SKELETAIv MUSCULATURE OF THE KING SALMON. 



59 



posterior border and tip of the corresponding fin ray. Each muscle slip is somewhat 

 thicker at its external border. 



The muscle slips are from 30 to 35 mm. long anteriorly and 20 mm. at the posterior 

 border of the series. They are about 4 mm. broad by i mm. thick in the middle of the 

 muscle belly. They are closely wedged in between the bellies of the erector divisions. 

 The anterior slips attached to the rudimentary rays are very small and slender. 



The contraction of these muscles depresses the rays of the fin, tending to close it up 

 against the body. 



Fig. 14. — Deep muscles of the anal fin. e. a., erector analis; d. a., depressor analis; inc., four reflected tendons of the inclinator 

 analis; re. i., retractor ischii (protractor analis); r. a., retractor analis. 



INTERFILAMENTI ANALIS. 



Between the fin rays of the anal fin, especially at the base and more strongly devel- 

 oped anteriorly, are found delicate muscle fiber bundles. These muscles are attached 

 to adjacent fin rays, being attached nearer the base of the anterior ray, and more distally 

 to the posterior ray, carrying them in an oblique direction from ray to ray. 



Undoubtedly these sHps aid in the elevation of the fin rays. They are very delicate 

 and consist of only a very few individual fibers, a fact which easily leads to their being 

 overlooked. 



The protractor analis and the retractor analis are longitudinal muscles of the anal 

 fin which have been described on page 34. 



