COMPARATIVE STUDY OF SCOMBROID FISHES. 343 



riljs, aud luiitctl to thoso vortobnie. In the ThunuifLie the curfe of f5nme 

 p)stmor ribs lie close on both sidfs of the thick group of interspinoiis bones 

 of the anal, nud in these the posterior pairs of one side run quite near their 

 fellows of the other side. 



Interspinocs Bones. 



In the skeleton of the median fins of the scombroid fishes, we distinguish 

 three tribes : — (1) that of the first dorsal, (2) that of the second doi-sal and 

 siual, and (3) tluit of the doreal and anal finlets. Each interspinous bmie 

 consists of the chstal and proximal segments, and the latter segment is fimiislicd 

 with latemland sagittal wings. The first intemeural is the longest. 



In the first dorsal, spines articulate with the proximal segment, lehind the 

 wide, doi-sallj 1x7 it distal s^;raent. The posterior end of the proximal 

 s^mont is also wide and dorsally bent, beliind the point of aiiiculation of the 

 dorsal spine. The exterior maigin of these dorsally bent pi'rts is often ser- 

 rated. These dorsallv bent pivts form the wall of the groove for the first 

 dorsal fin. 



In the second dorsal and aui'.l, tlje interspinous bones are anteroposteriorly 

 compressal, and the divided proximal end of spines or rays grasps the distal 

 s^ment, and articulates with the proximal segment. 



In the region of the finlets, the interspinous bones are elongated antero- 

 posteriorly, often with tha development of the middle segment. The distal 

 segment is very small, and is gi'asped by the proximal ends of fin-rays, and 

 aiiiculates with the proximal segment. 



Interspinous bones of the fii"st dorsal txüd finlets are genenilly found one 

 of each iu eai-h myotome, but those of the second dorstd and anal are 

 generally two in each myotome. No spmions iutei"spinou3 bones before 

 the first doreal. The inteispinoas bone of the last finlet of the doreal and 

 anal wants the pi'oximal segment, and is attached to the posterior end of the 

 proximal segment of the preceding finlet. 



In the Scombridae the interspinous bones are weak and narrow, and there 

 are some spmions bones between the two doi-sals, one in every myotome, and 

 the free lower end of the interspinous bones of the first dorstd are ioserted 

 between the tip of the neural si^ine of precaudal vertebrae. The anterior 



