SKULL 



237 



It is in the connection of the skull with the visceral arches that 

 the Dipnoi have diverged most conspicuously from other fish. The 



modern genera are completely autostylic (p. 95). The pterygo- 

 quadrate bar is firmly fused to the cranium in front and behind. 

 The spiracle disappears ; and the hyoid arch is well developed, with 

 a median basihyal, paired hypohyals, and large ossified ceratohyals 



