Three-dimensional structures of the Schwann cell in the rat motor endplate were observed by scanning and transmission electron microscopy. A few Schwann cells lodged over the surface of the motor endplates and their nuclear portion swelled roundly. From the Schwann cell body, a few processes extended downwards, divided several times and covered only the upper orifice of the synaptic groove; they did not cover the surface of the protuberances or the ridges of the sarcolemma which separated the

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... naptic grooves. The lateral sides and ends of the Schwann cell processes were frilled with finger-like projections. They fixed on the surface of the basal lamina of the sarcolemma and sealed the nerve terminals in the synaptic grooves.