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 



<rtli 



,. epiot 



dent 



FIG. 60. CRANIAL SKELETON OF THE SALMON. (From the left side.) 



Pmx, premaxilla ; eth, supraethmoid ; nets, nasal ; mx, maxilla ; jug, jugal ; 

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

 hyom, hyomandibular ; pal, palatine ; fr, frontal ; o, o, o, o, orbital 

 ring ; par, parietal ; sphot, sphenotic ; epiot, epiotic ; pter, pterotic ; socc, 

 supraoccipital ; op, operculum ; pra>op, preoperculum ; intop, interoperculum ; 

 sttbop suboperculum ; branchiost, 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: 



