No. 3.] 



VALVES OF TELEOST FISHES. 



I 19 



In this fish they are highly developed and efficient. The 

 upper valve is a sheet of membrane hung from the roof of the 

 oral cavity and covered by a continuation of its mucous mem- 

 brane. Its line of attachment is slightly bow-shaped, and lies 

 directly behind the teeth and parallel with them. 



The valve is broad with a straight lower edge, in the middle 

 of which is a thickened tooth-like projection. This projection 



mx 



mn 



Fig. I. — Maxillary and mandibular breathing valves of sunfisli, Eupomotis gibbosns (Linn,). Seen 

 from in front {A), and from behind (5). mx., maxillary breathing valve ; /««., mandibular 

 breathing valve. 



is the lower end of a vertical median thickening of the valve. 

 The lower valve is two-thirds as broad as the upper, and in 

 other respects is similar to it. The median thickening is 

 perhaps not so marked, and the valve tapers more at each lateral 

 extremity. Sections show that each valve is a membrane of 

 elastic connective tissue covered with a mucosa. The mucosa 

 possesses a well-developed layer of smooth muscle, while a layer 

 of the same kind of muscle extends from anterior surface to 

 posterior surface at the base or line of attachment of the valve. 

 In death the valves are found lying close to the surface of the 



