100 



COMPARATIVE ANATOMY. 



FIG. 85. PECTORAL FIN OF Ceratodus fosteri. 



a, b, the two first segments of the main axial ray ; f, t, lateral rays, or radii ; F8 t 

 horny rays, shown only on one side. 



HS 



FIG. 86. DIAGRAM OF THE PREDOMINANT UNISEHIAL TYPE OF THE ANTERIOR 

 EXTREMITY OF ELASMOBRANCHS. 



HS, the axis passing through the main ray ; ***, mimerous lateral rays of one side ; 

 ttt, few lateral rays of the other side. 



the main ray of the fin (basipterygium). This serves as the 

 chief support for all the other rays, and is to be considered as 

 the homologue of the axial ray of Ceratodus. The above 



