(folio 5 verso) There are ten layers of the head.
The _first_ is the _hair_ made by nature for the better protection of
the head from external things, and also for beauty.
The _second_ part is the _skin_, which has here to be very thick, so
that the hair may be firmly embedded, having its roots thick and long;
and also to be a better shield and covering for the bone and brain,
since there is no muscular part here.
The _third_ part is the _flesh_, developed only on the face, the
temples, and about the jaws, not on the other parts.
The _fourth_ part is an external membrane called _almochatim_ [Arabian
term for cranial periosteum] which, when the skin is raised, appears
to be continuous and covers the whole cranium. And nature made this
membrane firstly so that the skin which is soft should not come into
contact with the hard bone, secondly that the bone of the head should
have sensation through it, and thirdly that the internal membrane of
the head, called _dura mater_, should, by means of this membrane, be
attached to the bone of the cranium by certain nerves and ligaments.
These, issuing through the commissures of the bones, have thus their
origin in the aforesaid internal membrane, while on emerging through
the bone, they weave themselves into or rather compose the external
membrane called _almochatim_.
The _fifth_ part is the _skull_. This is a bone like a cap, inside
the cavity of which is located the brain. In the skull are four bones
sutured together. Nature made the skull not of one but of many pieces,
firstly, so that if harm should fall on one part it might not spread
to the others; secondly, so that by their joints or rather sutures
[Italian _cusiture_=sewings], the humours of the brain might be the
better exhaled; and thirdly, so that when there is need of applying
medicines, these might the better penetrate to the parts within.
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.
When thou examinest the first ventricle thou wilt see three things
before thou comest to the second ventricle.
[_a_] The first is itself double, and is formed of the very substance
of the brain, so that it forms the base of the anterior ventricle both
right and left [= corpora striata].
[_b_] To the side of this is another thing like a subterranean worm,
red as blood, yet tethered by certain ligaments and nervelets [=
choroid plexus and taenia semicircularis]. And this worm when it
lengthens itself closes these passages, and thus blocks the path
between the first ventricle and the second. Nature has wrought it thus,
so that when a man wills he may cease from cogitation and thought; and
similarly when, on the other hand, he would think and contemplate, this
worm contracts itself again and opens these passages and thus frees the
way between one ventricle and another.
[_c_] The third structure is a little lower and is a _lacuna_ or
rounded concavity [= infundibulum]. In the middle of this is a hole
which passes down towards the palate, and this lacuna provides also
a direct passage which descends from the middle ventricle to its
_colature_ [= sieve-like structure, i.e. certain parts of the sphenoid
bone]. And this lacuna has around it certain large round eminences
which support the veins and arteries that ascend to the ventricle. This
passage is wide above and narrow below, and by it the first and second
ventricles purge themselves of their superfluities, but the anterior
part [of the first ventricle] purges itself more by the colature of the
nose [= cribriform plate]. Thus nature has made two passages to cleanse
the superfluities of the brain.
When thou hast seen these three structures there will appear the
second or middle ventricle which is as a passage and transit from the
anterior to the posterior ventricle. Here are two faculties. One,
the _estimative_, deduces [Italian _elicere_] the insensible from
the sensible. The other, called the _cognitive_, comprehends both
things sensible and things insensible, synthesizing and analysing
them (_componendo e dividendo_). These [two] faculties in the middle
ventricle minister to the intellect. Now all the other faculties
described, and even the power of memory, are found in brute animals,
but this [intellectual power] is encountered in man alone.
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.
Farther on thou wilt see the third pair of nerves, one part of which
goes to the face to give it sensation and voluntary movement, while
another part goes to give taste to the tongue. Yet a third part of
these nerves mingles with the fourth[187] pair of nerves, and together
they descend to give sensation to the diaphragm, stomach, and other
viscera. A certain part also of the fourth[187] pair of nerves goes to
give sensation to the palate.
Then there is the fifth pair of nerves [which] go to the _petrous_ bone
around the ear; and of these nerves there are framed in the ear-holes
certain membranes, which are the organs of hearing.
Next there is the sixth pair of nerves, which divides into three parts.
One part goes to the muscles of the throat, the second to the muscles
of the shoulders, and the third and largest descends to the epiglottis
and to the diaphragm, and spreads into the chest, the heart, and the
lungs, accompanying the nerves of the third pair. From the nerves of
this sixth pair which go to the epiglottis arise the nerves of the
voice, called _reversive_.
The seventh pair of nerves arise at the back of the brain and give
voluntary movement to the tongue.
Of these seven pairs of nerves, the first two pairs originate in the
anterior part of the brain, the third pair originates between the
anterior and posterior parts, while the remaining four pairs originate
in the posterior part.
Proceeding still farther, the brain may be completely raised, and
the eighth part of the head will appear, that is, the two membranes
situated below the brain. When these in turn are raised there will
appear the ninth part, which is a certain net called _rethe mirabile_,
because it is composed of exceedingly strong and marvellous texture,
augmented by certain very fine arteries which are branches of arteries
that ascend from the heart, and are called the _apoplectic arteries_.
In these arteries of this net is contained the vital spirit, sent from
the heart to be changed to animal spirit. That the spirit may be the
better modified and distributed, nature made these arteries very fine,
and separated them into very small branches so that the spirit should
be minutely divided. Nature placed the rethe mirabile under the brain
because it was necessary to guard its site carefully, and also that the
moist vapours of the brain which fall upon the net, obstructing it,
should induce natural sleep.
After all these things thou wilt see the basal bone which is the tenth
and last part of the head, and called _basilar_, because it is the
base and foundation of the whole head; and it was made hard so that
the superfluities which descend to it should not putrefy it. This bone
can be seen to be formed of many other bones articulated together.
It is divisible into the petrous bones and the bones of the nose and
eyes and two other lateral bones which can only be seen by means of
disarticulation. [Folio 10 verso, line 22.]
* * * * *
[Illustration: Fig. 11. From M. Hundt, _Antropologium, de hominis
dignitate natura et proprietatibus_, Leipzig, 1501. The figure shows
the ten layers of the head, the cerebral ventricles and cranial nerves,
and the relation of the nerves to the senses.]
[Illustration: Fig. 12. THE LAYERS OF THE HEAD