OTOLITH SACS OF THE INNER EAR 



475 



canals which lie in the same plane are so arranged that particles moving in the 



same direction in the two move toward the ampulla of one and away from 



the ampulla of the other. 



In the sacculus and utriculus likewise are nerve endings contained in the 



maculae acusticoe. 



These nerve endings consist of cells with hairlike processes, which in turn 



are connected with the terminal filaments of the eighth cranial nerve. In the 



ampulla? the hairs are bound to- 

 gether by a substance which is 

 probably slimy and gelatinous in 

 life. This substance, however, does 

 not reach down to the epithelial 

 surface, but is separated from it 

 by a small space filled with endo- 

 lymph, through which the hairs 



FIG. 185. 



FIG. 186. 



FIG. 185. Schema showing the relations of the planes of the semicircular canals of the pigeon 

 to each other, after J. R. Ewald. The open skull is seen from behind. The anterior canal 

 lies in the plane A, the posterior in the plane P, a'nd the external in the plane E. 



FIG. 186. Schema showing the distance of the planes of the anterior and posterior canals 

 (prolonged) from each other. 



project before entering the slimy material. A small solid body, the so-called 

 otolith, rests upon the hairs in each of the macula? acustica3. All vertebrates 

 from the bony fishes up, with the exception of the mammals, have three otolith 

 organs on each side (one in each of the three parts: utriculus, sacculus and 

 lagena) ; the mammals have but two, since in them the lagena is absent, having 

 been developed into the auditory cochlea. 



These three (or two) otolith organs bear to each other the same spatial rela- 

 tions as the semicircular canals, the macula utriculi lying in the plane of the 

 external canal, the macula sacculi in the plane of the anterior, and the axis of 

 the lagena (where such can be made out) in the plane of the posterior canal. 



It was long supposed that the semicircular canals and the ear sacs were 

 called into play in the perception of noises i. e., of sounds not produced by 

 regular periodic vibrations while the musical tones excited the nervous end 



