A contribution to the anatomy and physiology of the air-bladder and Weberian ossicles in Cyprinidæ

Abstract

The Swim-bladder or Air-bladder of Fish is situated within the abdominal cavity between the alimentary canal and the vertebral column, but without the sac of the peritoneum which covers only its ventral portion. It appears in the embryo as a cæcal outgrowth from the dorsal surface of the œsophagus. The primitive connection with the alimentary canal may be retained by means of a duct, the ductus pneumaticus, or it may be entirely atrophied in the adult. In the Cyprinidæ the swim-bladder retains its connection with the œsophagus: it also develops an anterior chamber. In the Roach ( Rutilus rutilus ) three weeks after hatching a bud appears at the anterior end of the sausage-shaped air-bladder; this rapidly increases in size and within a week has formed the front half of the constricted air-bladder. The Cyprinidæ belong to the sub-order Ostariophysi of the Teleostei, a group which contains the Characines, Carps, Cat-fishes and Gymnotids. (Boulenger, G. H., ‘Cambridge Nat. History,’ 1904.) The most characteristic feature of this group is the modification of the anterior four vertebræ “often co-ossified and bearing a chain of Small bones, the Weberian ossicles, which connect the air-bladder with the ear.” The most posterior of these ossicles is attached to the anterior end of the anterior sac. The physiological significance of these so-called auditory ossicles is still an unsettled problem.