A surgical robot comprising an articulated arm, the arm having a terminal portion comprising: a distal segment having an attachment for a surgical instrument; an intermediate segment; and a basal segment whereby the terminal portion is attached to the remainder of the arm; a first articulation between the distal segment and the intermediate segment, the first articulation permitting relative rotation of the distal segment and the intermediate segment about a first axis; and a second articulation between the intermediate segment and the basal segment, the second articulation permitting relative rotation of the intermediate segment and the basal segment about a second axis; wherein: the intermediate segment comprises a third articulation permitting relative rotation of the distal segment and the basal segment about third and fourth axes; and the first, second and third articulations are arranged such that in at least one configuration of the third articulation the first and second axes are parallel and the third and fourth axes are transverse to the first axis.
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