Leonardo da Vinci - the anatomist (1930) 19
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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 XIX Embryology
The mysteries of development could not fail to incite to speculation even in the earliest times, and owing to the technical difficulties in the way of observation, speculation remained in control of the field for many centuries. One finds a brief statement regarding a human embryo in the Hippocratic writings, but the ideas of later writers were based, so far as they had a basis, on scanty observations on domestic animals and on the chick, and the facts so noted were straightway assumed to be applicable to human development. Aristotle, examining the chick, observed the embryo only when the heart began to beat and assumed that this punctum saliens was the first organ to form, an assumption that was an important factor in his assignment of the faculty of reason to the heart rather than to the brain. Further he assumed that the fetus was formed from the menstrual blood, the sperm contributing the element which caused it to take form, the female thus contributing the material and the male the formative element.
Galen opposed both these ideas, maintaining that the liver, on account of its predominating influence in the nutrition of the embryo, was the first organ to form, then the brain and then the heart. But the early visibility of the heart, “a palpitating bloody point, so fine that in contraction it disappeared, but reappeared on relaxation, looking like the point of a needle and of a ruddy color” in the middle of the rudiment of the chick, which had the form of “a little cloud” — the quotations are from Harvey’s description (1628) — gave support to Aristotle’s theory rather than to Galen’s and the punctum saliens and the embryological primacy of the heart continued to persist in the literature until a comparatively late date. According to Avicenna the first differentiation of the embryo is that of a locus cordis, from which two vesicles arise, one of these developing into the heart, the other into the liver; he does not definitely give primacy to the heart, but the influence of Aristotle is evident, while Galen’s theory is suggested by the association of heart and brain as the organ whose development precedes that of the umbilicus. Leonardo, however, expresses himself definitely in favor of Aristotle’s theory —
“All the body” he says “has its origin from the heart in so far as concerns the first creation. The blood also and the veins and the nerves do the like, although these nerves are plainly seen to spring all from the spinal cord, remote from the heart, and the spinal cord is of the same substance as the brain whence it is derived.” (AnB, 17v.)
This seems definite enough, but a further consideration of the condition under which the fetus lives led Leonardo to believe that during fetal life the heart did not beat (QIII, 7v; QV, 26). His argument was that since the fetus lies in a sac (amnion) filled with the purest water, it can not breath, for if it did it would at once be drowned. And if it can not breathe the beating of the heart would be unnecessary, and “it would be suffocated, as it can not get refreshment from the cold air that the lung draws in” (QV, 26). Such a belief does not necessarily contradict the theory that the heart is the first organ to be formed, but it detracts greatly from the importance of that organ as an essential to fetal development.
For Aristotle’s theory as to the nature and significance of the maternal and paternal contributions to the formation of the embryo, Galen substituted a more correct idea, namely, that the ovary as well as the testis produced sperm, the embryo being formed by a union of the two sperms. Avicenna followed the teaching of Galen, but again with a suggestion of Aristotle in that he speaks of the male sperm as being richer in the virtus formandi and the female sperm in the virtus inforviandi, and furthermore he describes the female sperm as a sort of menstrual blood, slightly digested and converted. Leonardo, too, followed Galen in believing that there was female as well as male sperm, both being derived from the blood, but receiving their generative virtue in the ovaries or testes by a process of coction. The female sperm thence passed to the uterus where it was stored and its generative virtue was only aroused to activity when it became mingled with male sperm (QIII, Iv). He applies this belief to a contradiction of a supposed case of action of the environment in a passage that is worthy of quotation.
“The blacks in Ethiopia are not caused by the sun, because if a black makes pregnant a black female in Scythia the latter brings forth black, and if the black male makes pregnant a white female, she brings forth gray. And this shows that the seed of the mother has equal potency in the embryo with the seed of the father.” (QIII, 8v.)
It would be easy to read into this last sentence a forecast of our modern knowledge of the process of fertilization, but of course Leonardo could have had no such prevision. He does, however, rightly interpret the facts at his disposal and with scientific acumen draws from them an important general conclusion.
Like his predecessors, Leonardo turned to the egg of the chick for information as to the processes of development, and several memoranda concerning such eggs occur among his notes. One refers to the advisability of first studying the anatomy of incubated eggs before representing the form of the liver in the child (QI, 10); another states the possibility of hatching eggs by the heat of an oven (QIII, 7) ; a third is a memorandum to inquire of the wife of Biagin Crivelli how capons when intoxicated may be made to hatch and rear the eggs of the hen (QIII, 7), a query apparently answered on the same folio:
“Their chicks are given in care of a capon that has been plucked on the under side of the body and then urticated with nettles and placed on the nest (lit. under the basket). And then the chicks go under it and it feels pleased by the heat and takes pleasure in it, so that thereafter it leads them about and fights for them, jumping into the air against the hawk in ferocious defence.” (QIII, 7.)
Another memorandum is a statement of what was probably a popular belief to the effect that eggs which have a rounder shape produce male birds, while longer ones produce females (QIII, 7); and still another is a note to inquire how the chick is nourished in the egg (QIII, 9v). But though these memoranda indicate clearly Leonardo’s intention of studying the process of development in the chick, there is no indication that his intentions were ever carried out; one finds no descriptions and no drawings of chick embryos.
There is, it is true, one rather indistinct sketch (QIII, 8v) that might be taken as a crude representation of a chick embryo lying in the center of the area pellucida. Across it is written “yellow crystalline in large quantity,” apparently a reference to the amniotic fluid; surrounding the embryo is a membrane, from which a leader extends to the label anima (i.e. amnion) ; surrounding the posterior half of this is another membrane labeled alanchoidea (i.e. allantois) ; surrounding all these is a third membrane labeled secondina (i.e. chorion); while enclosing everything is the matrice (i.e. uterus). The representation of these last two investments indicates that the sketch is intended as a diagram of the membranes surrounding a mammalian embryo, and two excellent figures on AnB, 38 (fig. 84) show that Leonardo had made a study of the pregnant uterus of a cow. In one figure he shows such a uterus with one of the ovaries and four blood-vessels supplying its walls, “these four veins a, b, c, d are tw T o of arteries and two of blood,” while the cotyledons show through indistinctly. In the second figure the fetus is shown still enclosed within the chorion, over whose surface the cotyledons, now plainly seen, are scattered and blood-vessels ramify in it, coming from the umbilical cord which is seen issuing from the ventral abdominal wall of the fetus.
It is evident, then, that Leonardo recognized the membranes which enclose the fetus, but it is equally clear that he knew them as they occur in the lower animals and not as they are in the human species. The amnion with its enclosed fluid is described; the fetus floats in the amniotic fluid and its weight is accordingly distributed over the whole inner surface of the uterus (QI, Iv). A second membrane is the allantois, which is described as passing — “between the hands and knees of the child as it lies curled up, and it passes between the arms and the inner ( silvestra ) part of the thigh as far as the flanks and ties and encloses, making itself an investment for the child from its flanks downward.” (QIII, 9v.)
Fig. 84. Two figures of membranes and circulation of fetal calf. (AnB, 28.)
Fig. 85. Representations of human fetus at term and of ungulate placenta. (QIII, 8.)
The description is not very clear, but notwithstanding that the fetus is spoken of as the “child” ( putto ) it is evident that it was not the very rudimentary human allantois that was being described, but the more highly developed allantois of a ruminant.
So too it is the chorion of the fetal calf that is described, and it was upon this that Leonardo, following the example of his predecessors, based his ideas of human placentation, assuming that it also was of the cotyledonary type. In the wonderful drawing (fig. 85) of the fetus still within the womb (QIII, 8) it is curious to note cotyledons of the ungulate type on the wall of the uterus, while the discoidal placenta is entirely overlooked, even although there is a memorandum to “Note well the umbilical vein where it ends in the uterus” (QIII, 7v). It is evident that Leonardo had examined a pregnant human uterus at term— he gives a number of drawings of the fetus as it lies curled up within the womb (QIII, 7, 7v, 8, 9v) — but in none of them is a placenta shown. Where the uterus is also shown there is usually no indication of how the fetus is connected with it; only in QIII, 8 are the cotyledons represented, on the assumption that what he had seen in the cow occurred also in the human pregnant uterus.
The structure of the cotyledons interested him greatly. He recognized that at birth each cotyledon divides, part remaining connected with the uterus and part adhering to the chorion (QIII, 8; AnB, 29v), and gives figures (fig. 87) showing the separation (QIII, 8; AnB, 29v, 38), but is somewhat uncertain as to their actual structure. Sometimes he figures and describes both maternal and fetal cotyledonary villi interlocking as the fingers of one hand may do with those of the other (AnB, 38; QIII, 8, 9v), and at other times he describes the villi as developed on only one of the two contributing structures, chorion or uterus, and fitting into depressions on the other half-cotyledon (AnB, 29; QIII, 8). The villous constituent he terms the male cotyledon and the other the female, and raises the question, without answering it, whether it is the male or the female cotyledon that remains attached to the uterus at birth. But, however that may be, he perceived thathalf of each cotyledon remains with the fetus “When it is born covered” (AnB, 38), that is to say in a “caul,” and the other half remains with the uterus. When this contracts after parturition the maternal cotyledons, widely separated on the uterus at term, are brought closer together, eventually come into contact, assuming by mutual pressure an hexagonal form, and finally fuse together to form a continuous membrane, separating again if a succeeding pregnancy occurs (AnB, 38). This seems to indicate that Leonardo had observed the discoidal human placenta and was endeavoring to explain it as a derivation from the diffuse cotyledonary type found in the cow and generally believed to be the functional type in the human species.
Leonardo’s adherence to the traditional ideas as to the movements of the blood and the significance of the arteries and veins made an understanding of the relation of the maternal and fetal blood-vessels impossible for him, even though he had gained a knowledge of the vessels concerned in the fetal circulation. On AnB, 29v there is a figure representing these vessels as he observed them in the fetal calf (fig. 86). A number of branches are shown passing from the fetal membranes, some represented as almost vertical and others as almost horizontal, the accompanying text stating that the former come from the chorion and the latter from the amnion, though it is more probable that the allantois was meant. These branches open into four main stems that pass to the umbilicus, where they converge to a single umbilical vein that passes up the inner surface of the anterior abdominal wall to the under surface of the liver. In the substance of that organ, it breaks up into numerous branches and is not continued further. From the umbilicus four other vessels pass downward to open into the right and left iliac arteries and veins; the arteries are evidently the hypogastrics, the veins are imaginary.
Another figure, on QI, 1, is of interest because it represents the supposed human conditions (fig. 87). The lower portions of the aorta and inferior vena cava and their division into the iliac arteries and veins are shown and below is an oval structure, apparently representing the uterus, within which is a mass which is presumably meant for the discoidal placenta. To this an artery and vein (uterine) pass from each of the iliac vessels— for the vessels passing upward from the iliacs, see p. 176 — and from the placenta there passes a single structure, evidently the umbilical cord. This extends to the fetal umbilicus and there gives off the ascending umbilical vein and the fetal hypogastric arteries. It seems probable that Leonardo believed the hypogastric vessels to carry vital spirit to the fetus, while nourishment was carried by the umbilical vein, since in another passage (QIII, 7v) the blood is said to pass from the fetal liver to the stomach, where it is converted into chyle; this passes to the intestine where a portion is absorbed by the meseraic veins, the rest remaining in the intestine and forming the meconium or fetal feces.
From the text on An, 29v one might gather that Leonardo believed that there was a complete separation of the maternal from the fetal blood, for he asserts that the umbilical vein of the fetus does not extend beyond the liver and, furthermore, that the umbilical vein is the origin of all the veins of the child and does not have its origin from any vein of the mother, “since each of these veins (i.e. the veins of the child) is entirely separate and divided from the veins of; the gravid woman.” And the same condition is implied by the statement that the veins of the child do not ramify in the substance of the uterus but in the secondina (chorion), which is, as it were, a shirt in the interior of the uterus that invests it and is connected, but not united, with it by the cotyledons (QI, 1).
Fig. 86. Diagram of the umbilical and hypogastric vessels. (AnB, 29v.)
Fig. 87. Diagram of the human fetal circulation. (QI, 1.)
Other passages, however, speak even more definitely in favor of a continuity of the two bloods, that of the mother passing directly into the child. A strong argument for this view was Leonardo’s belief, already mentioned (p. 229), that the fetal heart did not beat since the fetal lungs could not function.
“The beating of the heart and the breathing of the mother serve also for the child joined to her by the umbilical cord.” (QII, 11.)
The child in the womb can not weep or speak.
“Where there is no breathing there is no voice” (QIII, 7);. . . “If women say that the child may sometimes be heard to weep within the womb, it is the sound of the wind.” (QIII, 7v.)
If then there was no breathing and no beating of the fetal heart the only source for the vital spirits of the child is the blood of the mother and in discussing this point the word anima is used in its theological as well as its biological meaning. Thus he says —
“And the same soul governs the two bodies and the desires and fears and pains are common to this creature as to all the other animated members, and hence it results that the things desired by the mother are often found impressed on the members of the child which the mother carries at the time of the desire. So it is concluded that one and the same soul governs the bodies and that the same body nourishes both.” (QIII, 8.)
Another interesting passage with the same purport occurs on QIV, 10.
“Although human genius (reveals itself) in various inventions, corresponding with various instruments to one and the same end, it will never find an invention more beautiful, easier or shorter than that of Nature, since in her inventions nothing is lacking and nothing superfluous. She does not make use of counterpoises when she makes members suitable for movement in the bodies of animals. But she places therein the soul (anima), the producer of the body, that is to say the soul of the mother that first produces in the womb the form of the human being and in due time awakens the soul that is to be the inhabitant thereof and that at first remains dormant and under the tutelage of the soul of the mother, which nourishes and vivifies through the umbilical vein with all its spiritual members. And this it continues to do so long as the umbilical cord is joined to it by the chorion ( secondina ) and the cotyledons, by which the child is united to the mother. And this is the cause that one will, one supreme desire, one fear that the mother has, or other mental pain, has more power over the child than over the mother, since frequently the child loses its life thereby.”
Here Leonardo breaks off to remark —
“This discourse does not belong here but will be necessary in the (chapter on) the composition of animal bodies, and the rest of the definition of the soul I leave to the understanding of the friars, fathers of the people, who by inspiration know all secrets.”
With this remark, which has something of a sarcastic flavor, he breaks off again, and, as if to counteract the sarcasm, finishes the passage with a declaration of his belief in the inerrency of the Scriptures, “Let the crowned writings stand, since they are supreme truth.”
In both these passages Leonardo finds evidence of a community of soul in mother and unborn child in the supposed inheritance of maternal impressions, a well-known belief vouched for by the Scriptures in the story of Jacob and his ring-straked cattle. It is referred to again in a third passage, where it is noted “how one soul governs two bodies as is seen by the mother desiring a food and the child remaining marked (. segnato ) by it” (QIII, 3v). Another ancient belief, tracing back, however, only to the Hippocratic writings, was also accepted by Leonardo, namely, the belief that an eight-months child could not survive, while that born after only seven months of gestation might. Pie does not discuss the belief, merely making a memorandum to enquire 'why the child of eight months does not live (QIII, 3v).
Little is recorded regarding the development of the individual organs, but passages on QIII, 8v contain some remarks on the liver and spleen. It is stated that so long as the umbilical vein is functional, it occupies the chief position in the middle of the body both as regards length and breadth, but when it ceases to be of use it is drawn aside, together with the liver, wdiich is created and nourished by it. At first the middle of the liver is below the center of the heart and above the umbilicus, that is to say its right and left lobes are of equal size, and at this time the spleen is a viscous aquosity, pliable and flexible, and does not occupy its proper place. Later, however, it condenses to assume its necessary form and place and in so doing encroaches upon the left lobe of the liver, which withdraws toward the right lobe, pressing upon it, condensing it, and apparently being taken up into it, so that as much as seveneighths of the left lobe seems to be lacking and the middle of the liver, together with the upper part of the umbilical vein, lies to the right of the median plane of the body.
While the fetal nourishment, respiration and supply of vital spirits is cared for by the mother, the fetal excretion was carried on by the fetal kidneys. Exit of the urine by way of the urethra was, however, prevented by the position assumed by the child in utero, its right heel lying between the anus and the virile organ and thus compressing the passage. Nature therefore provided for its passage a canal which passed from the apex of the bladder to the umbilicus and from the umbilicus the urine passed in some unexplained way to the mouth of the uterus (QIIT, 7). Clearly the canal that Leonardo saw was the urachus, but he evidently failed, even in the calf embryo, to trace its continuity with the allantois.
Leonardo’s observations on the bodily proportions of the child have already been mentioned (p. 110), but in addition to these he has left a few memoranda as to the rate of growth and a statement to the effect that the length of the umbilical cord is the same as the length of the child (QIII, 7v), expanding this in another passage to an assertion that the length of the cord is the same as that of the child at all stages of growth and that this is not true of any other animal. The statement is fairly accurate as an average, but the length of the cord is subject to considerable variation.
As to growth, it is noted that the child at birth is generally one-third the average adult height (QIII, 7), and that the fetus at four months is half the length and one-eighth the weight of the child at term (QI, lOv). The growth in utero as well as in after life proceeds at a constantly diminishing rate until it ceases. The weight of the child nine months after birth is not double that of the infant after nine months gestation, nor is it so even after eighteen months (QIII, 7v).
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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. (2024, April 18) Embryology Leonardo da Vinci - the anatomist (1930) 19. Retrieved from https://embryology.med.unsw.edu.au/embryology/index.php/Leonardo_da_Vinci_-_the_anatomist_(1930)_19
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