MO BOOK REVIEW

axis. The latter is the imaginary line through the center of the pupil, normal to the cornea. It is determined by the re­flection in the center of the pupil of a small light held in front of the eye. Angle kappa is considered positive when the pupillary axis is temporal to the visual ax i s ; it is considered negative when the pupillary axis is nasal to the visual axis.

Herewith is an easy way to remember when the angle kappa has to be added or subtracted in order to arrive at the true value of the angle of squint. The angle of deviation in convergent squint may be considered a positive angle and denoted by the plus sign. For convergence is a positive function and the angle of over-convergence may be thought of as a posi­tive angle. Similarly, the angle of devia­tion in divergent squint may be considered as a negative angle and denoted by the mi­nus sign. Divergence may well be thought of as a negative function; in fact, it is of­ten referred to as negative convergence. Thus the angle of divergence from the point of fixation on the perimeter may be considered a negative angle.

If the angles are thought of in this way, all that is necessary is simply to add al­

gebraically the values of the angle kappa and the angle of squint. Thus if the squint angle in convergent squint measures 15 degrees, and the angle kappa is plus 4 degrees, the true angle of squint is plus 15 and plus 4 equals 19 degrees. If the angle kappa in this instance is minus 4 degrees, then plus 15 and minus 4 gives us 11 degrees as the true angle of squint.

Or, if the angle of squint in divergent strabismus measures 20 degrees, we then have an angle of minus 20 degrees. If the angle kappa is plus 5 degrees, we get minus 20 degrees and plus 5 degrees, which gives us minus 15 degrees as the true angle of the divergent squint. If the angle kappa in this instance is, say, minus 5 degrees, then adding minus 20 and minus 5 gives us minus 25 degrees as the true angle of the divergent squint.

This method of considering the devia­tion angle in convergent squint as positive and the deviation angle in divergent squint as negative and then merely adding the value of the angle kappa is generally easier than other methods designed as memory aids.

(Signed) Joseph I. Pascal, New York, New York.

B O O K L E S Y E U X E T L A V I S I O N D E S V E R T E B R E S . By A. Rochon-Duvigue-

and. 792 pages. Paris, Masson et Cie., 1943. This volume presents an exposition of

the comparative anatomy and compara­tive physiology of the eye that is consid­erably more extensive than would be pos­sible in a zoological handbook. The mor­phology of the human eye occupies the first 150 pages. The chapter on the origin of the vertebrate eye outlines the contribu­tions of paleontology, comparative anat­omy, and comparative embryology. The

R E V I E W remainder of the book is a systematic exposition of the anatomy, histology, and the functions of the eye in each group of vertebrates. A chapter is devoted to the eyes of the cyclostomes, the several orders of fishes, the amphibians, the four orders of reptiles, the birds, and the mammals. Five hundred beautifully clear, half-tone illustrations, chiefly from histologic prep­arations, clarify the text instead of merely decorating it. They also decorate it. There is an adequate bibliography in each sec­tion.

F. H. Haessler.