344 FISHES. 



to leave an orifice for the constricted part which connects the sac 

 with the vestibule. 



The liquor which fills the entire labyrinth, is slightly gelatinous 

 and perfectly transparent ; the sac and vestibule are swelled with this 

 fluid; they contain besides bodies of a peculiar nature, of the consist- 

 ence of starch in the chondropterygians, and of a purely stony nature 

 in the other osseous fishes. 



In the latter there is generally one of these bodies in the vestibule, 

 and two in the sac, a large and a small one, the latter are separated 

 from each other by a membranous septum. 



These stony concretions, and masses of amylaceous consistence, 

 are entirely calcareous, and are dissolved by acids with a brisk effer- 

 vescence. Nothing can be discovered in them resembling the organi- 

 zation of bones ; they are more like shells. 



Their form is A r ery determinate, and often very singular, and per- 

 fectly invariable in each species, indeed so much so, that bony fishes 

 may be distinguished by their ear stones, almost as easily as by any 

 other character : for instance, in the cod, they are elliptical, 

 notched on the edges, and raised in the middle ; in the scienas they 

 are oval, very thick, tubercular in some places, and marked by a 

 curved furrow, running along its surface, &c. (a,) 



The acoustic nerve is given off from the brain, nearly opposite the 

 junction of the sac with the vestibule ; superiorly it gives a twig to 

 each of the semi-circular canals; this twig enters the ampulla of the 

 canal to which it belongs and is there expanded. Another portion 

 of the nerve goes to the vestibule: but the most considerable part of 

 it expands into an infinity of filaments, which form a beautiful 

 apparatus under the wall of the sac containing the large stone. 



The disposition of the semi-circular canals in the rays and squalus 

 differs, in some respects, from that which is found in osseous fishes ; 

 in the former, they terminate at the vestibule in the form of a tube, 

 the superior extremity of which adheres to the fenestra ovalis : 

 his vestibule, after receiving the semi-circular canals, terminates in 

 a large oval sac, which has itself two appendices, an anterior and 

 posterior. It can scarcely be doubted, that this appendix represents 

 the small cavity, the only vestige of a cochlea which remains in 

 reptiles, and the rather as in reptiles it likewise contains a small mass 

 resembling starch. 



This conclusion ought probably to be extended to the sac in 

 osseous fishes, notwithstanding its backward position, the more so, 

 as it is frequently, and perhaps always, divided into tAVO cavities by a 

 membranous septum. 



The ears as we have now described them, it will be observed, are 

 much less perfect than the ears of quadrupeds, birds, or even those of 

 most reptiles. Destitute of the tympanum, the small bones and the 

 eustachian tube, they can scarcely receive the impression of the vibra- 

 tions of the ambient element, unless they are communicated to the 

 cranium, and besides, as the bones do not press closely on the mem- 



* Klein's treatise on these stones maybe consulted; it might have been con- 

 siderably augmented. 



