346 ANATOMY OF VERTEBRATES. 



lateral or transverse apophyses of the vertelara; ; and, with regard 

 to their relation to the ' ossicula anditus ' of the tympanic cavity 

 in Mftinmalia, Welder mistook a relation of analogy for one of 

 homology, when he called them ' mallens,' ' incus,' and ' stapes.' 

 They belong, like the capsules of the special organs of sense, to 

 the ' splanchnoskeleton.' And since the vestibule is prolonged 

 by the ' atria ' into the neural canal of the atlas, this -^'crtebra 

 must be added, in the Cyprinoid and Siluroid Fishes, to the 

 parts of the cranial vertebra enumerated at p. 115, as entering 

 into the formation of the chamber of the acoustic organ. In tlie 

 Herring a tubular prolongation of the fore part of the air-bladder 

 advances to the basioccipital, and bifurcates ; each branch pene- 

 trates the side of tlie base of the skidl, again bifurcates, and 

 terminates in two blind sacs, which are in contact with smiilar 

 caical processes of .the labyrinth. In the Holocentrura and 

 Sargus, cajcal processes of the swim-bladder also diverge, to 

 attach themselves to the membrane closing the part of the oto- 

 crane containing the sac of the great otolite. 



In Osseous Fishes the sonorous vibrations of their liquid clement 

 is communicated by the medium of the solid parts of their body, 

 and in some species, also, through the vibrations of the air in the 

 air-bladder, to the liquid contents of the labyrinth. In the Plaglo- 

 stomous Fishes the resonance in the walls of their cartilaginous 

 cranium is less than in the bony skull of ordinary fishes; but the 

 labyrinth is wholly inclosed in the cartilage ; and a further com- 

 pensation is made by the prolongation of its chamber to the siirface 

 of the body in some, and by a similar prolongation of the mem- 

 branous labyrinth itself in others. The position of the external 

 orifices on the top of the head in the Skate tribe, may relate to 

 the commonly prone position of these flat fishes at tlie liottom of 

 the sea. Professor Miiller concludes, from his experiments, ' that 

 the air-bladder in fishes, in addition to other uses, serves the 

 purpose of increasing by resonance the intensity of tlie sonorous 

 undulations communicated from water to the body of the fish."' 

 The vibrations thus commimicated to the peri- and endo-l}mph of 

 the labyrinth are doubtless made to beat more strongly upon the 

 delicate extremities of the acoustic nerve, in Osseous Fishes, by 

 their effect upon the suspended otolites : and it will be observed, 

 that the chief ])ortions of the nerve expand u]ion those chambers 

 of the vestibule, which contain the otolites. The large size of the 

 organ of hearing, and es])ecially Ihat of the hard otolites, also relate 

 to the meilium through which the sonorous vibrations arc propagated 



' i.xxin. p. 124 5. 



