MUSEUM OF COMPARATIVE ZOOLOGY. 15 



The hasipterygium of the ventral is elongate and triangular, the iliac 

 ridge being continued along its upper side. At its extremity there is a 

 series of three radials. The majority of the radials are in three series, 

 but some of the posterior form a single one. Thirteen radials articulate 

 with the side of the hasipterygium. 



The Cartilages of the Anal Fin. 



Plate XIII. h-b. 



These cartilages occupy an extent of three fourths of an inch at the 

 widest by about seven inches in length. The fin itself is less than half 

 an inch longer. The band of cartilages is widest forward and tapers 

 toward the tail ; it is widely separated from the hsemapophyses. The 

 radials are thin, and have not a great deal of rigidity. Segmentation 

 has been very irregular in its operation : in the lower half of the band, 

 the radials are directed backward in the usual manner ; in the upper 

 half, nearer the vertebrae, a few segments agree with the former, but 

 the majority are directed obliquely forward. The directions of the lines 

 of separation in either case are those separating the interneurals and 

 the neurapophyses, and are probably determined by similar causes, — 

 movements of the body in particular directions, or the directions of 

 the forces exerted by the muscles. 



The Cartilages of the Dorsal Fin. 



Plate XIII. Fig. a -a. 



The series of cartilages in the base of the dorsal is three fourths of an 

 inch in width by four and three fourths inches in length. It is widest 

 backward and tapers gradually in front. It is not near the vertebrae ; 

 its only connection with the latter is by membrane. That portion of 

 the base extending in front of the fin has its radials directed obliquely 

 forward ; the part beneath the fin, though irregular, has them directed 

 backward. 



The great extent of the band compared with the size of the fin, and 

 the manner in which it dwindles toward the front, taken in connection 

 with the fact of the continuation of the peculiar scales of the fin border 

 some two inches in front of the cartilages, show that in ancestral forms 

 of this animal the dorsal fin was much larger, and corresponded more 

 nearly in proportions with the anal. 



