Human skulls are enduring motifs in art history, and Jasper Johns has a longstanding acquaintance with them. A skull peers out from the corner of his work as early as 1964, in a bright, blocky painting called Arrive/Depart. The title alone offers a view of life as starkly unsentimental as any memento mori. We arrive in the world, we depart from the world, and there is no guarantee of happiness in between. The theme permeates Johns’s large, very moving show at the Matthew Marks Gallery in Chelsea.