In the case of the higher functions involving thought, the upper part of the brain, which performs these functions, seems to be a sort of duplex machine, so that we have two brains capable of thinking, just as we have two eyes capable of seeing. It is a remarkable fact that the areas of the brain which are appropriated to the lowest and most instinctive functions, which appear first, lie lowest, and as the functions rise the position of their nerve-centres rises with them. Thus, at the very base of the frontal convolutions at the lowest end of the fissure of Rolando, we find the motor areas for the lower part of the face, by which the lowest animals and the new-born infant perform their solitary function of sucking and swallowing. Higher up are the centres in the right and left brains for moving the upper limbs, that is, for seizing food and conveying it to the mouth, which is the next function in the ascending scale. Next above these are the centres for moving the lower limbs and for co-ordinating the motions of the arms and legs, marking the progression of an organism which can pursue and catch as well as eat its food. And still higher are the centres which regulate the motions of the trunk and body in correspondence with those of the limbs; while highest of all, at the front and hind ends of the enveloping cortex of the brain, come the organs of the intellectual faculties. It is easy to see that this corresponds with the progression of the individual, for the infant sucks and cries for food from the first day, soon learns to extend its hand and grasp objects, but takes some time to learn to walk, and still longer to perform exercises like dancing or riding, in which the motions of the whole body have to be co-ordinated with those of the limbs. And as the development of the individual is an epitome of the evolution of life from protoplasm, we may well suppose that the brain was developed in this order from its first origin in a swelling at the end of the spinal cord as we find it in the lowest vertebrates. It is a singular fact that the particular motor area which gives the faculty of articulate speech lies in a small patch of about one and a half square inches on the left side of the lower portion of the first brain. If this is injured, the disease called aphasia is produced, in which the patient loses the power of expressing ideas by connected words. The corresponding area on the right side cannot talk; but in left-handed persons this state of things is reversed, and the right side, which is generally aphasial, can be taught to speak in young people, though not in the aged.