COMPARATIVE STUDY OF SCOMBROID FISHES. 
343 
ribs, and united to those vertebrae. In the Thunnidae the ends of some 
posterior ribs lie close on both sides of the thick group of interspinous bones 
of the anal, and in these the posterior pairs of one side run quite near their 
fellows of the other side. 
Interspinous Bones. 
In the skeleton of the median fins of the scombroid fishes, we distinguish 
three types :—(1) that of the first dorsal, (2) that of the second dorsal and 
anal, and (3) that of the dorsal and anal finlets. Each interspinous bone 
consists of the distal and proximal segments, and the latter segment is furnished 
with lateral and sagittal wings. The first interneural is the longest. 
In the first dorsal, spines articulate with the proximal segment, behind the 
wide, dorsally bent distal segment. The posterior end of the proximal 
segment is also wide and dorsally bent, behind the point of articulation of the 
dorsal spine. The exterior margin of these dorsally bent parts is often ser¬ 
rated. These dorsally bent parts form the wall of the groove for the first 
dorsal fin. 
In the second dorsal and anal, the interspinous bones are anteroposteriorly 
compressed, and the divided proximal end of spines or rays grasps the distal 
segment, and articulates with the proximal segment. 
In the region of the finlets, the interspinous bones are elongated antero¬ 
posteriorly, often with the development of the middle segment. The distal 
segment is very small, and is grasped by the proximal ends of fin-rays, and 
articulates with the proximal segment. 
Interspinous bones of the first dorsal and finlets are generally found one 
of each in each myotome, but those of the second dorsal and anal are 
generally two in each myotome. No spurious interspinous bones before 
the first dorsal. The interspinous bone of the last finlet of the dorsal and 
anal wants the proximal 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 spurious bones between the two dorsals, one in every myotome, and 
the free lower end of the interspinous bones of the first dorsal are inserted 
between the tip of the neural spine of precaudal vertebrae. The anterior 
