THE RELATIONS OF THE ANTERIOR VISCERAL 

 ARCHES TO THE CHONDROCRANIUM. 



W. K. GREGORY. 







The articular relations with the chondrocranium of the upper 

 and lower jaw-cartilages and the hyomandibular, as typified in 

 Ceratodiis, in Sqiialns, and in Noiidanus, are in themselves of 

 course generally understood, but comparison of the current defi- 

 nitions and usages of the corresponding terms " autostylic," 

 "hyostylic," " amphistylic" reveals considerable discrepancy, 

 which is highly confusing to the general student ; hence the 

 present endeavor to standardize these terms and to give, as far as 

 needed, their synonymy. 



From the analysis necessary for the accomplishment of this 

 purpose it has become evident that all the current definitions of 

 "hyostylic," " autostylic" and "amphistylic " are in one way or 

 other unsatisfactory, and that if these conceptions are to retain 

 anything more than historic interest they will have to be ex- 

 tended to include the relations to the chrondrocranium not only 

 of the hyomandibular but also of the hyoidean arch as a whole 

 and of its distal or ventral half, the " hyoid " or ceratohyal. By 

 this extension we are enabled : first, to apply separate and clearly 

 diagnostic terms to the suspensorial conditions of the very phy- 

 logenetically separated groups Dipnoi (autostylic) and Holoceph- 

 ali (" holostylic" ), hitherto lumped together under the single 

 term "autostylic"; second, to differentiate under the generic 

 concept " hyostylic " four specifically well-marked modes, (<?) the 

 " hyostylic proper " of typical sharks, (b] the " amphyostylic " of 

 Notidanus, (V) the " euhyostylic " of most rays, (d} the " methyo- 

 lic " of the teleostomes ; third to group all the modern types of 

 suspensorial conditions under the term "csenostylic " in contrast 

 with the ancestral type here called " palaeostylic," which is only 

 a few steps below Gadow's 1 suggested form, the " simple auto- 

 stylic." 



1 " O.i the Modifications of the First and Second Visceral Arches, etc., " Philos. 

 Trans., Vol. 179 (1888) B, p. 459. 



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