Tubular aggregates and vacuoles in skeletal muscle of draggen mice. Transmission electron microscopy analysis of the tibialis anterior muscle from draggen (A–D) and control mice (E and F). (A) Representative view of single-walled tubular aggregates that have accumulated between myofibrils. (B) Longitudinal section showing triads of different morphological appearances (filled arrows). Note the presence of densities between adjacent membranes (open arrows). (C) Detailed view of T tubules and sarcoplasmic reticulum of triads (filled arrows) of irregular size and orientation. (D) Detailed view of a tubular aggregate region showing the continuity of the sarcoplasmic reticulum from a presumed irregular triad (filled arrow) with a large vesicle (star). (E and F) Wide and detailed view, respectively, of triads of normal size and orientation (arrows) from a control sample.