THE SKULL. 



In other points, however, they differ considerably from all these ; 

 and it is clear that the last-named group cannot have been directly 

 derived from them. The suspensorium, as well as the very massive 

 palatoquadrate bar, fuses with the skull, and, as in Amia calva (a 



J'/llJO 



Va 



A: 



':> W 







FIG. 53. SKULL OF Polypterus bichir FROM THE DORSAL SIDE. 



Pmx, premaxilla ; Na, external nostril ; N, nasal ; Sb, Sb l , anterior and posterior 

 suborbital ; Orb, orbit ; M, maxilla; Sp, spiracular bones; PO, preoperculum ('() ; 

 SO, suboperculum ; Op, operculum ; F, frontal ; P, parietal ; a, b, c, d, supra- 

 occipital shields. The two arrows pointing downwards under the spiracular 

 shields show the position of the openings of the spiracles on to the outer surface 

 of the skull. 



bony Ganoid), even some of the anterior vertebrae with distinct 

 neural arches and transverse processes are united with the occipital 

 region of the cranium (Fig. ~>4>, W, IV 1 ). (Cp. note on p. 56.) 



Posterior in addition to anterior nasal apertures 

 appear in the Dipnoi for the first time : this is an indication of 

 air-breathing. 



Cranial bones are not nearly so numerous as in Ganoids, and 



F 2 



