Now will appear the third ventricle in the posterior part; and it is hard, for it gives rise to the greater part of the motive nerves which are of a strong and firm nature. This ventricle is pyramidal in shape, and culminates in an apex directed upwards where images of visible things (_spetie_) are conserved, for these are better stored in a strait than in an ample space; but the part below is wide to receive these images, which are better received in an ample than in a strait place. This ventricle has two functions: it gives rise to the spinal cord [_nucha_, an Arabian term] and motor nerves; and it is also the storehouse of the _memorative_ faculties. From what [has been said] it will be apparent that when the back of the head is injured, the memory immediately suffers; when the middle part is injured, the estimative and cognitive faculties suffer; and when the anterior part is injured, the faculties of common sensation and of imagination (_fantasia_) suffer. And thus it is that the doctors have become aware of the location of these powers. This being disposed of, thou wilt next raise the brain carefully so as not to break the nerves. Commencing now with the part in front, there will first appear two small fleshy protuberances like two nipples, of like substance to the brain in which they originate, and covered by a thin membrane, the pia mater. These are the olfactory organs, wherein is the sense of smell. From the brain arise seven pairs of nerves. Proceed therefore farther with the anterior part, and thou wilt see the first pair of these nerves, which are large, and called the _nervi optici_. These have their origin in the front ventricle of the brain and proceed towards the eyes. But before they pass through the pia mater, they join together, and at their place of union there is a perforated spot. Galen maintains that these nerves only join or rather unite, but do not intersect, so that the nerve that comes from the right after union returns again towards the right, and similarly with the nerve coming from the left, which after the union returns towards the left eye.[185] But Rhazes maintains the contrary,[186] although the opinion of Galen is the more common. These nerves are subservient to sight, and they are united so that the images of the things received by the two eyes and conveyed by the two nerves should return in unity; so that one thing should not appear as two. After these two nerves, raise the brain towards its middle and thou wilt see another pair of nerves, thin and firm, which also go to the eyes, to give them voluntary movement, controlling certain muscles.