W. K. GREGORY. 6 1 



its own substance which constitutes the suspensorium. It may thus be said 

 to be antostylic. 



" Among fishes the only [other?] groups which possess an autostylic 

 skull or in which the dorsal end of the mandibular arch is continuous with 

 the cartilage of the brain case are the Chimasroids and the Marsipobranchii.' ' 



In this definition of autostyly attention is centered solely upon 

 the relations of the first arch with the skull. Huxley notes that 

 in the autostylic Ceratodus the hyomandibular is reduced and 

 fused with the skull, but he also uses " autostylic" for C1iivi(cra 

 in which the hyomandibular is separate (see above, Table A). 

 For comparison with " hyostylic " and " amphistylic >: we may 

 summarize Huxley's description as follows : 



AUTOSTYLIC SKULL : Mandibular or first visceral arch attached 

 to the skull solely by its ozvn dorsal moiety, the palatoquadrate, which 

 is continuous with the skull. 



Huxley describes the HYOSTYLIC and AMPHISTYLIC conditions 

 as follows (p. 41) : 



" In all other Fishes, except the Marsipobranchii, the mode of connec- 

 tion of the mandibular arch with the skull is different from that which ob- 

 tains in the Chimseroids and the Dipnoi. The palatoquadrate cartilage is 

 no longer continuous with the chondrocranium . . . but is, at most, united 

 with it by ligament. Moreover the dorsal element of the hyoidean arch, or 

 the hyomandibular, usually attains a large size and becomes the chief ap- 

 paratus of suspension of the hinder end of the palatoquadrate cartilage 

 with the skull. Skulls formed upon this type, which is exemplified in per- 

 fection in Ganoidei, Teleostei, and ordinary Plagiostomes, may therefore 

 be termed hyostylic. 



"But though the typical forms of autostylic and hyostylic skulls, as 

 exemplified, c. g., by a Sturgeon, a Pike, and a Dogfish or Ray, on the 

 one hand, and Chimcera, Ceratodus, and Menobranchus on the other, 

 are thus widely different, certain Plagiostomes present a condition of the 

 cranium which tends to connect the two by a middle form, which may be 

 termed amphistylic. 



" In the amphistylic skull the palato-quadrate cartilage is quite distinct 

 from the rest of the skull ; but it is wholly, or almost wholly, suspended by 

 its own ligaments, the hyomandibular being small and contributing but 

 little to its support. The embryo amphibian is amphistylic before it 

 becomes autostylic ; and, in view of certain palaeontological facts, it is very 

 interesting that the link which connects the amphistylic with the ordinary 

 Selachian skull is that of Cestracton." 



Huxley's conception of hyostyly and amphistyly may be re- 

 stated as follows : 



