412 



CHORD AT A, 



In the pigeon a further complication is involved in the 

 formation of the outer ear, represented by an external audi- 

 tory meatus leading from the exterior to the tympanum ; 

 and, lastly, in the rabbit, i\\Q pm?ia is added. 



In the mammals the columella appears to be represented 

 by three auditory ossicles, as noticed in the rabbit. 



These three sense-organs, their accessories, and the brain 

 mark out the head of the Vertebrata. 



Fig. 298. — A Diagram of the Vertebrate Ear. 



Pinna. 



Ductus Endo- 

 lymphaticus. 



External Audi- 

 tory Meatus. 



Fenestra Ovalis, 

 .Sacculus. 



"-^.Cochlea. 



Bony Labyrinth. 

 Perilymph. 



The whole diagram represents the ear of the rabbit (except that only one 

 ear-ossicle is indicated) ; all to the right of AA represents the ear of the pigeon ; 

 to the right of BB represents the frog with middle and inner ear only ; and the 

 ear of the skate is represented by the part to the right of CC, forming the inner 

 ear only. 



Skeletal Organs. — The skeleton of Vertebrata shows 

 a succession of three kinds, which replace each other in time 

 throughout the classes and in the development of the higher 



