IV. VERTEBRATA: PISCES. 



561 



the lower jaw oppose the tooth-bearing elements, premaxillary 

 and maxillary, of the maxillary series, while the pterygoquadrate 

 elements the palatine and the series of pterygoids are the an- 

 tagonists of the hyoid. 



A second characteristic of the bony fishes is already outlined in 

 the cartilaginous fishes : the modification of the hyomandibular to 



qio jiLo 



we. 



FIG. 589. Skull of haddock. Infraorbital ring and operculum. outlined in red. n, 

 angulare; ar, articulare ; as, alisphenoid; de, dentary; ee, ectethmoid; ekt, 

 ectopterygoid; eng, os entoglossum ; ent } entopterygoid; epo, epiotic; /r, frontal; 

 h'-ft 3 , hyoid elements: Jim, hyomandibular; ih, interhyal; ma, maxilla; me, 

 mesethmoid; mt, metapterygoid; na, nasal; neb, ncl, ocs, basi-, ex-, and supra- 

 occipital ; oo, opisthptic ; p, parietal ; pa, palatine ; y>rm, premaxillary ; pro, pro- 

 otic ; ps, parasphenoid ; pto, pterotic ; qit, quadrate; rbr, branchiostegals ; spfto, 

 sphenotic; xy, symplectic ; w, vomer; w, vertebra. Bones outlined in red: in/, 

 inf raorbital ; to, interoperculum ; o, operculum ; pro, preoperculum ; .so, suboper- 

 culum ; 1, 2, 3, axes of ..abial, mandibular, and hyoid arches. 



a suspensor of the jaws. In the elasmobranchs (especially the 

 skates) the parallelism of hyoid and mandibular arches is lost, the 

 hyomandibular separating from the hyoid and attaching itself to 

 the hinge of the jaws. In the teleosts the hyomandibular is thus 

 brought in connexion with the quadrate, and lies between it and 

 the cranium, the joint being thus indirectly supported from the 

 cranium, a bone, the symplectic (known only in fishes) helping 

 out the suspensor, while another bone, the interhyal, connects this 

 with the hyoid, which itself divides into two, so that the hyoid 

 arch, like a gill arch, consists of four elements. 



