QUANTITATIVE data on the dimensions of the eyeball as a whole and on many of its component structures have been reported in the medical and biologic literature over a long period. A number of observations have been visualized in the form of two dimensional reconstructions, commonly of median sagittal sections of the eyeball and its parts. Many of these figures are frankly schematic or semischematic. Nonetheless, they fulfil the purpose for which they were constructed, for they give clear, useful and approximately correct representations of the mean size and the spatial relations of the optic apparatus. A smaller number of two dimensional reconstructions have been made with particular attention to the exact quantitative data on the dimensions involved, and these are sometimes accompanied with extensive tabulations of these data. Perhaps the more notable of this second type of reconstructions are those of Merkel and Orr1 (fig. 1 a the