Leonardo da Vinci - the anatomist (1930) 7
|Embryology - 14 Jul 2020 Expand to Translate|
|Google Translate - select your language from the list shown below (this will open a new external page)|
العربية | català | 中文 | 中國傳統的 | français | Deutsche | עִברִית | हिंदी | bahasa Indonesia | italiano | 日本語 | 한국어 | မြန်မာ | Pilipino | Polskie | português | ਪੰਜਾਬੀ ਦੇ | Română | русский | Español | Swahili | Svensk | ไทย | Türkçe | اردو | ייִדיש | Tiếng Việt These external translations are automated and may not be accurate. (More? About Translations)
|A personal message from Dr Mark Hill (May 2020)|
|contributors to the site. The good news is Embryology will remain online and I will continue my association with UNSW Australia. I look forward to updating and including the many exciting new discoveries in Embryology!|
McMurrich JP. Leonardo da Vinci - the anatomist. (1930) Carnegie institution of Washington, Williams & Wilkins Company, Baltimore.
|Historic Disclaimer - information about historic embryology pages|
|Embryology History | Historic Embryology Papers)|
Leonardo da Vinci - The Anatomist
Chapter VII Leonardo’s Anatomical Methods
Leonardo’s opportunities for anatomical studies were no better than those available for others of his time. Why then did he, an artist, far excel in his results even the professed anatomists who were his contemporaries? The answer is to be found in the spirit of the man and in the methods he employed. He was in possession of an overmastering desire to know all things, to prove all things for himself, while his contemporaries were content to rely more or less implicitly on the statements of their predecessors and to interpret what observations they might make in accordance with those statements.
Leonardo’s methods of acquiring knowledge were observation and experiment. He followed the Aristotelian method and found little use for the Platonic method of introspection so generally relied upon during the Middle Ages, when argument and the appeal to authority were the chief methods of settling disputed points in natural philosophy as well as in theology. Not but that there were men in mediaeval times, such as Roger Bacon, Grosseteste and Albertus Magnus, who exercised their powers of observation for the advancement of knowledge, but their works stand out like beacons across a dreary sea of compilations, such as the Speculum Majus of Vincent of Beauvais. For authority Leonardo had little respect, “Whoever” he says “in discussion adduces authority, uses not intellect, but rather memory” (CA, 7G). If he wished knowledge he sought it himself by observation, and was assured that when observation failed to give the results desired, the fault was with the observer, not with the method.
“Wrongly do men blame innocent experience, accusing her of deceit and false results.” . . . “Experience is not at fault, it is only our judgment that is in error in promising itself from experience things that are not in her power.” (CA, 154v.)
His method was what we are pleased to term the modern method — it is the method of Hippocrates and of Aristotle — and it was his use of it that compels our recognition of him as a giant amongst the pigmies of the scientific world of his day. Indeed, one may almost speak of him as ultramodern on account of his belief that no scientific fact or theory is complete until it may be expressed in mathematical terms.
“No human investigation” he says “can be termed true knowledge if it does not proceed to mathematical demonstration” (TP, 1). . . “And therefore, O students, study mathematics and do not build without foundations.” (QI, 7.)
When one considers Leonardo’s numerous statements as to the value of personal observation and experimentation or, as he termed them, of experience, it seems strange that Roth (1907) could have asserted that—
“We are now certain that Leonardo did not dissect himself, but his dissections, as was then customary, were made by surgeons.”
And could have maintained that —
“This cardinal error in his method explains for us the poverty and confusion of his technique, the incompleteness, the insufficiency, the contradictions, the corrupted Galenism of his Anatomy. ”
The provocation that lay back of Roth’s criticism of Leonardo has already been mentioned (p. 4) ; it led him to overlook the essentially pioneer character of Leonardo’s work and to judge him by presentday standards. Using the same standards one might also apply Roth’s disparagements to Vesalius, who, too, was a pioneer; but pioneers are to be judged rather by what they accomplish than by what they of necessity leave undone.
The charge that Leonardo did not personally make dissections is open to discussion. It is based mainly on the undoubted fact that in the public Anatomies of the time it was customary that the actual dissection should be done by some subordinate, a surgeon for choice, the rest of those present, with the exception of one who was the expositor and a second who demonstrated the parts exposed, having the role of spectators (cf. p. 18). But in Florence and Milan, in which, in Leonardo’s time there were no universities, public Anatomies were in all probability rarely if ever performed, and what dissection there was, was done privatim, under circumstances in which the formalities of the public demonstrations were neglected. Indeed, since the dissections in which Leonardo took part in Florence and Rome were performed in hospitals, it seems probable that they were not only privatim but privatissime. If Leonardo did not himself dissect it is difficult to understand the success of the accusations of Giovanni degli Specchi which resulted in Leonardo’s exclusion from the hospital at Rome as “a heretic and cynical dissector of cadavers” (Solmi).
But we have Leonardo’s own words for it. When he speaks of the dissection of il vecchio he does not say “I was present at an Anatomy of him” but “I made an Anatomy of him (io ne feci 7iotomia),” and it is difficult to believe that he meant to say that he was merely a bystander and spectator of the Anatomy. In one of two passages on QI, 13v, undoubtedly a continuation of the passage on QI, 2, which is regarded as part of the preface to the projected treatise on anatomy, 1 Leonardo presents nn apologia for the new departure. The fact that the succeeding passages end with “Vale” is further evidence that they were intended to be a preface. He planned, in making his book, an atlas rather than a text -book. He says—
1 See page 77.
“And if you say it is better to see an Anatomy performed than to see such pictures, you would speak rightly if it were possible to see all the things that are shown in such pictures in a single body, in which with all your genius you will not see and will not have knowledge, unless it be of some few veins. Concerning which to have a true knowledge of them, I have dissected more than ten human bodies, destroying all other parts, consuming even to the minutest particles the flesh that surrounded these veins, without causing them to bleed, except for an insensible bleeding from the capillary veins. And a single body did not suffice for so much time, so that it was necessary to proceed with as many bodies, one after the other, as would complete the entire knowledge; which (work) I twice repeated in order to observe the variations.” (QI, 13v.)
Roth (1907) quotes only the first few lines of this passage and these might be interpreted to convey the impression that Leonardo set little store by dissection. But it means just the reverse and contains a definite statement that he dissected. His contention is that the knowledge to be obtained by attending an Anatomy as a spectator would be far inferior to that to be obtained from his illustrations, worked out by careful and repeated dissections. And he continues —
“And if you have love for such a thing [meaning dissection] you will perhaps be prevented by your stomach, and if this does not prevent you, you may perhaps be prevented by the fear of passing the night-time in company with bodies quartered and flayed and fearful to look upon. And if this does not prevent you, perhaps you will lack the good draftsmanship that should belong to such drawing, and if you have the draftsmanship it may not be accompanied by perspective. And if it is so accompanied you may lack the principles ( ordine ) of geometrical demonstration and the principles for the calculation of the forces and power of muscles; or perhaps you may lack patience, so that you will not be diligent.” (QI, 13v.)
Surely the dread of a night-time spent with bodies quartered, flayed and fearful to look upon is a recollection of personal experiences; it can not refer to a spectator at a public Anatomy. Nor is it likely that a mere spectator of an Anatomy could give such minute instructions for a dissection as are contained in the following passage.
“You will separate the substance of the brain as far as the contours of the dura mater, which is interposed between the basilar bone and the substance of the brain. Then note all the foramina where the dura mater penetrates the basilar bones, with the nerves covered by it, as well as by the pia mater. And this knowledge you will observe with certainty, if, with diligence, you raise the pia mater gradually, beginning at the ends and noting from part to part the location of the said foramina, commencing first with the right or left side, figuring it in its entirety, and then you will follow the opposite part, which will give you knowledge whether the former one is well placed or not and also will make you understand that the right part is like the left. And if you find variations, look back on other Anatomies, if such variation is universal in all men, women, etc.” (An B, 35.)
A study of the drawings and text of the Windsor collection should surely bring conviction that Leonardo was representing with his pencil what he himself had observed by dissection. There are his own repeated and definite statements that he dissected human bodies, and to these may be added his reported statement to Cardinal Louis of Aragon, when that prelate visited him at Amboise, that he had made Anatomies of more than thirty bodies, both male and female and of every age . 2 He undoubtedly dissected various animals with a view of obtaining suggestions leading to a more definite knowledge of the parts of the human body and, indeed, the whole endeavor and chief characteristic of the man was the striving to discover for himself the secrets of both Art and Nature in all its fields. From his methods applied in other domains of science one would expect, without further evidence, that in his anatomical studies also he would apply the methods of personal observation and experiment. Leonardo’s more immediate predecessors in anatomy were Arabists, and their Anatomies were made to illustrate Avicenna’s teachings. His contemporaries, such as Benedetti and Marc Antonio, had caught the spirit of the Renaissance, but it was that of the literary rather than of the scientific Renaissance, and their Anatomies were made to illustrate Galen’s teaching; but Leonardo was a forerunner, nay, rather one of the outstanding representatives of the scientific Renaissance, basing his knowledge not on the teaching of others, but on his own observations. He practised the method of personal observation used by Vesalius some thirty years later, but Vesalius completed his work and gave it to the world, while Leonardo’s remained uncompleted and hidden away in Melzi’s villa at Vaprio.
3 This statement is contained in a manuscript in the Bibliotheca Nazionale at Naples, entitled Itinerario di Monsignor R mo et Ill no il Cardinal da Aragona mio Signore, in cominciato dalla cittA di Ferrara nell’ anno del Salvatore 1516 del mese di maggio et descritto per me, Dom. Antonio de Beatis, Clerico melfictano. Attention was first drawn to the passage referring to Leonardo by G. Uzielli ( Richerche intorno a Leonardo da Vinci, Roma, 1884) and the portion containing the statement mentioned above has been quoted by Solmi (1910) and Bottazzi (1907).
It was then with knife, saw and chisel in his own hands that Leonardo made the anatomical preparations that -were recorded by his facile pencil. His ingenuity in invention suggests an inquiry as to whether he may not have improved upon the methods of dissection commonly employed, or invented special methods for the solution of special problems. The earlier writers speak of maceration and mummification as suitable methods for the study of certain parts. Thus Mondino after mentioning the “simple parts” says —
“I shall not give a detailed anatomy of them because their anatomy does not show perfectly in a dissected body, but rather in one macerated in running water.”
So too, Guy de Chauliac recommended for the study of the bones, cartilages, joints, the larger nerves, tendons and ligaments, bodies that had been dried in the sun, decomposed in the earth, or macerated in running or boiling water, and Berengario taught that the union of the nerves with the spinal cord could only be observed in bodies macerated in water, confessing at the same time that he had never himself observed the union; he also recommended the use of bodies that had been boiled for the study of the muscles. Leonardo had apparently made trial of the maceration method, but found it very unsatisfactory when employed for the study of the nerves. He says —
“And I remind you that the anatomy of the nerves will not give you the situation of their branches, nor in what muscles they branch, by means of bodies macerated in running water or lime water; because, while their origin remains to you without as well as with such water, their branchings by the current of the water come to unite, just as flax or hemp, hackled for spinning, make themselves into one bundle, so that it is impossible to discover again into what muscles they enter or with what or how many branches they penetrate the said muscles.” (QI, 2.)
He makes no other mention of the application of this method, not even in connection with the preparation of the bones, although it is evident from his figures that he used some form of maceration for these and did not rely upon mummified preparations as was the custom of mediaeval anatomists, whose manuscript representation of the skeleton are manifestly drawn from desiccated preparations.
Holl (1905) has suggested that in the preparation of the bloodvessels Leonardo made use of injections, basing his suggestions on the appearance of the vessels in the drawings. A conjecture based on such evidence alone necessarily rests on a very insecure foundation, for an artist would naturally represent tubes with flexible walls and known to be filled with fluid as if they were cylindrical in form. It seems probable that if Leonardo had employed some method of injection to distend the blood-vessels he would not have failed to give a description of it, and nowhere in his notes is there even a mention of it. The art of injecting the blood-vessels did not come into general use until after Harvey’s discovery of the circulation of the blood in the seventeenth century, though sporadic instances of its employment are recorded long before that time. Thus Galen mentions the inflation of the cerebral vessels as a means of facilitating their study, and M. Medici, without vouching for the accuracy of the statement, quotes from the advocate Alessandro Macchiavelli ( uomo d'altre parte eruditissimo) to the effect that Alessandra Giliani of Persiceto made dissections for Mondino with surpassing skill, and injected the bloodvessels with various colored fluids, the injection quickly hardening to a permanent mass.
But even if evidence is lacking that Leonardo used injections in the study of the blood-vessels, he did employ the method for another purpose, namely, to obtain a clear idea of the ventricles of the brain by injecting them with melted wax. His description of the operation is as follows:
“Make two air-holes in the horns of the greater ventricle and take melted wax with a syringe, making an opening in the ventricle of memory (i.e. the fourth ventricle), and fill through this opening the three ventricles of the brain. And then, when the wax has solidified, dissect the brain and you will see the form of the three ventricles distinctly. But first place slender tubes in the air-holes, so that the air that is in these ventricles may escape and give place to the wax which enters the ventricles.” (QV, 7.)
That Leonardo actually made such an injection is shown by the legend placed below one of the drawings on the same folio :
“Form of the sensus communis. Injected ( gittato ) with wax through the bottom of the base of the skull by the opening m, before the skull was sawn.”
In this case, however, the injection was made through the floor of the third ventricle instead of through the fourth as was prescribed in the directions for the operation.
This method of demonstrating the form of the cerebral ventricles has frequently been used in recent times, but Leonardo was the first to employ it. It is a method that must be used only with great caution, as the roofs of the third and fourth ventricles may readily be ruptured before the injection of the lateral ventricles is completed, and this seems to have happened with Leonardo’s preparation, for his figures give an entirely erroneous idea of the form of the third ventricle, and there is no indication of the prolongation of the lateral ventricles into the temporal lobes. But even with these and other serious defects, his figures based on the method correct fundamental misconceptions evident in his earlier figures of the brain, and credit should not be witheld from Leonardo for his ingenuity in devising so novel a method and for his skill in carrying it out, even though the results were only partially successful.
Nor was this the only instance in which Leonardo’s inventive genius led him to anticipate a method which was later made successful. His problem was to evolve a method by which the structure of the eye might be demonstrated without the loss of its humors and the consequent distortion of the parts. To accomplish this, he recommends placing the eyeball in white of egg and then boiling the whole; then when the white of egg had coagulated the eye might be cut across transversely, and nothing lost from the lower half (Iv. 119). This seems to be an anticipation of the modern method of imbedding tissues for the preparation of microscopically thin sections and, indeed, in the early days of this process, albumen was used by Calberla as the imbedding material. But Leonardo’s process lacked one of the essential features of the modern treatment in that he probably did not allow the albumen to thoroughly penetrate the eyeball that was to be studied, and so give it a uniform consistency. Indeed, the thorough permeation of an entire eyeball is a matter of some difficulty and without it the use of the albumen could be of but slight advantage. At all events it yielded Leonardo no important results, since his ideas as to the structure of the eye show no advance upon the erroneous views held by his predecessors. Nevertheless he was moving along the right path and his method, though crude, was no more so than the early methods of imbedding for section-cutting, employed more than three centuries later.
A third anticipation by Leonardo of a modern technique was his suggestion of the use of transverse sections for the study of the gross anatomy of the limbs. On QY, 20 (fig. 10) there is a sketch of a leg in which there is indicated a number of planes, three in the thigh and four below the knee, in which the limb might be transected, and beside this there are two sketches showing the leg divided through these planes, the structures cut across being represented in outline in certain of the sections and, finally, the upper surface of one of the sections, the third of the thigh, is shown with the cut structures outlined and lettered. Unfortunately no text accompanies the drawings and there is no explanation of the lettering employed. Perfect accuracy can not be claimed for the lettered drawing, for while the section of the femur (d), the vastus lateralis (a) and medialis (e), probably both heads of the biceps ( b and c), the sciatic nerve and the femoral artery can be identified, uncertainty remains as to the other structures represented. On QV, 19 there is a pencil sketch of the leg with planes for section represented in ink, three in the thigh and three below the knee, and again beside it is a figure showing the structures cut at the middle plane of the lower leg. The structures are lettered, but again there is no text to explain the lettering and again uncertainty exists as to what several of the structures represent, the figure being inaccurate. Leonardo had from his dissections a knowledge of practically all the muscles of the leg, but he evidently was not sufficiently familiar with their relations throughout their courses to identify them with accuracy in sections of the limb. So far as can be judged from his manuscripts he did not employ the method extensively and used it apparently only in connection with the lower limb. It was an experiment performed with knife and saw on material which lacked the previous preparation employed
Fig. 10. Transverse sections of the leg. (QV, 20.)
Fig. 11. Figures in which the muscles of the leg are represented hv cords or wires. (Q V. 4.)
in the present-day applications of the method, and the cut structure could not have had that smoothness of surface and sharp definition necessary for their ready identification. At all events it may be supposed from the limited use he made of it, that he found the method unsatisfactory, and it is only in recent times that it has been elaborated so as to become a recognized and valuable method in the study of anatomy.
Leonardo’s deep interest in the mechanical principles involved in natural phenomena found for him a fruitful field for study in the action of muscles and in the movement of the blood in the heart. So clearly did he perceive the necessity for a correct understanding of such principles in the investigation of muscle action that he intended to preface the account of the muscles in his projected book with a treatise on the elements of mechanics and their applications (An A, 10). Structure and function were for him correlated phenomena, the study of one necessarily involving that of the other. A muscle was an organ intended for the movement of a part, it served a definite purpose and it could not be properly understood until its purpose was determined. So he notes that one must remember to make sure of the origin of each muscle by pulling upon its tendon (AnA, 18), and that for each muscle there must be given the reason for all its offices, in what manner it acts and what moves it, etc. (AnB, 27). Pulling upon the tendon was an obvious procedure for determining the effect of the contraction of the muscle and was that recommended by Galen. But Leonardo desired a method that could be illustrated, and devised the plan of representing the muscles by means of threads (fig. 11).
“You will never avoid confusion in the representation of the muscles and of their positions, origins and insertions if you do not first make a representation of the slender muscles using threads, and thus you will be able to represent one over the other as Nature has placed them; and thus you will be able to name them according to the member which they serve, as the motor of the end of the great toe or of its middle or first bone, etc. And granted that you have such knowledge you will represent along side of this the true form and size and position of each muscle ; but remember to place the threads which indicate the muscles in the same position as is the central line of each muscle and so the threads will represent the form of the leg and their distance will be quickly known.” (AnA, 18; cf. AnA, 4v.) 3
3 The last sentence of this paragraph “e la lor distanzia spedita e nota” is somewhat obscure. Probably it means that the relative positions of the muscles will be readily perceived.
In another passage (QV, 4) he suggests the use of copper wires instead of threads, and from this it might be suggested that he contemplated the preparation of a model in which the muscles would be represented by wires attached to the skeleton and “bent into their natural form.” It is doubtful, however, that he really made such a model; he probably used the threads in his drawings merely to represent the muscles diagrammatically, so that their action and relations to one another might be more clearly perceived. This view is indicated by a passage (AnA, 10) in which he states that he uses threads to represent the muscles rather than lines, to show which muscle goes over and which goes under the other, “which thing would not be possible with simple lines.”
The method is used in the representation of quite a number of the muscles, one of the most interesting cases of its employment being in the comparison of the hip and thigh muscles of a man and a horse (QY, 22) (fig. 12). Unfortunately the representations are inaccurate in some details, but it is noteworthy as a study of corresponding muscles under different mechanical conditions. It was one of Leonardo’s maxims that “Every muscle uses its power along the line of its length” (QIV, 6), and the use of cords or wires was useful in determining that line. It must be remembered that for Leonardo the question of muscle action seemed much less complex than it does today. For him it was a question of the action of the individual muscles, not of muscle groups, and under such circumstances the use of the method might be of advantage, while for present purposes it can have only a limited value.
From the deep interest shown by Leonardo in problems connected with the movements of the heart and of the blood within it, one might expect that his inventive ingenuity would have led him to devise methods for rendering these movements apparent. And such was the case. He pondered much over the nature of the eddies and whirlpools that must be formed within the cups of the semilunar valves, when these were brought together by the reflux of the blood on the completion of the contraction of the ventricle. There are several sketches representing theoretical possibilities for these eddies (fig. 48), but these did not satisfy; the eddies could not be actually observed in the heart and Leonardo proposed to make a glass model of the basal portion of the aorta in which the course of the blood could be seen. On QII, 12 there is a sketch of a longitudinal section through a cylinder which becomes somewhat bulbous in its lower part, very much as the proximal portion of the aorta is represented in other drawings. Within the figure is written:
“Form of plaster (gesso) to be inflated and a thin glass within it and then break it from head to foot in an” and below this the passage continues — “But first pour the wax into the gate of an ox’s heart, so that you may see the true form of this gate.”
It is difficult to obtain from these statements a clear idea of what Leonardo was planning, but apparently he proposed to make first a wax cast of the cavity of the aorta in its ascending portion and to use this cast to prepare a plaster model of the vessel. A lining of thin glass was then to be blown into this model, and when the plaster was broken away the glass tube might be used to observe the currents of blood. On QII, 6v, there is again mention of a glass by which might be seen “what the blood does in the heart when it closes the valves of the heart,” but no further details as to its preparation and use are given. But on QIV, llv there is a memorandum, referring to the movements of the blood, “Make this experiment (prova) in glass and move within . . . membrane,” a sentence whose obscurity is increased by the illegibility of a word, but which seems to imply that Leonardo was planning to attach a membrane to the inside of the glass to represent one of the semilunar valves. There is no evidence that the suggested model was ever constructed, no mention of results obtained by its use.
Fig. 12. Figures of surface anatomy of the leg with a comparison of the hip muscles of a man and a horse, muscles being represented by cords or wires.
In connection with his studies of the heart-beat, Leonardo made use of another experimental method or rather adapted the method employed by the Tuscan farmers in slaughtering their pigs (QI, 6). The animal was tied to a board, back downward, and a drill ( spillo ), such as was used to pierce wine casks, was driven through the chest wall into the heart. The point where the drill pierced the chest wall served as a fulcrum and, as the heart contracted, the point of the instrument moved upward and the handle was depressed and vice versa as the heart passed into diastole, the range of motion of the handle indicating more or less accurately the extent and direction of the movements of the organ.
The history of the use of this method in modern times has been told by van Leersum (1913), who shows that Leonardo had anticipated its use by modern physiologists by over three centuries. Schiff, substituting a needle for a drill, used it in 1849 in connection with his studies on the nerve control of the heart, and Rudolf Wagner used it in 1854 as a method unusually favorable for counting the heart beats and for determining the intensity of the heart’s contraction. Later it was used by Moleschott and others, and more recently J. Berry Haycroft (1891) developed from it the more complicated, but more accurate, cardiograph.
In his investigations of the phenomena of vision Leonardo was continually resorting to experimentation, testing the effects of sudden illumination, studying the phenomena revealed by the pin-hole camera, etc. But these observations may be more appropriately considered later. One other experiment only need be mentioned here, that of pithing a frog.
“The frog suddenly dies when its spinal cord ( midolla della sciena ) is perforated; and before that he lives without head, without heart or any interior (organ) or intestines or skin. And it seems therefore that here is situated the foundation of motion and life.” (QV, 21v.)
Also on the recto of the same folio it is stated that the frog will live for some hours if deprived of its head, heart and all the intestines, but if the spinal cord be pricked the animal “suddenly twitches and dies;” “All the nerves of the animal arise here (i.e. from the spinal cord), and this nerve being pricked it suddenly dies.” Leonardo thus demonstrated a very important fact. A frog deprived of his brain becomes a purely reflex organism, without volition but capable of responding to certain stimuli in an unvariable manner. It would therefore seem to be still alive. But destruction of the spinal cord means destruction of the reflex centers and the animal lies flaccid and inert, apparently dead, but not really so. For death is not a sudden but a gradual process, and if Leonardo had varied his experiment or carried it further he would have found that the heart would continue beating and the muscles would contract if their nerves were stimulated for some time after the brain and spinal cord had been destroyed.
These examples will suffice to show that Leonardo approached his anatomical problems with originality and with ingenuity of method. But anatomy, being so largely a science of observation, did not give full scope to these characteristics; they are more clearly manifested in other fields of his activities, in his studies in hydraulics, for instance, and in his numerous mechanical devices. It was his fertility of invention that rendered his search for knowledge so productive and contributed to making him the greatest genius of the Renaissance.
|Historic Disclaimer - information about historic embryology pages|
|Embryology History | Historic Embryology Papers)|
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) 7. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Leonardo_da_Vinci_-_the_anatomist_(1930)_7
- © Dr Mark Hill 2020, UNSW Embryology ISBN: 978 0 7334 2609 4 - UNSW CRICOS Provider Code No. 00098G