SECT. II. _Of the Brains and Nerves._ The brains are by all Physiologists esteemed the most mysterious organs of life, being the fountain of the nerves, the organs of sensation, and hence allowed by all to be the seat of the soul, or the _sanctum sanctorum_ of the human understanding. They are distinguished into the common or great brain called _cerebrum_; the small part called _cerebellum_; and the _spinal marrow_, which projects down the back-bone. The great brain is divided into two great lobes, seated in the upper and fore part of the skull, of which it takes in the greatest cavity. It is so exceedingly sensible, that the least pressure puts an immediate stop to the sensation of the animal; and which is generally termed a _apoplexy_.[2] Footnote 2: Hence in a fracture of the skull, or any other heavy contusion, where the brain is compressed either by the fractured bone, or the extravasated blood, the patient will remain in a state of stupefaction, till either the fracture is reduced, or the extravasated blood removed by trepannation; after which he immediately comes to himself, as if suddenly revived from a trance. This part of the brain, though it is so exquisitely sensible, seems to be designed by nature as preparatory to the _cerebellum_, the immediate root of the nerves. The _cerebellum_ is the lesser, but the more material part of the brains. It is seated in the hinder cavity of the skull, (which for the sake of protecting this exquisite sensible organ, is remarkably strong and firm) and from thence as the fountain of life itself, the nerves, the instruments of sensation in the whole animal frame, take their commencement: For whereas the other is so sensible, as that the least pressure will cause a stupor; this is so far superior in point of exquisite sensibility, that a pressure on that part, not only occasions an apoplexy, but even stops life itself. From this _cerebellum_ prolongates the marrow in the back-bone, called _medulla spinalis_, which is but a continuation of the same, and is equally sensible, and of the same substance with the former. The whole brain, that is, the _great brain_, the _small brain_, _spinal marrow_, together with all the nerves which spring from thence, are covered with two coats, called the external stronger coat, _dura mater_; and the thinner and inner coat, _pia mater_; which continue with each nerve, even to its smallest ramification. The whole in a living subject is in a continual motion peculiar to itself.[3] Footnote 3: This motion in the brain is not unlike the peristaltic motion; this is an observation too seldom taken notice of by anatomists, though evidently plain in living animals, and is of singular service in physiological enquiries.