82 THE VERTEBRATE SKELETON. 



rod, the basi-pterygium (fig. 8, 2), running directly backwards 

 on the inner side of the fin, and articulating in front with the 

 pelvic girdle. From its outer side arise a series of about 

 fourteen parallel cartilaginous radials which bear smaller 

 polygonal pieces. The anterior one or two of these radials may 

 articulate independently with the pelvic girdle. In the adult 

 male dogfish the distal end of the basi-pterygium bears a stout 

 rod nearly as long as itself, and grooved on the dorsal surface. 

 This is the skeleton of the clasper (fig. 8, 3). 



