MORPHOLOGY OF TELEOSTEAN HEAD SKELETON. 573 



If Pollard was right in regarding the hyomandibular of 

 Teleosts as part of the same cartilage to which the quadrate 

 belongs, then this has a third connection through the auditory 

 capsule with the cranium, and increases the resemblance to 

 the Marsipobrancli, for both Myxine and Bdellostoma possess 

 an otic attachment in addition to the palatal and pedicular 

 ones. 



Tui-ning to Elasmobranclis, and descending from the more 

 specialised to the less specialised forms, it is noticeable that, 

 apart from the hyomandibular, in the former, e. g. Scy Ilium, 

 the palato-quadrate is suspended only by ligament ; in inter- 

 mediate forms, e. g. Acanthias, a palato-basal process or 

 pedicle is ]n'esent; and in the latter, e. g. Heptanchus, which 

 is undoubtedly a lowly type, suspension is by means of both 

 otic and pedicular processes. There are some forms, e. g. 

 Cestracion, Avhich do not conform to this, but the constant 

 recurrence of the pedicle amongst Selachii points back to an 

 ancestor which certainly possessed that feature. Whether 

 an otic articulation was also present must, in view of Huxley's 

 (76, p. 44) iind Sewertzoff's (99, p. 299) opinions that it is 

 secondary, and Gegenbaur's (72, p. 186) and Pollard's 

 (94, p. 28) that it is primary, be left undecided until the 

 homology of the Teleostean hyomandibular is definitely 

 determined. 



Seweftzoff considers that the palato-basal process was the 

 primary attachment for the mandibular arch (99, p. 299), 

 because at a very early period in the development of 

 Acanthias it is united with the trabeculge by dense tissue. 

 The fact that in Petromyzon the facial skeleton commences as 

 an outgrowth — the pedicle — from the trabecular (Parker, 83, 

 p. 441), that in Lepidosteus the pedicle appears very early, 

 and that in Teleosts the p;ilatine process always grows out 

 from the quadrate (Stohr, Pollard, and above in Stage 1), 

 strongly supports this view, and points to a remote time when 

 neither palatal nor otic processes existed. 



VOL. 45, I'AKT 4. NEW SERIES. QQ 



