MusFIG 19: Ultrastructure of the anal depressor muscle.

TEM cross section at the level of the anal depressor muscle. Each of the two vertically arranged, single sarcomeres ends in thin filaments, whereas the center of each sarcomere contains thick filaments. On the dorsal side, the half I bands of each myofilament sheet terminate in hemiadherens junctions (arrowheads in top panels of inset) that attach to the dorsal hypodermis just lateral to the dorsal muscle quadrants. On the ventral side, the half I bands attach to the rectal epithelium around the anal opening via hemiadherens junctions (arrowheads in bottom panel of inset). Hemidesmosomes in the rectal epithelial cell (arrows), in turn, function to link these myofilament attachments to the rectal cuticle. Bar, 1 μm. (Image source: B140 [Hall] 9550.)

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