398 DEVELOPMENT OF ORGANS IN MAMMALIA. [CHAP. 

 Fia. 132. 



C-- 



'—-irs 



'- — u 



V 



~-~s. 



Diagrams op the Membeanods Labyrinth. (From Gegen- 

 baur.) 



I. Fish. II. Bifd. III. Mammal. 



U. utriculus ; S. sacculus ; US. utriculus and sacculus ; Cr. 

 oanaUs reuniens ; R. reoesaus labyrinthi ; UC. commence- 

 ment of cochlea ; C. cochlear canal ; L. lagena ; K. cupola 

 at apex of cochlear canal ; F. CEScal sac of the vestibulum of 

 the cochlear canal. 



membrane and external auditory meatus resembles that 

 in Birds (p. 166). As in Birds two membranous fenestras, 

 the fenestra ovalis and rotunda, in the bony inner wall of 

 the tympanic cavity are formed. The fenestra ovalis 

 opens into the vestibule, and is in immediate contiguity 

 with the walls of the utricle, while the fenestra rotunda 

 adjoins the scala tympani. In place of the columella of 

 Birds, three ossicles, the malleus, incus and stapes reach 

 across the tympanic cavity from the tympanic membrane 



