THE LIVING BIRD 33 



by delicate bones (see figure) stretching across the 

 air-filled chamber of the middle ear (Fig. 6) to the 

 perilymph of the inner ear and so to the endolymph. 

 Projecting from the vestibule is another compart- 

 ment, known in mammals as the cochlea. It is 

 spiral in structure, relatively broad at the base and 

 narrow at the tip, provided with peculiar cells. 

 The apparatus may be likened to a series of strings 

 lying side by side, those at the base longer than 

 those at the tip with every intergradation between 

 them. If they are assumed to show sympathetic 

 vibrations to sound waves of various lengths coming 

 in from the drum, a very perfect arrangement exists 

 for analyzing a great variety of sounds. In mam- 

 mals the nerve supplying this organ terminates in a 

 highly developed (paired) brain-centre of its own 

 (posterior colliculus) , connected both with the cortex 

 and the cerebellum while at the same time function- 

 ing as a reflex centre. It is this intricate piece of 

 apparatus that makes speech in man comprehen- 

 sible and so possible. In the lower vertebrates the 

 cochlea is represented by the primitive lagena. In 

 birds a cochlea exists, but it is relatively simple and 

 lacks some of the essential features of the mam- 

 malian. Moreover, the colliculi do not exist as 

 such. It seems certain, in fact, that birds, in spite 

 of their great variety of song cannot experience the 



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