A question of much interest arises here. What is the precise function of this sense-receiving portion of the brain? Is _itself_ perceptive of the sense-impressions brought to it, or is it merely the medium for transmitting those impressions to the hemispheres above? That in health it does communicate to the intelligence the same impressions that it receives there can be no doubt, for we take cognisance of them in almost every mental act. We know also that when the brain is diseased false impressions are conveyed to the Intelligence. But in exploring the psychology of Sleep and Dream, it would be of great advantage to ascertain if the same receiving portion of the brain is an active or merely a passive agent. The experiments of Professor FERRIER are almost conclusive upon this most important point. He removed the two brain hemispheres of a monkey and of a dog. The animals lived and appeared to enjoy health, but _they had lost intelligence_. They had not, however, lost the use of the _senses_ and they were manifestly conscious of the impressions brought by the nerves of sense. The external world continued to exist for them and was perceived by them as before the organs of the intelligence were removed. But when this central division of the brain was taken away and nothing left but the lower lobes that govern muscular motion, all the senses ceased to act, or consciousness of action had ceased. Nevertheless the power of locomotion and the co-ordinate action of the limbs was preserved with very little loss of power. Above the central sense-organ tower two hemispheres—_two_ brains, each distinct and complete in itself and each capable to act without the other. The function of these hemispheres is that we term _mental_. They are the organs of the intellect and of the sentiments. Through them we think, reason and feel. Injury to parts of these injures more or less, _not_ the _whole_ mind, but _parts of the mind_—certain mental faculties only. Destruction of the entire of these hemispheres is not death but idiotcy. Let it then be clear in the mind of the reader, when surveying the phenomena of sleep and dream and inquiring into their causes, that for the purpose of such an outline of the Physiology of the Mind as this, the brain is to be viewed by him as having _three_ marked divisions—the organ of the _intelligence_ at the summit, of the _senses_ in the centre, of _bodily motion_ at the base. There are many sub-divisions of the brain known to anatomists and necessary to be known by the Student of Physiology. But these will suffice for the Student of Psychology. They are easily understood and readily remembered.