3892.] Contributions to the Anatomy of Fishes. 141 



tible, and therefore capable of responding to smaller variations of 

 internal gaseous tension by whatever cause produced than if the 

 anterior chamber were equally elastic and expansible in all .direc- 

 tions. 



The increased delicacy of the Weberian mechanism in the SiluridaB 

 normales, as compared with other Ostariophyseae, is probably the cause 

 of the extensive anchylosis of the anterior vertebrae, and their rigid 

 articulation with the skull, for if flexibly articulated with one another 

 and to the skull, so as to be able to participate in the lateral flexion 

 of the vertebral column in ordinary locomotion, while at the same 

 time the vertebrae and their processes retained their intimate re- 

 lations with the air-bladder, the anterior chamber and Weberian 

 ossicles could hardly fail to be affected by muscular compression. 

 Hence, anchylosis of the anterior vertebrae becomes almost a necessity 

 in the Siluridae, if the Weberian mechanism is to remain unaffected 

 by the more or less violent shocks produced by muscular contraction 

 and relaxation. From a physiological point of view, it may be noted 

 in connection with the Weberian ossicles, (a) that the anterior and 

 crescentic processes of the tripodesareof approximately equal length, 

 and hence the force and amplitude of all movements imparted to one 

 extremity will be exactly reproduced, without augmentation, at the 

 other; (6) the interposition of a lax, or at all events compressible, 

 ligament (interossicular ligament) in the series of ossicles ; and (c) 

 the rudimentary and functionless condition of the intercalarium. 



These and other facts suggest the conclusion that the We-berian 

 apparatus is far better adapted to register the more forcible, even if 

 more gradual, distensions or contractions of. the anterior chamber, 

 rather than slight or rapidly recurring vibrations of its lateral walls. 



Finally, it may be affirmed that no differential action of the two 

 auditory organs can possibly take place, at all events so far as im- 

 pulses received through the Weberian mechanism are concerned, 

 since the only channel through which any movement initiated in the 

 fluids of the atrial cavities by the motion of the Weberian ossicles 

 can reach them is the median, unpaired sinus endolymphaticus (the 

 " sinus impar " of Weber) ; hence it must follow that each auditory 

 organ will be affected by any such disturbances to an equal extent 

 and at the same moment. 



II. So far as the auditory organ is concerned, the functions of 

 audition and equilibration or orientation have to be considered, and 

 for the air-bladder those of phonation or sound production, respira- 

 tion, accessory to audition, or its function may be purely hydrostatic. 



Certain of these possible functions may be at once eliminated from 

 any discussion as to the use ot the Weberian mechanism. Equilibra- 

 tion maybe dismissed, inasmuch as there can be no differential action 

 of the two auditory organs. The absence of intrinsic muscular fibres 



