THE MAXILLARY AND MANDIBULAR BREATH- 

 ING VALVES OF TELEOST FISHES. 



ULRIC DAHLGREN, 



Instructor in Histology, Princeton University. 



While watching the living fishes in the aquaria of the 

 United States Fish Commission at Woods Holl, Mass., the 

 writer noticed that the jaws were scarcely moved in breathing, 

 the mouth being kept open all the time, except when used for 

 biting or for yawning, or other acts than breathing. Further, 

 when the fish was facing the observer and when the light was 

 favorable a pair of large and well-developed membranous valves 

 were seen inside the mouth, opening and shutting with a perfect 

 automatic motion as the fish breathed. 



One of these valves, which were both situated just inside of 

 the teeth, depended from the roof of the oral cavity, while the 

 other arose to meet it from the floor of the oral cavity just in 

 front of the tongue. They were crescentic in shape, widest 

 directly in front, and tapering down laterally to a point just 

 behind the angle of the mouth. Their lines of attachment to 

 the surfaces of the oral cavity were concentric with the teeth. 

 In texture they were semi-transparent and extremely flexible 

 and strong. 



A few minutes' observation was sufficient to demonstrate that 

 these structures were valves of great importance in breathing; 

 and an examination was made of the literature on the 

 subject. 



No mention of such valves appears in the standard works on 

 ichthyology and comparative anatomy, with the exception of 

 Owen,i who says : " The folds of membrane behind the upper 

 and lower jaws, of which ' internal lips ' the swordfish and 

 dory afford good examples, seem intended to prevent the reflux 



1 Owen, Anatomy of Vertebrates, vol. i, p. 413. London. 1866. 



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