It is somewhat remarkable that, in view of the numerous and extensive publications that have from time to time appeared from the pens of American writers on the ocular muscles, their physiology, their pathology and the treatment of the various anomalies of muscular balance, so little or so comparatively little space has been devoted to the physics of the subject. Whether one accepts the conclusions or not, the chief attraction of the book before us lies in the attempt to lay down certain fundamental principles based upon experimentation in the dynamics of the eye muscles—particularly of the extrinsic muscles. Having accepted these theories the mysteries of heterophoria are, according to the author, readily explicable.
We are, ourselves, mainly interested in the challenge given to the Helmholtz law of direction and to the reality of Listing's plane. As is well known, the latter is an imaginary vertical plane, which, passing through