Leonardo da Vinci - the anatomist (1930) 15
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McMurrich JP. Leonardo da Vinci - the anatomist. (1930) Carnegie institution of Washington, Williams & Wilkins Company, Baltimore.
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Leonardo da Vinci - The Anatomist
Chapter XV The Organs of Respiration
Leonardo’s treatment of the respiratory apparatus is less satisfactory to the human anatomist than much of his other work, for the reason that his observations are apparently made on animal forms exclusively. At least among all the illustrations of the organs of respiration there is not one that can certainly be regarded as representing a human structure, while many are obviously based on animal dissections. They are not human but animal lungs that he figures (fig. 62), it is not a human but an animal larynx that is shown, and yet the larynx is drawn into an outline sketch of a human neck and head (QV, 16) (fig. 65). Nevertheless, the figures are a marked advance on those of his predecessors; they are not merely conventional, but represent what Leonardo actually saw and he gave a more detailed portrayal of the structure of mammalian organs than had been available. To that extent they make an addition to the knowledge of the human organs just as did Galen’s observations on monkeys and pigs.
Leonardo’s views as to the mechanism of respiration have already been considered in connection with the thoracic musculature (p. 138). They were essentially those of Galen and, briefly restated, were to the effect that by the elevation of the ribs by muscular action and by the flattening of the diaphragm, a vacuum was created in the thorax and air rushed into the lungs to fill it (QI, 5). Expiration was also partly a muscular act, the internal intercostal muscles drawing down the ribs, while the abdominal muscles by pressing upon the intestines caused these and the stomach to press against the diaphragm, so forcing it upward (QI, 5v). There was thus an alternation in the contraction of the diaphragm and that of the abdominal muscles, the one acting in inspiration and the others in expiration. The expired air passed through the trachea and larynx and to the exterior either by the mouth or the nose, and Leonardo notes that one can not breathe by the nose and the mouth at the same time, as is shown by the fact that one can not blow a whistle or flute through the nose and through the mouth at the same time (An A, 3).
The larynx, sometimes termed epigloto after the Arabistic manner, was merely the constricted uppermost portion of the trachea, constricted so as to condense or compress the air issuing from the lungs and thus make it available for the production of voice and cause it to “press and dilate the various passages and ventricles of the brain” (QI, 5).
The function of the vocal cords in the production of sound was unknown, but they are represented in some figures on AnA, 3 (fig. 66), and the depressions between them, later known as the ventricles of Morgagni, are termed ventricles and it is stated that they may become filled with fluid (amove) and then produce a roughness of the voice.
Of the parts of the larynx the epiglottis is well shown and its function as a protection against the entrance of food particles into the trachea is noted, a figure (fig. 66) showing a bolus of food passing over the epiglottis ( linguella ) and forcing it back over the entrance to the larynx. On the same folio (fig. 66) is a diagram of a frontal section through the larynx showing two folds projecting forward from where the arytenoid cartilages might be (the ary-epiglottic folds) and between these and the thyreoid cartilage on either side a pocket, evidently a piriform recess, whose purpose is said to be to receive particles of food which might otherwise accidentally pass through the glottis, an event that would have fatal results. The food particles are retained by the recesses until, by coughing, the air from the lungs issues from the glottis with such force as to produce vortices in the recesses, whereby the food particles are carried back to the mouth. The thyreoid cartilage ( scu tola) is shown, but it is that of an animal, and below it is the cricoid cartilage separated from it by a distinct interval bridged by membrane. The arytenoid cartilages are not shown, but in a view of the larynx from above the tubercles on the ary-epiglottic fold formed by the cornicula laryngis and the cuneiform cartilages are distinctly figured (AnA, 3). There is a memorandum (QI, 10) to describe what and how many are the muscles that move the larynx ( epigloto ) in the production of voice, but no such description is recorded. A figure on AnB, 33v (fig. 75), drawn from il vecchio, shows the recurrent laryngeal nerve ascending alongside the trachea and sending branches to that structure and to the larynx.
The trachea is described in the notes as composed of a succession of cartilaginous rings, incomplete posteriorly where the trachea is in contact with the oesophagus (QI, 9), this incompleteness having two uses, (1) to aid in the production of voice and (2) to give room for the passage of food down the oesophagus, which is between the trachea and the cervical vertebra* (AnB, 33v). It would seem too that it was recognized that the successive rings were not in contact, the intervals between them being occupied by muscle tissue, but in none of the figures are these intervals shown, except in two small diagrams (QII, 1) (fig. 67), where they are represented as dilated during inspiration and collapsed in expiration. In fact there is no accurate representation of the structure of the trachea except in the figure of a moderately sized bronchiole in which the cartilaginous rings have broken up into irregularlv scattered plates (QII, 1) (fig. 67). It is to be noted that
Fig. 66. Various figures of larynx and trachea; surface modeling of leg. (AnA, 3.)
Fig. 67. The heart and bronchi after maceration away of the lung parenchyma. To the right representations of the bronchi. (QII, 1.)
Leonardo does not use the terms bronchus or bronchiole, the air passages being termed trachea or tracheal branches to their ultimate ramifications.
Deeply interested in all mechanical problems and seeking to explain observed phenomena in the terms of structure, Leonardo gave some attention to the mechanics of phonation. He was, of course, handicapped by his ignorance of the vocal cords and the part they play, but accepted the current view that sound production occurred in the upper part of the trachea, i.e. in the larynx, but true to his principle, experientia docet, he proposed to test this view by removing the trachea and lungs and suddenly compressing the latter (An A, 3). This experiment was suggested by the knowledge that it succeeds in the case of a swan or goose, "which frequently may be made to sing even when they are dead,” but evidently Leonardo was unaware that the organ of sound (syrinx) in birds is quite a different affair from that of mammals and one finds no record of the results of the experiment.
Accepting the larynx as the essential organ of voice, Leonardo goes on to point out that other organs are involved in phonation. He states that the trachea (larynx) takes no part in the formation of the consonantal elements of phonation, but merely produces the voice and especially the vowel sounds a, o, u, and ascribes the difference of these sounds to the air impinging on the curved surface of the soft palate and to the position of the lips. If the lips are protruded the sound a passes into o and if they are still further protruded o becomes u, this last sound also requiring that the epiglottis (larynx) be drawn upwards toward the palate (QIV, 10). Expressed in modern terminology he is pointing out the importance of the shape of the resonating chambers in the production of the vowel sounds. As to the mechanism by which the pitch of the voice is altered, as in singing, he is of course far astray. He compares the trachea to an organ-pipe and notes that the pitch of such a pipe does not depend upon the size of its mouth, but upon whether the pipe is long or short or broad or narrow (QIV, 10). Consequently he concludes that the pitch of the human voice is dependent upon the length and diameter of the trachea.
“Note well the use of the trachea and how it disposes itself to make high, middle and low voice, and what muscles produce these. Consider if the muscles between the oesophagus ( meri ) and the spinal column of the neck can, by their contraction, press the oesophagus against the flexible part of the trachea, where there is a deficiency in the rings. And also note if the movement that produces the size of the trachea in its contraction may not be made by the lateral muscles of the neck. The cause of the dilation need not be sought, since this is due to the rings acting like a spring and the dilation is increased by shortening the trachea, as do those who sing contrabasso; the shorter the trachea the lower the voice.” (QI, 9.)
In another note, however, he seems to doubt that the shortening of the trachea is sufficient and suggests that it also dilates to some extent in its upper part —
“which does not receive any degree of sound and the voice comes to rise in the rest of the shortened trachea ( channa ).”
This seems to contradict the idea that the voice is produced in the larynx, but it was merely a suggestion which he proposes to test on various animals,
“Giving air to their lungs and squeezing them, contracting and dilating the fislola which is the generator of their voice.” (QIV, lOv.)
Another point that interested him was how voice could be produced without sound, as when one whispers in another’s ear (An A, 3), but he does not attempt an explanation. Further he inquires as to the cause of the feebleness of the voice in aged persons and concludes that in old age there is a contraction of the trachea just as there is of the intestines (see p. 185).
Following the usage of his predecessors, Leonardo speaks of the lungs in the singular (il pulmone ), regarding them as a simple organ with two lobes, perhaps because they were regarded as being composed essentially of repeated branchings of the trachea, and this is a single organ. That the two lobes were separated by what was regarded as a median partition, the mediastinum, did not affect the case; the trachea and lungs were a single organ, just as was the brain with its two cerebral hemispheres. In addition to the branches of the trachea there were accompanying arteries, veins and nerves, the whole being bound together by a certain amount of proper substance or parenchyma, dilatable and extensible and placed between the branches of the trachea like a soft feather bed (AnB, 37v). In the figure of the tracheal branches after the parenchyma had been macerated away (QII, 1) (fig. G8), the terminal branches shown still had cartilage in their walls, so that the multitudinous systems of respiratory bronchi, alveoli, airsacs and air-cells, the actual respiratory tissue of the lung, were all included in the parenchyma.
Leonardo erroneously assumed that the total area of the cross-section of the ultimate branches was equal to the cross-section area of the trachea itself (QI, 5v), believing, presumably, that such an equality in size was necessary in order that there might be free passage for the air to and from the ultimate branches. He was considering only the tidal and complcmental air, but was aware that air, residual air, still remained in the lung after the completion of an expiration (AnB, 17). From his studies on animals and especially on the pig he was inclined to believe that when air was drawn into the lungs they expanded laterally only, not lengthwise (AnB, 17), perhaps finding support for this opinion in the idea that the muscular intervals between the rings of the bronchi bulged out in inspiration and contracted in expiration. In what is probably a later note, however, it is stated that the lungs increase and decrease in all directions, but chiefly lengthwise, since their expansion in this direction is useful in expelling food from the stomach (QIV, 3). It has already been noted (p. 177) that Leonardo had probably observed the bronchial arteries. The pulmonary vessels he describes as accompanying the branches of the trachea, the vein always lying above the artery, i.e. further away from the tracheal branch, an arrangement that was to be expected, since the arterial blood, being hotter, is in greater need of being refreshed by the air drawn into the lung (QII, 1). He represents (QII, 1) slender cords accompanying the branches of the trachea and identifies them as nerves, but the identification is more than doubtful.
Fig. 68. Sketch of lungs and heart, showing pleura! cavities. (QIY, 3.)
Galen held the opinion that a certain amount of the inspired air filtered through the lungs into the pleural cavities. Neither Avicenna nor Mondino mention this idea, but nevertheless Leonardo in two of his figures of the lungs (AnB, 17, and QIV, 3) (fig. 68) represents a distinct space between the lungs and the thoracic wall, and in the notes on AnB, 17 he definitely states that there is air between the lungs and the chest wall, and w T hen the lungs expand this air is forced downward between the lungs and the diaphragm, causing the latter to press upon the stomach and so aid in the expulsion of its contents. It also presses upon the pericardium and causes the small amount of fluid contained in the pericardial cavity to ascend and bathe the heart, moistening that heated organ and preventing it from drying up. Later Leonardo seems to have become sceptical as to the existence of this pleural air space, for on QII, 7 there is a memorandum inquiring w’hether or not there is such a space.
The traditional functions ascribed to the lungs were the cooling and refreshing of the heated blood sent to them by the heart and the supplying of the crude substance out of which the vital spirits were elaborated in the heart. Leonardo accepted the first of these functions, the cooling and refreshing of the blood, but improved on the Galenic view that some portions of the inspired air were actually brought to the heart. So far as he was able to trace them, the branches of the trachea in the lungs had thick walls and showed no pores by which they might communicate with the blood-vessels, and he was consequently inclined to believe that the relation of the pulmonary arteries to the tracheal branches was merely one of contact and that the refreshing of the blood took place through their walls. Of course he could not be certain of what might take place in the so-called parenchyma of the lungs, but, so far as he could determine, there was contact only and no communication, although he hesitates to pronounce positively on the matter until he should have completed a dissection then in hand (QII, 1).
Leonardo’s attitude as to the formation of vital spirits in the lung is not so clear. In certain passages he seems to imply quite definitely that the heart was the sole agency in the process as, when speaking of the heat produced by the friction of the blood on the heart walls, he
“And this heat subtilizes the blood, vaporizes it and converts it into air (i.e. spiritus).” (QH, 11.)
Or when speaking of what would result from the cessation of the flux and reflux of the blood he states that it would not be heated and “consequently the vital spirits could not be generated and therefore life would be destroyed” (QII, 4v). It may be, however, that the blood had already been refreshed in the lungs and had acquired some spiritual essence which the heat of the heart elaborated, and Leonardo may have been thinking only of the last part of the process. For in another passage where he refers to the psychic or animal spirits, “which command the nerves,” he ascribes their formation to the lungs without mentioning any participation of the heart (QI, 13v). But here again his attention was concentrated on the activities of the lungs and, indeed, the animal spirits are mentioned only incidentally. Notwithstanding the discrepant statements it is not unlikely that Leonardo accepted the Galenic theory as to the formation of the vital spirits, except that he doubted a direct transference of air from the lungs to the heart. A spiritual essence might, however, pass through the walls of the bronchioles into the arteries.
The passage on QI, 13v really is a setting forth of the necessity for a firm support for the lung tissue that the “compression, restriction and condensation” of the contained air may result from the action of the intercostal muscles and diaphragm. The ribs, with which the lung is in contact, provide this support, by which also “the lung secures itself against bursting from the violence of the air that is condensed in it.” Yet even with this support a rupture of a bronchiole may take place, and he describes the repair of such a rupture by the formation around it of a crust like a nut-shell, cartilaginous and callus-like, “and in the interior are dust and aqueous humor” (QI, 13v). Evidently Leonardo had observed a pulmonary tubercle.
Leonardo does not directly discuss the cause of the rhythm of respiration, but lie notes (AnB, 13) that the lungs may cease to act at will or by forgetfulness. During their inaction, however, the heart has returned to it the heated air which it sent to the lungs, and accordingly these can not long remain inactive lest the heart should be suffocated.
In several figures on AnA, 3 (fig. 66), which, as has been stated, were based on animal dissections, a bilobed structure, evidently the thyreoid gland, is shown attached to the upper part of the trachea, and regarding it Leonardo says:
“These glands were made to fill in where muscles are lacking and they keep the trachea apart from the clavicle (osso della for cula).”
This is the Galenic idea regarding glands, which were held to be merely a kind of flesh ( caro ) useful as a packing material (so here) or serving to retain moisture in subjacent structures. Bottazzi (1910) ascribes to Leonardo the discovery of the thyreoid. In one sense it may have been a discovery for Leonardo, for no mention of it is made either by Avicenna or Mondino; but it was known to Galen. It was a discovery for Leonardo in the same sense that the mesenteric lymph nodes were a discovery for Aselli.
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Reference: McMurrich JP. Leonardo da Vinci - the anatomist. (1930) Carnegie institution of Washington, Williams & Wilkins Company, Baltimore.
Cite this page: Hill, M.A. (2020, July 14) Embryology Leonardo da Vinci - the anatomist (1930) 15. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Leonardo_da_Vinci_-_the_anatomist_(1930)_15
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