SKULL 



91 



which appear later, are doubtless derived from them. They show, 

 moreover, a connection with the Dipnoi and with the oldest 

 Amphibia from the Carboniferous and Trias (Stegocephali). 



In the Teleosts, the skull (Figs. 69 and 70) presents a large 

 amount of variation ; its ground-plan, however, may always be 

 derived from that of the Bony Ganoids, as is best seen by a com- 



sp.eth-(- 



op.o- 



Ofl.O- 



occ.-\- 



Pa s P r fr 



Ptf 



Sb 



Sf> Na 



O.t 



f/a 



FIG. 68B. SKULL OF POLYPTERITS. A, LATERAL, AND B AND C DORSAL VIEWS, 

 THE LATTER AFTER REMOVAL OF THE DERMAL BONES, THE CARTILAGE 

 DOTTED. (From Traquair.) 



An, angular ; Ar, articular ; D, dentary ; E, mesethmoid ; f.m, foramen magnum ; 

 Fr, frontal ; l.e, lateral ethmoid ; MX, maxilla ; Na, Na', nasal and accessory 

 nasals ; occ, occipital : ol, nasal aperture ; op, operculum ; op.o, opisthotic ; 

 O.t, "os terminals"; Pa, parietal; Pmx, premaxilla ; P.t, posttemporal ; 

 Ptf, postparietal ; Qu, quadrate ; S.b, S.b', suborbitals ; S.Op, sub-operculum ; 

 Sp, splenial; *}>.eth, "sphenethmoid," in the orbitosphenoid and alisphenoid 

 region, resembling the like-named bone of Anura (q.v.) ; sp.o, sphenotic ; Spr, 

 prespiracular ossicles ; S.t, supratemporals ; Y, preoperculum (cheek plate); 

 Y', Y", smaller cheek plates ; z, postspiracular ossicles ; z', prespiracular 

 ossicles. 



parison of the Siluroids with Amia. On the other hand, no 

 relations with the Amphibia are observable, and we must consider 

 the whole group of the bony Fishes as a side branch of the piscine 

 phylum. 



Much of the cartilaginous primordial skull persists in many 



