SENSIBILITY OF THE INTEKNAL OKGANS 115 



those of the crista. These hairs are also held together by a 

 denser mass (ptoconium) and contain a small amount of carbonate 

 of lime (otoliths) (Fig. 50). All vertebrates except mammals 

 have three otolithic organs on each side (maculae utriculi, sacculi, 

 et lagenae} ; mammals have only two, because they have no 

 lagena, which has become transformed into the cochlea. 



The earliest view of the different functions of the two prin- 





FIG. 49. Section of the'fmacula acustica of recessus utriculi, human. Magnified. (G. Retzius.) 

 n.utr., bundles of utricular branch of the eighth nerve; h., hair-cells; p-l.s., perilymphatic 



cipal divisions of the membranous labyrinth is that of Scarpa 

 (1772), who attributed to the ampulla and utricle the capacity 

 of conducting sound-waves from the bones of the skull, whereas 

 they are conducted by the tympanic cavity to the cochlea. This 

 theory rests exclusively on the anatomical fact that the vestibular 

 labyrinth is in closer relation with the bones of the skull, while 

 the cochlear labyrinth is in more direct 

 connec.tion with a special apparatus for 

 conducting sounds by the air. 



Duge's (1838) propounded the far 

 more satisfactory hypothesis that the 

 saccules of the vestibule are excited by 

 noises, that is by irregular sound-waves, 

 and measure the intensity of these, and 

 thus estimate their distance, while the 

 neural apparatus of the cochlea is capable 

 of excitation by musical tones. Helm- 

 holtz supported this theory without adducing any conclusive 

 proof of it. It was founded on a phylogenetic concept which led 

 to the assumption that the cochlea, the best developed organ, 

 was intended to convey the finer and more complicated auditory 

 sensations in the higher vertebrates, while the saccules, which 

 form the whole labyrinth in the lower vertebrates, are only able 

 to receive coarser auditory sensations, and at most the simplest 

 musical tones. 



If auditory sensations were common to all classes of animals 

 provided with otocysts, this theory would be impeccable in a 

 general sense. More recent observations, however (Vol. III. p. 



i i 



PIG. 50. Otoliths. (Schwalbe.) 



