COMPARATIVE STUDY OF SCOMBROID FISHES. 
341 
Ribs and Intermuscular Bones. 
The ribs are developed along the internal anterior margin of the precaudal 
myotomes, on both sides of the abdominal cavity, running obliquely backward, 
to a point where the myotome turns to bend anteriorly. Hence the length and 
the direction of ribs are determined by the internal boundary lines of the upper 
portion of the hypaxial half of the lateral muscle. Generally the rib is developed 
from the third vertebra and is united either directly to the centrum or to the 
transverse process, or to the distal end of the haemal process or the precrudal 
haemal spine. Ribs near both extremities of the abdominal cavity are short ; but 
the other ones are nearly the same in length. They are broad, and form the 
roof of the abdominal cavity, especially those at the anterior half of the series. 
In the Scombridae the ribs are slender, roundish in cross-section, nearly the 
same in shape and length, separated from each other, and reach quite near the 
ventral median 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 are well developed, slightly 
curved in anterior precaudal vertebrae, their tips reaching the external surface 
of the lateral muscle, and are bent backward below the skin. The inter- 
musculars are developed from the first vertebra to about the twentieth in 
Scomber japonicus. In the latter species the intermuscular bones are inserted 
just at the base of the haemal arch or process, and seven or eight anterior ones 
are long enough to appeal* on the surface of the lateral muscle. The tips of 
these long intermuscular bones do not overlap each other, and they are at a 
little distance above the lateral median line of the body (fig. 1). In the other 
scombroid fishes tips of the intermuscular bones appear at the lateral median 
line. 
In the Cybiidae the ribs are generally slender, sul equal, and lie close to, but 
do not touch each other. In Acanthocybium sdandri and Sarda orientalis some 
ribs are very broad. Intermuscular bones are found between some cephalic 
myotonies too, and sometimes we find two pairs in the region, both on the 
exoccipitals. In the genus Acanthocybium the intermuscular bones except the first 
are attached to the head of ribs, as was observed by Starks, not on the centrum 
as in the other scombroid fishes, and in this genus only the first rib is found on the 
