760 FISHES — TECHNICAL TEEMS, 



llary extending to posterior border of pupil," indicates that the maxillary reaches a ver- 

 tical line passing throiigh that point. In the same way, the position of the month may 

 ha fixed by stating on what level as compared with the eye, the pre- maxillary or upper 

 lip is placed. 



The jaws are sometimes provided with lips. These may be plain, plicate, puolcered, or 

 pappilloee (with little tubercles, as is the case with the Brook Sucker). At the angle of 

 the month, attached to the maxillary, is sometimes a fleshy appendage, called a larlel. 

 This may be extremely short and scarcely visible, as in the Chub, or very long and con- 

 spicuous, as in the Catfish. Sometimes the nostrils or the chin, or both, may have 

 barbels. 



The npper jaw is said to he protractile, when there is a deep farrow in the skin, sepa- 

 rating it from the skin of the forehead, as in the Sucker, and not protractile, when the 

 skin of the upper lip, in the middle at least, is continuous with that of the forehead, as 

 in the Log Perch. 



The membrane bones of the head may be readily recognized by taking a Sucker. The 

 large " gill cover," occupying most of the side of the head behind the eye is the oper- 

 culum or opercle; below this and extending np obliquely behind it is the siibopercle; in 

 front of the opercle, nearly parallel with it and separatiog it from the eheelc, is thejjre- 

 opercle, and below the angle of the preopercle, wedged in between it and the subopercle, 

 is the narrow interopercle : below the eye is the series of sutorMtal bones, and in front of 

 it, below the double opening of the nostril, is the preoriital. On the top of the head in 

 the Sucker, and rather posterior, is a characteristic hole in the skull covered by skin, 

 known as the fontanelle. The presence of the fontanelle may be verified with a pin. 



The eye is proportionately much larger in a young fish than in an old one ; its relative 

 size is usually expressed by comparing its diameter with the length of the muszle (dis- 

 tance from front of eye to the tip of the snout), with the length of the head (measured 

 from the tip of the snout along the side of the head to the posterior border of the 

 opercle), and with the width of the interoriital space (distance between the eyes above). 

 Thus eye five in head, is a concise way of stating that the diameter of the eye is one-fifth 

 the length of the side of the head. 



Tne tooth-bearing bones of the mouth can be recognized in the Black Bass. The 

 principal of these are, 



1. Dentary, the bones of the lower jaw. 



2. Premaxillary, above described. 



3. Maxillary, above described. This bone is usually toothless, or merely toothed on 

 its edge. 



4. Vomer, the bone on the middle line of the palate, immediately behind the upper 

 jaw. This bone has a patch of teeth in the Black Bass. 



5. Palatines, a bone extending outward and backward on each side from the vomer, 

 provided each with a band of teeth in the Black Bass. 



6. Pterygoids, behind the palatines on each side, without teeth in the Black Bass ; but 

 armed with a small patch in the Bock Bass (^Ambloplitea). 



7. Tongue, toothless in the Black Bass, but with a patch of teeth in the Eock Bass. 



8. Syoid bone, the base of the tongue, on each side of which the gill arches are 

 attached. 



9. Gill rakers, the stiffened appendages of the anterior pair of gill arches ; the gills are 

 on the outer or convex edge, the giU rakers on the interior or concave side of the arch. 



