Page:An Introduction to the Study of Fishes.djvu/122

filled by an embryonal muscular substance which contains a large quantity of fat and blood-vessels, and therefore differs from ordinary muscle by its softer consistency, and by its colour which is reddish or grayish. Superficially the lateral muscle appears crossed by a number of white parallel tendinous zigzag stripes, forming generally three angles, of which the upper and lower point backwards, the middle one forwards. These are the outer edges of the aponeurotic septa between the myocommas. Each septum is attached to the middle and the apophyses of a vertebra, and, in the abdominal region, to its rib; frequently the septa receive additional support by the existence of epipleural spines. The fibres of each myocomma run straight and nearly horizontally from one septum to the next; they are grouped so as to form semiconical masses, of which the upper and lower have their apices turned backwards, whilst the middle cone, formed by the contiguous parts of the preceding, has its apex directed forward; this fits into the interspace between the antecedent upper and lower cones, the apices of which reciprocally enter the depressions in the succeeding segment, whereby all the segments are firmly locked together (Owen).

In connection with the muscles reference has to be made to the Electric organs with which certain fishes are provided, as it is more than probable, not only from the examination of peculiar muscular organs occurring in the Rays, Mormyrus, and Gymnarchus (the function of which is still conjectural), but especially from the researches into the development of the electric organ of Torpedo, that the electric organs have been developed out of muscular substance. The fishes possessing fully developed electric organs, with the power of accumulating electric force and communicating it in the form of shocks to other animals, are the electric Rays (Torpedinidæ), the electric Sheath-fish of tropical Africa (Malapterurus), and the electric Eel of tropical America