433 



maxillse, 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 arch, 



Fig. 4.— Jaws and Hyoid Arch of Catfish, from the side. 



Mx, maxilla ; pmx, premaxilla ; pi, palatine ; hrad, 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 torm 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 fisfure, 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. 



Fig. f). — Visceral Skkleton of Catfish. 



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



and epibranchials of first arch ; o, oiso^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 pliaryngeal (epipharyno-eal and 

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



