Muscles of the oviduct and uterus. A. Electron micrograph of a cross section of the common oviduct to show the outer muscular layer (M), surrounding the epithelial lining (EL) and the oviduct lumen (L). The epithelial lining has an apical surface rich in convoluted multimembrane structures. B. Detail of the muscle layer shows a myofibril with interdigitated thick and thin filaments (white arrow) and perforated Z-discs (black arrow). Occasionally some thick-thin filament lattice (asterisk) is seen cut transversely suggesting that not all the myofilaments run in parallel with the circular muscle layer, though these exceptions may be tangentially cut. C. A confocal image of a region of common oviduct with F-actin filaments stained (magenta) with rhodamine-phalloidin. This shows that the common oviduct is covered by circular muscle fibres (also seen in lateral oviducts, not shown); there is no evidence of longitudinal muscle fibres. Note that some of the phalloidin bands twist and a few split, and this may account for the transversely cut filaments seen in B. D. Electron micrograph of a uterus cross-section shows the muscle (M) and epithelial layers (EL). The muscle layer is considerably thicker than that of the oviduct and again exhibits perforated Z-discs. E. Confocal fluorescence image of uterine muscle, immunostained with myosin FITC-labelled antibody (green) and F-actin labelled with rhodamine-phalloidin (magenta) shows that the myofibrils within these cells seem to form side-by-side associations, often in partial register. The fibres have tapered ends. All the myofibres encircle the uterus; no longitudinal myofibres were seen. Scalebars: A: 2 μm, B: 0.5 μm, C: 20 μm, D: 2 μm, E: 10 μm.