MORPHOLOGY OF TELEOSTEAN HEAD SKELETON. 560 



In the former the pterygo-quadrate cai'tilage is attached 

 to the cranium at two points ; the hinder one under the post- 

 orbital process, by means oE the otic process, aud an anterior 

 one between the exits of the second and fifth nerves, by means 

 of the paUxto-basal process. In front of this the cartilage 

 contiuues forwards as the " oberkiefersfortsatz " under the 

 ethuioid reg'ion to unite with its fellow. The hyomandibuhir 

 is slender, and lias no articulation with the auditory capsule, 

 and is fastened to this by ligament some distance behiud the 

 post-orbital process. 



Oue glance at these two types suffices to show that the 

 palato-quadrate of one possesses just those crauial attach- 

 ments which are absent in the other, and vice versa. To 

 derive either condition from the other is therefore impossible. 



The position of the hyoiuaudibular i-elatively to the 

 auditory region in Teleosts, together with other considerations 

 concerning the associated muscles and the variations in the 

 related uervo, led Pollard (94, p. 23) to conclude that the 

 elements of that name in these two great groups of fishes 

 were not houiologous; and to seek for the Teleostean 

 hyomandibular in the otic process of Heptauchus, and for 

 that of the Elasmobrauchs in the stylohyal of Teleosts. In 

 view of his observation that in young Silurus the two sets of 

 cartilages form a continuous whole, and that in Gasterosteus 

 the broad head of the hyomandibular is formed by backward 

 growth during development, it must be admitted that his 

 case, though startling, is strong, and if true, at once puts all 

 other Selachian types of suspensorium out of court as possible 

 conditions for the derivation of the Teleostean type (cp. 

 Gegenbaur, 72, p. 175). 



In 1876 Huxley introduced tiiree useful terms — autostylic, 

 hyostylic, amphistylic — to express the ^ manner in which the 

 mandibular arch is connected with the skull." He regarded 

 the second of these as '^ perfectly exemplified by Ganoids, 

 Teleostei, and Plagiostomes," and characterised by the fact 

 that the " palato-quadrate cartilage is no longer continuous 

 with the chondrocraninm, but is, at most, united with it 



