HIGH SCHOOL ZOOLOGY. 25 



matoly united to it by an intervening symplectic cartilage 

 is the quadrate, a bone which furnishes the articular surface 

 for the lower jaw or mandible. Wedged in between the liyo- 

 mandibular and quadrate is a flat bone, the metapterygoid, 

 to the anterior end of which (by means of an intermediate 

 scale-like bone,) the palatine is related, a rod-like bone articu- 

 lated to the parethmoid and anteriorly carrying the maxilla. 

 In most fishes this bone forms part of the gape ; here it acts 

 merely as a support for the large maxillary barbels, while the 

 premaxillse attached to the ventral surface of the horns of the 

 mesethmoid, and connected with each other in the middle line, 

 bear most of the teeth of the upper jaw. 



22. The mandibles also bear teeth on their so-called dentary 

 part, while near the "angle" of the jaw is the articular part ; 

 on the inner surface of both the remains of the cartilage 

 (Meckel's) on which this jaw is built are to be seen. 



23. Closely united to the hinder border of the hyomandibular 

 and quadrate is the preoperculum through which a sensory 

 canal runs to reach the lower jaw. Behind it is the moveable 

 operculum, the chief bone of the gill-cover, which however 

 articulates separately with the hyomandibular. Between the 

 operculum and the mandible, and united with both, is the third 

 bone of the gill-cover, the interoperculum. In most fishes, but 

 not here, there is a fourth bone, the suboperculum. 



24. By means of a short interhyal piece of cartilage the 

 hyoid arch is connected with the lower end of the hyoman- 

 dibular ; it is itself divided on each side into three pieces, the 

 epi-, cerato-, and hypohyals, which are united in the ventral 

 middle line by an unpaired bone, tlte basihyal or glossohyal, 

 which gives attachment to the retractor muscles of the arch. 

 Articulated to the pos'erior border of the cerato- and epihyals 

 are eight branchiostegal rays, the uppermost of which occupies 

 much the s.une position as the suboperculum of other fishes. 



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