The isocortex of tarsius

The “ tarsier-hypothesis ” has stirred the scientific world for so long that it appears unnecessary to motivate by many words the reexamination of the brain of Tarsius which is here offered. Nor does it seem necessary to explain the “tarsierhypothesis” in detail, since that has been done only a short while ago by Stranss (’49) in an easily accessible article. TThatever the exact line of man’s ancestry, the study of a primitive primate which, so it has been said (Matthem, ’as), has not much changed during the last 12-20 million years, might throw light on the evolution of the human brain. I n primates, the recognition of the environment shifted from olfaction to vision, and this shift might be reflected in the structure of the cortex. It is therefore not without interest to know the living habits of the animals whose brains one is about to study. Relevant data have been communicated by Clark (’24), Cook (’39), Catchpole and Fulton (’39). That Tarsius is a nocturnal animal, is well known. Tarsius can leap with astonishing accuracy from branch to branch. His leaps may be as long as 6 feet, far beyond the length of his own body, even including his tail. He will jump on his prey (grasshoppers, lizards, etc.) much as a cat does. But when a tidbit is offered on the point of a forceps, he may grasp clumsily the forceps instead of his food. Should the food drop to the ground, tarsius will close his eyes, nose around for the morsel and find it only when his nose is almost in contact