Erratum.
In the article "Dynamics of skeletal pattern formation in developing chick limb" by S. A. Newman and H. L. Frisch (17 Aug., p. 662), a clause was omitted. The clause should be inserted on page 667, third column, line 31, as follows: "[. . . respectively,] at t = t(0), but subsequently we would like the gradient in the z direction to be maintained, and thus require [see equation in pdf] at z = 0 and z = d, for all times (radiation boundary conditions). [ The number. . .]."