INTRODUCTION xix 



is most protractile in Cyprinoids such as the Bream, 

 and forms a sort of tube when it is protruded. 



Near the mouth there may be barbels, fleshy 

 filaments which are used as feelers when the fish is 

 in search of food. In the Cyprinoids one or two pairs 

 may be attached to the upper lip, and in the Loaches 

 three or more pairs are present ; the Burbot has a 

 single barbel at the end of the lower jaw. 



The mouth is toothless in the Cyprinoids, which 

 are mainly herbivorous, and the teeth are minute in 

 the Whitefish and Shad, which feed chiefly on minute 

 animals, as also in the mud-eating Grey Mullets. In 

 most cases the jaws are provided with teeth, usually 

 conical or subconical in form ; the predaceous Pike 

 has strong erect canines in the lower jaw. The 

 presence or absence of teeth on the bones of the 

 palate, and their arrangement when present, are 

 characters of considerable importance. The vomer 

 is a bone which lies in the middle of the roof of the 

 mouth, commencing immediately behind the junction 

 of the praemaxillaries ; it usually presents a broad 

 anterior part, or head, and a tapering posterior part, 

 or shaft. The palato-pterygoid arch includes five 

 bones on each side palatine, pterygoid, quadrate, 

 meso-pterygoid, and meta-pterygoid ; the palatines lie 

 on each side of the vomer, and the pterygoids connect 

 them with the quadrates, to which the rami of the 

 lower jaw are articulated ; the meso-pterygoids lie 

 above and internal to the pterygoids, and behind them 

 are the meta-pterygoids. 



The gill-openings are usually wide, but may be 

 restricted by the union of the gill-membranes with 

 the isthmus, as in the Cyprinoids and Sticklebacks, 



