﻿Note on the AtUostyhc Skull of Vertebi^ates. 169 



XIV. Note on the Autostylic Sktdl of Vertebrates. 

 By J. Graham Kerr. 



(Read 28th October 1907.) 



The object of this note is to emphasise the need, for the 

 sake of clearness, of modifying current nomenclature so as 

 to distinguish between the two very different modes of 

 suspension of the jaw apparatus, which are confused together 

 under the term autostylic. Huxley, when he invented the 

 term autostylic, used it in reference to Ceratodus and 

 Chimaera, there being at the time no embryological data 

 available regarding these forms. 



The condition in Chimaera appears to be a further 

 development of that found in Heterodontus, where the 

 primitive upper jaw (palato-pterygoquadrate cartilage) is 

 firmly adherent to the cartilaginous cranium. In Chimaera 

 complete fusion has apparently taken place, the upper jaw 

 being perfectly continuous in substance with the cranium. 



In Dipnoans, on the other hand, the attachment of jaw 

 apparatus to skull is not through the primitive upper jaw, 

 i.e., through the palatopterygoquadrate outgrowth from the 

 mandibular arch, but through the upper part of the original 

 mandibular arch itself. That this is so seems perfectly clear 

 from Sewertzoff's account of the young skull of Ceratodus, 

 and from Agar's reconstructions of the skull in the young 

 Zepidosiren and Protopterus. In other words, the suspension 

 of the lower jaw from the skull is here (as also in Amphibia) 

 a relatively primitive one, and it should be marked off 

 by the use of a distinct term, e.g., protostylic, from the 

 clearly secondary mode of suspension through the palato- 

 pterygoquadrate outgrowth. 



VOL. XVII. 



