Hearing, and the Ear. 469 



The eustachian tubes of birds in proceeding from the two ear drums, 

 first join each other, and then open into the pharynx by one median 



passage, like some of the 

 amphibians already men- 

 tioned. Tlio cochlea* of 



FIG. 203.I)i<i!/r<itii* of Audi- 

 tor// Labyrinth. (Waldeyer.) 

 I. A Fish. 

 II A Bird. 



III. Mammal and Man. 

 s. Sacculus. 

 u. Utriculus. 

 c. Cochlea. 

 Cr.Canalis reuniens. 

 a. Ampullae. 

 6. Semicircular canals. 

 R. Acqueduct of the vestibule. 



birds is only slightly 

 twisted like that of the 

 reptiles. The interior of 

 FIG. 209. their scala media is much 



less complicated than that of the higher mammals and does not possess 

 the arches of Corti. In fact, these belong to the mammsib ilone. The 

 other sac, however, the labyrinth, is amply developed m birds, and the 

 three semicircular canals 

 are large. The lowest of 

 the mammals are, like the 

 birds, derived from reptil- 

 ian stock. And as they 

 are close to the point of 

 separation, in many par- 

 ticulars they resemble the 

 birds, as they resemble the 



FIG. 210. 



A. Ear bones of Perameles, a 

 Marsupial. 



FIG. 211. 



Stapes of Kangaroo, 

 a Marsupial. 



reptiles below them. Thus 



in the Monotremes the 



cochlea is only slightly bent upon itself, not coiled, as in other mammalia. 



The stapes bone is similar to the columella of birds. But the additional 



FIG. 212. Stapes of Aquatic Mammals. 

 A. Ornithorhynchus. B. Porpoise. C. Walrus. D. Seal, E. Manutee. 



incus and malleus bones are already present, the three bein^ t he .successors 

 of the ancient reptilian columella. In all the mammals, above the marsupi- 



