164 University of California Publications in Zoology [Vol.18 



quite simple except in the ease of the pelvic fin of the male, where 

 an elaborate system of muscles is developed in connection with the 

 clasper. In all except the anal and caudal fins the muscles are differen- 

 tiated into radials. 



Muscles of the Paired Fins 



The radials of the pectoral fin {ra., fig. 7) form a dorsal and a 



ventral series. Dorsally they take origin posteriorly and laterally 



from the scapular portion of the pectoral girdle, from the pro- and 



mesopterygia, and from a band of tendinous connective tissue along 



Fig. 7. Left pectoral fin, Heptanchus maculatus, lateral view (X %). co., 

 coraeoid cartilage; sc, scapula; ra. d., dorsal radial muscles; ret. v., ventral 

 radial muscles. 



the posterior dorsal edge of the fin. Deeper fibers have their origin 

 dorsally along the metapterygium. The origin of the fibers is not 

 restricted to the proximal cartilages, but extends over the entire dorsal 

 surface of the cartilaginous radials of the fin-skeleton. The muscle 

 fibers making up the radials are short and do not extend the entire 

 length of the muscles. Their direction is outward and distal. They 

 insert in the connective tissue which covers each radial muscle. This 

 tissue is tendinous and is continuous with the dermal fin rays. The 

 radials number about thirty-two including the small posterior parts 

 which are not very distinctly separated. 



In the ventral series about twenty-six distinct radial muscles may 



