# Leonardo da Vinci - the anatomist (1930) 11

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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 XI The Muscles

Galen in his Be administrationibus had left a very full, though verbose, account of the muscles as he found them in monkeys, and Avicenna briefly epitomizes his account, by condensation and omission covering in a few pages what Galen had spread over many. In Mondino this condensation is carried to almost complete omission, only two groups of muscles being mentioned, those of the anterior abdominal wall and those of the thorax. Concerning the former, he cites Galen as stating that they are eight in number, i.e. the two recti, the two pairs of oblique and the two transversi, and of the thoracic or pectoral he says :

“This anatomy does not allow you to perceive all the muscles of the chest. All are not to be observed because there are eighty-eight (according to Avicenna there are seventy-eight) of them, but nevertheless you ought to know that some are dilators and some dilators and constrictors.”

He then mentions, without description, the two muscles of the diaphragm, two in the neck that dilate the upper part of the chest cavity as the diaphragm does the lower part, and two muscles between each pair of ribs, one with its fibers “latitudinal,” while in the other they are transversal. Of the muscles of the limbs he says nothing; indeed in the public Anatomies of his and later times the structure of the limbs received but slight consideration or none at all, these parts being left to the last and the main interest being directed to the anatomy of the three ventres — abdomen, thorax and head, in that order.

And if in pre-Vincian times the muscles had fallen upon evil times so far as their description went, in illustration they were in a yet sorrier plight. The muscle-man of the Five-Figure Series (fig. 30) is naive in its imperfections and could only make confusion worse confounded. It was not until 1496 that a figure is found worthy of being called a representation of a group of muscles. It is contained in the Venetian edition of that year of the Conciliator differentiarum philosophorum et prcccipae medicorum by the Averroist Pietro di Abano, whose death in 1316 alone saved him from suffering the extreme penalty for heresy and the practice of magic. The figure (fig. 31) which represents the muscles of the abdominal wall does not appear in the first edition of the book printed in Mantua in 1472, nor in three succeeding editions, but it is found for the first time in the fifth edition, printed one hundred and eighty years after the death of the author. It is clear that Pietro di Abano had nothing to do with the illlustration ; the publisher of the edition, Octavianus Scotus, was probably responsible for its insertion

Fig. 30. Muscle man from Raudnitz Five-Figure Series (1399). From Sudhoff, Archiv, vol. 3, pi. 12, 1910.

Fig. 31. The abdominal muscles from Pietro di Abano’s Conciliator dijjerentiarum (1496). From Sudhoff, Archiv, vol. 3, pi. 2, 1910.

and it was evidently drawn by some one who had at least witnessed an Anatomy, but was more influenced by his interpretation of Mondino’s statement, with Galen for its authority, than by what he might have observed. The peculiar features of these figures will be discussed in connection with some similar ones by Leonardo.

It was probably the simplicity and conciseness of Mondino’s statement regarding the abdominal muscles that led to their representation by a diagram in the Antropologium of Magnus Hundt (1501). It is a diagram of extreme simplicity, consisting of a St. Andrews cross imposed upon a St. George. The limbs of the St. George cross represent the longitudinales and latitudinales, while those of the St. Andrews cross represent the transversales (i.e. the obliques). This and the figures in the Conciliator are the only serious attempts in pre-Vincian times to represent the arrangement and structure of individual muscles.

It must not be forgotten, however, that in Leonardo’s time and earlier, the development of Renaissance art had led to an awakening interest in the surface modeling of the human body in rest and in action. In a truly modern spirit, some of the artists, notably Leonardo’s preceptor Verrocchio and his contemporary Michel Angelo, 1 endeavored to obtain understanding of this modeling by a study of the musculature underlying the integument, but such studies were solely from the standpoint of the artist and did not lead, as they did in Leonardo’s case, to the investigation of the individual muscles. That was a field that, so far as the Renaissance anatomists were concerned, was almost unworked, for Galen’s labors in it were practically unknown to them. Berengar di Carpi in his Commentaria on Mondino’s Anathomia had done something, but his work was not published until 1521, two years after Leonardo’s death, so that the latter in his abundant myological studies had to rely upon his own observation, with slight assistance from Avicenna.

Leonardo’s ideas as to the ultimate structure of muscles have already been considered in the discussion of his definitions of the similar parts (p. 99). On the basis of their form he divides muscles into groups, those that are short and are termed muscles (s. sir.) and those that are long and are designated lacerli (An A, 15). Lie also gives a more extended classification based mainly on the form of the tendon (AnA, 13v), recognizing four groups; (A) those that begin and end in tendons and of these there are two subdivisions, (a) those in which the tendons are dilated and “converted into cartilage” i.e. broad and flat, and (6) those in which the tendons are round and cord-like; group (B) includes those muscles that have tendons at one end only, and of these there are also two subdivisions (a) and ( b ) according as the tendon is round or flat ; group (C) has those muscles that are attached to the bone throughout its whole length; and group (D) contains those that arise by tendon

1 Three drawings of corpi sscorticati ascribed to Verrocchio have been reproduced by Duval and Bical ( L’Analomie des matlres, Paris, 1890) and one by Michel Angelo, apparently of the same character, is given by Choulant.

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and end in flesh, these differing presumably from those in group (B) in that the latter begin with fleshy substance and end in tendon.

On QII, 15 there is a more extended description of the various forms under which muscles occur, and the passage is interesting in showdng how far Leonardo had carried his studies of individual muscles. Muscles, he says, are of many kinds. Thus, some are without tendons, as the chains of the right ventricle of the heart, etc. ( i.e . as the moderator bands of the heart), and others are round, as the one that had been previously mentioned, which is detached and does not join itself except by bridles to the member moved by it. Others are large and slender, others large and thick, others long and narrow, others long and thick, some slender and oval, others fish-like, others lizardlike ; some twisted, others straight. Some have a tendon from only one part, others on both ends, and others are divided by many tendons, like the longitudinal muscles of the body ( recti abdominis) . Some move the members from either end, some from one end only; some move directly ( dirieto ) on their tendons, others draw the tendons to them. The occurrence of bicipital muscles is also noted (An A, llv, and QIII, 9v), these being explained by the suppositions that the parts to which they are attached may require to be moved by two almost similar motions, or that the bicipital condition gives a margin of safety, since if one head be injured the other may still continue to function.

On AnA, 15v there is a sketch showing a muscle with a short, broad tendon above and a rounded one below. At one side is represented a nerve which sends a branch to the muscle belly and, on the other side, an artery and a vein also sending branches to the muscle. All these structures are labeled, indicating their functions; the upper tendon is force ( forza ); the muscle, motion; the nerve, sensation; the vein, nourishment; and the artery, spirit. This might be interpreted as meaning that the muscle acted by virtue of vital spirit conveyed to it by the artery, the nerve being purely sensory. But, as will be shown later (see p. 210) Leonardo used the word sentimento, sometimes to imply what would be termed sensation and at other times in the sense of stimulus, and was fully aware that the stimulus to function came through the nerve. This is shown by statements such as "the muscles retract or extend solely on account of the nerve from which they receive a stimulus ( sentimento )” (AnB, 3v), and many similar passages might be cited. According to the view current in Leonardo’s day, the nerves were tubular structures, whence he speaks of them as corde forata (AnB, 2), and through their lumina vital spirit could flow to the muscles, whereby an expansion of the muscle, accompanied by a shortening, ensued. He had doubts, however, whether the "air” of the nerves could suffice to render the muscles as tense as they are in full contraction and recalls the case of a stallion, which could scarcely move on account of excessive fatigue, and yet, at the sight of a mare, quickly recovered his forces

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and overtook the mare, which fled before him (AnA, 18). He doubts if the nerves could furnish enough “air” for so sudden a recovery, but he has no other explanation to offer. He believed, too, that under certain conditions muscles could contract automatically, without stimuli from other officials, i.e. from nerves, the senso commune, or the soul, and instances as examples —

“the movement of paralytics, of those benumbed by cold, whose head and members move without control of the soul, who can not stop the movements. The same happens in epilepsy and in severed members, such as the tails of lizards.” (AnB, 2v.)

On AnA, 15v Leonardo sets forth an important principle in muscle physiology in the statement that when the sartorius and tensor fasciae latse ( a andV) contract, the leg is drawn forward and the gluteus medius and anterior part of the gluteus maximus ( b and c) relax, while the posterior portion of the gluteus maximus ( d ) elongates, and he then goes on to note that “this rule is to be described in the action of all the muscles.” Thus he establishes a general rule that when a muscle contracts there is a relaxation of its antagonist, an interesting foreshadowing of the law of the reciprocal innervation of antagonist muscles so admirably worked out by Sherrington. Leonardo’s rule implies a recognition of muscle tone, as does also his statement that at death all muscles extend in length (QII, 8v) ; Galen had remarked on it long ago, terming it innate contractility, but it is not mentioned by either Avicenna or Mondino. Naturally its real significance as an effect of the central nervous system was unknown, as was also the mechanism of the relaxation of the antagonist muscle, as an inhibition of its tonus. Such concepts as nerve reflex and inhibition were quite beyond the physiology of the period, they were still far in the future; even though its real significance was undreamt of, Leonardo’s observation was an important advance in muscle physiology.

Leonardo was deeply imbued with the prevailing teleological philosophy and seems inclined to believe that each muscle was formed to produce a certain definite movement and that each had a definite antagonist. Thus he states (AnA, 16) that each muscle attached to the spine of a vertebra has an antagonist, and adds a curious explanation of this particular case, namely that the spines of the vertebrae to which muscles passing to the head were attached would break when the head was bent, were it not for the antagonist passing to the spines from below. He does, indeed, recognize combined action of muscles, as when the sartorius and tensor fasciae latae flex the thigh or when the hand performs the movement of circumduction, noting, however, in this latter case, that there are four principal movements, namely, what would now be termed flexion and extension, adduction and abduction, and in addition to these an infinite number of secondary inter

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mediate movements (AnA, 14). As a rule, however, he ascribes to a muscle a single definite action which it exercises quite independently of others. There is little suggestion of synergic action.

Holl (1905) has ascribed to Leonardo the recognition of voluntary and involuntary muscles. He uses these terms (AnA, 15 v), but of movements and not of muscles and not at all in the sense in which they are applied to muscles today. He is speaking of what may be either the intercostal muscles or the serrations of the serratus anterior and their action in breathing, and states that they have “a voluntary and an involuntary movement, for they are those that dilate and compress the lungs.” It is not a question of two different kinds of muscles, but of a group of muscles that at one time may act voluntarily and at another involuntarily.

A few epigrammatic statements scattered through the folios may be quoted as indicating Leonardo’s comprehension of the mechanics of muscle contraction.

“It is the function of muscles to pull and not to push, except in the cases of the genital members and the tongue.” (AnB, 29.) . . . “The muscles

always arise and terminate in bones conjoined one to the other and never in one (and the same) bone, since (then) they could move nothing unless it were themselves, as regards their rarity or density.” (AnB, 18v.) . . . “No muscle uses its power in contracting, but always in drawing to itself the parts conjoined by it.” (AnB, 38v.) . . . “Every muscle uses its power along the line of its length.” (QIV, 6.)

And, finally a passage whose meaning is somewhat obscure —

“A man can draw only his own weight. If he stands in one pan of a balance and puts his shoulders against something solid, he will raise in the other pan as much weight as he has strength.” (A, 30v.)

Leonardo has left no systematic description of the muscles, such as is found in modern text-books. Indeed, it seems doubtful, even if he had completed his treatise, whether he would have given such detailed descriptions of the morphology of the muscles as is now customary. His interest lay chiefly in their action, and for an idea as to their form and position he was inclined to rely upon his drawings rather than upon description. Such, at least, is the impression one obtains in studying his statements and this impression is confirmed by what seems to be a preliminary draft of a portion of the anatomy (AnB, 29), in which he gives an account of the muscles moving the lips and cheeks, arranged in a series of paragraphs, each with an appropriate heading. If one may judge from these and similar passages his treatment of the muscles would have been very similar to that of Avicenna, though with somewhat greater detail, with more attention to their action and with the added advantage that the text would have been abundantly illustrated by excellent drawings.

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Many of his figures show merely the surface modeling produced by the muscles and are more interesting to the artist than to the anatomist, but in many others the dissection is carried to a greater extent and in some cases the muscles are represented by cords or wires with the object of more readily perceiving their action. A difficulty in the way of concise and lucid description with which Leonardo had to contend was the absence of a definite system of myological nomenclature. Galen had the same difficulty and resorted to the plan of considering the muscles in topographic groups and numbering the individual muscles of each group. There were a few recognized terms in Galen’s day such as crotaphitic (temporal), masseter, psoas and cremaster and these he used, but they are not found in Avicenna nor in Mondino, and Leonardo did not know them, or at all events did not use them. Even Vesalius in his Fabricd adopted Galen’s device; his older contemporary Dubois (Sylvius) made attempts toward the introduction of a definite nomenclature, as did Riolan later, but it was not until the eighteenth century that a special myological terminology, such as we now possess, was elaborated by the endeavors of Cowper (1694), Douglas (1707) and especially Albinus (1734). Leonardo in many cases met the difficulty by reference to his illustrations in which the muscles were designated by letters of the alphabet, sometimes, however, bestowing a name, as when he speaks of the infraspinatus as muscolo massimo della spalla (AnA, 2).

One finds many omissions and numerous errors in Leonardo’s myological notes and drawings. The omissions will be pardoned when it is remembered that he passed away with his great plan uncompleted ; the errors, too, may be forgiven when one compares his work with that of his more immediate predecessors, and recognizes that he was, in these studies especially, a pioneer. His muscle drawings, sure in touch and as a rule accurate as to form and proportion, can not, indeed, be compared with previous efforts — the contrast is too great. His physiology is undoubtedly ancient, his treatment of his subject rather mediaeval, but his illustrations are altogether modern.

The muscles of the head receive rather scanty consideration, those of the orbit being omitted, while of the trigeminal groups only the temporal, masseter 2 and digastric are indicated (AnA, 13v), the pterygoids remaining unnoticed. The stylohyoid is represented on AnA, 3v. The muscles of expression (the platysma or facialis group) were naturally of interest to him as an artist and he makes a memorandum to “figure the cause of the movement seen in the skin, the flesh and the muscles of the face and whether the muscles have their motion from the brain or not” (AnA, 13v). The platysma itself is not described, unless it be

2 Piumati identifies this as a pterygoid. It has the direction of the internal pterygoid, but clearly inserts into the outer surface of the mandible, the ramus of which is exposed when the muscle is removed.

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in the definition of the term pellicle (see p. 99), but a number of the muscles of the face are shown, some of them being given special names to indicate the expression in which they are active. Thus the frontalis is termed the muscolo del dolore, and what seems to be the corrugator supercilii is the muscle of anger, this term being also applied to the zygomaticus minor (AnA, 13v). The zygomaticus major, levator labii superioris, pyramidalis nasi and buccinator are also shown, but strange to say he fails to represent the orbicularis oculi.

The movement of the lips he considers at some length (AnB, 29 and 38v), but it can not be said that he has gained an accurate idea of either their arrangement or action. He starts on the assumption that in man there are more muscles acting on the lips than in any other animal, because in man the lips have more varied movement. He seems to have dimly perceived the orbicularis oris, stating that the muscles which constrict the mouth are "in the lips themselves or rather the lips are the actual muscles which close themselves,” but he failed to perceive its true arrangement. He notes that other muscles unite with the muscles of the lips, but of these other muscles he mentions only the lateral ones which antagonize the constricting action of the muscles of the lips. These lateral muscles seem to have been the buccinators. Apparently, however, he recognized the necessity for further observations on the lip muscles, for in addition to the muscles that constrict and extend the mouth he assumes that there are others which protrude the lips and others which restrict them, others that evert them and others that antagonize this movement, others that twist them sideways and others that bring them back into place.

“In fact there may be found as many muscles as there are movements (accidenti) in the lips and as many more to counteract these movements, and these I intend to describe and figure in full, proving the movements by my mathematical principles.”

Leonardo evidently felt the necessity for a more thorough study of the muscles of expression and makes a further memorandum to — “Figure all the causes of movement that the skin, flesh and muscles of the face have and whether the muscles receive movement from nerves that come from the brain or not. And thus do first in the horse, which has large muscles and parts very evident.” (AnA, 13v.)

But here again the good intentions were never carried out.

From the head-line and opening paragraph of AnB, 28v one is led to expect an extended discussion of the muscles of the tongue. The head-line reads “Of the muscles which move the tongue” and the opening paragraph states that “no member has need of so great a number of muscles as the tongue, of which twenty-four 3 are known without

According to Avicenna there were only nine.

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counting the others that I have found.” But on reading further instead of the description of these muscles, or even of those Leonardo believed he had discovered, one finds first of all some remarks as to the sensory function of the tongue and a statement that he intends in this place to consider only its movements. Still one may have hopes, but continuing further he speaks of the part played by the tongue, together with the lips and teeth, in producing speech and then goes on to discuss the changes and growth of languages. This leads him on to compare the mutability of human inventions with the permanency of Nature’s work; man can only combine the simple products of nature, he can create nothing, “unless it be another self, that is to say his children.” This idea leads him on to discuss the futility of the aims of the alchemists for they can not create anything. Gold in the rocks is continually but slowly growing, the tips of its ramifications changing into gold that which they touch, “and note that here there is an anima vegetativa which it is not in thy power to produce.” From this he passes on to consider (AnB, 28) 4 how the animal body continually dies and is remade and this leads to an invective against necromancy (AnB, 31v) and this in turn to a consideration of the “spirito,” a force united to the body and without which the body can not live (AnB, 31, and AnB, 30v). All this is most interesting, but it is not anatomy. Led by his thoughts far from his starting point he quite forgets it and nothing more is said in this place about the muscles of the tongue.

But he returns to their consideration on QIII, 10, where it is again stated that the tongue has twenty-four muscles, 6 but this statement is modified by the assertion that these twenty-four muscles combine to form the six which make up the substance of the tongue. It would seem that the twenty-four were all extrinsic, for he goes on to make a memorandum to inquire as to how the twenty-four combine to form the six and how they arise, some from the cervical vertebrse in contact with the oesophagus (superior constrictor of pharynx), some on the inside of the mandible (genio-hyo-glossus) and some from the trachea. The movements effected by these muscles, extrinsic and intrinsic, are seven, namely, extension, retraction, attraction, thickening, shortening, dilating and thinning. But of these seven movements three are compound ones and can not be produced except in cooperation with one of the others. Thus it is impossible to extend the tongue without at the same time narrowing it and, similarly, it can not be shortened without thickening it, while dilation involves both thinning and shortening.

The sterno-mastoid and trapezius are represented several times, the former with a pleasing accuracy (fig. 32), the latter not so success 4 In these folios Leonardo not only writes from right to left but passes in Semitic fashion from verso to recto.

6 On QIII, 9v, there are said to be twenty-eight muscles in the roots of the tongue.

A H 4

l'ig. 32. The muscles of the neck and shoulder. (AnA, 3v.)

. 33. Two representations of the muscles of the back and shoulder. (AnA, 16.)

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fully. Usually only its upper part is represented (AnA, 3v, 4, 4v), but in one figure practically the whole muscle is shown (AnA, 16) (fig. 33), its lower portion in this figure, however, inserting into the vertebral border of the scapula, an error which is emphasized in another figure of the same folio in wffiich the muscle is represented by cords or wires. The mistake is a curious one, since the figure is the first of a series of five designed to show the successive layers of the muscles of the back, and it is difficult to understand how the trapezius could be removed without revealing the true insertion of its low r er fibers into the spine of the scapula. In the second figure of the series (fig. 33) the trapezius is removed, showing the inferior belly of the omohyoid, the levator scapulse and the teres minor, and below the last what may be intended for the teres major, but if so its relations to the scapula are not correctly represented. In the third figure the superior posterior serratus is shown as three separate muscles, instead of a single muscle inserting on the ribs by four digitations, but in the fourth and fifth figures, which represent the true dorsal axial muscles, the identification of the different parts shown becomes difficult. The dissection of these muscles is no easy task, and even Vesalius, thirty or forty years later, was unable to completely unravel their complexities. Leonardo observed that their deeper portions were made up of short slips passing from spinous process to spinous process, and came to the conclusion that each vertebra had ten tendons attached to it, five being antagonistic to the other five (AnA, 16; QII, 5v). He evolves an explanation of this arrangement to the effect that were there no antagonists the spine of the vertebra would be fractured by the great strain to which it was subjected (AnA, 16), since the attachment of the muscles to the spines rather than to the bodies afforded them greater leverage (AnA, llv).

The mechanics of the movements of the head upon the summit of the vertebral column exercised him not a little, since he seemed to associate with these movements a necessity for a considerable rigidity of the column, inasmuch as the muscles that produced these movements arise from the vertebrae. How the rigidity could be imparted is illustrated by a figure on QII, 5v, in which the muscles are represented by stout cords (fig. 34), and concerning which he writes —

“First you will make the spine of the neck with its tendons, like the mast of a ship with its stays, without the head; then make the head with its tendons that give it movement on its pole.”

The cords can not be identified with any actual muscles and the figure must be regarded as a representation of an idea rather than of actual conditions. At first he supposed that the stabilizing muscles passed from the cervical vertebrae to the shoulder girdle, but later, on AnA, 16v, where he returns to the idea of the mast and its rigging, he concludes that —

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“The muscles of the shoulder do not aid (in the fixation of the vertebrae), nor those of the clavicle ( forcula ), since the man will relax these muscles arising in the shoulders and forcula when he raises the shoulders to the ears and will take away the power of his muscles. And with such relaxation and shortening, movement is not wanting in the neck (head?) and there is not wanting the resistance of the spine in sustaining the head.”

Then he proceeds to assign the main stabilizing action to the superior posterior serratus, which he invariably describes as formed of three separate slips (see fig. 35). His earlier notion as to the function of these muscles was that they were elevators of the ribs, acting in respiration (AnA, 16; AnB, 27v), but on An A, 16v he finds reasons for supposing that they really act as stabilizers of the cervical vertebrae in the facts, firstly, that the ribs are especially strong at the points of attachment of the slips of these muscles, that is to say, in the region of the angles, and, secondly, that the obliquity of the muscles to the ribs places them at a disadvantage as elevators of these parts. Taking this second reason in conjunction with the belief that all parts were perfectly adapted to the functions they had to perform, there would be sufficient reason to doubt the action of the muscles in respiration.

Of the ventral muscles of the neck region a dissection, in which the sterno-mastoid is removed, shows the infra-hyoid muscles (AnA, 3v). The omo-hyoid is figured several times (fig. 31) and in one passage is said to be inserted into the clavicle; on AnA, 15v and 16, however, it is clearly shown to be attached to the upper border of the scapula.

The general mechanism of respiration had been established long before Leonardo’s time, and he was familiar with the fact that the capacity of the chest may be increased by muscular action, that with this there is an increase in the capacity of the lungs and, since there can be no vacuum, the air rushes in to fill them (AnA, 16v; QI, 5). Leonardo’s problem was the determination of the muscles that were active in enlarging the capacity of the thorax. The intercostal muscles, which he terms the mesopleuri, naturally suggest themselves and are represented in a number of drawings, the external and internal muscles, with the correct inclination of their fibers being shown in separate figures (AnB, 27v; Q1I, 6v), while in another the fibers are represented by cords which form a lattice-like arrangement between the ribs (AnA, 7). In the text (QI, 13v) it is stated that there are twenty of these muscles, which may be interpreted to mean that there are ten sets on each side, those of the eleventh intercostal spaces having been overlooked.

The actions assigned to these muscles are the traditional ones; the external intercostals serve to raise the ribs, thereby increasing the capacity of the chest, while the internal ones — their fibers having a direction at right angles to those of the external — will have a contrary action and serve to depress the ribs. Leonardo notes that the eleva

I

Fig. 34. A cord diagram of the muscles supposed to stabilize the cervical vertebrae in movements of the head. Also a sketch showing the insertions of muscles into the spine of a vertebra. (QII, 5v.)

l ie. 35. Diagrammatic representation of superior serratus posterior and serratus anterior. (QO, 8.)

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tion of any rib will tend to raise all those below it and, furthermore, that the lower ribs have more motion, successively, than the upper ones (QII, 6v). That the elevation of the ribs will increase the dorsoventral diameter of the thoracic cavity is clearly perceived by Leonardo and he gives diagrams to illustrate how it is done (QI, 2v), but that it also increases the lateral diameter is not so clearly brought out, although his reference to the movement being through a “curved obliquity” (QII, 6v) is probably a recognition of that fact. One would, however, have expected that Leonardo, knowing as he did the form, position and attachments of the ribs, would have shown greater interest in the mechanical principles involved in this lateral enlargement. When the external intercostals relax, the ribs return to the position of rest by their own weight, provided the body is in an upright position, but if recumbent, then the internal intercostals come into play (AnB, 27v); the elasticity of the costal cartilages, wdiich are bent when the ribs are raised (QII, 6) is not considered.

But while recognizing the action of the external intercostals as elevators of the ribs, Leonardo for a time at least attached much greater importance in this respect to the serratus posterior superior; indeed in one passage (QI, 8) in speaking of the dilation of the chest he mentions only this muscle and the serratus anterior. It is figured and described as three separate muscles (fig. 33), and there is some uncertainty as to the insertion of these, one passage (QI, 2v) stating it to be into the three upper ribs, another (QI, 8) that it is into the second, third and fourth ribs, (fig. 32) and it is figured (QI, 5; AnA, 16v; AnB, 27v) as passing to the third, fourth and fifth ribs. Leonardo evidently mistook the dentations by which the muscle is inserted for separate muscles and overlooked one of them, and a further error is the statement that the muscles are supplied by branches of the nervi reversivi (AnA, 16; QI, 2v), by which term the vagi are meant.

The change in Leonardo’s views as to the action of these muscles has already been mentioned (p. 138). At first he assumed that their sole action was to elevate the ribs (AnA, 16) and for that reason proposed to term them li tiranti (AnB, 27 v). Later he argues that they may raise the ribs and also serve in the fixation of the cervical vertebrae, which he believed to be necessary for the proper functioning of the muscles that move the head, and finally he concludes that the latter is their only function (AnA, 16v).

Another muscle regarded by Leonardo as important in respiration is the serratus anterior, concerning which he again falls into grievous error. One is inclined to suppose that in his dissections he did not remove nor look beneath the latissimus dorsi and so failed to see the main portion of the serratus extending backward to be inserted on the vertebral border of the scapula. Only the serrations of the lower portion of the muscle w r ere known to him. Of these he shows

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five (QI, 5; AnB, lov; 27v) in most of the illustrations, but on QI, 8 there are six (fig. 33) and on AnA, lov, seven (fig. 36) and the diagram on QI, 8 indicates that he supposed the serrations to be continued into round cord-like tendons that passed backward to be attached to the vertebral column. This is another case in which Leonardo's conclusions outran his observations, and apparently his conclusions altered with time, for on AnA, 15v he represents the serrations diagrammatically as passing obliquely from one rib to the next over the intervening intercostal space, without any suggestion of their being attached to the vertebral column. 6 The muscles are supposed to dilate the ribs, withstanding the tendency of the diaphragm to draw them inward; hence Leonardo proposes to term them li dilatanti (AnB, 27v).

Leonardo believed that if the shoulders were raised by the muscles of the neck, the lowering of the ribs would be prevented and, similarly, if the shoulders were depressed the ribs could not be raised and so, to obviate the difficulties. Nature provided the diaphragm to attend to the necessary increase of chest capacity (AnB, 16v). This is a thick tendinous (nervous) sheet surrounded by muscles (QIV, 2v) which are attached to the costal cartilages or the ends of the ribs (QI, 5); its form is that of a deep spoon (fig. 37) and by the contraction of the muscle the concavity is diminished and to that extent the vertical diameter of the chest is increased. The flattening of the diaphragm can, however, occur only if the lower ribs are fixed or dilated by the serrations of the serratus anterior, the part the diaphragm plays in respiration being thus of a complex character and, to be effective, requiring the cooperation of the serratus. Its return to the vaulted condition is not due to any intrinsic effort. "When it contracts, it presses upon the liver and stomach, which lie in its concavity, and through them upon the intestines, which force outward the anterior abdominal wall ( mirac ). When the diaphragm relaxes the muscles of the abdominal wall contract, in turn pressing upon the intestine, stomach and liver, forcing these last against the under surface of the diaphragm and so causing it to become concave. There is accordingly an alternating contraction of the diaphragm and the muscles of the anterior abdominal wall (QI, 6v; QII, 16v). But the diaphragm not only serves in respiration, it has other functions. By pressing upon the stomach it causes the ejection of chyle into the intestine; with the aid of the abdominal wall it expels the superfluities of the intestine; and it serves to separate the spiritual organs from the natural ones (QI, ov; QII, 16). The action of the diaphragm on the abdominal contents will be considered in the chapter on the digestive organs.

‘ Piumati identi6es the muscle slips shown in this diagram as intercostals, but their position and form does not at all correspond with those muscles, while they do with the serrations of the Serratus. The fact that the same sheet has a beautiful scorticato showing the serrations is contributory evidence that the diagrams are representations of these.

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Reference has been made (p. 128) to an illustration of the muscles of the ventral abdominal wall in the 1496 edition of Pietro d’ Abano’s Conciliator differ entiarum. The illustration shows two human figures in which the muscles of the anterior abdominal wall have been dissected, one figure showing the two recti ( longitudinales ) and on either side of these the transversi (latitudmales) . The other figure shows the obliques (tr ansver sales) , the more superficial or external one on each side attached to the iliac crest by a broad origin and passing upward and medially, narrowing as it goes, to cross its fellow in the median line and to be inserted into the ribs of the side of the body opposite to that from which it arose. The deeper or internal muscles have essentially the same form and relations, but are reversed, their fibers running downward and medially. The obliques, therefore, are incorrectly represented in crossing the median line and in the direction of their fibers. In the very crude diagram in Hundt’s Antropologiion (1501) they are again showm as crossing, but the external and internal muscles are not distinguished. Further, Sudhoff has found in a copy of the 1495 edition of Ketham’s Fascicidus a marginal diagram drawn by a student in 1499 as an interpretation of Mondino’s description of the abdominal muscles, and again the obliques cross the median line.

There was apparently, at the close of the fifteenth century, a fairly general belief that the oblique abdominal muscles, being oblique, must necessarily cross the median line, since otherwise they could find no bony parts into which they might insert. Leonardo seemed to have acquired the idea of a crossing in the abdominal muscles, either from his reading or from hearsay, but he applied it to the recti instead of to the obliques. In two sketches (QIII, 7 and QIV, 6) (fig. 38) he shows the two recti crossing the median line and each other a short distance above their attachment to the pubis, so that the muscle attached above to the ribs of the right side inserts into the left pubic bone, concluding from this arrangement that the action of each muscle is to bend the trunk forward and at the same time draw it laterally, or, as he expresses it “the right shoulder inclines toward the left thigh.” When, however, the recti are drawn from a dissection, as on AnB, 15, they are represented accurately and with no indications of a crossing, though they are still supposed to incline the trunk laterally as well as to flex it. This last figure also shows each of the muscles divided into four portions by tendinous inscriptions, an arrangement that makes for strength, “for where there is life with thickness there is force, and where there is so much length of movement there it is necessary to divide the motor into several parts.” The same muscles and their division by tendinous inscriptions are also considered in TP, 230, and here the number of portions is given as three. That the arrangement conduces to greater strength is again referred to, but it is also pointed out that since each part will furnish only one-third of the entire contraction,

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LEONARDO DA VINCI — THE ANATOMIST

there will be less distortion of the anterior abdominal wall and little alteration of the general beauty of the body.

In discussing the actions of the recti (QIV, 6), Leonardo perceived the necessity for antagonistic muscles that would counteract the forward bending produced by them and so allow a purely lateral inclination. Such antagonists he describes and represents in sketches as two muscles on the dorsal surface of the body, said to arise from the ninth vertebra of the back and shown as passing, downward without crossing, to the crests of the ilia. The identification of these muscles is difficult. The sacrospinalis suggests itself, but the insertion forbids its acceptance and it is possible that they are intended for the quadrat! lumborum, even though they do not resemble them in form.

But if the identification of these muscles with the quadrati is uncertain there is no doubt that Leonardo observed the psoas. For in speaking of the action of the recti in bending the trunk forward he says “And their assistants ( adherenti ) are the lonbi, which are on the side of the spine within” (QII, 16v). There is no evidence, however, that he knew of their relation to the thigh.

The external and internal obliques are indicated in a diagram on QIII, 7, and the serratious of origin of the external muscle are well shown on AnB, 15v. In the text (AnB, 16) this muscle is said to arise from the sixth rib, its serrations alternating with those of the serratus anterior, and below, becoming aponeurotic or, as Leonardo expresses it, “converted into cartilage,” it is attached to the ilium and to the pubis. The internal oblique is described as arising from the spinal column opposite the umbilicus and inserting on the eleventh rib and the pubis, in the interval being converted into “cartilage” which covers the rectus; the fan-shaped arrangement of its fibers is distinctly shown in the lower figure on AnB, 16.

But the transversus interested Leonardo more than the obliques, since he believed it to be par excellence the muscle that compresses the intestine and so expels its contents. It is partly shown on AnB, 15, on either side of the posterior wall of the sheath of the recti, again spoken of as “cartilage,” beneath which it is supposed to pass, being in close contact with the peritoneum ( sifac ), a relation that leads Leonardo to speak of it as the transverse muscle of the sifac (QII, 16; QIV, 3), and, going a step farther, to ascribe the act of expulsion from the intestines to the sifac (QII, 16).

Leonardo’s treatment of the limb muscles is the most satisfactory portion of his myological contribution, but the merit of it does not lie in verbal description, of which there is little, but in the illustrations, many of which are sufficiently accurate in detail and execution to satisfy even modern standards. They form, indeed, a startling contrast to the pre-Vincian attempts and it was not until many years after Leonardo’s time that illustrations appeared that could be compared

l'ig. 39. Scapular ami hracliial muscles. (An A

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143

with them. From the artist’s standpoint attention may be especially called to the figures showing the surface modeling of the neck and shoulders on AnA, 2v; An A, 4 and 5v, and of the lower limb on QV, 22 and 23.

The scapular muscles receive a good deal of attention, a fact that renders all the more remarkable the failure to perceive the correct attachment of the trapezius and serratus anterior. The muscles of the dorsum of the scapula, together with the teres major and the upper part of the latissimus dorsi are shown in several illustrations (AnA, 2, 4v and 14v) (fig. 39), and on AnA 12 there is a representation of the scapula with the spine cut away to show the tendon and insertion of the supraspinatus. On AnA, 2 the same muscles are represented by cords, and a figure shows the bone tilted so that the supraspinatus and infraspinatus, which Leonardo terms il massimo, are seen, while another figure shows the muscles severed and the humerus slightly withdrawn from the glenoid cavity, so that the insertions of the teres minor, supraspinatus and infraspinatus into the tuberculum majus and of the subscapularis into the tuberculum minus are clearly shown. The action of the latissimus dorsi and teres major is stated to be the inward rotation of the humerus (AnA, 4v, 14v) and the latter muscle also serves to adduct the arm (AnA, 14v).

The deltoid appears on a number of folios of AnA (figs. 32, 35, 38 and 39) ; on 6v and again on 13v it is labeled as if consisting of four separate parts, and on 4v, in which it is seen from behind, there is a gap in the continuity of its origin, the portion arising from the base of the spine being separated by an interval from the acromial portion. To the more posterior portion is strangely attributed the action of rotating the arm inward. The pectoralis major is said to arise from the thorax as far down as the seventh rib, alongside the xiphoid cartilage ( pomo granato ), and at its lower border it is transformed into fascia or aponeurosis ( panniculo , cartilagine) which covers all the abdomen and terminates below on the pubis. It is regarded as consisting of several muscles (AnB, 16v), an idea which finds expression in figures on AnA, 2v, and AnA, 4v, where it is represented as four separate muscles which reverse their original succession from above downward just as they approach their insertion on the humerus, Leonardo having perceived the curious twist of the tendon of insertion. On AnA, 6 it is represented as a single muscle, although the separation between its clavicular and sterno-costal portions is well marked. Its action is to adduct the arm and it is of large size so that the arm may be drawn with force from the hands of any one attempting to seize it (AnA, 14v). It is represented by cords on AnA, 4v. The pectoralis minor is also shown with a fair amount of accuracy; its origin is not quite exactly given, but its insertion into the coracoid process ( rostro del spatolo ) is correctly shown (AnA, 2v, 4v; AnB, 15v). Its action is to

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raise the ribs and hence it is one of the muscles of respiration (AnA, 14v). It is represented by cords on AnA, 4v. On AnA, 4 a small muscle is shown extending from the clavicle to a rib. Piumati (AnA) and Holl (1905) identify it as the subclavius; it may be this muscle, but the drawing makes it seem to be on the upper rather than on the under surface of the clavicle.

Of the muscles of the upper arm the biceps, which is termed il pesce del braccio, receives the most thorough treatment. It is represented together with other muscles of the arm on AnA, 9v, 13v and 14v; it is figured alone on QII, 19, and in five figures on AnA, lv the origins and insertions are clearly and correctly shown (fig. 27), as they also are in a sketch on QIII, 9v. Figures showing the origin also occur on AnA, 2, 4v and 14v. Leonardo attributes to it as its main function the supination of the forearm, its action as a flexor manifesting itself only when the supination is complete (AnA, 9v; QIII, 9v). This view of its function is interesting, since it is only in recent years that the supinating action of the biceps has been given the recognition it deserves. Leonardo seems to regard it as the sole agent in supination, apparently overlooking the supinator, through failure to remove the superficial extensors. The origin of the biceps by two heads is naively explained by the supposition that it is double above, so that if one head fails the other may act (QIII, 9v; AnA, llv). The coracobrachialis is represented in a figure on AnA, 4v, but receives no mention in the text. The brachialis is the important flexor of the forearm (QIII, 7v, 9v; AnA, 2, 9v) and is a strong muscle since it must support great weights; its insertion into the ulna ( fucile maggiore ) precludes it from any share in supination (AnA, 2). The triceps is recognized as the extensor of the forearm (AnA, 9v); its insertion is accurately represented, but only two of its heads, the long and the external, are shown (AnA, 2).

The superficial muscles of the forearm are well shown in a number of figures (AnA, G, Gv, 9v, ]2v, 13v, 14v) (fig. 40) but no dissection of the deeper ones, except the pronator quadratus, was made, and special mention in the text is made of only a few. The tendons of the long flexors were, however, dissected out and the palmar muscles w T ere studied. The pronator teres attracted attention as the antagonist of the biceps, it being noted that the latter muscle can not act, that is to say in supination, if the pronator teres keeps its power (QIII, 9v). The pronator quadratus is figured (AnA, 10) (fig. 41) and described as a strong fleshy muscle passing from the radius to the ulna, but in TP, Ch. 218, it is termed a tendon ( corda ); its sole purpose is to keep the two bones from separating. The relation of the tendons of the flexor sublimis and flexor profundus are worked out (AnA, 10) (fig. 41), one figure showing the deep tendons passing to the fingers, another both superficial and deep tendons together with the tendon sheaths, and in a

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third figure the tendon of the profundus is shown perforating the corresponding one from the sublimis. It is noted that the tendons of the flexors are stronger than those of the extensors and also that the long flexors are able to flex the middle and terminal phalanges; it is queried, without an answer, as to how y the flexion of the basal phalanx is brought about.

In the dissection showing the long flexor tendons in place (fig. 41) the lumbricales are shown, and in addition there is on the same folio a representation of a dissection of the palmar region in which the long tendons and lumbricales have been removed, so that the deep muscles, as well as those of the thenar and hypothenar eminences, are shown. Unfortunately no mention of any of these muscles is made in the text; Leonardo makes a memorandum that they are to be represented as cords in order that their relations and action may be readily seen, but apparently this illustration w T as never made.

As with those of the arm, the muscles of the low r er limb are shown chiefly as surface modeling (fig. 12) or in scorticati, comparatively little dissection being done upon them. Indeed, if one may judge from what Mondino says, the limbs received very scant treatment in the "Anatomies,” and it is all the more to Leonardo’s credit that he should have considered them as fully as he did. Admirable representations of the muscles of the lower limb from the front are given on AnA, 3, 7, 15, 15v and on QV, 3 and 23; from the side on AnA, 9, 1 Iv, 15v (fig. 36), and from both the side and back on AnB, 19, 19v; QV, 3 and 22. Figures in which certain of the muscles are represented by cords are given on QV, 4 (fig. 11). It will be recalled, also, that it is in connection with the lower limb that Leonardo suggests the possibility of studying anatomy by means of sections, giving representations of the surface of certain sections (QV, 19 and 20) (fig. 10). Two of these, one from the thigh and the other from the crus, have the different muscles labeled with letters, but unfortunately no text accompanies the figures. The outlines of the muscles shown are not quite accurate ; in the thigh section the vastus medialis and intermedius, together with the rectus tendon, are unlabeled and the semimembranosus and semitendinosus are not separated, while in the crural section the soleus is represented as three muscles and no separate tibialis posterior and flexor longus hallucis are shown. The figures are more interesting as suggesting the possibilities that lie in the method of study, than as exact anatomical illustrations.

The glutei are noted as being the largest and most powerful muscles, whose strength is showm in the lifting of weights (AnA, 6v), but only the maximus and medius are shown, the former labeled as if two separate muscles (AnA, 15v). The tensor fasciae latse (fig. 36) is also shown and is figured separately, rather diagrammatically however; it is said to connect with the vastus lateralis below (AnA, 15) and also

14G

LEONARDO DA VINCI — THE ANATOMIST

with the ligament that binds the knee, i.e. the ilio-tibial band. Xo dissection of the deeper portions of the gluteal region is shown and hence the gluteus minimus and other muscles of this region receive no recognition. The tensor fasciae latae and sartorius act in drawing the thigh forward (AnA, 15v) and also in effecting abduction and adduction (AnB, 18), and when they contract the gluteus maximus relaxes and the medius elongates; furthermore the tensor is said to produce an internal rotation and the sartorius an external (QV, 4). The glutei and the other two muscles are represented by a string figure on QV, 22.

The rectus femoris and the vasti are shown in the front views of the thigh, and on AnA, 9 it is stated that the patella is in relation to the rectus, here termed pesce di coscia, to the muscles on either side of this, i.e. to the vasti, and to the patellar tendon that is attached to the tibia. The sartorius is well shown on AnB, 20, in a leg flexed at the knee. On QV, 15 is a representation of a dissection in which the rectus and sartorius have been removed, exposing the vastus medialis and intermedius, and a memorandum suggests the removal of the tensor fasciae latae to see what lies below it, but there is no indication that this idea was carried out. Curiously, there is no satisfactory figure of the hamstring muscles; apparently their relations were not understood, for on AnA, 9 the bones of the leg are shown both extended and flexed, with two cords attached, the one to the condyle of the tibia and the other to the head of the fibula. They might be supposed to represent the semimembranosus and the biceps, but the one is attached above to the lesser trochanter and the other to the greater one. They are supposed to rotate the crus to one side or the other when the leg is flexed at the knee, but when it is extended they will merely press the tibia more firmly against the condyles of the femur.

The gastrocnemius and tendo Achillis are well shown on QV, 22, and it is noted that the two heads of the gastrocnemius, regarded as separate muscles, and the soleus, also regarded as two muscles, unite to be attached to the tendo Achillis (AnA, 11), and Leonardo inquires why Nature did not make of them a single muscle, but does not answer the inquiry. The conjoint muscle is regarded as that which draws the heel upward and so raises the body upon the toes, and he calculates that when the body is so raised one half its weight is borne by the balls of the toes and one half by the muscle in contraction (AnA, 9 and llv).

The deep muscles of the calf were not exposed, but their tendons as they pass behind the internal malleolus are well shown (AnA, 11 and 1 lv) (fig. 42) as well as the distribution to the digits of the flexor longus hallueis and flexor longus digitorum, the connection between the former and the tibial tendon of the latter being emphasized. Similarly, only the superficial muscles of the extensor surface of the crus are shown, but the tendons of all are shown. In AnA, 7v the tendons of the three peronei are seen in one figure and in two others the tendon of the

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peroneus longus is seen passing obliquely across the sole of the foot to be inserted in the base of the first metatarsal. The insertion of the tibialis anterior is shown on AnA, llv, and on AnB, 28, there is an excellent drawing, also showing the tendon of this muscle together with those of the extensor longus hallucis and extensor longus digitorum. On AnA, 17 the tendons of the last-named muscles and that of the peroneus tertius are well shown, and they are represented even more admirably on AnA, 18, the extensor brevis digitorum being also accurately shown.

Leonardo quotes from Mondino, wrongly attributing the statement, however, to Avicenna (AnA, 18), that the muscles of the foot are sixty in number. He does not endeavor to confirm this statement, however, and his dissection of the plantar region is less complete than that of the palmar. He figures the abductor minimi digiti and the flexor brevis digitorum, showing the latter, however, with only three tendons, that to the fifth digit being overlooked (AnA, 11). Of the deeper muscles he shows the flexor brevis hallucis, drawing special attention to its relation to the sesamoid bones, here termed ossi petrosi (AnA, 7v), but fails to observe the adductor hallucis. The flexor brevis and abductor minimi digiti are indicated as are also the plantar interossei and what may be two of the lumbricals (AnA, 7v), but the quadratus plantse seems to have escaped observation.

On AnA, 17, he attributes to Mondino a statement to the effect that the muscles that dorsiflex the digits arise from the outer side of the thigh. As Roth (1907) has pointed out he was probably relying upon an imperfect text or upon his recollection of Mondino’s words which are to the effect that the tendons that extend the digits arise from muscles that are in the outer part of the tibia (i.e. crus), they can not be located on the dorsal surface of the foot since this region should be without muscles, lest it increase the weight of the foot. His erroneous recollection of Mondino’s words seems to have impressed him, since he returns to the idea in. two other passages (AnA, 11, and AnB, 20), pointing out that the thigh muscles act on the crus, the foot as a whole is moved by the muscles of the crus and the digits partly by the muscles of the crus and partly by those of the foot. The last portion of this statement he expands (AnA, 11) by stating that the terminal phalanges are moved by muscles that arise in the crus, but the muscles that produce movement of the whole digits have their origin in the foot; he extends this law also to the upper limb, forgetting that the flexor sublimis is a muscle of the forearm.

Mention should be made of Leonardo’s analysis of the movements made in ascending a flight of stairs (AnB, 21 v), although these are of more interest to the artist than to the anatomist, no mention being made of the muscles concerned. He gives two figures representing a man in the act of mounting a step, one being a representation from in

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LEON'ARDO DA VINCI — THE ANATOMIST

front and the other from the side, and in each the axis of equilibrium is shown and it is demonstrated that in shifting the weight to the upper foot the body must be bent forward and to the side in order that the equilibrium may be properly maintained. It is not a very important matter, but it is pertinent in illustrating Leonardo’s penchant for mechanics and his endeavors to apply the principles of that science to the correct representation of the human body.

In the above account of Leonardo’s contributions to myology it may be that the omissions and inaccuracies that have been noted may obscure the real merits of his work, which are great. It must be remembered that his manuscripts are for the most part merely notes, intended to serve as a basis for a work that was never completed. Indeed the notes themselves are manifestly incomplete, as is shown by the frequency of queries and memoranda scattered through them, queries that remained unanswered and memoranda for future observations that were never made. .Vnd Leonardo recognized their incompleteness, for in one passage he abruptly breaks off a discussion with the words “but since I have not yet completed these observations (tal discorso ) I shall leave them for the present and this winter of 1510 I hope to finish all this anatomy” (AnA, 17). Furthermore, the work of four centuries ago can not with justice be judged by the standards of today; its worth is to be estimated by comparison with the available knowledge and, when this is done, Leonardo’s myology constitutes a remarkable achievement, which becomes all the more remarkable when one considers the difficulties with which he had to contend and the multiplicity of his other interests. But with all this it must be emphasized that it is his illustrations that command our highest admiration, executed as they are with the comprehension, observation and skill of a great artist. They alone mark him as one of the World’s great anatomists.

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Reference: McMurrich JP. Leonardo da Vinci - the anatomist. (1930) Carnegie institution of Washington, Williams & Wilkins Company, Baltimore.