Part 22

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.

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 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. But Rhazes maintains the contrary, 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 pair of nerves, and together they descend to give sensation to the diaphragm, stomach, and other viscera. A certain part also of the fourth 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.]

* * * * *

From the Anatomia of Johannes Dryander, Marburg, 1537.]

The ten parts or layers of the head are a commonplace of the anatomy of the period, taken from Avicenna. We may illustrate the division by the crude contemporary diagram of Fig. 11, which is improved in the later drawing reproduced in Fig. 12.

Manfredi’s account of the brain itself is amplified from Mondino. The division of this organ into three ventricles, each associated with a corresponding division of the mental functions, was very familiar to medical writers of the fifteenth century. The idea is found among Western writers as early as St. Augustine (354-430), and is encountered in the writings of Roger Bacon (1214-94). It had long been popularized in mediaeval psychology by the writings of Albertus Magnus (1206-80). The anatomical distinction is found in Haly Abbas, Avicenna, and Rhazes, and in some of the best MSS. of the latter writer a rough diagram of the ventricles is given. These writers are all clearly indebted to the anatomy of Galen, but on the psychological side Albertus Magnus probably drew mainly either from Ghazali (1059-1111), who in turn derived his inspiration from Nemesius (fourth century) and Johannes Damascenus (died 756), or else from early writers of the Salernitan tradition, such as Constantine (eleventh century), or Petrocello (twelfth century), who drew largely on Theophilus (seventh century).

This outline of a tripartite division of the brain and its cavities was closely followed throughout the Middle Ages, as was also the curiously naïve and excessively ‘materialistic’ psychology to which it gave rise, and which Manfredi adopts. We illustrate his views of the relationship of the different parts of the brain and their parallelism in mental processes, from a series of diagrams extracted from contemporary works (Figs. 13-18).

The brain was regarded by mediaeval and early Renaissance anatomists as having two channels of discharge through which the phlegm, the especial product of this organ, could be evacuated when in excess. One of these channels communicated with the anterior ventricle of the brain and poured its secretion into the nose. It may be identified with the anterior colature or cribriform plate. The second, the lacuna, led down from the second ventricle and poured its secretion into the pharynx. It may be identified with the infundibulum, pituitary body, and ‘cella turcica’. The term ‘pituitary’ which we still use is derived from its supposed association with the ‘pituita’ or phlegm. At an early date this process was connected with the four humours (Fig. 14). The rest of the description of the brain can be easily followed. The comparison of the choroid plexus to a worm is very common. The suggestion originated with Galen and was developed by the Arabians.

COMPARATIVE TABLE OF ANCIENT AND MODERN NOMENCLATURE OF CRANIAL NERVES.

Mondino and Manfredi following Galen, | especially in the περὶ χρείας τω̑ν ἐν | Modern usage. ἀνθρώπου σώματι μορίων. De usu partium | corporis humani. | ---------------------------------------+---------------------------- Not regarded as separate nerves. | I. Olfactory nerves. ---------------------------------------+---------------------------- I. τὰ μαλακὰ νευ̑ρα τω̑ν ὀφθαλμω̑ν. | II. Optic nerves. ---------------------------------------+---------------------------- II. τὰ κινητικὰ τω̑ν ἀμφ᾽ αὐτοὺς μυω̑ν. | III. Oculomotor nerves. ---------------------------------------+---------------------------- Not mentioned. | IV. Trochlear nerves. ---------------------------------------+---------------------------- III. τρίτη συζυγία. } | V. Trigeminal nerves. IV. τετάρτη συζυγία. } | Mondino and Manfredi confuse | Galen’s fourth pair and Galen’s | sixth pair. | ---------------------------------------+---------------------------- Not mentioned by Manfredi. By | VI. Abducent nerves. Galen probably united with II. | ---------------------------------------+---------------------------- V. πέεμπτη συζυγία. |{ VII. Facial nerves. |{VIII. Auditory nerves. ---------------------------------------+---------------------------- VI. ἕκτη συζυγία. | {IX. Glossopharyngeal | nerves. | { X. Vagi. | {XI. Accessory nerves of | Willis. ---------------------------------------+---------------------------- VII. ἑβδόμη συζυγία. | XII. Hypoglossal nerves. ---------------------------------------+----------------------------

The nomenclature of the cranial nerves adopted by Manfredi is taken from Mondino and is almost identical with that of Galen, whose classification is summarized above. Manfredi’s description of Galen’s fourth pair is confused and inadequate, but his account of Galen’s sixth pair is an improvement upon Mondino.

The ‘rete mirabile’ is an interesting survival of Galenic anatomy. This structure is hardly present in man, but is developed in the lower animals, and especially in calves, upon whose bodies Galen worked. The father of physiology regarded the ‘rete mirabile’ as the place where the psychic pneuma was elaborated. Galen’s findings in the lower animals were assiduously transferred to the human body, to which his descriptions are much less applicable, while his views on the pneuma lasted in more or less misunderstood form well into the seventeenth century.

(b) THE EYE

Tractate i, Chapter 3