584 STRUCTURE OF VERTEBRATES 



bones develop from the skin of the roof of the mouth ; these are 

 the paired palatines, dermal pterygoids, and ectopterygoids, 

 with, in front of them, the vomers, which we have already 

 treated as dermal bones of the nasal capsule, to which they are 



Paid eosty Lie 

 Ancestor 



HoLostyLic 

 HoLocephaL 



Para utosty Lie 

 CycLostome 



Autodiasti/Uc 

 Primitive 

 \ Chond rich til yes 



HyostyLic 



Modern 



SeLachii 



Batoidei 



Chondrostz'i 



MethyostyLic 



Modern 

 TeLeostomi 



Amniota 



Fig. 455. — Diagrams to show the evolution of the jaw suspensions of vertebrates 

 from a hypothetical ancestor in which the visceral skeleton is completely free 

 from the brain case. — From De Beer, The Development of the Vertebrate Skull. 

 1937. Clarendon Press, Oxford. 



