52 BULLETIN OF THE BUREAU OF FISHERIES. 



Contractions of the abductor ventralis superficialis produce ventral flexions of the 

 ventral fin. It tends to bend the fin downward, i. e., away from the body. If the fin 

 rays are at the time spread then approximation of the rays also occurs. 



ABDUCTOR VENTRALIS PROFUNDUS. 



This is a large and strong muscle which lies external and dorsal to the superficialis. 

 It takes its origin from the entire ventral surface of the ischial plate, from the septum 

 which connects the external margin of this bone with the skin, and from the similar 

 septum that runs from the internal or median border to the mid-ventral line. This 

 last septum joins the median longitudinal pelvic septum just at the mid-ventral line 

 of the abdominal cavity; hence the peritoneum, the dorsal border of the median longi- 

 tudinal septum and the internal border of the ischial septum are fused. 



The muscle fibers from this extended origin converge in the general caudal direction 

 toward the base of the anal fin. The insertion is by very short tendinous slips into the 



Fig. 8. — Ventral view of the superficial muscles of the ventral fins and of the pelvic arch. ab. s., abductor ventralis superficialis; 

 ab. pr,, abductor ventralis profundus; ad. pr., adductor ventralis profundus; Pr. i., protractor ischii; re. i., retractor ischii; 

 Lat., lateral mtiscle, ventral margin. 



ventral half rays of the fin. The tendons run dorsal to the tendons of the superficialis 

 and are inserted into the inner border of the ventral half ray, i. e., the border next the 

 median plane of the fin itself. The fibers arising most anteriorly are inserted into the 

 rays of the external border of the fin. The fibers of the extreme posterior portion of 

 the muscle, arising in the deep angle in front of the ischial thickening, run almost dor- 

 sally to the tips of the bases of the rays. 



The two halves of the individual rays are more widely separated in the ventral fins 

 than in the unpaired fins, and a distinct synovial joint is formed here as described for 

 the pectoral by Pychlau." The manner of insertion of the abductor profundus and the 

 presence of this very efficient joint insures a strong abduction of the ventral fin on its 

 contraction. There is only a minimal approximation of the fin rays, if any at all, accom- 

 plished by this muscle. This latter function seems limited to the superficialis. 



o Pydilau, loc. cit. 



