1^22.] the Organ of Hearing in Fishes. 323 



swimming bladder. This osseous capsule answers the same 

 purposes as the annulus of the tympanum in the human infant'. 

 Consequently sonorous tremors have access to the swimmin]^ 

 bladder through the apertures covered with skin; from which 

 they are transferred by means of the malleus, incus, and stapes, 

 to the membranous labyrinth. 



12. This conjunction of the swimming bladder and internal. 

 feav is brought about in other fishes not by ossicula auditoria, 

 but so that canals from the swimming bladder ascend directly to 

 the head, and are joined to the ear in different ways. 



13. In the sparus, salpa, and sargus, the top of the swimming 

 bladder ascends to the base of the cranium divided into two 

 canals. A peculiar membrane unites the apices of these canals 

 to the margins of two oval bones situated on the right and left 

 sides of the base of the cranium. 



14. In the clupea harengus {herring), two very narrow canals 

 of the swimming bladder enter into two bony canals on the' 

 right and left side of the base of the occipital bone. Each of 

 these canals is again divided into two small bony canals" w^hose 

 extremities swell out into hollow bony globules, the anterior and 

 posterior. The canals of the swimming bladder fill up these 

 bony canals and globules. The appendix of the membranaceous*' 

 vestibulum enters into the right and left anterior bony globule? 

 near the bullous end of the swimming bladder; so that reaching- 

 the extremity of the swimming bladder, it forms a septum, which 

 separates the cavity of the appendix of the vestibulum filled with 

 vt^ater from the cavity at the extremity of the swimming bladder 

 filled with air. The circumference of this septum is surrounded 

 by a ring nearly cartilaginous. Hence in the herring the sono- 

 rous tremors of the swimming bladder are transferred to the 

 membranous vestibulum itself. 



15. The anterior part of the right membranous vestibulum of 

 the herring communicates with the anterior part of the left mem- 

 branous v^estibulum, by means of a transverse membranous 

 canal passing below the cerebrum, in such a manner that mer- 

 cury cannot be injected into either vestibulum without filling 

 at the same time the membranous vestibulum and the semicir- 

 cular canals of the opposite side. 



16. The lower end of the swimming bladder of the herring 

 and anchovy is produced into a canal situated between the two 

 ovaries, and behind the rectum which opens into the ostium 

 genitale. 



17. The swimming bladder of the cobitis fossilis is not simple, 

 but consists of two parts, the upper greater, and the lower, very 

 small, situated without the bony capsule. A fibrous process 

 passes from the skin to the swimming bladder by an external 

 opening of the osseous capsule. 



18. The canal for air {canaiis jmeumaticns) of the swimming 

 bladder of the cyprini entering into the cesophagus cannot be 



Y 2 



