376 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



referred to above, and in the preparations from which the figures on 

 PI. VI. are taken. Fig. 8, PI. I., represents the medial macula 

 neglecta from one of the horizontal sections. 



ON THE RELATIONSHIP BETWEEN THE AIR-BLADDER AND 

 THE AUDITORY LABYRINTH. 



E. H. Weber, in his treatise ' Be aure animalium aquatilium ' first 

 made known the fact that the Cyprinoids and Siluroids are character- 

 ized by a remarkable communication between the auditory labyrinth 

 and the air-bladder, which is effected by a chain of bones named by 

 him stapes, incus and malleus after analogy with the auditory ossicles 

 in the mammalia. It was soon ascertained that this chain of bones 

 represents certain altered constituents of the anterior vertebrae, but 

 the precise morphology of the parts involved was first ascertained by 

 Baudelot, 1 and afterwards by Nusbaiim (I. c.) for the Cyprinoids. 

 Weber's interpretation of the number of vertebra? concerned in 

 Silurus is even further from the truth than his account of the parts 

 in Cyprinus, owing to the more intimate coalescence of certain of the 

 altered vertebras. 2 



These it will be convenient to describe in the first place. The sixth 

 vertebi*a resembles in all respects those which immediately follow it. 

 It is the first rib-bearing vertebra, the ribs being articulated to the 

 extremities of the costiferous pedicles or ' Basal-Stiimpfe.' The 

 vertebrae in front have only structures homodynamous with the basal 

 pedicles ; they are generally spoken of as transverse processes. In 

 front of the sixth all the vertebrae are coalesced in the adult. Of 

 these the fifth is the most independent, especially as regards its neu- 

 ral arch, and spinous and transverse processes, but its body, which 

 resembles those in front of it and differs from that of the sixth in 

 having a deep ventral furrow for the aorta (aortic canal), is completely 

 fused with that of the fourth. The suture may still be evident on 

 the outside (Pig. 7, PI. IV.), although generally concealed by mem- 

 brane bone deposited in connection with the air-bladder here, but 

 can always be seen on vertical section (Fig. 8, PI. IV.) The second, 

 third and fourth vertebral centra are completely fused in the adult. 

 The neural canal over them is a continuous tube of membrane bone, 

 the ossification of which originates near the rudimentary cartilaginous 



1 Comptes Rendus, 1808, p. 330. 



3 See my preliminary note on this subject. Zool. Anz. VII., 248. 



