IV. VEnTEDEATA: PISCES. 



5(U 



the lower jaw oppose the tooth-hearing 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 

 tlic cartilaginous fishes: the modification of the hyomandibular to 



Fig. .189.— skuU of harldock. Infraorbital riiif? and operculum outlined in red. a, 

 annulare; ar. articulare ; as, alisphenoid: </e, dentary; cr., ectethmoid; efef. 

 ectopterygoid; f ;»;, os entoglossum ; eiif, entopterygoid; cjio, epiotic; /r, frontal; 

 h^-V\ hyoid elements: )im, hyomandibular; i7i, interhyal; \iin. maxilla; »u', 

 meRethmoid; ^nt, metapterygoid; »a, nasal: oc/>, oct, uc.5, basi-, ex-, and supra- 

 oceipital ; no, opisthotic ; |<, parietal ; pn, palatine ; jirm, premaxillary ; pro, pro- 

 otio : ps, parasphenoid ; p(o, pterotic ; qu, quadrate; rhr, hranchiostegals ; .ipfei, 

 sphenotic: sy, symplectic ; tv, yomer; u\ yertebra. Bones outlined in red; in/, 

 infraorbital ; 'Uu interoperculum ; o, operculum ; pro, preoperculum ; in, suboper- 

 culum ; i, :.', J, 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 

 livomandibnlar separating from the hyoid and attaching itself to 

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

 Tn'ouglit in connexion with the quadrate, and lies between it and 

 the cranium, the joint being tlius indirectly supported from the 

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

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

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

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



