RELATIONS OF ANTERIOR VISCERAL ARCHES. 59 



c. Amphyostyly * Second visceral arch intact, of slight sus- 



pensorial value, much smaller than first arch ; palato- 

 quadrate deep posteriorly, articulating by its " otic 

 process" with the chondrocranium. Notidanus, 

 Pleur acanthus. 



d. Methyostyly? Second visceral arch broken up (i. c., with 



the component segments more or less shifted out of 

 their primitive sequence or relations) ; symplectic^ 

 metapterygoid, pre- and interopercular when pres- 

 ent assisting the hyomandibular in the support or 

 bracing of the quadrate and mandible. 



The value and permanence of this classification will depend on 

 whether the hyomandibular of teleostomes is homologous, as 

 generally supposed, with that of elasmobranchs. This has been 

 called into question by Pollard ('94) but as his conclusions have 

 not been adopted by subsequent authorities it seems best to ac- 

 cept the traditional view that these elements are truly homolo- 

 gous in the two groups. . 

 The application of these terms in classification and phylogeny 

 is illustrated in the diagram on page 60. 



PREVIOUS DEFINITIONS. 



Huxley. - -The terms " autostylic," " amphistylic," " hyosty- 

 lic " were first used by Huxley in his paper of 1876 on Cerato- 

 dus? The passage in which " autostylic " is defined is as follows 

 OA dt. t p. 40) : 



"The part of the palato-quadrate cartilage [of Ceratodus\ which is 

 united with the skull, between the exits of the fifth and second nerves, an- 

 swers to the " pedicle of the suspensorium " of the amphibian, while its 

 backward and upward continuation onto the periotic cartilage corresponds 

 with the otic process. As in the Amphibia and in the higher Vertebrata, 

 the mandibular arch is thus attached directly to the skull by that part of 



1 ' ' Amphyostyly " ; this term retains the element " amphi," so long used (in 

 amphistylic] of these forms, while clearly indicating its subordination under hyo- 

 styly. 



2 " Methyostyly," in allusion either to the prominence of the w.?Azpterygoid in the 

 suspensorium, or to the fact that methyostyly represents a morphological advance 

 upon earlier modes. 



3 Proc . Zoo/. Sor. Lond., 1876, pp. 24-59. "The Scientific Memoirs of Thomas 

 Henry Huxley," Vol. IV., 1902, pp. 84-127. 



