(E) Myoseptal intervals of slow skeletal muscle at 1 dpf in smyhc1+/+ (n = 54), smyhc1-/- (n = 31), smyhc1R673H/+ (n = 45), and smyhc1R673H/R673H (n = 49). Distance between myosepta was measured perpendicular to rostral-caudal body axis at defined mid-body regions in phalloidin stained slow skeletal muscle fluorescence images. The central bands of the boxplots represent the median, the boxes of the boxplots represent the interquartile range (between the first and third quartile), and the whiskers represent the minimum and maximum values, up to 1.5 times the interquartile range. Outliers displayed are outside of this range. (F) Myoseptal intervals of slow skeletal muscle at 3 dpf in smyhc1+/+ (n = 51), smyhc1-/- (n = 32), smyhc1R673H/+ (n = 64), and smyhc1R673H/R673H (n = 38). The central bands of the boxplots represent the median, the boxes of the boxplots represent the interquartile range (between the first and third quartile), and the whiskers represent the minimum and maximum values, up to 1.5 times the interquartile range. Outliers displayed are outside of this range. 