70 EVOLUTION AND GENETICS 



Amphibia. In the skulls of Amphibia the dermal bones are no 

 longer external as in some fishes at any stage of development, but 

 have become definitel}^ incorporated with the cartilage bones as 

 parts of the internal skeleton. In addition the characteristically 

 piscine elements, like the rostrals, the orbitals and those associated 

 with the operculum, have been lost, and the remaining bones 



Fig. 46. — Dorsal view of schematic skull, the chondrocranium dotted, mem- 

 brane bones outlined, premax, premaxilla; pref, prefrontal; postfr, post- 

 frontal; postor, postorbital; squamos, squamosal; quju, quadratojugal; inp, 

 interparietal; exocci, exoccipital; supratem, supratemporal; supraoc, supra- 

 occipital; other names in full. (From Kingsley's Comparative Anatomy of 

 Vertebrates, with the permission of P. Blakiston's Son & Co.) 



more nearly approximate the number and relationships of the 

 higher terrestrial forms. We find among them a pair of small 

 bones behind the anterior nares, behind which a similar pair of 

 larger bones reach the orbits on the sides. Still another median 

 pair lie behind the orbits. The first correspond in their orientation 

 with the nasals of the fishes, and are called the nasal bones. The 

 next are the frontals, representing these and some of the smaller 

 scutes of the sturgeon and the last are the parietal bones. A pair of 

 prefrontal bones lie behind the nasals and lateral to the frontals, 

 as in the fishes. Caudad this portion of the skull is associated, 

 through the supra-occipital, with the basal or occipital part of 



