1950 年 1 巻 2 号 p. 89-100
In 52 species of Japanese bony fishes (Table 1), the horizontal septum was found to be separated into two tendons, and these tendons were here called anterior oblique tendon and posterior oblique tendon respectively. The d: stal end of each tendon, in the form of connective tissue attaches to the superficial red muscles in the teleosts other than the scombers and tunas. (Fig. 1 and 5).However, in the scombroid fishes examined here, the end of the tendon reaches the deep: seated red muscles with a simiiar patern as in other bony fishes. The two tendons are running (Figs. 4, 5, 6, 7) with a loose mechanism so as to make the two tendons slide with each other. This is especialy significant in scomboroid fishes.
The Superficial red muscles runs horizontally along the horizontal septum in non-scombroid teleosts, on the other hand, the same muscles of scmbroids, though homologus with those in the former referring to the position and the direction, was found to be light in color as other non-red-muscles. It has been known that the red-muscle fibres are thinner than those of ordinary muscles in bony fishes. The writer's histlogical examination, however, showed that the superficial muscles noted above in scombroids are consisted of thick fibres same as those of ordinary muscles.
This change found in the scombroids, however, do not take place in the same degree in this particular group of fish. The differentiation occurs gradually (Fig. 8) in the order of Scomber-Sardai-Thunnus-Katsuwonus
The three facts clarified here (1. structure of tendons, 2. histology of the superficial muscles, and 3. sliding mechanism of two tendons) convinced the writer to believe that the deep seated red muscles in scombroid fishes derived from the superficial red muscles in ordinary bony fishes, and the former red muscles sunk from the body surface to the inner part of body accompanied also by function as red-muscle. Such anatomical deformation in scombroid teleosts tested here seems to have developed adapting to their speedy moving by beating of the tail.