58 



THE ANATOMY OF YERTEBRATED ANIMALS. 



nous, and even of the bonj, constituents of tlie pectoral and 

 pelvic arches of the latter are traceable in Fishes, the cartila- 

 ginous, or ossified, basal and radial supports of the fins them- 

 selves cannot be identified, unless in the most general waj, 

 with the limb-bones, or cartilages, of the other Vertehrata. 



In its least modified form, as in Lepidosiren^ the endo- 

 skeleton of the fish's fin is a simple cartilaginous rod, divided 

 into many joints; and articulated, by its proximal end, with 

 the pectoral arch. The £lasmohranchii possess three hasal 

 cartilages w^hich articulate with the pectoral arch, and are 

 called, respectively, from before backward — propterygial^ me- 

 sopterygial, and metapterygial hasalia. With these are artic- 

 ulated linear series of radial cartilages, upon which osseous, 

 or horny, dermal fin-rays are superimposed. (Fig. 15.) 



Among the Ganoid fishes, the fins of Polypterus are, fun- 

 damentally, like those of the Elas'mohrancTiii ; but the pro- 

 pter3^gial, mesopter3^gial, and metapterygial hasalia^ are more 

 or less ossified, and are succeeded by a series of elongated 

 radialla, w^hich are also, for the most part, ossified. Beyond 



Fla 1B.--Tht right pectoral member of the Monkish (Sgnafina): ^i, propterj'giani . r>t3, 



mesopteiygium; ?/i^, metapteryg-iuui. 



