433 
~ maxilla, but these are small in the Catfish and merely serve to support the large 
barbels. Fig. 4 illustrates how closely the jaws are related to the hyoid pes 
(Pt he 
Wor 
Fig. 4.—Jaws anD Hyoip ARCH oF CATFISH, FROM THE SIDE, 
Mx, maxilla; pmx, premaxilla; pl, palatine ; hmd, hyomandibular; op, operculum; mpt, metapter 
goid ; qu, quadrate ; pr, preoperculum ; sop, interoperculum ; d, dentary ; ar, articular; h, hypohyal ; gh, 
_ glossohyal ; ch, ceratohyal; eh, epihyal; br, branchiostegal rays. 
which is similar in general character to the following gill-arches, but which is 
altered in form by reason ofits carrying the jaws and the skeleton of the gill-cover, 
Indeed the jaws are regarded as another similar arch in front of that, formed of an 
upper palato-quadrate and a lower mandibular segment, part of the latter carrying 
teeth (dentary) and part forming a joint with the quadrate, but all suspended to 
the skull by the hyomandibular, the upper part of the hyoid arch. ‘The lower part of 
_ this arch is sub-divided as shown in the figure, and forms a bony support for the 
_ tongue, while its hinder margin performs, with the attached branchiostegal rays, 
a similar function for the free part of the gill-cover, these rays being related to 
it ina manner somewhat similar to that in which the bones of the gill-cover—pre- 
operculum, operculum proper, and interoperculum (there is no suboperculum in the 
Catfish)—are related to the hyomandibular part of the arch. 
Fig. 5.—VIscERAL SKELETON OF CATFISH. 
H, hypobyal ; ch, ceratohyal ; eh, epihyal ; i, interhyal ; b’, first basibranchial ; hb", cb’, eb?, hypo-cerato- 
and epibranchials of first arch ; 0, esophagus ; ep and hp, epi- and hypopharyngeal tooth plates, 
The mode in which the skeleton of the gill-arches proper is sub-divided an@ 
_ the relationship to the superior and inferior pharyngeal (epipharyngeal and 
_ hypopharyngeal) tooth-plates, may be gathered from fig. 5. 
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