Introduction
It is said that no self-respecting biologist would state or imply that the eyes of the primates are in front of the head for the purpose of providing the animal with stereoscopic depth perception. Certainly, however, the fact that the two eyes are so placed, whether by design or by mutation, has provided the most favorable situation for the development of such perception. Even if one believes that the second eye is simply a reserve organ for security and that stereoscopic depth arises as some sort of learned by-product of the dissimilar images in the two eyes due to their location, we still must concur in the statement that stereoscopic depth perception plays an important role in spatial localization. Phylogenetically, the gain in obtaining stereopsis has perhaps been accompanied by a loss of panoramic vision, but much more important, this gain has so very greatly complicated the physiologic processes