“376 PROCEEDINGS OF THE CANADIAN INSTITUTE. 
referred to above, and in the preparations from which the figures on 
Pl. VI. are taken. Fig. 8, Pl. 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 ‘ De awre 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 vertebre, but 
the precise morphology of the parts involved was first ascertained by 
Baudelot,! and afterwards by Nusbaum (/. c.) for the Cyprinoids. 
Weber’s interpretation of the number of vertebre 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 vertebre.’ . 
These it will be convenient to describe in the first place. The sixth 
vertebra 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 
vertebre 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 vertebre 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 (Fig. 7, Pl. [V.), 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, Pl. [V.) 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, 1868, p. 330. 
2 See my preliminary note on this subject. Zool. Anz. VII., 248. 
