760 | FISHES—TECHNICAL TERMS. 
llary extending to posterior border of pupil,” indicates that the maxillary reaches a ver- 
tical line passing through that point. In the same way, the position of the mouth may 
be 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 piain, plicate, puckered, or 
pappillose (with little tubercles, as is the case with the Brook Sucker). At the angle of 
the mouth, attached te the maxillary, is sometimes a fleshy appendage, called a barbel. 
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, 7 
The upper jaw is said to be 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 up obliquely behind it is the swbhopercle; in 
front of the opercle, nearly parallel with it and separating it from the cheek, is. the pre- 
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 suborbital bones, and in front of 
it, below the double opening of the nostril, is the preorbital. 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 muzzle (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 interorbital 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 tho 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 teothed on 
its edge. . 
4, Vomer, the bone on the middle line ofthe 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 eachside, without teeth in fae Black Bass; but 
armed with a small patch in the Rock Bass (Ambloplites). 
7. Zongue, toothless in the Black Bass, but with a patch of teeth in the Rock Bass. 
8. Hyoid 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 gill rakers on the interior or concave side of the arch. 
le 
