PELVIC GIRDLE AND FIN OF EUSTHENOPTERON. 317 



that the pelvic girdle originated as an ingrowth of the base of 

 the primitive fin skeleton, or whether, following Gegenbaur, 

 we consider it to have been derived from a gill arch, it will 

 be admitted that the girdle was primarily differentiated as a 

 right and a left support and fulcrum for the fin, and as a 

 point of attachment for the muscles whereby the fin is 

 moved. The girdle plate must have been from the first 



I'iG. G. — Ventral view of tlie pelvic girdle and fins of Polypterus bichir, 



Geoffr. 



embedded in the ventral body-wall from which sprang the 

 free lobe of the pelvic fin. 



Such appears to have been the structure of the paired pelvic 

 girdle of the Plenracanthidge (Fritsch [3] and Figs. D and 

 E), and such it is essentially at the present day in the Holo- 

 cephali (Fig. B). The development of the pelvic girdle iu the 

 Selachii (Balfour [1], Mollier [6]) warrants the view that the 

 median cartilage there found has been formed by the fusion 

 of two originally separate halves. Presumably iu this way 

 has also originated the median cartilage of the Dipnoi. 



