THE EAR OF MAN. 2O9 



to diverge, and the planes of the canals now meet in 

 the middle of the common tube which unites them. 

 Their angle at this time is 150°. 



This method of origin is most interesting and impor- 

 tant in its bearings on the spacial relations of the adult 

 ear canals. The cochlea has now made nearly a whole 

 spiral turn. About the second month the internal ear 

 has assumed the foetal conditions, and its development 

 from this point on consists in the perfection of the parts 

 already marked out. The canals and ampullae have 

 acquired their adult characters, and the cristae are 

 distinctly formed, although the sensory cells have not 

 acquired their mature structure. Each canal has at 

 this stage a noticeable swelling at the opposite end 

 from the ampullae. In these you will recognize the 

 amae which I described in the fish ear as an adult 

 characteristic. In the human ear the ama of the ex- 

 ternal canal is the only one usually persisting beyond 

 the foetal condition. 



The cochlea has continued its development, and is 

 readily seen in the greater number of spiral turns it has 

 acquired, and the row of sense-organs, formed by the 

 budding of the original cochlear sense-organ or papilla 

 lagenae, has now several hundred discreet sense-organs 

 which are so closely related in structure and function as 

 to pass as one organ, the organ of Corti. 



One very important matter belonging with the ana- 

 tomical facts I intentionally neglected, for, until we had 

 gained a knowledge of the course of development of the 

 ear as a whole, and of the details of canal formation in 

 particular, we were not likely to fully appreciate its 

 bearings on the problem of the inter-relation of the 



