496 



CHORDATA. 



upper ends are frequeiitl_v toothed and, in chewing are opposed b)' the 

 rudimentary last arch, on wliich account these are spoken of as the 

 superior and inferior pharyngeal hones. The anterior visceral arches are 

 greatly diiferent in cartilaginous and bony fishes. In the former (hg. 546) 

 the pterygocjuadrate {J>q) and the jMeckelian cartilage (.!/</) bear teeth 

 and oppose each other in biting. In the bony fishes (fig. 547) the 

 teeth of the lower jaw oppose the tooth-bearing elements, premaxillary 

 and maxillary, of the maxillary series, while the pterygoquadrate ele- 

 ments — the palati)ie and the series of pterygoids — are the antagonists of 

 the hyoid. In the elasmobranch type the two halves of the pterygo- 



i^ ff/!j{. po tr 



Fig. 546. — Cranium, nsceral arches, and part of vertebral column of Muslchis 

 vulgaris. ao, antorbital process; co, copula; gp, foramen for glossopharvngeal; H, 

 otic capsule and hyoid; Hm, hyomandibular; ic, inlercalarc; ild. mandible (.Meckel s 

 cartilage"); A^, nasal capsule; o, optic foramen; oh, neural arch; /)<), poslorbital process; 

 Pq, pterygoquadrate; ps, spinous process; R, rostrum; r, ribs; tr, trigeminus foramen; 

 V, vagus foramen; i-S, visceral arches; i, labial; 2, mandibular; 3, hvoid; 4-S, gill arches. 



quadrate meet by symphysis in the middle line; in the others thev are 

 separated by the floor of the skull. 



A second characteristic of the bony fishes is already outlined in the 

 cartilaginous fishes: the modification of the hyomandibular to 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 quad- 

 rate, and hes Ijetween it and ihe cranium, the joint being thus indirectly 

 supported from the cranium, a bone, the sympleelic (known only in fishes) 

 helping out the suspensor, while another bone, the iii/erliyal, connects 

 this with the hyoid, which itself divides into two, so tliat the hyoid ardi, 

 like a gill arch, consists of four elements. 



