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Two types of articular motion that can be explained in terms of a pencil. In the first, the tip of the pencil remains stationary and the angle of the shaft remains unchanged as the shaft spins around its longitudinal axis. In the second, the tip of the pencil remains stationary while the shaft, held at an angle less than 90 degrees, describes a complete circle. Both movements are permitted by the shoulder joint. (Martini et al., 2012, p. 215).
What are rotation and circumduction?