Hence it is that four pieces of bone are sutured and joined together by nature in a denticulate fashion, so that they might be the firmer and stronger. Nor are they bound with ligaments as are the joints, for these would not have been so strong, and furthermore the bones of the head do not need to move.
These sutures are five in number, three being true and two false. The true sutures are those which pass right through the bone, while the false do not. Of the true sutures one is in the anterior part and is called coronal; it is made like the letter C, and stretches from right to left of the head, the two wings of the C being directed towards the forehead. The second true suture extends along the length of the head, beginning from the coronal and reaching the back part of the head. It is like a shaft or rather arrow that goes backwards from the brow, wherefore it is called sagittal ——(. The third true suture is in the posterior part and is called laudal, for it is made like a Λ, the letter called by the Greeks lauda. The sagittal suture extends from the coronal to the lauda 〉——(.
The false sutures are two, one on each side. They are called cortical because they do not penetrate.
Now if we consider these five sutures we shall see that there are four bones articulated together. One is the forehead bone [frontal] which begins at the coronal and ends below at another suture, which itself begins as a branch of the coronal suture and proceeds by way of the eyebrow to the corresponding branch [of the other side] Ɑ.
A second bone is behind and terminates at the laudal suture. There are two other bones which form the temples. These terminate at the false sutures which themselves begin at the laudal and end at the coronal suture.
The sixth part [of the head] consists of two membranes. One of these is called dura mater, and lies in contact with the cranium. The other is called pia mater and is in contact with and covers the brain. And nature contrived it thus, having great solicitude for this latter member, that while close to the bone, it should yet not be touched by it. Wherefore, taking due precautions, she made the one [membrane] harder than the other. Furthermore she made two membranes, so that if harm befell one of them, it might not be communicated to the underlying brain.
In the pia mater are woven certain veins by which the brain is nourished. [The brain is] everywhere covered by it except on the posterior part; because this part being dry, it has no need of this membrane, as have the anterior and middle parts. The two membranes in many places penetrate the substance of the brain, dividing it into a right and a left, a front and a back section. By this division, divers cells or rather small chambers are made therein, in which the soul (anima) performs its divers operations, for which reason it is necessary that these parts should be of different structure.
When the two membranes are raised, the seventh part of the head, namely the brain itself, appears. The brain is wrought by nature so that the vital spirit from the torrid heart should be tempered by its cold, for here it is converted into animal spirit, which is the beginning of the perceptive (cognoscitiue) and motive processes.
The brain is of a substance like marrow, white, soft, and viscous, and from it the nerves arise. The anterior part is moister, softer, and less cold than the posterior because the senses [sentimenti = senses + mental processes], which are themselves moist and soft, have here their origin. In the posterior part the motor nerves arise, and it is therefore drier and firmer.
The brain is divided into three parts or ventricles. The first ventricle or anterior part is itself divided into two, right and left, and is moreover larger than any of the other ventricles, for in this first ventricle nature has placed the two faculties subservient to perception (al cognoscere). One of these is called common sensation (senso comune); in it the external senses terminate as at a centre and deliver the images or rather species of sensible things, so that this faculty may perceive and distinguish between one sensible thing and another, and also comprehend the operations of particular senses; which two things none of these [senses of themselves can do]. The other faculty of the first ventricle is called fantasia and by some imagination; it retains and preserves the species of sensible things in the absence of the material objects themselves.