COMPARATIVE STUDY OF SCOMBROID FISHES. 
345 
and is inserted between tlie two moieties of the fin-ray. 
The lateral margin of the distal segments and that of the dorsal posterior 
end of the proximal segment are mostly serrated in the Tliunnidae, but is 
straight and entire in the Katsuwonidae. 
MUSCULAK SYSTEM. 
I have chiefly examined the lateral muscle, the other muscles were scarcely 
touched. The great lateral muscle is originally composed of as many transverse 
segments as there are vertebrae, and each segment is attached internally to 
the respective vertebra and its processes and appendages,—neural and 
haemal processes, ribs, and intermuscular bones. The first three muscle- 
segments, however, do not correspond to the first three vertebrae, as these 
three segments belong to the cephalic, or rather occipital region, where we 
find one or two auxiliary intermuscular bone3 between them, in the Cybiidae 
and Plecostei. These cephalic myotomes are inserted between the foramen 
magnum and the pterotic processes of the cranium, and connects the skull with 
the pectoral girdle. Hence the fourth muscle-segment or myotome corresponds 
to the body-segment of the first vertebra. Moreover, some myotomes seem 
sometimes to augment by subdivision, in fishes of the Katsuwonidae. In Auxis 
one or two auxiliary myotomes are added in the hypaxial half. Generally one 
auxiliary myotome is added near the boundary between the precaudal and 
caudal portions. When there is another auxiliary myotome, it is found in the 
anterior part of the precaudal region, where the cutaneous artery appears to 
the surface of the body. These auxiliary myotomes are not always bilaterally 
symmetrical. Moreover two auxiliary myotomes are sometimes found in one 
side, and only one in the other. At the caudal region some myotomes are 
coalesced and they are much elongated anteriorly. The myotomes in the caudal 
peduncle are united into one in the Plecostei, in the region where the lateral 
keel makes its appearence in the vertebrae, and where the neural and haemal 
processes are broad and horizontal. Thus in the anterior part of the adult 
fish, the number of myotomes is greater than that of the vertebrae, and in 
the caudal region the number is reduced from the confluence. The cephalic 
myotomes as well as some following myotomes project anteriorly as a triangula r 
mass, and their thin, dorsal limb is bent forwards along the dorsal median 
