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The types of cell-to-cell contacts and the relationship between the nerve endings and the smooth muscle of the estrogen-treated rabbit oviduct have been investigated. The cell contacts most consistently found in the oviduct were simple appositions, with a 20-nm cell separation, which occasionally included a more dense region, and interdigitations of muscle cell processes with the same separation distances. Very rarely, wider intermediate contacts were present. Gap junctions (nexuses) were absent. It seems likely that simple appositions and interdigitations form the low resistance pathway for conduction of electrical activity. Nerves containing small dense-cored vesicles were present both within and near muscle bundles; they were rarely found close to smooth muscle cells.

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K E Y WORDS. Smooth muscle cell, morphology, nucleus alignment, brain artery. SUMMARY We undertook to ascertain how well aligned is the rod-shaped nucleus within the spindleshaped cell of vascular muscle in order that we might use the darkly staining nucleus in histological sections to indicate precisely the directional alignment of the cell. We fixed cerebral arteries from five monkeys under physiological pressure and embedded portions of the tissue so that mid-plane longitudinal sections of the arteries were obtained; the circumferentially arranged muscle cells were cut in cross-section. From the electron micrographs we obtained the cross-sectional profile of the cell and its nucleus, determining that the centre of the nucleus was on average 9.5 & 5.8% (SD) away from the centre of the cell (expressed as a ratio of the cellular diameter). We calculated the alignment between the cell and nucleus to be from 0 to 3", and obtained a volume fraction of 59% for muscle tissue in the tunica media of these arteries.