Let us not however exaggerate the relation which connects the muscular to the cerebral phenomena; observation would prove us incorrect. There are various examples of aqueous, sanguineous and even purulent congestions in the brain, without having produced any alteration in muscular motion. Different tumours and defects of conformation have occasioned disturbance of the intellectual functions, without affecting those of the muscles; how many times is the brain disordered in various species of alienations; how many times do the understanding, memory, attention and imagination indicate these derangements by their irregular aberrations, without their being felt by the muscular system. Is there not often an alteration of the external sensation, without an alteration of motion? In general the brain has three great functions. 1st. It receives the impressions from the external senses; it is in this relation the seat of perception. 2d. It is the principle and the centre of the voluntary motions, which are not exerted but by its influence. 3d. The intellectual phenomena are essentially connected with the regularity of its life; it is as it were the seat of them. Now it can be deranged as to one of these functions, and remain sound as to the others; it can be a regular principle of the motions, and an irregular centre of the phenomena of the understanding; not communicating with external objects by the senses, and determining motions, or presiding over intellectual functions, as happens in sleep which is disturbed by dreams, &c.