62 \V. K. GREGORY. 



HYOSTYLIC SKULL : Mandilndar or first visceral arch no' con- 

 tinuous with the skull in its dorsal portion (the palatoquadrate) ; 

 the hinder end of the palatoquadrate is cliicfly connected with tlic 

 chondrocranium by means of the hyomandibular or dorsal portion 

 of the hyoidean arch. 



AMPHISTYLIC SKULL : Mandibular, or first visceral arch attached 

 to the skull wholly or almost wholly by means of its dorsal portion 

 the palatoquadrate, not Jwivcvcr by fusion or continuity, but by liga- 

 ments ; the hyoidean arch contributes but little to its support. 



The Huxleyan conception of amphistyly is that it is in some 

 respects a "middle form," resembling autostyly in the suspen- 

 sorial self-sufficiency of the first visceral arch, but resembling 

 hyostyly in the lack of confluence of the palatoquadrate with the 

 skull. A similar use of the prefix "amphi" occurs in " Amphi- 

 theriunt" which genus was at first supposed to combine mam- 

 malian and reptilian characters. 



The element " stylic " from THV.OC, a pillar, evidently refers to 

 the quadrate region in its architectural relation to the skull. The 

 skull of Chim&ra seems to have been regarded by Huxley as 

 primitive (so far as I can determine from a careful study of the 

 entire article) and hence in an autostylic skull the palatoquadrate 

 must have been conceived as belonging to the skull: therefore 

 the forces acting upon the jaws in eating would be transmitted 

 to the skull chiefly through the quadrate, its oivn pillar (hence 

 auto, stylic), whereas in the typical hyostylic skull these forces 

 would be transmitted chiefly through the pillar of the hyoidean 

 arch (the hyomandibular) hence "hyostylic." 



Huxley's conception of the phylogenetic relations of the three 

 types of cranial structure are expressed in the following diagram 

 (op. cit., p. 45): 



Amphibia. - Ganoidei. Teleostei. 



CERATODUS. Cestracoin. Raia. 



Chi mar a. Not i dan us. 



Autostylica. Amphistylica. Hyostylica. 



The left-hand column (autostylica) includes the (to Huxley) 

 more generalized types, the most primitive, Chiuuzra, standing at 



