COMPARATIVE STUDY OF SCOMBROID FISHES. 
429 
Portions of the lateral muscle surrounded by these sheets of the vascular 
plexus are situated on both sides of the vertebral column, and are dark red, 
nearly black in colour. Another peculiar vascular plexus is developed on the 
inner side of the liver or in the haemal canal. Moreover the circulation of 
blood in the liver is especially well developed. 
Thus this group of fish is distinctly defined from the other forms of the 
Teleostomi, and comprises the most highly specialized forms of fishes. There 
is no doubt that they are descendants from the Acanthopterygii, among w r hich 
they should have been classified. They are most closely allied to the genera, 
Sarcla and Gymnosarda of the Cybiidae. 
The body is well adapted for swift locomotion, being plump, pointed at 
both ends, and smooth at the surface. Caudal peduncle very slender, but with 
broad lateral keels. Head triangular, nearly flat at the top. Snout shorter 
and the mouth smaller than in the Cybiidae, the upper jaw scarcely reaching 
the vertical from the middle of the eye. The posterior part of the external 
margin of the upper jaw is not straight, but lient downward, due to the over¬ 
lapping of the maxillary over the premaxillary. Posterior end of the upper jaw 
is straight, due to the form of the supplementary bone. The anterior nostril is a 
mere point, and the posterior nostril a transverse slit. Scales large and thick 
in the corselet, and those behind the eyes are thick and elongated. Scales are 
ctenoid at the margin but smooth at the surface. Opercular region is entirely 
naked. Corselet is covered with a thick membrane of strong connective tissue, 
to protect the thick pari of the peculiar cutaneous vascular system. 
Fins are well developed with thick spines and strong fin-rays. In the 
first dorsal the first spine is not inferior in size and thickness to any succeed¬ 
ing spines, and the posterior side of the dorsal outline of the fin is concave. 
The caudal fin is firm and very widely forked, more or less lunate in shape. 
Gill-rakers are long and fine, and are developed on both sides of branchial 
arches. Abdominal cavity is narrow and depressed, as the ventral processes of 
the precaudal vertebrae are well developed, consequently the hypaxial portion 
of the lateral muscle in the precaudal portion is very thick (Figs. 18, 19). 
Portions of the lateral muscle on both sides of the vertebral column are 
coloured dark red or blackish. These portions are called “ chiai ” in Japanese, 
and each dark red portion is thick at the anterior end, tapering gradually 
