C YPRINIFORMES 



373 



sc. 



the air-bladder, first described by Weber [481]. It is essentially 

 the same in all the families (Sagemehl [379], Wright [510], 

 Bridge and Haddon [58], Bloch [37], Grassi, Storensen). The 

 right and left membranous labyrinths join across below the 

 medulla by a transverse canal, from which pass backwards a 

 pair of sacculi and a median sinus endolymphaticus. The latter 

 lies in the atrium, an extension of the perilymph cavity lodged 

 in the basioccipital (Fig. 

 358). On each side, from 

 a membranous fenestra of 

 the atrium, stretches a 

 chain of four ossicles to 

 the air-bladder. The 

 largest and hindmost 

 ossicle, the tripus (mal- 

 leus), lies on the anterior 

 wall of the air-bladder ; 

 the foremost and smallest, 

 the claustrum, on the 

 membranous wall of the 

 atrium ; the scaphium 

 (stapes), with a process 

 fitting over the atrial 

 fenestra, and the inter- 

 calarium (incus) complete 

 the chain (Fig. 359). 

 Observers differ as to 

 the exact homology of 

 Weber's ossicles. The 

 tripus is believed to 



..ut. 



represent the rib of the 

 third vertebra (Sage- 

 mehl) ; the ii 



re. 



FIG. 359. 



Macroms nemwus. A, the Weberian ossicles. B, por- 

 tion of the skull, the labyrinth, and Weberian apparatus 

 diagrammatically represented from above (from the 

 the neural arch of the n R tires of Bridge and Haddon). tt.ft, air-bladder ; a.r, 

 T /ITT i \ anterior vertical canal of the ear ; d, claustrum ; to, 

 Second Vertebra ( Wright) ; exoccipital ; h, horizontal canal ; in, intercalarium ; pto, 

 4.1 .,v.;,,^ 1 pterotic ; n, sacculus ; sc, scaphium ; tr, tripus ; vt, utri- 



the SCaphllim the neural culus ; r.c, Vertebral column. 



arch, and the claustrum 



the spine of the first vertebra (Wright). Sagemehl and Grassi 

 consider that the claustrum is derived from the skull. More 

 probably the two last ossicles represent the first neural arch and 

 rib. The anterior vertebrae are much modified in connection with 

 Weber's apparatus. 



The air-bladder often comes quite close to the skin, just 

 behind the pectoral girdle, forming a sort of tympanum, in many 

 Cyprinidae, Characinidae, and Siluridae. 



An adipose fin is found in all the families excepting the 



