MORPHOLOGY OP TELEOSTEAN HEAD SKEl,ETON. 563 



of Selachii led him to regard the chondrocranium of all the 

 higher Vertebrata as derived from a similar type ; a conclusion 

 to which he was guided mainly by a consideration of the carti- 

 laginous condition in the former as opposed to the osseous con- 

 dition in the latter. No doubt he was right as far as the mere 

 substance of which the cranium was composed was concerned, 

 but apparently it did not occur to him to inquire whether the 

 chondrocranium of a higher vertebrate with its numerous 

 fontanelles did in reality arise fi'oui a simple box-like Selachian 

 cranium. Nevertheless, since he published his unique memoir, 

 workers upon the piscine skull have largely assumed that such 

 was the case; that the fontanelles of the one have arisen by 

 fenestration of the other. Thus, beyond what has already 

 been mentioned, Sagemehl in dealing with the Characinidup, 

 which have anterior and posterior fontanelles in the roof of 

 the chondrocranium, regarded the former as the homologiie 

 of the Selachian " Prjefontalliicke," but the latter as an 

 entirely new formation. More recently Pollard looked upon 

 a small cai'tilage in the large supra-cranial fontanelle of 

 Polypterus as the last remnant of an originally complete 

 cartilaginous roof, and started a comparison of its cranium 

 with that of Notidanus, Avith the " obvious postulate " that 

 " the supra-cranial fontanelle be considered to have a complete 

 cartilaginous tegmen cranii of which only the rema^ins are 

 now known" (92, p. 402). 



Gegenbaur, comparing Alepocephalus with Salmo and 

 Esox, concluded that mass of cartilage was no criterion of a 

 lowly position, but the form and ossification of the same, and 

 says : " Aus diesem Allen geht hervor, dass das reiche Maass 

 von Knorpel in phylogenetischer Beziehung nicht verwerthet 

 werden kann. Es wird nur auf die ontogenetische 

 Anlage bezogen werden konneu,^ und wird dann als 

 eine Weiterentwickelung dieser Anlage gelten diirfen " (78, 

 p. 27). Again, Huxley, as early as 1858, says : " There are 

 discrepancies in the structure of the skull itself, which would 

 forbid too close an approximation between the bony and the 

 ' Tlie italics are not, niiue. 



