THE SKULL 



79 



premaxilla vary much as to their development : the latter may even 

 be absent. 



Besides the above-mentioned bones in connection with the 

 palatoquadrate bar, the cranial capsule of Teleosts is sur- 

 rounded by other outworks consisting of bony plates and bars. 

 These arise as true dermal bones in the region of the eyes (orbital 

 ring), and in the gill-covers (opercular bones) : the latter are similar 

 in number and name to those of bony Ganoids. A large number of 



sphot 'par 



Fig. 60. — Cranial Skeleton*' of the iSalmon. (From the left side.) 



Pmx, premaxilla ; aih, supraethmoid ; nas, nasal ; mx, maxilla ; jiiij, jugal ; 

 pt, pterygoid ; mpt, mesopterygoid ; mtpt, metapterygoid ; Quad, quadrate ; , 

 hyom, hyomandibular ; p"^, palatine; fr, frontal; u, o, o, o, orbital 

 ring ; ^ar, parietal ; sphot, sphenotic ; tpiot, epiotic ; pttr, pterotic ; socc, 

 supraoccipital ; op, operculum ; prcKop, preoperculum ; intop, interoperculum ;- 

 subop, suboperoulum ; branchiont, branchiostegal rays ; dent, dentary ; art, 

 articular ; Zunge, tongue. 



branchiostegal rays are developed in the ventral part of the- oper- 

 cular fold, or branchiostegal membrane (Fig. 60). 



Anteriorly, the opercular apparatus lies against a bony chain 

 consisting of three pieces — the hyomandibular, symplectic, and 

 quadrate — which serves as a suspensorial apparatus for the lower 

 jaw (Fig. 60). The latter consists of Meckel's cartilage and of 

 several bony elements, the largest of which is the dentary : 



