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The Salmon has an air-vessel consisting of one elongated cylindrical tube 

 lying close to the back-bone, which opens almost directly into the pharynx, or 

 without the intervention of a distinct duct. The air-vessel is much more deli- 

 cately formed than that of the Pike, and is connected -with the ribs and spine by 

 much finer ligaments. Trout and nearly all the Salmonidce have similarly shaped 

 air-bladders. The Grayling, however, has an air-bladder communicating with 

 the ojsophagus by a very small tube. 



The Carp family, consisting of the Carj), Roach, Chub, Rudd (or Red-eye), 

 Barbel, Bream, and Dace have large air-vessels divided by narrow and short 

 necks into two or more chambers. The Chub, Roach, and Rudd, have two 

 large chambers, the anterior one slightly truncated at the upper end, and 

 connected with the posterior one by a short tubular neck. From the upper 

 end of the posterior one a duct runs forward into the oesophagus. The air-vessel 

 of the Dace is similar, except that the posterior chamber is comparatively 

 longer, more narrow, and cylindrical. The air vessel of the Gudgeon 

 resembles that of the Dace, though the posterior chamber is hardly so narrow, 

 and in both the anterior one has a slightly truncated end. 



In all the family of Cyprinoids the air-bladder, though closely packed in 

 and enveloped by the intestines, is loosely fixed in the abdomen, and is not 

 connected with the ribs or spine by any strong ligaments as in the Pike. The 

 covering is, however, muscular, and the fish has thus the power of contracting 

 the vessel and expelling the air through the pneumatic duct. 



The air-vessel of the Pike forms one long and large sac extending the 

 whole length of the abdominal cavity, and only separated from the spine by the 

 blood vessels. Externally it has a very tough fibrous membrane of great 

 strength, and is connected on both sides to the ribs, and also to the spine by short 

 strong ligaments. At the upper end there is a small round tube of about half an 

 inch in length communicating with the gullet. If you attempt to pass a probe 

 from the gullet into the air-vessel it is stopped, but if you pass the probe from 

 the bladder into the gullet there is no resistance. It is clear therefore that the 

 communication between the air-vessel and the gullet is guarded by a valve, which 

 allows the air to escape outwards, but not to enter. In a pike of 122lbs. weight 

 the air-vessel was 12 inches long. 



The Eel has an air-bladder of very delicate construction. It is fusiform, 

 with two short processes at the anterior end, enveloped in the common integu- 

 ment ; the inferior one, or vertical isrocess, is closely bound to the oesophagus, 

 and is cellular, as is also the posteiior end of the vessel. There are, moreover, 

 several membranous diaphragms in the air-vessel of the Eel, with a vascular 

 ganglion ; and a duct leads from it to the alimentary canal near the stomach. It 

 is closely connected with the intestines, and is with difficulty separated fronj 

 them in making an examination. 



The Perch has a simple largo air-vessel or chamber fixed close to the spine. 



