433 



maxillae, 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 ai 



Fig. 4. JAWS AND HYOID ARCH OF CATFISH, FROM THE SIDE. 



MX, maxilla ; pmx, premaxilla ; pi, palatine ; hmd, hyomandibular ; op, operculum ; mpt, metapter 

 goid ; qu, quadrate ; pr, preopsrculum ; 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 of its 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 in a 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. 



eb 1 



Fig. 5. VISCERAL SKELETON OF CATFISH. 



H, hypohyal ; ch, ceratohyal ; eh, epihyal ; i, interhyal ; b 1 , first basibranchial ; hb 1 , cb 1 , eb 1 , hypo-cerato- 

 and epibranchials of first arch ; o, o^so^hagus ; ep and hp, epi- and hypopharyngeal tooth plates. 



The mode in which the skeleton of the gill-arches proper is sub-divided and 

 the relationship to the superior and inferior pharyngeal (epipharyngeal and 

 hypopharyngeal) tooth-plates, may be gathered from fig. 5. 



