The first edition of this book was reviewed in these pages on April 14, 1928 and the second edition on Oct. 24, 1936. The demand for a third edition thus indicated speaks more for the caliber of the work than can the few hundred words allowed to a review. There hasn't been much change in our knowledge of the anatomy and physiology of the muscles during the fractional part of a generation covered by the span of these three editions. The author's knowledge of various phases of heterophoria has not changed materially, but the general ophthalmologist is beginning to know more about the subject, and consequently the logical sequence in which this chapter is written will undoubtedly have wider application. In the review of the last edition it was pointed out that the author of the book states unequivocally that the amblyopia of a squinting eye is due to disuse.