XIV 



SENSE-ORGANS 



389 



outer surfaces of the fibrous membranes which close a pair of 

 vacuities in the outer bony walls of the periotic capsules, the 

 inner surfaces being bathed by the perilymph surrounding 

 the auditory organs. This method is characteristic of certain 

 Serranidae, Berycidae, Sparidae, Gadidae, and Notopteridae/ and 

 probably in the Hyodontidae. In the second method, of which 

 several Clupeidae {e.g. Herring, Pilchard, etc.) furnish examples, 

 the periotic vacuities are open in- 

 stead of closed, and the sac-like 

 ends of the tubular extensions 

 from the air-bladder are in actual 

 contact with protruding outgrowths 

 from the utriculus.^ The third 

 method, by far the most elaborate, 

 is by the intervention of a series 

 of movably connected " Weber- 

 ian" ossicles, of which the most 

 posterior on each side (the tripus) 



is inserted into the dorsal wall of Fi«- 222.-Cavity of the air-Madder of 



a Siluroid (Macrones nemnrus) ex- 



the air-bladder (Fig. 223), while 

 the anterior one (scaphium) forms 

 the outer wall of a median back- 

 ward prolongation (sinus impar) 

 of the perilymph-containing spaces 

 surrounding the two auditory 

 organs. This in turn encloses a 

 similar median prolongation (sinus 

 endolymphaticus) from the two sub-cerebrally united endo- 

 lymphatic ducts (Fig. 223).' This complex mechanism is present in 

 the Cyprinidae, Siluridae, Characinidae, and Gymnotidae ; and hence 

 the term " Ostariophysi " * as a collective name for these families.* 



^ Bridge, Journ. Linn. Soc. xxvii. 1900, p. 503. 



^ Ridewood, Journ. Anat. and Phys. xxvi. 1892, p. 26. 



^ E. H. Weber, De aure et auditu Hominis et Animalium. Pars i. De aure 

 Animalium Aquatilium, Leipzig, 1820 ; Bridge and Haddon, Fhil. Trans. 184, 

 1893, p. 65. 



" Sagemehl, Mmyh. Jahrh. x. 1885, p. 22. 



^ The Weberian ossicles are modified components of certain of the anterior 

 vertebrae. The scaphium represents the neural arch of the first vertebra ; the inter- 

 calarium is the arch of the second vertebra ; while the tripus is probably the rib 

 of the third vertebra. In the Characinidae and the Cyprinidae an additional 

 ossicle, the "claustrum" is present. 



posed by the removal of its ventral 

 wall, a.c, Anterior chamber ; b.o, 

 basioccipital ; b.ic, body wall, here 

 reduced to the external skin ; 

 cl, clavicle ; l.c, lateral chamber ; 

 l.s, longitudinal septum , pt, post- 

 temporal ; tr.a, anterior portion of 

 the tripus ; tr.c, crescentic portion 

 of the tripus ; t.s, transverse sep- 

 tum ; t.s', shorter transverse sep- 

 tum. (From Bridge and Haddon.) 



