Nicolaus Steno’s myology in light of Johannes van Horne’s muscle atlas

Anatomical illustrations in Leiden↑

Nicolaus Steno enrolled at the University of Leiden in July 1660, after medical studies in Copenhagen for three years, and a few weeks in Amsterdam.¹²12. Steno enrolled (…) As an anatomy student, Steno was familiar with the usage of images in anatomical books. Then as now, anatomy textbooks were filled with images of bodily parts. The Institutiones anatomicæ, which was republished with updates by Steno’s Copenhagen mentor Thomas Bartholin (1616-1680), is one among many examples.¹³13. Bartholin, Tho (…) The important role of images in anatomy was reinforced by Johannes Van Horne, who was Steno’s professor of ‘anatomy and surgery’ at Leiden.¹⁴14. Steno, Observa (…)

In April 1661, Steno visited Van Horne’s home with Ole Borch (1626-1690), Steno’s former teacher in Copenhagen who also stayed in Leiden for some time.#¹⁵15. For Steno’s pr (…) Borch wrote in his journal that they saw at Van Horne’s place ‘all the muscles of the human body most accurately painted in their original colors.’¹⁶16. OBI, vol. 1, 8 (…) Van Horne himself told them that ‘he made sure that they [i.e. the images] were made by an extraordinary craftsman with great effort’ and that he ‘believed that nowhere else in the world has such a work of art existed.’¹⁷17. Borch to Thoma (…) Indeed, in a letter to Copenhagen, Borch further described these plates as ‘most elaborate’ and ‘splendid.’¹⁸18. Borch to Barth (…) These plates were likely the images of the anatomical atlas of muscles that Van Horne had worked on together with the painter Marten Sagemolen.¹⁹19. Huisman, The F (…)

Van Horne’s atlas was more than just an illustration of muscles and seems to have served as a way to think about new ways of cataloguing muscles. For instance, in January 1661, Ole Borch mentioned a dissection led by Van Horne of a female corpse in Leiden.²⁰20. OBI, vol. 1, 2 (…) Among other things, Van Horne renamed a muscle of the neck usually known as ‘sternohyoid,’ with the different name of ‘cleptohyoid,’ ‘because the muscle originates not in the sternum but in the clavicle,’ he said. In the atlas, the name of this muscle is still related to the sternum, but its caption points to the possible origin in the clavicle (Figure 1).²¹21. Paris, BIU San (…) This and other examples show that Van Horne’s images of the muscles were linked to what he saw in dissection.²²22. See Castel-Bra (…)

The sternohyoid muscles of the neck labeled with ‘D’. BIU Santé médecine, Ms 27 (6) (plate no. 4)

At the time, Steno had been studying the glands of the head.²³23. Moe, Harald, ‘ (…) Among other things, Steno discovered a new salivary duct connected with the parotid gland, which Van Horne first named as ‘Steno’s duct’ [ductus stenonianus], the name it still has today.²⁴24. Van Horne, Mik (…) After several months dissecting, Steno concluded that the salivary fluid was produced in different glands around the mouth, including the parotid and the maxillary glands. When Thomas Bartholin learned of Steno’s discoveries, he wrote to Steno, encouraging him to publish his discoveries. Yet, rather than asking directly for a text, Bartholin asked Steno to ‘publish an image of the external salivary duct.’ ²⁵25. Steno to Barth (…) Not unlike Van Horne, Steno’s images of glands were more than just merely illustrative and reflect the observational techniques he had developed as a researcher in anatomy. Steno’s discovery of the parotid salivary duct occurred when Steno inserted a probe through the gland, into the duct. Thus, Steno’s image highlights an enlarged parotid salivary duct, almost as if with the probe inside it. Steno also used probes to identify new paths and vessels in the tongue. Therefore, these paths are particularly visible in Steno’s images: not just the salivary duct, but also the little holes through which saliva arrived at the mouth through the cheeks and the palate (Figure 2). Less than a year later, in January 1662, Steno released a study of the glands of the eye with even more images. These images are similar in style to the glands of the head. But as Steno’s research moved further, his illustrations also changed.

Parotid glands in the head of a calf. Steno, Observationes anatomicae (Leiden, 1662), p. 21. BIU Santé médecine, cote 32043-3

Early research on muscles↑

Steno started doing dissections of muscles in 1662. He mentions dissecting the muscles in a letter to Thomas Bartholin, adding later that Van Horne was present when he opened the leg of a rabbit.²⁶26. Steno to Barth (…) Steno’s dissections led to a series of important results that, once again, needed illustrations. But unlike what he saw in the salivary glands, his results on the structure of muscle fibers were not as easily illustratable. Therefore, his first publication on the muscles, the De musculis et glandulis (Copenhagen, 1664) had no illustrations, with the exception of a beautiful frontispiece. This lack of illustrations is particularly intriguing because Steno knew the important role of illustrations in books of anatomy. Moreover, one of his main goals with his theory of muscles was to criticize the recently-published editions of René Descartes’ Treatise on Man (Leiden, 1662; Paris, 1664), which were filled with anatomical illustrations. Indeed, Steno commented that the illustrations in the Latin edition of Descartes’ De homine were ‘not inelegant,’ but he doubted ‘whether such images can be seen in any brain.’²⁷27. Steno to Barth (…) In the Discours sur l’anatomie du cerveau (Paris, 1669), written in 1665 while in Paris, Steno used illustrations of varied dissection cuts of the brain as a way to argue against Cartesian neuroanatomy. And yet, even though the main elements of Steno’s theory of muscle were already well-established in De musculis et glandulis, Steno did not include a single image inside the book. Why not?

Steno’s decision not to publish images in 1664 highlights two important features of his anatomical research: the importance of a novel dissection cut of the muscles, and his increasing use of mathematics in anatomy.²⁸28. Steno did not (…) In De musculis et glandulis, Steno suggested that muscle fibers form an ‘oblique parallelogram or the figure of a rhomboid.’²⁹29. Steno, De musc (…) This distinction was related to Steno’s method of dissecting the muscles, in which he cut ‘along the course of the fibers … not in a plane cutting everything transversely through the middle,’ but in a plane in which ‘the tendons remain intact with the flesh.’³⁰30. Steno, De musc (…) Steno represented them with three images in a 1663 letter to Bartholin, but he did not include the drawings in his book.³¹31. Steno to Barth (…) This longitudinal cut was a major deviation from Van Horne’s dissection practices, whose atlas drawings show a cut of the muscles in the extremities, in order to distinguish them. Van Horne’s method was the typical way in which anatomists dissected muscles. Indeed, as far as we know, no one before Steno attempted to cut muscles longitudinally.

Secondly, the more Steno researched the muscles, the more skeptical he grew of previous studies on them. Thus, as a way to reach a more accurate description, Steno increasingly used mathematics to study the muscles. For instance, he used mechanical analogies and geometry to speak of the abdomen and the intercostal muscles.³²32. For a survey o (…) But how could Steno represent mathematical insights with illustrations? Even though Steno never states it explicitly, in light of his later diagrams, it is possible to conclude that Steno was looking for a way to incorporate mathematics in his illustrations. He wanted to combine mathematics with observations, almost as if he saw the geometrical structure of muscles. The ongoing difficulties in representing muscle fibers are confirmed by Steno’s writings and the writings of those he met between the publication of De musculis et glandulis (1664) and the Elementorum myologiae specimen (1667), as we show in our article.³³33. Castel-Branco (…)

Mathematical diagrams in Florence↑

The Elementorum myologiæ specimen (Florence, 1667) was Steno’s final and most important book on myology and was filled with geometrical diagrams. Steno first showed the traditional representation of a muscle as it was represented since antiquity (Figure 3). Yet, he wrote, ‘it seems to me most trustworthy to represent the structure of muscles the way I found it in many simple muscles,’ as well as in ‘all compound muscles.’³⁴34. Steno, Element (…) Therefore, in his first new illustration, on the book’s third page, Steno represented ‘a muscle through a collection of motor fibers arranged in such a way that the middle flesh forms an oblique parallelepiped, but the tendons form two opposite tetragonal prisms’ (Figure 4).³⁵35. Steno, Element (…)

Traditional representation of a muscle, in Steno, Elementorum myologiæ specimen, p. 2. BIU Santé médecine, cote 5530

An oblique parallelepiped as a muscle as conceived by Steno, Elementorum myologiæ specimen, p. 3. BIU Santé médecine, cote 5530

Steno’s contribution in this book was twofold.#³⁶36. See Kardel, Tr (…) First, he showed that muscle fibers looked like a two-dimensional parallelogram or a three-dimensional oblique parallelepiped, also called rhomboid. Then, Steno showed how the specific structure of a rhomboid functioned in a muscle, most especially that it does not increase in volume even though it looks inflated. This geometrical structure, with the addition of a few propositions of Euclid’s Elements, allowed Steno to demonstrate that the variation of the oblique angles alone was enough to increase the muscle thickness [crassities].³⁷37. Steno refers t (…) Even though the muscle looked inflated, its volume remained constant. This was Steno’s most important claim. Therefore, he said that ‘it is amply demonstrated in every muscle, that when contracted, it reaches a swelling, even though no new matter arrives at the muscles.’³⁸38. Steno, Element (…) That is, no animal spirits were necessary: the inflated shape of a contracted muscle was caused by its geometry.

However, Steno’s insight that muscle contraction relied on its shape alone was more complex than simply describing his observation of the muscle fiber structure. Indeed, Steno’s text looked more like a mathematical treatise, filled with lemmas, propositions, and corollaries, than it looked like an anatomy book. His option for the images matched this mathematical approach. Steno’s argument also included a time-dependent process. Thus, he opted to use multiple diagrams to guide the reader through the necessary geometrical steps, just like a treatise of mathematics. First, he began with definitions of what was a single fiber and a group of two-dimensional fibers and then moved to define three-dimensional fibers, like the muscles are supposed to be. Then, he drew a diagram for almost every step of his geometrical reasoning demonstrating the geometrical properties of the rhomboid.

After extensive geometrical explanations and diagrams, Steno also said that he had ‘to demonstrate their certainty with examples taken from Nature herself,’ that is with observations.³⁹39. Steno, Element (…) Thus, he included ‘figures of different muscles … displayed at the magnitude at which I have measured them in cadavers.’⁴⁰40. Steno, Element (…) Steno used several examples of animals, such as a calf, fish, lobsters and, most importantly, humans. Just like in Leiden, Steno’s images helped the reader see what the dissector himself had seen. In fact, these images represent the new longitudinal cut of the muscles made by Steno in different animal species. Steno’s goal was to link observations to his mathematical insights as much as possible. Only then could he describe muscle contraction in mathematical terms.

Conclusion↑

Our research shows that Nicolaus Steno’s interest in images developed alongside an increasing interest in empiricism in anatomy shared by most of his professors and colleagues at the University of Leiden, such as Johannes Van Horne. This attitude of having the images closer to the act of dissection is seen in Van Horne’s atlas and also in Steno’s book on the glands. Yet, precisely because of this link between images and observation, the geometrical diagrams drawn by Steno are particularly mysterious. Steno never saw a perfect three-dimensional geometrical shape in the muscles, but he still was convinced that the rhomboid was a good match for muscle fibers. Moreover, he wanted to bring his readers closer to this mathematical insight and have them see a muscle contracting like a parallelogram changes its shape by variation of its oblique angles. Recent biomechanical research has shown an impressive similarity between Steno’s diagrams and ultrasounds of a contracted muscle, which confirms the rigor of Steno’s observations.#⁴¹41. See BOP, pp. 1 (…) However, Steno did not have ultrasound machines. Thus, to stress the importance of observations he had recourse to geometrical diagrams in parallel with life-size images of his longitudinal cuts.

It is our hope with our research also to shed light on the visual aspects of mathematization in early modern science. Indeed, Steno used diagram illustrations and longitudinal dissections to argue that the body could be understood in geometrical terms, or in a mathematical language. That was, in fact, one of Steno’s main goals with the Elementorum myologiæ specimen. He believed that anatomy should become a mathematical discipline, like those that fit under the early modern category of mixed or physico-mathematics. He wrote: ‘why can we not give to the muscles what astronomers give to the sky, what geographers give to the earth and … what writers on optics concede to the eyes?’^{4242. Steno, Element (…)} For Steno, these writers ‘treated natural things mathematically so that their knowledge may be more clear.’^{4343. Steno, Element (…)} Moreover, unlike a traditional drawing of muscles or glands, these diagrams allowed the reader to visualize with rigor a time-dependent process, such as muscle contraction, that they could not see otherwise.

Interestingly, Steno continued to rely on diagrams and mathematics to describe processes that were hard to observe. In his most famous book in the history of science, the De solido intra solidum naturaliter contento (Florence, 1669), Steno also used geometrical diagrams when explaining the time-dependent formation of mountains and fossils (Figure 5).⁴⁴44. See also Karde (…) Besides listing all observations that he made in his tour of Tuscany, Steno drew the process of superposition of the Earth’s strata with diagrams, making the first geometrical depiction of the Earth’s history and of modern geology. That is, although diagrams were not as real as a muscle atlas nor as a mountain landscape, they were still intrinsically related to Steno’s observations and they allowed to see things that were not easily observed such as the dynamics of muscle contraction and the formation of the strata.

Diagram of the geological formation of Tuscan mountains, in Steno, De solido intra solidum naturaliter contento (Florence, 1669). Courtesy of Biblioteca Nazionale Centrale di Firenze