COMPARATIVE !?rUDY OF SO^MBROU) FLSHES. 341 



KlBS AXD lNTERMl'SOür,.\R BONES. 



The ribs are developed along the iutenml anterior margin of the prccaudal 

 myotomes, on both sides of the alxlomiual cavity, ninniiig obliqnelj- backward, 

 to a point wliere the myotome turns to ]x;ud anteriorly. Hence the length and 

 the direction of ribs are determined by the internal boundary lines of the upi)er 

 iwrtion of the hypaxial half of the lateral muscle. Generally the rib is developed 

 from the thud vertebi-a and is xmited either directly to the centnuu or to the 

 transverse process, or to the distal end of the haemal proceas or the precfudal 

 haemal spine. Eibs near both extremities of the abdominal cavity axe short ; but 

 the other ones are nearly the same in length. They are broad, and form the 

 roof of the abdominal cavity, especiiilly those at the anterior LtIT of the scries. 



In the Scomlmdjxe the ribs ai'e slender, roxmdish in cross-section, ncivrly the 

 same in sha^xj and length, separated &'om each other, and reach quite near the 

 ventral mediixn line (fig. 1). The intermuscular bones form a series of slender 

 bones between the epaxial and hypaxial portions of the lateral muscle, and 

 along the anterior surface of the myotome. They ai'e well developed, slightly 

 ciu^ed in anterior precaudal vertebrae, their tips reaching the external surface 

 of the lateral muscle, and are bent backward l)elow the skin. The intei- 

 muscuhirs are developed from the firet vertebra to about the twentieth in 

 ScomLer joponicus. In the latter species the intermuscular lx)nes are iusei-ted 

 just at the base of the haemal arch or process, and seven or eight anterior ones 

 are long enough to appear on the sm-face of the lateral muscle. The tips of 

 these long intermuscuLix bones do not overlap each other, and they are at a 

 Uttle distance above the lateral median line of the body (fig. 1). In the other 

 scombroid fishes tips of the intennuscidar bones appear at the lateral median 

 line. 



In the Cybiidae the riljs are generally slender, sul equal, and lie close to, but 

 do not touch each other. In Acaidhocyhivm sdaiidrl and Sarda orientalis some 

 ribs are very broad. Intermuscular bones are found between some cephalic 

 myotomes too, and sometimes we find two pail's in the region, both on the 

 exoccipitals. In the genus Acanthocijbium the intermuscular bones except the first 

 are attached to the head of riljs, as was observed by Stakes, not on the centrum 

 as in the other scombroid fishes, and in this genus only the first rib is found on the 



