PHYSIOLOGICAL OBSERVATIONS. 183 



nations of the nerves, run to the internal hair cells in Mammals. 

 The internal hair cells do not form double cells, and are not at- 

 tached in the peculiar mode of the external. Whether special 

 structures corresponding to the tooth cells (Zahnzellen) of Has se, 

 exist between them in Mammals, as sometimes appears to be 

 the case in longitudinal sections of the lamina spiralis, must 

 still be regarded as doubtful. The arches of Corti, there can 

 be little question, are essentially a supporting apparatus for the 

 hair cells. 



The membrana tectoria and the otolith masses demand 

 closer investigation. Hasse (20 24) has associated the two 

 structures together, as an apparatus specially adapted for 

 propagating vibrations excited from without to the termi- 

 nations of the nerves lying in close proximity with the cilia of 

 the hair cells ; they thus constitute the essential sensation- 

 exciting arrangement of the internal ear, a function that has 

 long been attributed to the otoliths. I am disposed to attri- 

 bute to these structures a not less important but still directly 

 opposite function, that, namely, of damping vibrations. Helrn- 

 holtz (Ton-empfindungen, etc.,) has shown that a very perfect 

 damping mechanism must exist in the apparatus of the internal 

 ear, and I am of opinion that no constituent of the labyrinth 

 is better adapted to act in this way, by virtue of its anatomical 

 construction and of its position, than the membrana tectoria 

 and the otoliths. The latter are for the most part aggregates 

 of small crystals, destitute of any definite arrangement, but 

 suspended in a mucous substance, which is itself in contact 

 with the auditory hairs. Even the large simple otoliths of the 

 Fish and of other animals are essentially accumulations of 

 smaller crystals. It will be conceded that an apparatus of 

 this nature, which calls to mind a " sand sac," cannot in any 

 way occasion regular vibrations, but is much better adapted 

 to deaden the vibrations of other bodies with which it is in 

 contact. In favour of this view is the observation made by 

 Hensen (73), that the Decapoda, to some extent, make use of 

 certain quartz granules or uric-acid crystals, brought into their 

 vicinity, to supply the place of these otoliths, when lost during 

 each act of moulting. The mucous consistence of the mem- 

 brana tectoria, to which attention has already been called, its 



