416 PROCEEDINGS OF THE CANADIAN INSTITUTE. 



THE AIR-BLADDER. 



The air-bladder of the cat-fish takes up in length about one half 

 that of the belly cavity, and measures across at its broadest end 

 from one-half to two-thirds its length. It narrows posteriorly and 

 has a rounded termination, while the anterior face is broad and is 

 covered by the head portion of the renal oi-gans. It is covered up 

 on its lower surface by the peritoneal folds. 



The dorsal surface has a groove into which the vertebral column 

 fits, elsewhere the surface is even. The duct arises from it at the 

 commencement of the middle third, and passes forward and down- 

 ward to the oesophagus. 



There are three cavities in the air-bladder, two of which each 

 communicate with a third, the anterior one. The long axis of the 

 last named is directed transversely and occupies the broadest portion 

 of the bladder. The long axis of the two others are parallel and are 

 directed backward. The connection of each of these with the 

 anterior one is by an aperture narrower than its own transverse- 

 diameter. It is with the anterior chamber that the duct communi- 

 cates, opening at its posterior lower edge. 



There are two coats in the wall of the ah-bladder. The outer 

 white, and of some thickness, exists as such at all points, except a 

 part of the dorsal surface. On the sickle-like auditory ossicle and along- 

 several vertebral segments it is but a thin transparent membrane, 

 closely connected with and united to the ossicles and vertebrae. 

 Opposite the opening of the duct into the bladder the membrane 

 again becomes thick and opaque white. This coat alone is connected 1 

 with the auditory ossicles, and to its thickness, as well as to its 

 constituents, it owes some of its stiffness. 



The inner coat is very thin and membrane like, and is conformed 

 to the walls of the various chambers. Between the median walls of 

 the posterior chambers is a single wall due to the fusion of the two 

 outer coats. The outer coat also surrounds and enters closely into- 

 the constrictions of the openings of the posterior chambers into the 

 anterior one. 



The outer coat is formed of connective tissue fibres and elastic 

 fibres. The former are long, needle-like, and whitish as if calcified. 

 The stiffness of the outer coat is due wholly to these fibres. When 

 put into dilute acetic acid for several hours they swell up into a 



