>ou 



Clio IIB ATA. 



xiiipiiired, wliile in all other vertebrates it is paired. Most con- 

 stant of the cartilage hones are the ethmoids (the paired ecteth- 

 moids, ce, and the sometimes pjaired mesethmoid), and the four 

 occipitals. On the other hand the otic and optic regions vary 

 considerably; the otic region, from its gi'eat size, has several bones, 

 nsnally (fig. 589) five in number: jjterotic, 7;/©, often called 



r ffpM pot/r 



S. 7. 



Fjg. "iftw.— Cranium, viscera] arches, and part nf vertebral ci'lumuof Musiclua vulgaris, am 

 antorbital process; c<i, copula; (iji. foramen for glossopharyngeal; H, otic capsule and 

 hyoid; Hia. hyoQjandibular; /r, iutercalare : Md, mandible (Meckel's cartilage) ; 

 A, nasal capsule; <', optic foramen; o^, neural arch; pa. postorbital process; Pi/. 

 pterygoquadrate ; ^^'-■. spinous process; R. rostrum; >\ ribs; ?r, trigeminus foramen ; 

 (', vagus foraiueu; 1-s, visceral arches: 1, labial; r?, mandibular; .;, byoid: ^S. gill 

 arches. 



s([uainosal; splienotic, .yjio, frequently called postfrontal ; epiotic, 

 epoj prootic, i>nj; and opisthotie, oo, tlie last sometimes lacking. 

 In the region of the eye the cartilaginous S2)henoids are rarely 

 well develojied, the large parasphenoid taking their phice. The 

 same is true of the ali- and orbitfisphenoids, these sometimes form- 

 ing an iuterorbital septum (fig. .tOO) or a more or less wide in- 

 terorbital fenestra (fig. 58!i). 



The character of the visceral skeleton is related to the a(|uatic 

 life. All fishes have numerous gill arches (five to seven, mostly 

 five), which, since their function — gill supporting — is similar, are 

 similar in structure. So far as they are not degenerate they con- 

 sist each of four parts tind are connected by unjiaired t'opuhv, these 

 often being fused. The upper ends ;ire frei(uently toothed and, 

 in chewing, are opposed liy the rudimentary hist arch, on which 

 accf)unt these are spoken of as the superior and inferior pharyngetil 

 bones. The anterior visceral tirches are greatly different in car- 

 tilaginous and bony fishes. In the former (fig. 588) the pterygo- 

 quadrate (pq) and the Meckelian cartilage bear teeth and oppose 

 eacli other in biting. Tn tlie bony ll.shes (fig. 58!l) the teeth of 



