarged Four Times.) 



vertical ; it is, however, inclined from the vestibule in front, backward 

 and outward, and from above, downward and outward. The plane of 

 the external canal is often described as horizontal ; it is, however, 

 directed from in front, backward and outward, and from within, 

 outward and upward. 



One end of each canal enlarges as it enters the vestibule to form a 

 flask-shaped ampulla. 1 The ampullae of the superior and external 

 canals are on their upper ends, the ampulla of the posterior canal is on 

 its lower end. The lower non-ampullar end of the superior canal 

 unites with the upper non-ampullar end of the posterior canal to form 

 a single passage which opens into the vestibule between the external 



1 A wine-jar. 



