58 BULLETIN OP THE BUREAU OF FISHERIES. 



The posterior slips of the erector anaUs are somewhat modified from the regular 

 arrangement. The last pair of erector and depressor muscle slips is greatly enlarged, or 

 rather the erector is greatly enlarged and the depressor moderately so. The fibers near 

 the tendon of insertion pass over the modified interhemal cartilage to which the retractor 

 ischii is attached, to insertions into the posterior border of the last anal fin ray. This 

 fin ray is itself very small. The tendinous end of the muscle slides over a groove formed 

 by the modified cartilages supporting the ray. 



At the anterior margin of the series of erector divisions there is a muscular slip which 

 seems to belong to the series, judging by its origin, but the insertion of which passes into 

 the skin in front of the fin and near the base of the anal papilla. 



The contractions of the erector muscles tend to elevate the anal fin and in con- 

 tinued contraction to hold it in the erect position. This is favorable in increasing the 



Fig. 13. — Superficial muscles of the aual fin. inc., inclinator analis showing divisions lor each ray; re. i., retractor ischii (pro- 

 tractor aaahs): r. a., retractor anahs; Lai., great lateral muscles. The dotted line indicates the ventral limit of the lateralis 

 superficiahs. 



efficiency of the lateral movements which this fin contributes in balancing the fish in 

 the water. 



The contractions of the larger posterior muscle slip described tend to draw the pos- 

 terior end of the anal fin sharply against the body and to some extent to antagonize the 

 retractor analis. The function of the most anterior slip which has an insertion into the 

 skin in front of the fin would seem to be in connection with the movements of the anal 

 papilla. 



DEPRESSOR ANALIS. 



The depressor muscle consists of a series of slips which arise from the anterior surface 

 and lateral margin of the interhemal of the segment to which each belongs and from the 

 fascia separating it from the erector muscle attached to the same ray. The fibers of 

 each slip run as a slender ribbon over the shaft of its interhemal to an insertion into the 



